I'm trying to install a 12" rear kit for my 10 bolt but the caliper will not fit over the rotos with the pads in place. The pistons are fully pushed in and there is still not enought clearance by about 1.5mm or so. Has anyone experienced this before and how is it best to solve the problem?

Also, how much clearance should there be between the caliper and the rotor?

Thanks.

 

Is the cap off the master cylinder? I found that makes a small difference.

 

if it's anything like a vette the 12 inch calipers are only designed to fit those rotors because of the rotors thickness. the 13 inch vette rotors are visibly wider then the 12" ones.

 

Hi,

Thanks for the reply. The brakes are not yet fitted so have no connection to the master cylinder.

This is actually the Ed Miller 12" rear kit so I would have hoped that it would have gone together fine. However, you've now got me thinking that the pbr calipers supplied, with are 3rd gen ones, just will not work with the rotors, which are 12" rears for a late model C4 Vette.

Not good.

Any other ideas while I try to reach Ed?

Many thanks.

 

I've just finished installing a hose & cable kit from Ed, and he has been very responsive to emails on weekdays.

I'd recommend you hit the local parts chain store and have them get you a C4 caliper for comparison. Keep it clean and don't bolt it up, just compare the piston and bracket geometry and see what you find...then return it.

 

Hi Kevin,

I'm in contact with Ed too but time is an issue here. I'm in the UK which doesn't help but will be over in the US from Monday, so getting an idea to the solution before then is ideal so that I can bring anything back that I need to. I'm waiting for Ed to call me back today so we shall see how it goes. I'd like to say that he is working with me to solve the problem, so there are no problems with that respect. Just time is of the essence.

 

I'm currently trying to find out the thickness of stock late model rear discs to see if there is anyway these 12" ones will fit, which I'm starting to think that they wont!

 

those rotors look wider then my 1990 12" rotors. Those look more the thickness of the 13" rotors. The 12" rotors are say around .90 something and the 13" 1.00 something. That could explain your 1.5mm clearance issue however even the large brake vettes with 13" fronts I believe still had rhe standard rear brakes.

I will try and get a picture of my 90 vettes rear setup if you want it.

 

Thaks Jeff, I'd appreciate that.

From what Ed has told me, the rear rotors in the C4s changed in later years to these ones. I'm now starting to wish I'd just gone with the standard 11.6" rear rotors that came with the late model thirdgens- I was trying to fill the wheels up just that little bit more. Were the thirdgen ones vented or solid?

Also, from speaking to Ed, the calipers in this Kit I have are the standard thirdgen ones.

 

If by "late model" you mean LS1 12" rotors, they specify 1.25" thickness. I just finished swapping LS1 rear brakes onto my '82 car, bought the basic pieces at the junkyard and got the hoses and cables from Ed.

The stock 3rd/4th gen rear rotor is either 0.81 or 0.87" thick depending on where you get your info.

There is a 1.05" thick rotor somewhere but I can't recall where I saw the info or what vehicle it fit.
EDIT: found it, base model C5 has a 12" x 1" rear rotor:

http://www.pro-touring.com/forum/sho...d.php?p=604676

The LS1 rotor is 1.25" thick.

 

Thanks again Kevin,

I just went and measures the rotor and caliper again with a tape measure. The rotor is 26/32s thick while the caliper gap with pads installed is 22/32s wide. I think that there is no way that this combination is going to work with the parts I have.

 

3rd gen calipers will work w/ 12" vette rotors, I have that exact setup (only used Ed's brackets, the rest I got myself)

Do you have the proper abutment bracket? Try to fit the caliper w/ the pads in place over the rotor without the abutment bracket. if it fits then, you have the wrong abutment bracket. They are different for the JL9 and J55 brakes.

This is my setup, sorry don't have a better close up pic but this is the same as what you are trying to put together


EDIt, now that I think about it...I thik I used 12" (JL9) corvette FRONT rotors. Didn't need to shim anything either. The JL9 stuff is only about .9 wide and it's a 12" rotor.

The rear rotors from a J55 are 1.1" wide or thereabouts, it will never fit without using the vette abutments & calipers.

 

I think in 95-96 C4 vettes went to the grand sport style calipers and rotors or something like that. but just visibly your rotor look thicker then my 1990 vettes and my 90 vettes rotors appears the same thickness as my 97 camaro rear rotors as well. I think the very late C4 vettes din't have PBR calipers as well. As for pictures will have to jack my 90 up for that so that would be later today. You should ask member twin_turbo he knows a lot about brakes on the C4.

 

Jeff, you have JL9s on yours, 12" front 11" rear, the J55 (grand sport, zr1) has 13"s front and 12s on the rear that are 1.1 thick instead of .9 for the JL9s.

 

there time is limited LOL .... As long as my stock rims will clear different rotors and calipers.

 

Yes it will clear.

 

Twin_Turbo,

Is that gold part of the caliper the abutment bracket?

 

Yes, that's it.

 

Just checked it without the abutment in place and it still wont go in with the pads sitting flush against it.

The number on the abutment is K332-071C5 if that means anything to anyone?

 

means back to the drawing board.

 

Get some 12" JL9 front rotors, they will fit.

 

those calipers kinda look like what on the back of my 6 banger 97 camaro

 

They are late 3rd gen calipers, same as the vette calipers and 4th gen, all PBRs. Only diff is the parking brake setup

Rotor specs: (diameter - thickness)
front
82-92 F-Body 10.50" 1.04"
88-92 F-Body 1LE 11.85" 1.04"
88-96 C4 Corvette NON-HD 12.01" 0.79"
88-96 C4 Corvette HD J55 12.99" 1.10"

rear:
88-92 F-Body PBR 11.67" 0.78"
93-97 F-Body 11.54" 0.79"
C4 Corvette 12.01" 0.79"

 

The rotors I have are well under an inch though. Something is serriously wrong with all of this I feel.

 

Picture would help.

 

I just checked, the rear rotors for the J55 setup are the same as the JL9s so they are .8 (see above post)

The abutment brackets hug the rotor pretty close, that's normal
Those pads, what are they? Are they the correct ones for these PBRs?

 

Rotors for PBR equipped 3rd gens are 11.6" x .81". Both front AND rear rotors for C4 Corvettes equipped with standard brakes are 12" x .81" thick with the only difference being that the front C4 rotors have a different offset.

The '89-92 3rd gen PBR rear rotors and all '88-96 C4 rear rotors have the SAME thickness and offset so, when used with the correct backing plate, they interchange. Period.

As far as clearance between the caliper and rotor, it should be .13-.16" per side. This is found by taking the abutment space where the rotor sits (.940")- .78-.81" :

.94-.81"= 0.13"
.94-.78"= 0.16"

C5/C6 and LS1 rear rotors are 1.00" thick, just some useful info others may want.

I will be posting up some pics shortly but here's a short description. The PBR rear caliper pistons have a hole in them where the piston actuator assembly sits. The actuator has a threaded rod that is shrouded by a rubber bushing. Even if the piston is seated fully in the caliper bore, if this bushing isn't pushed all the way up the threaded rod so it is flush with the end of it, this may cause the actuator to not be fully inserted into the piston which may be the cause of Robert's issue. You can pull the actuator out of the caliper, check to be sure this isn't the case and insert it back into the caliper without issue, just make sure you don't pinch the circular dust boot when you push it back in.

Ed

 

That's just the casting number, they're all the same since the C4 rear and '89-97 PBR calipers are the same.

Ed

 

Only the GS 'Vettes got GS calipers, all manual '95 Vettes and ALL '96 Vettes got the large 13" HD front brakes with the HD calipers. ALL '88-96 C4s have the SAME rear calipers and rotors, regardless of brake options. Grand Sport rear calipers? Only difference is black powdercoat to match the fronts.

Ed

 

Here are some pictures of the caliper with the actuator? out.


Thanks Ed,

Hopefully your pictures will shed more light on what I'm looking to do with it.

 

Here ya go:

Here's the parts in question. The piston, collar, and actuator assembly. Note the bushing on the end of the actuator that inserts into the piston. The bushing needs to be pushed all the way onto the threaded part, which is what the bushing is on and covers up but is seen in another pic below.







When installed, the actuator needs to bottom out in this hole, lube it up with brake fluid or the clear fluid that comes in a rebuild kit. The piston goes in first, then the assembled actuator with the collar and dust boots which is shown in the last pic.



Also, in this pic, make sure the short pin that the e-brake lever pushes on to engage the parking brake is seated in the notch in the brake lever as shown here, if not it will push the actuator out which will also cause the rotor not to fit inside. The pin is to the left of the return spring and goes through the caliper casting:



Ed

 

I measured the actuator distance you posted and got the same and with a set of new HPS pads, the space between the pads was right at 28/32" (.875") between the pads. The actuator pin length should be 1.10" overall when removed, I measured 4 of them I have on hand and they all were the same length.

Ed

 

RMK!!!

I think I got it. In this pic you sent me, you have a metal shim installed on the pads. Remove it and you should be good to go, they arent' needed and take up space:



Ed

 

Hi Ed,

No time to test it as I've just about to leave. I didlook at the pads and see the metal shim you are referring to. They are not very thick, but it could just be enough. I'll post updates in 2 weeks.

Thanks again to everyone who has replied.

Robert

 

metal shim? those super thin stock on peel backing shims? they are to reduce rattling and squeeling. Should fit just fine with them.

 

 

The ones that came w/ my pads are hair thin plastic, nowhere near 1.4mm. I used original delco pads.

 

The only ones I have ever used with success are the adhesive backed ones found on PBR pads. Anything else I trash.

Ed

 

the delcos had adhesive backing on the anti squeel pads too.

 

Ed,
What kind of price you get for the calipers and brackets? It's the only thing I need to finish my rear disc swap.

 

Well I finally got time tonight to mess about with this project again. I have removed the shims from the pads and the discs do now fit! Hell of a tight fit though. Not sure if I should just let the first few miles wear the pads down slightly or if I should san them so they are not quite as snug?

I'm planing to mock fit the whole thing up on Sunday to see how it looks.


Ed,

Did you receive those brackets I posted back to you?

 

Yes, got them just fine, thank you. Just let the pads wear down a bit, the return springs on the piston assembly will keep pressure off of them.

You should be good to go now.

Ed

 

I'll keep you posted. If I have any other questions I'll just post them in this thread to keep it all in one place.

Thanks again.