[Damo]

My master cylinder has crapped out and I was thinking while I have to replace it I should go for the Vit one that apparantly is a good thing. I have Vit LWB front calipers so I guess it should be a pretty good match!

Is it just the LWB Vit master cyl I should be looking for or is it a different model?

[paulv]

Read on some American forum about people bolting in a master cylinder from a Subaru.
Think they were looking for an increase in the piston diameter. Understand the stock master cylinder piston in a sierra is 7/8 but a Subaru is over an 1".

Think they were using Liberty ABS Master Cylinders.

[Damo]

paulv wrote:

Read on some American forum about people bolting in a master cylinder from a Subaru.
Think they were looking for an increase in the piston diameter. Understand the stock master cylinder piston in a sierra is 7/8 but a Subaru is over an 1".

Think they were using Liberty ABS Master Cylinders.

I have heard of using Suby ones too. I might try pulling mine apart tonight to measure it.

[appsie]

from the few threads that have been popping up lately with links etc it seems that the zuk is 7/8" and that the subaru liberty and foresters too???? are 1 1/16" so theres a fair gain there in fluid.

The little push rod?needs to be modified or lengthened tho out of the boost i think they were saying.

Hasn't Pj zook or joe done this?

[paulv]

Hmm.. Yes, I think the Subaru one bolts up ok to the original Sierra booster.
Just some mods to the rod that pushes on the Master Cylinder piston.

Wonder if it would be possible to just change over the lot, Subaru booster and master cylinder?

Trick will be in finding the right Subaru stuff - there are probably differences between models, ABS/non ABS etc, at a good price - as is all a bit experimental.

[eldo]

use a GQ 2 bolt MS and it bolts up with only a mod to the pushrod

[Nik]

I fitted my subaru m/c up yesterday, it was from a 96 outback.
From What Ive seen it should work it is the 1 1/16 bore and has an outlet at the rear on the d/s and on the front at the top.
I bleed the brakes then tested it. The pedal is great but the rears lock up before the front.
Could I have the hardlines back to front. Standard suzuki the rear hardline went to the front hole on the m/c and the front went to the rear. Is that correct?
Do I have to run a proportioning valve?
Im running toy diffs with the standard toy disc/drum set up.
Nik

[joeblow]

i have a v6 booster (2.0 litre 4 pot same) and master. nice fit and the rod is a bolt up fit. works aaaawwwweeeessssooooomeee!

[Damo]

joeblow wrote:

i have a v6 booster (2.0 litre 4 pot same) and master. nice fit and the rod is a bolt up fit. works aaaawwwweeeessssooooomeee!

I know the H20A Vit (2.0 V6) has different rotors to most other Vits so it is no suprise the mater cyl are different too. I guess i'm after a MC from a H20 or J20 Vit.

Hen's teeth anyone?

[joeblow]

Damo wrote:

joeblow wrote:

i have a v6 booster (2.0 litre 4 pot same) and master. nice fit and the rod is a bolt up fit. works aaaawwwweeeessssooooomeee!

I know the H20A Vit (2.0 V6) has different rotors to most other Vits so it is no suprise the mater cyl are different too. I guess i'm after a MC from a H20 or J20 Vit.

Hen's teeth anyone?

i think i might have one in some boxes under the house. use the booster to.

[royce]

I dont understand what either of these things achieve, can somebody enlighten me?

bigger subaru master will give a better pedal but youll have to lean on it harder to get it to pull up

2.0l stuff I assume is the correct bore for the calipers but the bigger booster doesnt make the brakes any better, just left pedal effort needed

i would put a vit wagon setup on, I reckon suzuki would know a bit about matching brake parts up and mine pulls up pretty well

[Damo]

royce wrote:

I dont understand what either of these things achieve, can somebody enlighten me?

bigger subaru master will give a better pedal but youll have to lean on it harder to get it to pull up

2.0l stuff I assume is the correct bore for the calipers but the bigger booster doesnt make the brakes any better, just left pedal effort needed

i would put a vit wagon setup on, I reckon suzuki would know a bit about matching brake parts up and mine pulls up pretty well

Did you change the master cyl and booster? I thought you only did calipers.

[Damo]

joeblow wrote:

Damo wrote:

joeblow wrote:

i have a v6 booster (2.0 litre 4 pot same) and master. nice fit and the rod is a bolt up fit. works aaaawwwweeeessssooooomeee!

I know the H20A Vit (2.0 V6) has different rotors to most other Vits so it is no suprise the mater cyl are different too. I guess i'm after a MC from a H20 or J20 Vit.

Hen's teeth anyone?

i think i might have one in some boxes under the house. use the booster to.

You got PM!

[royce]

Damo wrote:

royce wrote:

I dont understand what either of these things achieve, can somebody enlighten me?

bigger subaru master will give a better pedal but youll have to lean on it harder to get it to pull up

2.0l stuff I assume is the correct bore for the calipers but the bigger booster doesnt make the brakes any better, just left pedal effort needed

i would put a vit wagon setup on, I reckon suzuki would know a bit about matching brake parts up and mine pulls up pretty well

Did you change the master cyl and booster? I thought you only did calipers.

No cause mines the same as a wagon

[Damo]

royce wrote:

Damo wrote:

royce wrote:

I dont understand what either of these things achieve, can somebody enlighten me?

bigger subaru master will give a better pedal but youll have to lean on it harder to get it to pull up

2.0l stuff I assume is the correct bore for the calipers but the bigger booster doesnt make the brakes any better, just left pedal effort needed

i would put a vit wagon setup on, I reckon suzuki would know a bit about matching brake parts up and mine pulls up pretty well

Did you change the master cyl and booster? I thought you only did calipers.

No cause mines the same as a wagon

Is that because you changed it or because they come stock like that.

Way to drip feed me the info you bastard

[royce]

I would of thought you saying did you change it then me saying NO cause its the same would conclude it came like that

wheres the pics of your fish tank from 4 months ago

[Damo]

royce wrote:

I would of thought you saying did you change it then me saying NO cause its the same would conclude it came like that

wheres the pics of your fish tank from 4 months ago

True, but I don't like to assume anything when it comes to stuff like this

I did a water changed yesterday, i'll take some pics tonight.

[Damo]

I figured I would do a few calculations based on hard data, and you might find the results interesting.

royce wrote:

bigger subaru master will give a better pedal but youll have to lean on it harder to get it to pull up

I do believe this is correct, because using a master cylinder of larger bore will displace more fluid (better pedal) at a reduced pressure (pads press against rotor with less force). So the pedal will feel good, and take up early in the stroke, but will ultimately not push the pads against the rotors with as much pressure as a smalled bore master cylinder.

Now I have just pulled my braking system apart this morning and taken measurements, the pedal is a 6:1 ratio and the master cylinder bore is 22.2mm. That measurement is approximate as I don't have anything that will get down into the bore to measure it properly, but it is consistant with what I have heard the Sierra master cylinder is, 7/8" or 22.225mm.


Pressure out of master cylinder = Pressure exerted on pedal x pedal ratio / cross sectional area of master cyl. bore

So for a nominal 50kg force on the pedal...

= 50 x 6 / 387
= 0.7750 kg/mm^2

or converted to something a bit more "chewable", ~1102 psi.

Say we wanted to go to a 1 1/16" master cylinder...

= 50 x 6 / 572
= 0.5245 kg/mm^2

or converted, 746 psi.

So for a 4.8mm difference in the master cyl bore the output changes by over 30%.

But you can't just whack on the tiniest master cylinder you can find and call it good, it's not just all about output pressure. If the cylinder is TOO small then it will not displace enough fluid to actuate pistons in the brake cylinders. That basically means no brakes. Also more pressure out means more pressure in, so the pedal will be overly hard to push if the balance isn't correct.

So what does all this mean?

Measuring the Sierra side of things is pointless if you can't compare it to something else. Hence i'd like to find out what the master cylinder bore size for. However I do know that I have been running LWB Vit front calipers on the standard Sierra master cylinder and stock rear drums without problems. That says to me that the stock 7/8" Sierra master cylidner is pushing enough fluid. Whether that is still the case now that i'm using Skyline rear calipers is unknown. That is something i'm going to have to look into further.

But to summarise, given that the stock Sierra 7/8" bore master cylinder is pushing enough fluid, the only thing going to a larger master cylinder is going to do is give me less braking performance.

[Nik]

I only did mine because even though my zuk does very well in the brake tests on 35s the rta engineers deemed my canister (yes canister) too small as running bigger (hilux) brakes reguires more fluid when the pads wear I needed to hold more.
Now I couldnt find any other canisters that will fit up to the zuk one and are larger but in my search I found the subaru swap is very popular in the U.S. to stop 35+ tyres so I ran it by the rta and the said they would accept that.
I still need to add a propertioning valve as the rears lock up first, but still it pulls up alot quicker than without the subie m/c.
Just my experience
Nik

[Damo]

Nik wrote:

I only did mine because even though my zuk does very well in the brake tests on 35s the rta engineers deemed my canister (yes canister) too small as running bigger (hilux) brakes reguires more fluid when the pads wear I needed to hold more.
Now I couldnt find any other canisters that will fit up to the zuk one and are larger but in my search I found the subaru swap is very popular in the U.S. to stop 35+ tyres so I ran it by the rta and the said they would accept that.
I still need to add a propertioning valve as the rears lock up first, but still it pulls up alot quicker than without the subie m/c.
Just my experience
Nik

You might have mentioned it already but I couldn't find it, but what booster are you running. The booster is just another part of the equation and will definitely make a difference.

[paulv]

The surface area of the caliper piston in a rear disk setup (skyline or otherwise) would be quite a bit bigger than standard wheel cylinders wouldn't it?

Would imagine the simple thinking for those that now have a 4wheel disk sierra, is that a master cylinder from a 4wheel disk car like a Liberty would be a good thing.

Nice work with the force and presure calculations. Looks like someone was awake in post trade hydraulics. I certainly wasn't.

[royce]

paulv wrote:

The surface area of the caliper piston in a rear disk setup (skyline or otherwise) would be quite a bit bigger than standard wheel cylinders wouldn't it?

Would imagine the simple thinking for those that now have a 4wheel disk sierra, is that a master cylinder from a 4wheel disk car like a Liberty would be a good thing.

Nice work with the force and presure calculations. Looks like someone was awake in post trade hydraulics. I certainly wasn't.

yes but the distance the piston needs to move is less as well BUT requires a shit load more pressure than drums do for the same braking force

interesting that minis use smaller rear cylinders on disc brake cars due to teh booster

[Nik]

Sorry mate, Im still running the stock master cylinder. I did think of the points raised about needing a bigger booster but it seemed this was the way others had done it with good results.
Nik

[Damo]

OK so I got me a Vit master cyl and booster, it's off a 95 (i think) SWB 16v Vit.

Has anyone actually put one of these bastards in a Sierra?

I fouls on the heater tap and the battery tray. And my stardard 6x9 battery (it's biggest that goes in the stock location) will bit too big to fit in there any more.

Have other ppl had the same experience???

[royce]

vits dont have a tap there and I have a real small battery on that side cause of the big booster

[Damo]

royce wrote:

vits dont have a tap there and I have a real small battery on that side cause of the big booster

My plan is to relocate the tap over slightly and get a smaller battery. I'm just suprised no one had mentioned it as I thought this had been done plenty of times before.

[royce]

can you put the mastercyl on the sierra booster?

you have the bigger booster as well, earlier vits are smaller diameter

[Damo]

I could use the Sierra booster, but I think the Vit booster is going to be better matched to the larger bore dia of the Vit master cylinder. And considering I have Vit calipers on the front it makes sense to keep it all Vit. At least in my head.

Oh, and as long as we forget about the calipers on the back too

[royce]

I reckon small or no boosters work better, more feel and better pedal

[Damo]

royce wrote:

I reckon small or no boosters work better, more feel and better pedal

I think it depends on the rest of the system, if the pedal ratio and master cylinder are setup to use a booster, than running without one will be shit.