R32 GTR front brake disc size upgrade!!

[GTRgeoff]

The other thing worth trying without going overboard is a set of slotted rotors, good pads like RB74's and Motul DOT5.1 brake fluid. On both standard and semi-comp rubber I had no issues with fade or consistency until the pads wore down to about 3.5mm left.

Most won't drive to anywhere near the limits of this basic change, even though it doesn't have the rice cred but for a tired old 33 it helped me to some decent laptimes.

[salival]

Roy: If i'm following correctly (which I have been follwing your progress for a while, you give us great information.. basically the pad is overhanging the disc by approx 1mm or so (confirmed by looking in your photos) .. Now to run these bigger diam discs arent you using spacers or similar to space the calipers out? couldnt you just use 1mm smaller spacers.. or am I not understanding the whole spacer idea?

Because i'm building a track attack/drift/drag car at the moment and i've been heavily interested in the caliper brackets for mounting the 324mm rotors or whatever size they are.. but not if I get funky brake problems..

Your thoughts?

[BoOsTeD_RB26]

What he said.

Just to clarify, I am 90% sure that the person who I spoke to was not Howard. I have spoken to Howard before hand, and seems like a legit guy who seriously knows his stuff! He has advised me before to go with the AP Calipers etc, and depending on what is needed, you can spend upto 16K for brakes alone! (As he said he's quoted a GTR before with 8 pot brembos up front and 4 pots on the rear!). However, this wasn't the same person who I dealt with yesterday. Extremely sorry if I have offended anyone. I am under no circumstances trying to "bag" Racebrakes.

Anyway, after doing a little bit of shopping around, for the money, the six pot Porsche caliper kit that's on UAS for 3.3k seem to be a bit of a bargain!

[GTRgeoff]

The issue with spacing the caliper away from the hub centre is that the caliper has a design limit for the maximum radius disc. so to continue to clear the disc the pad eventually (as radius of disc increases) starts to overhang causing it's own set of problems. With a 5mm radius smaller disc this would probably be OK.

[Roy]

If only i ran 18: wheels...Porsche 6 pot :whackit:

Has anyone read or heard that the monobloc calipers can after hard/heavy use start to flex more then when new...moreso then other calipers? I have read and have also heard someone give me that reason why you always see so many sets of Porsche 4 pot calipers on ebay:confused:

Thats the problem with this sort of fluff, you just dont know where to turn for the unbiased facts...me reading it, and someone else giving me the ebay story doesnt make it fact:(

And yeh, if i try to bring my caliper in 1-2mm the caliper will no longer be able to saddle the rotor without rubbing the outer edge of the rotor on the bridge of the caliper:(

And because im pig stubborn, i recognise the problems / limitations with my setup, but im still not convinced its the sole source of my problem .Contributing factor yes, but not soley responsible. I have the weekend to get to the bottom of it all:(

I was having trouble pulling the car up at the drags again tonight because of the soft pedal:( ...im haiting this brake crap...dont know how i can quickly / cheaply fix them

[GTRgeoff]

OK mate, losing perspective.

1. pull the discs off an take a few mm off the outer radius... maybe get the slots taken to the circumference as well. What point having slots if they are not going to clean the discs fully and allow escape of all the gas out.

2. pull the spacer block off and have the same amount plus a little taken off, so now the pads should not sit over the edge.

3. try it with the Comp9's but I'd recommend a piece of glass with some emery on to take them back to flat.

I'd guess the cheapest workable solution could be RB74's back on but guess both work work out close.

[Roy]

Take it for a drive and tell me your thoughts Geoff. Plus your still to experience RB20 POWAH!!!

[GTRgeoff]

hmmmm, wet day. Looks perfect

[Roy]

Big weekend at Michaels stripping the brakes down and installing that data logger so didnt get a minute to swing around:(

But, interesting revelation after about 6 hours work on the brakes:)

All is not as it appears. When a friend emails me the pics i will post them up. But basically the findings were as follows.

The offset GTST calipers mean that the pads sit about 1mm off the edge of the rotor. What i wanted to quantify was whether the caliper pistons did the same. So i removed the pads, put a square across the edge of the rotor to see if the pistons did overhang, or was it a matter of paralex error (spelling?)

It turns out the piston does sit off the edge of the rotor. But be are talking about 0.5-1.0mm. If you consider the wall thickness of the piston, well the id of the piston is sitting on the rotor, but the OD hangs off the edge.

So there is no way the pistons are able to rock over the edge of the rotor and cause pad knock off! The pads appear to be wearing unevenly more as a result of the slots not wiping the entire pad area, but instead sweeps the dust to the outside of the rotor where it is eroding the outside edge of the pad. So one day this week ill get the rotors machined and square up the pads.

So at this point i was left thinking that, ok so the caliper could be located 2-3mm futher in to ensure the piston face are well and truly on the rotor face...BUT

What i found next throws all previous thinking out the window. Looking at my std rear calipers, rotors and pads, would you believe the caliper sits relative to the rotor exactly the same as the fronts. The pistons offset to the rotor is the same, and the evident pad wear looks to be the same:)

So that tells me if Nissan set up the rear calipers to be orientated to the rotor this way, then the people that did my front upgrade and offset the calipers the way they have, are on par with the factory rears...so cant be the cause of my current problems.

So what i now need from someone is to have a close look at how the caliper and pistons are offset relative to the rotor on the std 280mm GTST setup.

I will post up pics later in the week, but right now im thinking the calipers are fine. I will talk to Race Brakes during the week, he will probably laugh at me, but thats cool, if you want to learn anything in this world you sometimes have to risk looking like an a55:)

So after this, i cleaned off all the dust , checked/nipped up all the connections, and bled the brakes with 600ml of Motul RBF600. The lines looked pretty clean, and their didnt appear to be any air pockets.

When i put the pads with backing plates back in, i watched the caliper/pistons as a friend pumped the pedal...the movement / flex in them was disgusting:(

LOL...now Geoff told me to get rid of these 6 months ago, but if Nissan put em there, i wanted to keep them. But im now a convert, i immediately ripped out the backing paltes/shims and put the pads nack in. This time watching the caliper/piston move as the pedal was pumped showed a lot more direct force being applied to the pad back.

Taking the car for a drive the pedal immediately feels a lot firmer and harder. So whether it was the shims being caked with crap and meant that some of the pedal pressure was being used to take up the give on the shims instead of move the pistons/pads onto the rotor ... or.... there was a bit of air in the lines which have now been bled out. I think more the former, but probably a bit of both

So for now the car is stopping a lot better:)

I suspect that there is still something a little suspect about my master cylinder, mainly because of the noise you can hear from pedal/master cyulinder when you pump it.

So this week will get the rotors machined and pads squared up and have the experts have another look at the master cylinder, im thinking im in the clear and there is nothing wrong with my setup. But im not informed enough to be stating this for a fact, but ill talk to a few more ppl and see where we sit:)

So right now, my thinking is if the caliper/rotor offset is good enough for Nissan engineers then its good enough for my brakes. So stay tuned i should have some more answers mid week:)

[GTRgeoff]

How's about I whip up a master cylinder stopper for you? will need the car for about 1/2 hour. Maybe the firewall has developed some previously undetectable flex.

The backing shims I took out because they wanted a lot of money for the replacements, and mine were cooked and warped from running metal on metal rear pads at Sandown when the pads collapsed. Was giving a really bad pedal so I looked closely and decided that I would try to live without them. Given the brakes still don't boil I consider it was worth the effort. That was my only concern. Even Brembo's will have some movement on the shims. They are only there to stop brake squeal.

[Roy]

Brake stopper,

You arent goign to like this but i bought a $85 Cusco one on the weekend, figured you were busy enough with the renovations and all:)

[SABBAi]

Geoff, you can feel free to make me up one if you have the time.

Besides, your not allowed to play with the twin turbo setup anymore are you????

[GTRgeoff]

Scott

sure mate, and as for the TT, well until some other tasks are completed I have a self imposed moratorium. Can't even drive it

[Roy]

Ok so an update...my verdict, there is nothing wrong with this upgrade...it will work a treat as it has for years for me. My hitch was maintenance related..

I still think the better caliper to use would be of an R34 GTT, R32 GTR etc, but the 32 GTST calipers still get the job done. But going off my last post and how the std rear braks are set up, well Race Brakes dont like the upgrade and thats fine, their setups are of course a much better approach, but of course cost more money.

So the reason i was having problems. As my rotors are around 60,000 old and have seen a few track days, they had started to taper towards the edge of the rotor, as touched upon in an earlier post. After machining up the rotors they are still not 100% but they are close. The main problem with my rotor is the combination of the offset caliper and where the pads are located, and the slots in the rotor.

The slots do not go all the way to the edge, which means pad material build up at the end, and the pad then runs over it. So this increases localised wear of the rotor in this area, casuign an uneven taper towards the outer edge of the rotor. For brake to work at theoir best you want two square faces being forced against one another.

And after machining a lip is still evident but much better now.

Now the numbers here may be a little out, but you will get the idea. Any give/slack in a braking system can result in a spongy pedal. The backing plates, flex in the caliper, in the brake lines etc all can add add up to a spongy pedal, which whilst stil lstopping fine, deosnt inspire confidence as its vague under foot.

So considering the difference between a good caliper and a bad caliper is in the realm of 4 thou flex vs 21 thou then it goes a long way to explaining why my pedal was soft.

The lip in my rotor where the slots were was quite pronounced. And the pad was riding this lip. Now consider this lip is probably about up to 40 thou, well that was the main reason for a spongy pedal as the pads were riding/rocking/wearing on this lip in ther centre:(

On top of this, the rotors didnt quite run true on the hub because of a bit of rust/corrosion between the rotor and hub. This being a few thou out more then desired meant that i was getting a bit of pad knock off, and when combined with the other issues, well it was all compounding.

And finally i also had a bit of a friction problem, as the pad was wearing against an uneven surface (remember the localised wear around the slots) the pad had hot spots which again was not helping stopping.

So with a good machining of the rotors, i have about one set of pads life left in them before they will become undersized.

My problem was not the offset of the caliper, or this sort of upgrade, it was the fact that my slots cause localised dust buildup on in the middle of the pad and cause uneven wear on the rotor face, and an age/maintenance issue.

In an attempt to get better wear out of the rotors if you have similar slots to mine, then see the pic below, its a simple mod i have done to these pads...and the car is stopping very well again. It does reduce the surface area a little, which in theory means a bit mroe heat accross the pad face, but the reduced surface area also increases the bite of the pad into the rotor, so in the wash up with ying and yang will make no difference in pad performance

Will see how it all goes at Sandown this weekend, a track that is meant to be very hard on brakes:(

[GTRgeoff]

The short slots, isn't that some DBA gimmick to "prevent" cracking at the slots? So they now have the radius short slots as standard at the opposite angle? Evrery cheap[ solution has a cost I suppose, and you always find out when most inconvenient (and I'm not talking about the actual brake setup)

Good to hear a solution was found.

[GTS20X]

Roy, whilst reading this thread i was going to suggest maching the pads. With the pad backing plates as mentioned they are only there to reduce sqeal, when i was working at Mitsubishi we used to remove them & apply CRC anti-squeal instead as they contributed to brake shudder, also i've removed them on my on cars & noticed improved pedal.

Carlos

[Gav]

Sorry if it's been covered here already, but I didn't quite understand the following:

Will this system (i.e adaptors and larger discs) still fit within the 16" wheel?

Specifically thinking of factory R32 GTR wheels.

[GTS20X]

Does anyone know where to get adapters to mount R32 GTR calipers over larger discs?

[saga]

hi guys, how do i find out if R32GTR brake calipers fit on R34 25GT(nonturbo) standard discs(both front and rear) ? ist a bolt on upgrade? any modifications needed? i couldnt find anything about brakes upgrading for nonturbo r34s on this forum.

thanks

[saga]

generally which calipers performs better: R32GTR's(sumimotos not brembo) or R34 GTT's? assuming all other components are the same: rotors, braided lines, etc.