R32 Front Brakes not fitting

[Chopstick Tuner]

Hey folks, 

Long story short I had an issue with brake squeal, and since fitting the oem shim kit, they're tight af on just the inner pad.

Just want to see if anyone has previously encountered this issue before I go spending more money on rotors/ machining etc

 

So full story. Since replacing front brakes I've been chasing an issue with horrible brake squeal at all temps.  I had fitted DBA T3 296mm front rotors (as car evidently has R33 gtst/32gtr calipers since 296mm were on it when i bought it), Bendix Ultimate Pads and rebuilt the front calipers using an OEM rebuild kit so pistons now move nice and free. With these pads I couldn't fit the oem anti squeal shims/plates whatever you prefer to call em (they have their own built in shim which obstructs the oem ones), so I didn't and they screamed at medium braking no matter what I did. 

So to solve the squeal I've swapped them out for a set of Project Mu pads meaning I was able to fit a full new set of oem shims. However once pads were in I noticed there was twice as much pad free play on the outer pad than the inner (inner was quite tight) and once wheel was on and tightened it couldn't turn, as it has pressed the rotor against the inner pad. 

 

So while the problem may seem silly, I'm struggling to think of reasons for this aside from rotor offset being incorrect or rotor being too thick, or caliper pistons being stuck but they move fine and all 4 pistons are sitting in the same position. Is there a difference in rotor thickness between 32 gtr and 33 gtst? Is there difference in offset/depth? Have I missed something completely stupid?

I could remove the shims but that doesn't really solve the underlying issue lol. Happens on both sides if that helps.

 

Thanks for reading this long post. 

[Duncan]

FWIW, I believe that while we often say r33 gtst and r32 gtr (non brembo) have the same size discs, i seem to remember R33 has a 30mm disc thickness and GTR had 32mm. How thick is the disc you have? The caliper/disc offset is the same.

This is on a r32 gtst, right? I would check there is no shim or washer of any sort between the hub and caliper mounts

 

[GTSBoy]

Yup. GTR is 32mm. Plain R33 is 30mm.

Caveat being that the 324mm rotors on the Brembos go back to 30mm also. Makes it confusing and you need absolute clarity when talking about these brakes.

I don't know for sure, but I suspect that a 32mm rotor is not a good fit in the GTST caliper. I think they might actually be different (the calipers, that is).

[Chopstick Tuner]

12 hours ago, Duncan said:

FWIW, I believe that while we often say r33 gtst and r32 gtr (non brembo) have the same size discs, i seem to remember R33 has a 30mm disc thickness and GTR had 32mm. How thick is the disc you have? The caliper/disc offset is the same.

This is on a r32 gtst, right? I would check there is no shim or washer of any sort between the hub and caliper mounts

 

Yes on a R32 gtst, there's nothing between the caliper and hub though. But yes I'm fairly certain the rotors I ordered were for R32 gtr which would be 32mm. Still doesn't explain the issue unless it's a manufacturing issue with the rotors which seems unlikely given the brand. 

I really don't want to buy any more parts just to diagnose 🙈

 

Tried to reply earlier but wasn't working for some reason so I'll reply to both comments*

 

Yeah it wasn't as easy as I'd like to slide the pads over the rotor with all the hardware attached unfortunately. Thinking I may have to do the unfortunate compromise of getting rotors machined down to fit rather than buy more new ones. Perhaps chassis matters slightly ie 33 calipers + 32gtr rotors on a 32 gtst. I'm not sure, I find it unusual

[GTSBoy]

1 hour ago, Chopstick Tuner said:

Perhaps chassis matters slightly ie 33 calipers + 32gtr rotors

See my suspicion above. R32 has nothing to do with it. I had R33 calipers on R33 296x30 rotors on a 32. It's fine. But if, as I suspect, the R33 calipers are not as wide in the body as the GTR calipers are.....then snap. There's your problem.

[Duncan]

The thing is, the offset is meant to be the same so when the disc is properly centred in the caliper it should be equal spacing for both inner and outer pads, so disc thickness should not make a difference (although, it might show up a difference). New pads can also show up a difference because they can be taller than factory pads too

With the rotor bolted to the hub, what is the gap to the caliper on each side?

I'm not sure what is happening in your case, but personally I'd be happy to put a spacer of the right width to centre the caliper on the disc if it is only out by a mm or 2 (the spacer needs to be half the difference between the 2 gaps). It is possible the 33 gtst calipers had their mounting machined before they were installed, you really couldn't tell without comparing/measuring them to another set.

BTW if you go down the machining route, you also have the option of having the pads machined instead of the disc which might be a cheaper solution over time

[Chopstick Tuner]

The gap seemed pretty equal tbh, I measured quite roughly using a tape yesterday so I'm not 100% on the measurement (perhaps 19mm from caliper inside edge to rotor,  from memory) but were the same both sides of the caliper. On passenger side both inner and outer pad seemed equally jammed and same result, can't spin it. 

I've pulled them out for a look and rotors are definitely 32mm if not a hair thicker. I did consider machining rotors as I thought it would be a more permanent solution but discovered there's a marking stating minimum thickness of 30mm 😅 

 

Just to clarify, where would you consider a spacer on the caliper? As the caliper sits on the rotor side of the hub, the only way to sit it further away from rotor would be to machine a bit off the mounting point of the caliper. 

[Duncan]

All good, I misunderstood, I thought the issue was the rotor was not centred in the caliper but it sounds like it is OK. Which is a good thing because it is a much easier problem to solve

So for sure, I'd be looking at reducing the pad thickness. Its 1mm per side so not a lot required to get them fitting, some aftermarket pads are just that bit higher and while it isn't surprising suppliers treat R32 GTR and R33 GTST as identical for supply it looks like the combination of both being just a bit bigger has caused a problem.

[Chopstick Tuner]

1 minute ago, Duncan said:

All good, I misunderstood, I thought the issue was the rotor was not centred in the caliper but it sounds like it is OK.

So for sure, I'd be looking at reducing the pad thickness. Its 1mm per side so not a lot required to get them fitting, some aftermarket pads are just that bit higher and while it isn't surprising suppliers treat R32 GTR and R33 GTST as identical for supply it looks like the combination of both being just a bit bigger has caused a problem.

Totally understandable, my post wasn't entirely clear because I wasn't yet sure what I was dealing with. But having fitted up the other side it seemed just too tight a squeeze to get pads past the rotor both sides. It's entirely possible it pressed slightly harder against one pad but I think the issue still stems simply from thickness unfortunately. 

I'm going to look into getting pads altered and see how that goes. It's definitely not much, as everything fits with no shims fine like I had before,  but that's obviously not ideal lol

 

Always more to learn working on these. Cheers for the insights!