I have a 9 Bolt to put in a 87 Formula I am building (the car has the WS6 package but drums in the rear....WTF is up with that?). Anyway I need the complete brake assembly for the rear end with the exception of the caliper mounts and perportioning valve. I can not seem to find a set up for a 9 bolt but have found a few for 10 bolts. What parts are interchangable between the two set ups? I have "searched" on here and havent gotten a clear answer but it looks like everything except the mounts (which I do have) are the same....is that so??? I just want to be sure before I buy a set and cant use them!

Thanks!

Everything is exactly the same except for the backing plates, which are exactly the same except just different enough not to interchange. You gotta have 9-bolt ones to go on a 9-bolt.

Not sure what you mean by "mounts".

No offense to you personally, but....

This prevalent "WS6" foolishness is so amusing. NOBODY cared about that, until cars started appearing in the late 90s with badges that say that. Now everybody, especially the Firebird people, just get all feverish and weak in the knees over "does my car have WS6" and stuff like that. WS6 has been around for a very very long time; it's just meant different things in different years. It's a SUSPENSION package, which means, it has to do with things like steering and springs and sway bars. It's NOT a BRAKE package, since as we all know, the RPO codes for those start with J. So there's not necessarily any connection between the 2. And it certainly doesn't mean, "the baddest possible of everything everywhere on the car".

Incidentally, my 83 car (Z28) has WS6, and it came with drum brakes. In my year, it meant you got something like 33/21 sway bars, some extra frame bracing, tight-ratio steering, and about 450 lbs/in springs in front. Maybe some different struts & shocks, I don't know about that and they were totally worn out by the time I got it at 40,000 miles anyway. One of the first things I did to the car was to replace them because they were so non-functional. It included different details in other years.

Thank very much for the info on the braking componets. I think the mounts I am talking about are the backing plates you are talking about....they are the pieces that bolt in between the axel and axel housing and hold the caliper. If so I have those but just didnt know the proper terminology for them.

Thanks for the lesson on what WS6 means too....I have only had 4 cars equipped with the WS6 option. A 88 GTA in HS (got it in 92) a 1999 30th Aniv WS6 and now currently a 1987 Formula I am "restoring" and a 2002 WS6 Vert with 2,800 miles on it. I am well aware that the compenents of the WS6 package changed from year to year and on 3rd gen cars it was primarlily a suspension package, but the reason I mentioned the car had the WS6 package and rear drums is because supposedly (and accoarding to the tech data on this site as well) starting in 86 ALL WS6 equipped cars came equipped with a 9 bolt and rear discs. Well not all of them did.

But seriously thanks for the info on the brakes...that will certainly ease my search!

I believe the main difference between the 9-bolt and the 10-bolt brackets are that the 9-bolt ones have a bigger hole in the center, and the bolt hole pattern is bigger and the bolts aren't spaced the same. It might be possible to grind the center holes out of 10-bolt ones, and maybe flip them over and put them on the other sides, and drill 4 new holes. I'd have to go out and compare the sets of them that I've got of the 2 kinds.

There was a thread describing how to do just that not so long ago.

These are brackets I have (I know they are for the 9 bolt I have)...are these the brackets your talking about or am I missing something else?

Also can you tell me if the side pictured goes to the inside or the outside and if the caliper mounts to the front or the rear of the axel (2 o'clock ish or 10 o'clock ish?)

I do apprecaite the help...its been a while since I have had a 3rd gen car!

Yup, those are they.

The side you have pictured goes against the axle flange.The "inboard" side.

They only go one way because the bolt hole pattern isn't square. The calipers will mount to the rear of the axle flange with the caliper below the axle centerline. So the one in your pic is the right side one and it goes on the axle in roughly the orientation in the pic.

Thanks again...you have been a huge help!

Youi might find some pics/info in the following link that will be helpful:

https://www.thirdgen.org/forums/faq-...iscs-89-a.html

JamesC

Well that opened up a whole new can of worms....my 9 bolt is from an 89 Iroc. So I asume the brackets I have are for PBR calipers...right? So that means I have to find a disc brake set up from a 89 or new car..right?

I have a chance to get the rear brakes from an 87 GTA...I can use all those pieces as long as I get the mounting brackets with them? I know the PBRs are better, but the standard 87 GTA disc brakes will work just fine for my needs...I am just trying to get the rear end in the car at this point.

Correct.

JamesC
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Yes.

JamesC