[Beery]

Hello all.

Doing something about my rear suspension has been on my mind for a while now. For context, the car is a Leaf sprung SWB sierra, 32" sticky roxxzillas, lockers, 6.4's etc etc. Pretty much just used for difficult 4x4 trips.



I think I'm at the point where I'm just asking too much of leaf springs. The back of the car is pretty stiff, partly because I'm running a heavy-ish pack to try and reduce axle wrap, and I'm also running a limit strap as a sort of "anti-wrap bar" which also adds some bind to the suspension under compression. Basically when an obstacle isn't crawlable, the car just goes to pieces. If a step needs a bump, the back of the car just bounces off the step, instead of the suspension absorbing some of the impact, which upsets the car and it all just turns into a bouncing mess. Also, forget about searching for traction on a surface that has some grip, the car just starts hopping around. I have to be really mindful about how I drive to avoid the bounce/axle wrap from starting, but obviously that's not always possible.

The front of the car is RUF, and I'm happy enough with how it performs, so I'm looking for something that will pair ok with leaf spring front.

Anyway, changing to coils/links in the rear is hopefully the answer. Due to the car having a mid mounted winch just forward of the rear axle, as far as I can see, I pretty much have two options that will fit:

A) Radius arms + panhard.

B) Three link + panhard.

Originally I was pretty set on radius arms, for a few reasons. Pretty simple, strong and easy to build. Also the added roll stiffness from bushing bind would be an advantage if the coils end up inside the chassis rail. Downsides are the geometry is basically set - they kind of fit where the fit and that's that. everything's locked in. My main worry with radius arms is the High anti squat they will provide - I've read this can cause wheel hop, due to them kind of "locking out" the suspension under power, and also (depending what arm you use) the bush separation can be on the low side so more prone to axle wrap. The last thing I want to do is do all this work only to still have hop/wrap issues.

So, the idea of a three link started to become appealing. Geometry is much more customisable to get the behaviour I'm after, and it should still package with the winch. Roll stiffness is an issue with the coils inside the rail, and I would rather not have to package a sway bar.

I had a quick measure up, and I think if put the springs behind the axle tube (similar to Gwagen's front end below), I can mount them under the chassis rail and therefore out near the wheel. Enough roll stiffness to avoid a sway bar? I would think so, but not sure.



This is based off using SWB Vitara rear coils, which are short, so not a lot of travel, but it's what might make the mounting outboard possible without notching/re-making the rear chassis. I believe they're the softest coil springs to pick from too, however jb74 jimny coils are all over marketplace for nothing, so that could be another option.

Also worth noting I plan to extend the wheelbase. I'm basically going to try get all I can out of a SWB body - around 86-88inches. yes, that will require body modifications, and a new fuel tank etc. but I think it'll be worth it. I'm happy enough to do the work.

I've thrown some rough, but semi-accurate numbers into a three link calculator using some basic rules of thumb, and this is what I came up with:



I've assumed centre of gravity height is around top of the tyres (?)

The lower links are just some stock patrol lowers that I had laying around, so lengths are based of those.

Upper link length is based off what will line up with the crossmember for mounting.

for my application (slow speed, offroad) I think I basically want the Roll centre as high as I can get, which basically just means mounting the panhard as high as practical.

I'm under the impression I want anti squat under 100% for my use, but I'm not really sure how much. Small changes in upper link height have pretty big changes though, and it should be easy to build some adjustment into the link bracket so it can be adjusted on the car.

I'm aware the upper link in particular sees a lot of force, so it needs to be strong.

I know this is a bit of a in depth/niche subject, but I'm keen to hear peoples opinions. This is the first time I've looked into this at any reasonable depth, and there's a lot to unpack.

Let me know! cheers.

[Brenno]

Loving these ideas.

Maybe I am not understanding the layout you are wanting, but area you looking to put the coils behind the rear axle, similar to Steves? If so, where is the panhard going, or is this only if its 3 link?


As you may be aware, I have Disco radius arms in mine (eye front end, not pin), and a disco panhard. I get about as much rear travel as I did with extra long leaves, but much smoother. I think for a lighter build you would want maybe Jimny arms or similar? I would suggest the bush bind and stiffness would be too great in a light SWB.

FWIW, I don't get any hop in my set up, but that might just be mine. It is auto as well, and 99 inch WB so I don't need to bump it up things as you would in a SWB.

What ever you do, make sure you update this thread!

[Beery]

Certainly if 3 link, I'd want the coils behind the axle, and out near the wheel. I think the panhard would just have to go between them - yes, it may be a bit shorter than desirable, but using vitara coils, this setup isn't really going to have much travel. I'm not sure how much travel vitara coils have, i assumed ~8 inches. A quick test on the bench shows around 12-13mm lateral movement from a panhard that will fit between the coils, which is fine i think.

Even if I go radius arms, I'd still maybe like to put the coils outboard. I could then put the radius arms inside the chassis, which would reduce bind, and there'd be more leverage on them to help them move, which would be helpful if I end up using arms out of something that's much heavier, like a disco. Again though, not really sure how this would play out in the real world. I think if I put the arms inside the chassis I'd have to mount them under the axle tube, as they'll get close to the winch on full bump, so that's a bit sucky for ground clearance.

I do like the thought of jimny arms if I went radius arm. They're light, small (easier to package) the bushes are soft and don't have massive separation, so they should move ok. They're a bit short, but using vitara coils, they'll more than cover that. The main issue is I've lost count of how many I've seen bend/break over the years. Admittedly the rears are better, but ehhhhhh. Not sure if want to build the car around them.

I've been looking through your build again to get some idea's.

[BlueSuzy]

3 link+panhard will work.
Panhard:
It will cop a lot of left right action so you'll want decent bushes. My front is a used Toyota Surf adjustable Toughdoggy Rear, but shortened a bit, poly bushed.
Antisquat:
Use an adjustable top arm with multiple chassis mount holes to play with antisquat% and pinion angles. Mine was around 80%? I fitted the Honda motor and then she was squatting a lot.. So i moved the top arm up a hole and bobs my aunty. I also think i've squatted when the rear left was in a massive hole and i ended up on my side. Now, She's pretty level when accelerating and when i brake onroad, My front raises and my rear stays put because of these settings.

An older build with a central top 3rd link. viewtopic.php?f=4&t=37415&start=510

Clints (unsure if you know him) rear works good with his RUF. SWB but stretched a bit, Inboarded springs, triangulated uppers, 4 link

Radius arms..
Pajero rears. They're flexible. Almost used these then went another way. The "Grand Sierra" has these in the front.
Defenders..flexy bushes but quirky pins

I'd stay away from Coily's/Jimnys radius's unless aftermarket. They seem to be made of cheese.

[sideways]

Here's some radius arm dimensions I've collected.

Fwiw I'd agree with Bluesuzy, I think the Jimny radius arm is to marginal in strength for your use. It's certainly not the worst place to have a couple of extra kilos. That said, I've never bent one.

[Brenno]

I've bent a Jimny rear that I have in the front, but I think that's from hitting something hard and the wheel not riding up over it. I think in the rear it would be OK and there are attendant options of you do bust one.

Paj ones seem to flex heaps. Could be an option.

[Gwagensteve]

Great thread.

I’ll chime in more when I have a chance but I ran my rear springs in front of the axle for quite a long time in piggles. This allowed a long/tall spring without it coming above the top of the chassis.

[Beery]

BlueSuzy wrote:

Clints (unsure if you know him) rear works good with his RUF. SWB but stretched a bit, Inboarded springs, triangulated uppers, 4 link

I know the car, but I've never met Clint or wheeled with him. I assume he runs a rear swaybar? or no?

I'm hearing everyone on the jimny arms. I agree with brenno though, I think in the rear they might be ok. Most of the bent ones I've seen are from the front, however I have seen a rear one completely snap once. With that said, I don't think I'd use them, I'd just be worried about them the whole time.

Cheers for the chart, sideways!

While I haven't ruled radius arms out, I am more interested in building a three link, so long as roll stiffness will be ok. I think that's the main hurdle, apart from that, on paper, it should be a better outcome than radius arms. If I have to package a sway bar though I'm going to be in a world of hurt.

[Beery]

Gwagensteve wrote:

Great thread.

I’ll chime in more when I have a chance but I ran my rear springs in front of the axle for quite a long time in piggles. This allowed a long/tall spring without it coming above the top of the chassis.

I look forward to hearing your thoughts!

[Beery]

A bit more context.

I pulled a spring out of a SWB hardtop vitara, and started having a bit of a look.



This is basically where I'm thinking of putting the spring. I believe I can flip the calliper brackets and put them forward of the axle, then I'll be able to move the spring out as close to the wheel as possible.

When the spring was installed in the vitara, it sat about 100mm into it's travel. If it sits at that same height in the sierra, that'll put the spring basically where the shock mount bolt is. (mine are raised, in comparison to a stock sierra) So a little below the axle tube, but I'm happy with that as far as ground clearance goes.



However, the spring has a freight height of around 320mm. At absolute coil bind, it'll be about 120mm, so 200mm of available travel.

I'm going to safely assume the rear of my sierra is lighter than a swb vitara - I run a softop tailgate, no spare, no glass, fuel tank is smaller than a Vitara. (and the new one may even be a bit smaller than stock sierra) I have a high mount winch and tools back there, but they're both forward of the axle.

Current ride height in the sierra has about 50mm until it contacts the bump stop. I can raise that a bit when I chop the guards up again, and modify the bumpstop position, but it's not going to be heaps - maybe 25mm. A little bit more ride height would be ok, but I don't want much.

Basically, I think the spring is going to offer too much compression travel and by the time I keep a bit of preload on the springs at droop, I might only have 50-75mm available. Although, if I mount the bumpstops inboard of the springs, I may need that extra compression travel during flex.

hmmmmm. I think a softer, longer spring would be ideal....

Fun fact: a patrol lower control arm will literally bolt into the front leaf spring mount.



This mount is already raised on my car, and actually isn't in a bad spot, so that could save me some work if I go down the three link route.

Also where I would put the third upper link:



I can use the chassis rail to make a solid mount adjustable off of, and also the new tube crossmember for the winch to add some support.

[Beery]

So, someone on the facebooks asked about coils spacers in a jimny. Long story short, I found out that stock JB74 front coils have a free height of 350mm (30mm more than Vitara), and are softer than vitara rears

Here's a link to a bunch of different spring listings Richard chopping has put together.

https://teamghettoracing.com/vehicles/c ... ifications

I ended up getting exact measurements off Richard, and put both the jimny and vitara spring specs into a calculator to confirm.

These springs are everywhere, and basically free because people rip them out at the showroom and fit a lift. so, these seem like a better option.

[Beery]

I picked up some JB74, 3 door standard coils today. Indeed the fronts are taller by about 30-40mm, and have slightly smaller wire diameter. so that'll be the coil of choice I think.

Left to right: jb74 rear, swb hardtop vitara rear, jb74 front



I think I've decided to go three link.

Standard length patrol rear lowers look like there going to work sweet. (already have them laying around)

I picked up a fresh sheet of steel for the fuel tank too.

I've got some other stuff on the go, but will start work on it in the next few weeks hopefully!

[Gwagensteve]

OK, I have some time sitting in front of a (personal) computer - I'll chime in with my thoughts.

I ran rover front radius arms in the rear for ages. I like the pin at the chassis end - it massively reduces roll stiffness. Great traction, very predictable, very strong and zero maintenance. Downsides - they're heavy and unless you flip them they hurt clearance. Flipped, they can cause chassis clearance problems depending on how deep into compression you're running. They also bind on articulation so flex is not significantly different to standard rear leaves, although ride can be heaps better obviously as spring rate is decoupled from axle location. They need to go outside the chassis which makes them widely spaced and this increases roll stiffness.

I'm not liking the patrol lowers. Those bushes look like they are going to be a bear for a sierra to twist up. Summit machine make (made?) high misalignment joints that pressed into FJ cruiser lowers, my guess is they're the same as prado - this would provide servcicable and zero bind bushes in a "factory" arm.

Don't worry about going to low on roll stiffness - I'd be more worried about suspension that moves freely and resists bind so you can then tune each element individually. Starting with bind adds an unpredictable rising rate into articulation which highlights another downside of radius arms - they're always trying to force the suspension into a no-bind poisition. When the car is on big compound angles they will try and straighten the suspension out rather than settling and they are very susceptable to drive torque. With my Gwagen when it was on big angles I would left foot brake the car until everything wound up and then ease my foot off the brake withouing changing RPM - this release some of the bind and "relax" the car as it moved off the obstacle. This was, er, spooky.

I have a couple of other areas of feedback to consider. I don't believe it's possible to get a usefully long panhard rod high enough in the car to provide a high enough roll centre to allow optimum stability off road. When my car was radius arm and three link I ran the panhard as high as I could and it still felt very mismatched with the front and lacked stability. it would also tag the chassis at full flex so I definitey couldn't have gone higher. I as using a rover panhard which are very strong (forged) I still use one on the front.

I think your current plan with the heavy offset of the top link to the RHS will put a lot of force into the axlehousing long side. Id try for closer to the centre of the axle. Bushings with compliance may cause the car to feel like it's not putting it's power down straight with that much offset on the top link. When I was 3 link + panhard rear i used the vitara A frame pad on the top of the diff housing, which was obviously offset, and it was OK, but that whole setup was a bit of a nasty compromise. and felt very loose compared to the 4 link I now run.

I'm going to suggest that springs behind the axle and a panhard are going to clash really badly. I would do some head screatching and see if you can run a A frame 3 link with an assymetric A frame that mounts up on the driver's side of the crossmember to keep away from your winch but sweeps as close to the cenrte of the diff as possible. Kind of like a J arm fron top wishbone on a trophy truck.

Attachment:

J arm.png

Imagine the chassis end being the crossmember and the top of the knuckle being the diff housing.

This would provide complete control over roll centre, and no panhard to package behind the rear axle.

With a higher roll centre and an A frame, theres more room between chassis and tyre during articulation, and the axle doesn't move left to right during travel. This should allow enough room to get the shocks outside the chassis (assuming you use a slender shock like a 5125) There are huge gains in stability to be had by doing this as the car doesn't roll over the top of the shocks. (it's also ess to package between the rails) What I mean by that is when properly inclined and with the bottom mount out near the wheels, there is very close to 1:1 ratio between wheel speed and shock shaft speed during travel AND articulation. With inboard shocks, wheel speed and shaft speed are close on travel but the shaft speed drops massively on articualtion so the car feels unstable and loose when flexing, even if it feels fine in normal use. Nissan don't understand this; Rover and Toyota do - note where the rear shocks are on the GR Hilux compared to a normal hilux. Land rover worked this out back in 1968, but "Spen" King seems to have had a real knack for suspension design.

Just some thoughts to ponder.

[Beery]

Thanks for the reply! this is good stuff.

The patrol bushes look like they're solid in that pic, but they do have a fair bit of void in them.



One end clamped in a vice, and I can easily get it to 20-25 degrees of twist with one hand before you have to start physically squashing the bush. As far as travel, that's basically unlimited. They're very free in that direction. i'm not committed to them, but I feel like that should be fine?

Gwagensteve wrote:

Starting with bind adds an unpredictable rising rate into articulation which highlights another downside of radius arms - they're always trying to force the suspension into a no-bind poisition. When the car is on big compound angles they will try and straighten the suspension out rather than settling and they are very susceptable to drive torque. With my Gwagen when it was on big angles I would left foot brake the car until everything wound up and then ease my foot off the brake withouing changing RPM - this release some of the bind and "relax" the car as it moved off the obstacle. This was, er, spooky.

I've seen this play out many times. That's part of the reason I want to avoid radius arms. if I can get the car flexed up and not have it react to adding power i'll be stoked. Obviously still leaf front, but if I can minimise it, happy days.

Good point about the offset upper link. I honestly was only putting it there so I could incorporate the chassis rail easier to get some strength in the mount.

I should be able to get the upper link basically central on the housing, I'll just need to beef up the crossmember substantially. I built the winch around clearing the limit strap I currently have, which is in the centre:



Blusuzy and i were chatting about this off thread, and he mentioned an assymetric upper link too.

He sent this photo:



Which i could package. Something like this:



(yes, I put lots of time into that drawing)

My main concern was getting enough separation on the chassis end to adequately control lateral movement. Similar to not having enough triangulation in a 4 link. I'd possibly have to move away from flexible bushes and go to something like the summit flex joints and/or a ball joint like Vitara? Now that i've said that though, vitara don't seem to run crazy separation on the upper link, but it's also very short.

Agreed it would be lovely to not have to run a panhard.

As far as roll centre. That was easy when I was thinking panhard, as I knew I basically just wanted it as high as I could get it. With an A frame though I could put it where I want - how high do I go?

I've already been looking at mounting the shocks outboard of the chassis, partly because mounting them inside on the winch side is going to be a pain, but also for the reasons you've mentioned. I think it should be doable if I mount them similar to an 80 series - tucking the lower mount way down inside the rim. I note 300 series now have a revised chassis, and the entire shock is outboard of the chassis now too, not just the lower. I'm happy with the bilsteins in the front, so yea, I'll go with those again I think. They are long though, not sure if that will cause dramas outboard the chassis at the top, but that's something to check further down the line.

[Gwagensteve]

Back on my phone and at work but I would use urethane bushes on the chassis end and a summit joint at the diff end. You are correct though, the vitara a frame is pretty tiny and does ok for bushing life.

My roll centre is roughly level with the bottom of the chassis rail at ride height. (That’s with ~100mm between the top of the axle tube and the bottom of the chassis rail) I like the feel but with a short wheelbase that might make the car a bit to oversteery. I don’t have a firm feel on where the front roll centre is with leaves but I suspect it’s fairly low, you want to avoid making the roll axis too steep or it will handle like a vitara. Compared to my car, inboard rear springs will lower roll stiffness a bit so should help to keep the suspension working under lateral loads a bit more.

Agreed with 80 series lower shock mounts. That’s sort of what I copied for my car but note that in the 80 Toyota pull the shock inside the chassis rail at the top. I haven’t found that possible with a sierra as the chassis intrudes too much. When I was trying to set up bilsteins outboard originally in my car I was still running a panhard and the krawlers so there was just no room. I think it’s quite possible with a higher roll centre and narrower tyres. Also, in front of the axle the chassis narrows so there’s more space. (Have a look at Range Rover shock mounting for ideas.

[Gwagensteve]

To clarify- bottom of the chassis rail above the rear axle.

[Beery]

Gwagensteve wrote:

I don’t have a firm feel on where the front roll centre is with leaves but I suspect it’s fairly low, you want to avoid making the roll axis too steep or it will handle like a vitara. Compared to my car, inboard rear springs will lower roll stiffness a bit so should help to keep the suspension working under lateral loads a bit more. .

I don't have a panhard in the front yet, but it is something I would like to add, or heck, we'll see how this goes, maybe the front will get coils too. However, either way, if I put a panhard in the front, that should get the roll centre up higher I would assume, making the roll axis not as steep.

Also, my rear springs will end up basically where yours are. Or are you suggesting I should inboard them a bit? Or am i better off putting the roll centre somewhere between a panhard and where yours is as a bit of a compromise.

I'll deffintley aim to get the entire shock outboard of the chassis, it just might be a bit hard with a 5125 due to length. Ill loose some of the chassis taper due to the wheelbase extension too. We'll see, i haven't
Had a really good look yet.

[BlueSuzy]

Beery wrote:

Thanks for the reply! this is good stuff.

The patrol bushes look like they're solid in that pic, but they do have a fair bit of void in them.



One end clamped in a vice, and I can easily get it to 20-25 degrees of twist with one hand before you have to start physically squashing the bush. As far as travel, that's basically unlimited. They're very free in that direction. i'm not committed to them, but I feel like that should be fine?

I use Patrol rears in my lowers, but with a heim on one end in my uppers to reduce the diff torquing up like axle/spring wrap. They're squishy and do rip over time but I'm probably asking too much from my $4.50 bushes.

Vitaras rears feel stiffer and are bigger. I have them for motor mounts etc.

[Beery]

Cool! I think i'm happy enough to give them a go. My car should be pretty kind on them compared to yours - much less travel/flex. Genuine bushes are good. They aren't showing signs of wear in my patrol and they've been in there for a few years, ~60,000km's.

[Beery]

Okie dokie, I've finally made a start. I'll post in here as I go through the process.

The wheelbase extension looks like it's going to land around the 100-125mm mark. I was hoping to use a standard front driveshaft for this, because I have one, they bolt it, and having the same shaft for both ends of the car is cool, however, they're about 200mm longer than a rear. This puts the tyre in all the complex panel work at the rear where there's a thousand layers of steel, and a tailgate seal etc, so it's major work for a couple of inches. So, I'll have to come up with something else.



After some digging, it looks like a front driveshaft from a hzj75 cruiser will work. Same bolt pattern as WT flanges, just needs some minor machining to open up the locating bore. I have a mate with access to one, so he's going to get some measurements and confirm for me. Shortening a sierra front shaft is an option, but it's more work and while I'm sure I could give it a good crack with the lathe, the result isn't guaranteed. This car also does lots of trips far from home, so on the rare chance I take out a rear shaft, I'd like to have a chance of being able to get one, unlike something that's custom made.

Next up, I threw the springs under the chassis and put the weight of the car on them to see how far they sit into their travel. This is with 2 20L jerry's in the back, all tools/gear and the tailgate back on, so it's pretty close to weight.

JB74 front:



Unfortunately, they only sag about 75mm. At a ride height I'm after, this is going to put the spring too far below the axle tube, ( ~60mm ) and that's even before I add bracketry to mount the coil. And of course only 75mm of sprung droop travel available.

JB74 rear:



These sag the same amount, but are a 50mm shorter coil to begin with, so these would be almost flush with the bottom of the axle tube which is acceptable. Although they're a shorter coil, it might not actually matter that much, as all the extra travel in the front coils is in compression, which I don't really need, so it'll go to waste anyway. I'd prefer if the coils sagged more under weight, so i could run the ride height low, and have more droop to play with, but these are the lightest coils I'm aware of to use without going into custom stuff, so I'll just have to make it work I guess. hmmm.

Here's a rough mock up of the layout I'm thinking:







I was simply able to rotate the calliper bracket, so that's easy. Coils behind the rear axle as planned, and it looks like I'll be able to get a shock outboard of the chassis fairly comfortably in front of the axle.

I think next step is going to be to square the axle up under the car and start making some link mounts so i can start to cycle the suspension and find out none of this stuff will fit

I've cut all the bracketry off the chassis - bumpstop pads, fuel tank mounts, rear shackle hangers. And also the diff housing.





I'm really having regrets about these recessed leaf spring mounts I made now...



I have a fresh WT housing here i considered using, but that means doing the shave again, and moding a good housing. I'll persevere with this one for now. I picked up a piece of round bar, and have some aluminium on the way to make some pucks so I can have a proper alignment bar setup. I'm thinking I'll put a light truss on this housing. That, plus filling in the axle tube is going to make it move a bunch, so I want an accurate bar to make sure I can keep it straight and/or straighten it afterwards.

My summit machine flex joint also turned up:



This will be the main centre pivot on top of the axle. I got the threaded shank style so I can have some adjustment over pinion angle. This is the "medium" size - 1 1/4" main thread, M14 bolt or something for the through bolt - it's very stout, and looks well made. P.S, I rang them last Wednesday, and it turned up today! (these are out of the US) I'm flat out getting stuff out of Brisbane that quick which is 4 hours away from me

I got a weld-in tube adapter with it. I was hoping it would fit ok inside a piece of NB pipe, but it's fairly sloppy, and the next size down is too small. DOM/CDS tube isn't available where I am, so it's got to be shipped, and there's a minimum length order requirement, But I might just have to pony up and get some so I can make the upper link/A-arm. the chassis side are weld-on style polyurethane mounts, which are on the way.

[sideways]

HZJ75 front shaft is about 650mm measured flange to flange in the car. It looks like it's got about 35mm more it can compress. Solid axle Hilux front is around the same length. New HZJ75 front shafts are dirt cheap on eBay.

[Beery]

Thanks mate! That should work out spot on. Yes, I did see those $150 shafts on ebay

[Brenno]

I run hilux rear, same bolt pattern as WT, just need a bit lathed or if the pinion flange to fit. Not sure on length though but probably am option. Keen to see more updates

[Beery]

update!

I picked up some material to upgrade my alignment bar setup so I can have a chance of getting this housing straight. Some time on the lathe and we have these:



Which go together like this:





So, how bent is my housing? Surprisingly, not bad.



on the drivers side the puck just barely nicks the side before sliding in and seating - call that good enough.

The passengers side is a little bent, but only a few mm.



Before I started plating the axle tubes, making a truss and welding a bunch of link brackets to it, I figured I'd get it straight first so at least I'm starting with a good base. It was pretty much a non event. Sierra housings are very bendy and easy to straighten. That's a tiny bottle jack - like, 1 ton or something? - and it had no dramas getting the passenger side back straight.



(the housing is upside down here, that's about how far I had to take it the other way to account for the amount of spring back)



Tada!!

I then welded in the the axle tube plates. I had an old low mount winch drum laying around, and it was the same diameter as the axle tubes, so it got cut up and burned in. These got a heavy V-prep, and the welder turned way up - I can see a nice penetration line from the inside, so I'm confident these will be leak free and strong. The same couldn't be said about my old spring mounts. They always wept oil, and I noticed one in particular was er, quite *damp* when I went to cut them out, like it may have begun to crack.



Anyway, with a now good housing, i squared it up under the car at a rough desired ride height, and tacked it to the chassis with some scrap steel.





Made some lower link mounts:





And the main upper link mount. This is made out of 5mm, because it was in the discount bin at the steel place, and I also went to ultra 4 a couple of weeks back and seen an upper link bracket break, soooooo I'm keen to avoid that for obvious reasons. I also punched two holes in it for some adjustability if needed. It's not complete yet, it'll get tied into the truss, and some extra bracing, but there's the main structure.





Lower link:



I then spent much time staring, wondering how I'm going to do this upper link/ A-arm. In the end I decided to tack together some scrap so I could visualize it better.





After doing so, I'm not really sure this is going to be a success. I'm worried there's not enough separation to control lateral movement at the chassis end.

Here it is out on the bench.







I'm really only able to get the bushes at the chassis end 285mm apart. and the length of the link is ~430mm.

A Vitara for example has a bush spread of 320mm, and the length is only 210mm, so it both has more separation on the bushes, and the length is basically half, so there's much less leverage on it.

The summit flex joints don't have any give in them, and the poly bushes for the chassis feel very stiff, so it might be ok, so long as all the mounts are strong as they're going to be under some stress. I dunno, it doesn't really fill me with confidence. Anyone got any thoughts?

going to a single upper link and panhard isn't out of the question yet if this is no good.

I can't really get any more separation on the bushes. I can make the link shorter, so there's less leverage, but that's not really ideal from a geometry standpoint.

[Beery]

I spent majority of the afternoon flipping my vitara onto it's side so I could easily get to the coil mounts and remove them. Then I got back to thinking about my upper link situation.

I revisited the idea of a panhard, and it certainly looks achievable if I want to go that way.



That's a 680mm long bar, which fits between the chassis. This lets it clear the coil springs, but also means i can raise it significantly, so i can get the roll centre up higher than would otherwise be possible with a longer bar.

I'm aware longer is better, but I really don't think it's cause for concern. At this length, I'll have roughly 4mm of lateral movement in droop, and compression. Or 8mm over the full range. If say, the bar was 900mm, it only takes away about 1mm in each direction, so 6mm over the full range. That's not something I'm going to be able to feel.

I'll also be able to mount it much higher, so I can get the roll centre up higher. Very similar to what I can get with the A-frame setup. Similar to the link brackets, I could also add some extra holes for easy adjustments in the future if needed.

Even though I need to package a bar and make mounts for it, they're easy to make. The A-frame mounting is going to be a bit of a nightmare - trying to make it strong enough, clear a driveshaft, clear a winch, and get a decent bush spread. Mounting a single upper link will be much easier, and mounting the panhard doesn't look too difficult.

Anyway, just my thoughts currently.

[Brenno]

I'm a bit of a geometry noob, can you give me some insight into why a high roll centre is beneficial?

[Beery]

oh, so am I. I'm not really qualified to answer, but my basic understanding is that it reduces body roll, and in my case that's the aim for side angles/slopes etc. The higher the roll centre, the closer it is to the centre of gravity (and my centre of gravity would be considered high, compared to a road car or something), which means the centre of gravity has less leverage over the suspension to cause roll - at least that's how I imagine it. It moves some of the force from going into the springs/shocks/swaybars, and transfers some of it into the suspension links. I aim to exploit this, along with having the coils out wide, to hopefully negate the need for a rear swaybar.

You can take it too far, and if it's too high, it can kind of "lock out" the suspension, which isn't desirable, especially at speed, where you want the suspension to remain compliant and soak up the bumps during cornering. An off road race car/buggy would typically run a lower roll centre, but something like a dedicated, low speed rock crawler would run higher - this can be pretty obvious looking at some buggies that run a panhard that's mounted way above the housing.

It can also cause handling quirks if the front roll centre is significantly lower, and I think with leaves it is. but even if it had a panhard, it would still be lower. In a swb the roll axis can become quite steep. (which is the line connecting the front and rear roll centres) I'm trying to build some adjustability into this setup as I really have no idea what to expect, so it'll be nice to be able to easily change things if need be.

If it wasn't obvious, my car isn't made for going quick so I think it will mostly benefit me for my use, but we'll see.

[Gwagensteve]

That’s pretty much nailed the effects of a high roll centre.

The a frame is preferable to a panhard for a few other reasons beery-

Roll centre doesn’t change with ride height
Axle path is consistent regardless of which way the axle articulates
Two connections at the chassis end spreads the load and means the chassis crossmember doesn’t need to be as strong
It’s easier to make the top link strong. (It sees a lot of load)
Other than packaging the only real advantage of a single upper link is articulation is shared between two joints rather than it all happening at the diff end but I don’t think that’s an issue at your travel level.

[Beery]

update!

Driveshaft situation is sorted. I took one for the team and ordered a $150 special off ebay, and it actually looks ok. Hzj75 front.







110mm longer than stock, bigger uni's, and a much bigger slip joint with a better sealing method and more spline engagement. Pretty much all my sierra driveshafts have some play at the slip joint, so this should be a good upgrade.

I was pretty close to banging a panhard in, but I've persevered with the A-arm setup, and I'm quite happy with the outcome. This all looks pretty simple, but getting it to clear the winch, get acceptable bush spread at the chassis end, clear a driveshaft, making sure i can install/remove the bolts, have some adjustability, make sure both pivots are in line, and get it in a spot that provides good geometry numbers took some doing.

So, a new crossmember was put in:





New tool. Panbrake!!



I've wanted one of these for ages. I'm getting to an age where I'm a bit sick of doing things the hard/long way This will be especially handy when I get around to the fuel tank, however it had a hand in basically every part of this crossmember too. One of those things you don't realise how usefull they are until you have one.

Folded up some brackets for the bushes



Put a little kick in this piece to clear the body.



And it goes together something like this









Dimple dies for street cred, and also allows the handbrake cable to pop through and remain in a stockish spot.

I managed to offset the passenger side way over next to the winch. This both ties it into the existing winch mount for strength and adds about 50mm more bush spread than I had before. I'm now at 340mm, which is 20mm more than a Vitara, and my bushes are much stiffer, and wider, so my mind is at ease a bit now. I think this should be fine.

Then i could start on the upper link. I managed to source some CDS tube locally for this. While i still had a straight bit of tube, i threw it in the lathe so i could weld the threaded tube adapter in for the flex joint.



I got 4 plug welds at the base, as well as the perimeter.

Because the bushes are offset, i ended up with this wacky looking thing:



I fully welded the A-arm on the bench before welding the chassis end bushes on, just to minimise any distortion so I don't find I can't fit the thing back on the car. And with that done, i could run a few stitch welds across all my bracketry, fit the A-arm and finally cut the housing free from he chassis











I'm happy to report it all moves very freely. I can easily move the whole show about. The A-arm is true and swings freely, and for my travel numbers, the patrol bushes aren't posing an issue. With the housing at a rough full flex scenario I can still rotate the lowers with my hand. The summit joint is sweet too, plenty more travel left in it.

It's so nice to be able to just move the housing around to work out clearances etc, unlike with leaf springs, or if I had of gone radius arms.

Shocks turned up



Same as the front, but these are only 8" travel. These should work well, and fitting them outside the chassis doesn't look like it'll be a drama.



I have a bit of guard work ahead of me I should be able to get a fair bit more compression/flex out of it here.



Next up I'll start playing with spring and shock mounts and hopefully get it sitting under it's own weight soon. The springs aren't ideal, but I'm hoping I can make them work. I've had a rough measure up, and if I play with bump stop position a bit, I can hopefully run them pretty close to bind at full flex to get the most out of them while still maintaining a reasonable ride height.

[Beery]

Productive day today.

I quickly made some rough coil mounts that I could tack in and get a feel for where the cars going to sit and clearances etc.



And here it is under its own weight.







A little bit high in the rear, but not too bad. I'd prefer it ~15-20mm lower.

By the time I get a truss on the housing (I'll use it as a flat bump stop land), it'll have around 70mm of compression travel.



The coil mounts obviously hang down below the axle tube. It's about 45mm, which isn't terrible, but I'm not stoked about it either. The lower control arm mount hangs down too, but it needs to so i have adequate separation without putting my upper link through the floor. The coil mounts are pretty bulky in comparison though, and I would prefer them a bit higher.



I can't raise them without raising ride height (which is already too high) or notching the chassis, which I'm trying to avoid. So, I'm back to looking at springs. Really, I think something softer would be good. I can buy 12" coil over springs at 100lb/", which I think would be ideal. Jimny springs are around 126lb/" I believe. Some quick maths tells me they'll sag about an extra inch, so I could raise the coil mounts, and maybe even loose a bit of ride height while I'm at it. This will also mean I'll have more droop. Otherwise the specs are pretty similar to the current springs.

While I'm still thinking about the coil situation, as to not halt progress, I've made a start on the fuel tank.

(I know this isn't really about suspension, but it's part of the job, and i'll just copy and past this over to my build thread once done, so I may as well just post it here too)

I've made it out of 2mm mild steel. Hopefully a mix of being not too heavy, but still able to take the odd hit without the need for a guard. Also easier to weld than something thinner.



I don't use this saw all the time, but jeez it's nice when I do. Basically a circular saw designed for steel - I've cut a fair bit of 10-12mm plate with it, but on this thinner stuff it rips through like its a piece of plywood. leaves a machined like edge with barely a burr to clean up.

Then got to folding!







I rolled the top two edges in, as this should mean easy welding for the two long sections. The ends will just be corner to corner, but I think it'll be ok.



The tank is pretty wide. It basically fills out between the chassis rails, so I've made a baffle for the centre of the tank. This will also add some support, as it'll no doubt get landed on one day.



As you can see, it's also quite narrow, because there's now a diff in the way. This means it has to be tall to get some useable capacity, Annnnnd to avoid it being a ground plow like a stock sierra tank, that means its coming up through the floor.





I've sat it 50mm below the chassis rail, so much higher than a stock tank with a guard. It's also much narrower, and now completely forward of the rear of the tyres, so it should be much less susceptible to hits and getting dragged on absolutely everything.

It should hold about 43 litres, which is more than stock. #tourer!

Happy with my progress there, i decided i'd keep hacking the car up and get the tyres to fit.

Here's where I've ended up this afternoon.









I'm more or less there. it's a little complex at the rear of the tyre, there's a few layers of steel etc, but I've got plenty of clearance now. I may just need to take more out of the quarter panel, but I really need to sort springs/bump stops out before I go too much further.