Installing 1989 & newer PBR rear brakes on my 1988 GTA 9 bolt. Sourced the parts (mainly the caliper backing bracket that mounts to the rear end and rear brake cables) from a 1990 GTA 9 Bolt that I purchased complete. All other parts are new or rebuilt. Issue: caliper, loaded with pads, and slipped over the rotor will not allow the caliper bracket to reach the backing plate mount. There is about a 1/4-9/32" gap. This is true on both sides.

At first I thought it was the axles not fully seating but after many hours of messing around with the axles and differential I finally determined that the axles were seated properly since the axle retainer fits flush on the axle plate.

I thought I read somewhere in the Brake Board that spacers were required for this setup but there is no mention in the shop manual. Any ideas or suggestions would be welcomed!

 

As far as I know 89 was the last year for the 9-bolt. But I digress. IIRC, only the 10-bolt required shims. Though the following link is about a 10-bolt conversion, everything concerning the brakes, aside from the backing plates, is the same. Perhaps the pictures will be helpful.

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

JamesC

 

James, thanks for the feedback. I had already read your very complete posting on this brake conversion to your 10 bolt rear end and it was very informative and helpful - great job! The new rotors match the used ones exactly in height and diameter so that isn't an issue. I still have the axles from the 1989 (or whatever year) 9 bolt that came with the PBR setup and I will compare the length to the 1988 versions - maybe that is where my issues are coming from. I honestly don't know what else it could be unless the calipers are not from a 3rd Gen. even though that is what I ordered from Rock Auto. Working on this conversion, and with the 9 bolt, has been one of the most frustrating experiences of my long, amateur, mechanics career.

 

Humm, well, though 9-bolt axles are different lengths from side to side (unlike 10-bolts), I've never heard that they differ from year to year. You might have received fourthgen LT1 calipers (93-97), but they're nearly identical to the 89-92 version. How about backing plates? What did you use there?

BTW, can I assume this a disc to disc swap? If not, the axle flange/rotor interface may be the issue.

JamesC

 

James, I agree, there is no indication from the parts manual that there is any difference in axles between the years, the 1985-1991 7.75" J65 rear disc axles have the same part numbers. The 1985-86 drum brake axles are different for the 7.75" however (must have dropped the drum brake option after '86?).

I've thought all along that my issue was with the axles properly seating in the differential but after taking out the diff. and checking that the two sections of splines were aligned (they were) and then checking the depth of engagement of the axles after re-assembly with grease they seem to be fully engaged into the diff.

This is a disc-to-disc conversion if successful although I'm about ready to go back to the factory set up if I can't get this figured out. Thanks again.

 

Update & Resolution: Finally found an outstanding local expert mechanic and all-around car restorer to examine my 9 bolt. Needed to be rebuilt, as one of the cones was close to bottoming out, all the pinion pre-load was gone and one of the carrier bearing cups was flaking. Found a new posi. unit and a slightly used set of 3.27 gears even though my gears were still in VG shape. Replaced all bearings and seals and set the clearances to factory spec.

One thing I had overlooked is that the factory backing plates are marked R & L. Also, the lips on the backing plate face to the inside, the opposite of what we thought they should (look in Factory shop manual and it shows the correct orientation but I missed that). All said and done, I have a "new" freshly painted axle with the brake upgrade that should last another 50-75-100,000 miles - very happy at this point to have this behind me.

Thanks again for everyones comments and suggestions.