I am in the process of doing the rear PBR conversion on my 88 GTA that originally had discs. I got the 9 bolt backing plates from AndyZ28, and have them mounted as directed, against the flange. I followed the stickers on them as to which was left or right and such. When installed, the welded on washers where the carrier bolts to are on the outside. I got a pair of rear rotors for a 93 Trans Am from the parts store. Rotors are the right diameter, and slide right on. Problem is, my PBR carriers are not centered over the rotor and rub on the inside. It seems that thr rotor itself needs to move outward a bit. I did not use any shime at all, and by looking at it, if I put some in, it would move the carrier bracket even closer to the rotor, making it worse. In theory, putting some washers behind the rotor would do the trick, but somehow this doesn't seem right. Did I do something wrong here, or am I just missing something simple. Any help here would be great. Thanks.
Terry

 

Hi Terry. I also have a set of his plates but haven't looked at them in a while. Do you think it would work if you swapped plates from side to side or even turned them around? I'd try that stuff first, and give him a call.

Ed

 

I thought about turning them around, with the welded on washers or spacers facing inside, but it seems like that would make it so that things would be even further out of place. Is it possible that the rotor is my issue? Maybe the parts store gave me the wrong ones? I am tempted to go back and get the 3rd gen rotors listed for rear 1LE, even though they are much more money and see if they fit. The only way I see things working here is to space out the rotor, or shave some off the plates on the welded spacers. I guess I'll email Andy and see what he says. Thanks.

Terry

 

When you mounted the plates, are the washers on the inside? In other words, if they were removed for a thinner washer, would that work?

Ed

 

The way the plates are mounted now, the washers are facing the wheel, and the carrier mounts against them with the bolt coming in from the other side. If those washers were thinner, then yes it would work fine. Sadly, they are welded on, so not much I could do with them. I emailed Andy, but haven't heard back yet.

Terry

 

I read somewhere that 4th gen Rr rotors are thicker that 3rd gens(1in vs 7/8 or thereabouts).Sounds like the thicker rotor may be the problem.If im right about the rotor thickness?

 

The LS1 rear rotors are thicker but the '93-97 LT1 rear discs are the same thickness as 3rd gen '89-92 rear discs. They use the same caliper so the have to be.

Here's an idea. Put thin washers between the backing plate and the axle flange, that would do it without having to mod either the carrier or Andy's nice backing plates. That's the route I'd probably take.

Ed

 

Hmmm...From what I can tell, if I put washers between the axle falnge and the backing plate, that would move the backing plate closer to the rotor, making things worse. Since this is a 9-bolt, and the axles bolt in, wouldn't the distance between the backing plate and the rotor remian constant no matter if there were washers in ther or not? Maybe I am just visualizing this wrong, but it is worth a try, cause I am stumped. Thanks for all the help Ed. I did manage to get the front torn apart, so i have the spindles to send to you and i will get them out next week. Thanks again.

Terry

 

BIG Oops there, I dont' know what I was thinking but it was backwards....


Thanks for the heads up on the spindles, I need a few sets actually but please don't rush, I'll get some on Monday.

Ed

 

I took some pics, so maybe that will help. First time posting pics here, so they may or may not work.













Hopefully, this will make more sense now. Thanks.
Terry

 

Go order the correct 1LE rotors for an 1989 and up 3rd Gen. Part numbers and Rotors ARE different. A minor difference in rotor offset and or thickness can cause the problems you are having.

Raybestos number for 89 to 92 is #6995. 93 Trans -Am is #56407.

Edit: Just checked my Raybestos Master Catalog. Offsets ARE different. #56407 has an overheight of 1 13\16". #6995 has an overall height of 1 63\64". That's enough to cause a problem. Don't have thickeness for #56407 rotor listed. Raybestos master Catalog shows different rear calipers between 1889 through 1992 and 1993 thru 1997.

Go get the correct rotors and problem will likely be solved.

 

I have the same thoughts on thr rotor as far as offset goes. I think I will take a chance and return the 93 rotors I bought and order the Raybestos. If nothing else, it will eliminate one possible problem. Thanks for the part numbers.

Terry

 

I just called the local NAPA as a possible alternative, and they have a rotor listed for like 22 bucks. The guy said it measured out at 11 43/64'' diameter, which sounds right. I had to explain to him what the 1LE rotor was, but this seems right. I am curious as to why the Raybestos lists at 51 at Advance Auto, and this one from NAPA would be so much cheaper. Any thoughts before I buy?

Terry

 

Beware of cheap off shore brands. They are often made in places like Taiwan and Thailand. Cheap materials and poor machining. You get what you pay for. Stay with a name brand such as Raybestos, Bendix, Wagner or AC-Delco. You already got in trouble once for trying to go cheap. Why try for problems again?

If the Partsman isn't sure what a 1LE is....I'd look for a better shop. It's pretty simple to look up Rear rotors for a 1989 to 1992 Camaro\Pontiac. It's also pretty simple to cross reference Part Numbers.

 

You have an excellent point. I called Advance to check on availability, but of course they said they do not carry Rabestos(even though they are on their website, listed at 51 each). So I called Pep Boys (cringe), and the have the Raybestos 6995 for 24.99 each. Go figure. If I didn't hate Pep so bad, I would have called them in the first place, and had no issues. Gonna run out and get em (they are in stock) and see what happens. Hopefully in a few hours, I'll have something good to report.

Terry

 

Success!! I went and got the Raybestos rotors and they fit perfect. I don't know if the first ones I got were simply the wrong rotors or if there is such a big difference from 3rd to 4th gen's. Either way, problem solved and i can finally get this thing back together. Thanks for all the help and info.

Terry

 

Terry, thanks for the pics.

Chickenman, thanks for the great info on the offsets. I know the 4th gen rotors could be used be used to fit over drum rear axles but the different offsets are indeed important, thank you much. I've had very good luck with Raybestos rotors and use them almost exclusively.

Correct, but the only differences are in the casting and the e-brake cable bracket, that's it. They'll interchange beautifully. The only interchange issue is that if you have relo brackets, the 4th gen calipers may interfere with them due to that big round cast iron vibration dampener thing bolted to the e-brake cable bracket. I take them off all of the rear calipers I deal with.

Ed

 

Good to hear you got it solved. Now go out and bed those puppies in !!

 

Not quite ready fior the road yet. I have the front all torn apart doing Ed's C4 upgrade, along with ball joints/tie rods and shocks/struts. Basically a complete suspension/brake revamp all at once, but i am getting closer.

Terry

 

Hmm that makes me think i hope my rear rotors are thirdgen.