Master Cylinder Upgrade For R32 Gtst, Bm57?

[Rolls]

I have an R32 GTST with R33 297mm brakes, since the upgrade the brakes feel worse around town, when flogging it they are better as less fade due to heat and if you really stomp the pedal they pull up good, the issue is around town you need more pressure than you should to pull up due to the stock BM44 cylinder.

Is BM50 or BM57 a better upgrade? I realise the BM57 is the largest bore but will this make the brakes TOO boosted and be like a brand new car which is impossible to heel and toe due to the over boosted brakes?

Anyone driven with all 3 boosters able to comment?

Cheers

[GTSBoy]

There's no difference in the calipers between your original and new ones Rolls. Ergo, you don't need a master cylinder upgrade to fix the problem. The problem is something else, and you need to find and fix it.

Did you change pads at the same time? Different pads? Could be as simple as that. For example, when I went from stock Nissan pads in my R32 on original brakes to Metal Kings all around, I got horrible extra rear bias out of it. That's because the compounds on the stockers are different front to rear, but same on the aftermarket ones. Changing to aftermarket dialled out the bias adjustment that Nissan had dialled into the stockers. When I upgraded to R33 on the front, I ended up with some stock pads in the front, and the bias improved quite a bit. Put the same pads in all around again (aftermarket) and rear bias reared its ugly head again.

Your new(er) R33 calipers might have tight/crusty seals or sone other issue that makes them take more of a pedal prod to get them to bite the disc. Lots of options for what could be wrong.

[Rolls]

So the R33 callipers which look bigger than the R32 gtst ones have the same size pistons? I could have sworn they were larger hence the change in pedal feel, my mate said exactly the same thing.

I recently changed my pads and it feels a bit better, I mean the car stops fine, I just don't want to have to push as hard on the pedal that is all.

edit: Appears you are right, same piston size.

http://www.gtrcanada.com/wordpress/2011/11/r32-nissan-skyline-gts-t-brake-caliper-rotor-specs/

http://www.gtrcanada.com/wordpress/2011/11/r33-nissan-skyline-gts-t-brake-caliper-rotor-specs/

Whilst I may be bypassing a problem by upgrading master cylinder size, would this make my pedal feel better ?

Edited November 23, 2013 by Rolls

[Rolls]

http://www.jdmlegion.com/KnowledgeBase/Brakes/Nissan-Skyline-brake-disc-and-caliper-information-33633030-5ca2-4f69-b247-5cb9366bcaf1

Looks like the early R32s had a single pot calliper, do you know what the size of this was compared to the 4 pot ones? Curious if it is any different.

Are the 4 pot callipers from R32 and R33 the same? Or are they different but with the same piston size?

[GTSBoy]

They are "the same" but not exactly the same. The legs are different lengths, obviously, and in my experience something about the casting of the R33 ones is better than the R32s, because the R32s creak and groan and clearly flex pretty badly, and the R33 ones do so to a lesser extent.

Pistons are the same same. Same as the GTRs too for that matter.

AFAIK, no turbo R32 came with single piston brakes.

[Rolls]

Both myself and my mate did the upgrade and aren't satisfied with the brake pedal feel so there must be something different eg slightly more friction, perhaps we both just ended up with older cruddier pistons than our original R32 GTST callipers. Would a BM57 upgrade boost the brakes too much and go too far, would a BM50 be more suitable?

http://forum.silviansw.com/viewtopic.php?t=35033

This website has user saying that BM57 will probably be too big.

What about the bias, is the BM50/57 bias the same as the BM44?

This website sells them for $140

https://holfordmotors.com/store/Categories/Brakes/HFM-46010-30p02

Edited November 23, 2013 by Rolls

[Sinista32]

Rolls - Save your money it wont make a difference.

I know this as I have the same issue. Although I have an R32 GTR

After my upgrade to R33 GTR callipers (I had full refurbished by PBR)

New Braided lines

New PMU HC+ Pads

New DBA 4000

New BM57 (ABS)

At least 6 full bleeds (including pressure bled) Motul BF600

ABS bled and tested

2 brake shops and 2 JDM garages

I have even had the original BMC refurbed, re sleeved and refitted - to no difference.

Now I wish I had never changed them. They work but you have to push most of the way down and they feel soft BUT they work.

Left to Try

In my GTR you can adjust the brake peddle like the clutch. You may be able to do this on a GTS-t (dunno)

Brake Booster and one way valve but I have been Guaranteed by all shops they are fine.

So hopefully this may help you diagnose

I have even considered removing ABS. I like to feel my brakes (it is unnerving ATM)

Edited November 23, 2013 by Sinista32

[Rolls]

So after going BM50 to BM57 your pedal feel has not changed at all? I don't really understand how it could feel the same, the extra bore diameter means that for the same foot pressure you must get greater brake piston pressure and hence more braking, or are you saying it improved but barely? Perhaps the ABS is the reason why, I do not have ABS.

The issue is just that the pedal doesn't feel like it does much at the top, only the last 25% seems to do the braking, they felt great with the stock R32 GTST callipers so the calliper change seems to have caused this issue.

What would people suggest myself and my mate look at?

Edited November 23, 2013 by Rolls

[Sinista32]

was not noticeable between BMC's

with all the work done it has barely improved along the way. It has improved but is streets behind what it was prior to upgrading

Edit: Yes I understand the theory of going BM57 (17/16ths or 1.1"). Srsly tho no change.

Edited November 23, 2013 by Sinista32

[KiwiRS4T]

You have it the wrong way round. If you go to a bigger diameter master cylinder piston then you need to apply more foot pressure because you are pushing against a bigger area but the travel will be less. A bigger booster may help..

I have changed to a BM57 but also have a MC stopper and braided brake lines so that less effort is lost on the way to the caliper pistons. You should of course put fresh high quality brake fluid in the system (such as Motul RBF600 or RBF660).

[Sinista32]

In my case peddle travel was greater, softer before engaging

(also have a cusco brake stopper)

thanks re larger booster may assist ....

Edited November 23, 2013 by Sinista32

[Rolls]

Hmmm

Edited November 24, 2013 by Rolls

[Rolls]

You have it the wrong way round. If you go to a bigger diameter master cylinder piston then you need to apply more foot pressure because you are pushing against a bigger area but the travel will be less. A bigger booster may help..

I have changed to a BM57 but also have a MC stopper and braided brake lines so that less effort is lost on the way to the caliper pistons. You should of course put fresh high quality brake fluid in the system (such as Motul RBF600 or RBF660).

You are right, P = F/A, so by increasing the area you decrease the pressure, so you need more force for the same pressure.

Well now I have no idea what to do.

[Rolls]

Someone suggested that whilst a bigger bore will reduce pressure, it will have more fluid so has more actual travel meaning the pads will contact the disc sooner, so pedal will get harder sooner, but at the same pedal travel will actually stop better?

Eg it won't travel as far so max pressure with bigger bore is less eg car won't stop as well, but at comparable travels it will stop better with the bigger bore.

Thoughts?

edit: Read a few more articles, summary is:

Bigger bore = harder pedal, less pressure so at max braking won't stop as well, shorter pedal travel, due to the shorter pedal travel will stop better at half travel so around town will stop better for the same pedal travel.

Might be worth a shot, as the bore isn't that much bigger the max braking won't be reduced that much, I guess it could go either way, only one way to find out?

Edited November 24, 2013 by Rolls

[Sinista32]

Trying not to Hijack Rolls but your subject is topical for me at the moment.

I went back to the reco'd and re sleaved original BMC 2 weeks ago.

Gave the new BM57 to my mechanic as no one on SAU wanted to buy for $300 (paid over $500), - you can get copies for less than $200.

I will try a larger booster and some pedal adjustment to try fix my similar issue. I like to feel the brakes come on in the first 25% of pedal travel not the last 25%

[Rolls]

No probs, sounds like we want the same thing anyway.

I wonder if you can space your pads out to decrease the brake knock off, anyone know?

[GTSBoy]

You can't space your pads to reduce knockoff, because "knockoff" is driven by the rotors. If you space the pads closer then they'll still get pushed just as far off the rotor. The amount that the piston seals pull the pads back would also remain the same, because it is based on how much forward they move under actuation, which, after the first time they were used after being "spaced out" would be the same again.

So the question/discussion about piston sizes above can be summed as follows.

1) For a given amount of movement required at the pads to get them to contact the rotor, a bigger MC diameter will give shorter pedal travel.

2) After the pads contact, the bigger MC diameter will then cause a harder pedal.

3) There will never be a point where you will get less maximum braking from the available bigger MC sizes unless you have muscular dystrophy or otherwise cannot push the pedal hard enough, because most people should have no problem applying enough force to lock the brakes even with a quite a large increase in pedal force required.

[Sinista32]

lol had the same thought

I used that link further up in your thread and took down the disk measurements to compare

Will grab a micrometer and check my Rotors for thickness. 2mm on each disk may make a difference?

Edit: or Not

Edited November 24, 2013 by Sinista32

[Rolls]

1) For a given amount of movement required at the pads to get them to contact the rotor, a bigger MC diameter will give shorter pedal travel.

2) After the pads contact, the bigger MC diameter will then cause a harder pedal.

3) There will never be a point where you will get less maximum braking from the available bigger MC sizes unless you have muscular dystrophy or otherwise cannot push the pedal hard enough, because most people should have no problem applying enough force to lock the brakes even with a quite a large increase in pedal force required.

Thanks for the reply, so how much harder will the pedal feel and how much less travel are we talking? Currently my pedal is very soft until about 75% when it feels very hard and brakes much harder from there on, is it likely the bigger bore would just shift this up higher?

I guess the only way I will know is if I buy a bigger bore, if you were to guess would you go BM50 or BM57 ?

[KiwiRS4T]

Thickness of the rotor is immaterial. Excessive runout will push the pads further away.

As noted above when you are approaching a corner at 250km/hr you will have no difficulty finding the strength to apply the brakes!

NB if you are using race pads you will find that if you use them on the street then they may have little or no stopping ability when cold no matter how hard you brake!