[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.