i bought a 9 bolt disk for $75 last summer.off course it's my luck that it's a 2.77 gear and out of a 88 Z so it doesn't have the PBR calipers it has the crappy iron calipers.so i started to do some research as to what i needed to do to put the PBR calpiers on this rear end.through my almost endless searhing it was mentioned that the 10 bolt backing "may be" modified to be used on a 9 bolt rear end but i never found anything else about using the 10 bolt backing plates.i called the local chevy dealerships parts department.the 10 bolt backing plates were only $15 apeice so i ordered the backing plates thinking if they didn't work i was only out around $30.i picked them up yesterday and took them home and marked them up as to where they needed to be modified.i took a trip to work to use one of our horizontal milling machines.i brought them home and mocked them up and this what it looks like.

This link, which is on the FAQ board, might have proved usedful:

https://www.thirdgen.org/techbb2/sho...hreadid=246768

JamesC

that page is refrenced on a few dozen different threads and it was helpful but it doesn't go into any detail on modifing the 10 bolt backing plates for use on a 9 bolt.

True, but it does provide a "possible" source for the 9-bolt backing plate. Ed Miller is perhaps another. Personally, I would have preferred the correct (unmodified) plate if possible.

JamesC

I don't know if I'd trust those elongated holes to keep the bracket in place.. just MHO.

Ed

i agree and i'm not going to trust them.my plan is to make a template of the hole pattern then weld the holes up and redrill the new hole pattern.

Probably could have just swapped them left for right and drilled 4 new holes in each.

Thats what I did

if you have a welder and some copper round stock, you could stick a copper 3/8" bar in the 'good' part of the hole, and weld up the rest.

then again, they were only 30 bucks. like others said, just swap the left for the right, and the holes will fall in new material, with no problems 'ovaling' holes.

why would you want to use copper?

Because copper wont weld with steel, and when done filling in, you have your hole for you bolt. no drilling needed.

i did what Apeiron had suggested and flipped them around and drilled new holes.i still welded in the old holes so it wouldn't look like swiss cheese.

also, i can't tell in your picture, but the mounting holes for the PBR calipers need to face the REAR of the car or the will interfear with most of your suspension, it almost looks like the yolk is peeking out from behind there so i just wanted to make sure you knew that.

they are facing rearward at about 4 o'clock

You can still get the 9-bolt plates from GM, I just ordered a set this morning. they only list them for '90 model year, at least that is what my friend at the chevy dealership said when he tried to look up an '89 model year.
thanks
Luke

I've been under the impression that GM had long ago discontinued the 9-bolt backing plates. Let us know if you actually receive them.

JamesC

Sounds like you're getting 10 bolt backing plates. There was no 9 bolt in 1990.

That is what I thought also, but he said they where for a 7.75 ring gear rear end. I guess I will have to wait and see what I get. I may have spoken too soon I guess.


thanks
Luke

Have you got part numbers?

The 10-bolt part numbers are as follows: 10136853 and 10136854.

JamesC

I just called him this morning and had him order them, I should have them tommorrow or monday morn. I will post the part numbers when I can. I really hope they are correct, but I now have my doubts.

thaks
Luke

yup they are 10 bolt brackets, same part numbers as above. The computer listed them for 7.75 ring gear diffs. I have brackets now anyway. I wil just swap side to side and redrill. are there any bigger brakes that will fit with these brackets?


thanks
Luke "spoke too soon" Johnson