Ok since the 89 is the only year the 9 bolt had the PBR's and the backing plates are disc. from GM, can the 90-92 10 bolt plates be used if I welded the holes in and redrilled for the 9 bolt flange ?

 

As far as I know this cannot be done practially. Also for any OE parts swap to rear disc. you must start with a rear that was originally a disc rear. The drum brake rears use completlely different axles.

 

This is starting with an 88 disc rear and swapping to the 89 up pbr's since the backing plates are different, wanted to know if really the spacing off the flange to axle on the 9 and 10 bolt disc's is the same, thats all that reall matters, the holes can be redrilled.

 

Here is a parts list of what was used by Tad Nixon to convert his non PBR 10 bolt disc rear to the '89-'92 rear disc setup. It doesn't look too expensive.

Caliper carrier #10112652 need 2 $23.22 ea.
Backing Plate #10136853 L/H $10.73.
Backing Plate #10136854 R/H $10.73.
Parking brake cables #10164125 need 2 $14.11 ea.
From gmpartsdirect
Earls Braided Flex Lines # 361-28A190 $100.00
Fine lines pre-bent brake lines $29.00 a pair.
.I got my calipers from T/A creations for $30.00 ea

I would say a lot of work could be saved by doing the conversion using his method. He used GM parts primarily. I would quess that the 9 bolt stuff can be adapted. But it seems like a lot of extra work.

 

i have these backing plates, if anyone wants i can upload some pics or take mesurements of them, i know their hard to find since they were only made in 89, but they look so easy to make, someone could probably make some money if they have the time to build a few.

 

I'd like to see pics and measurements. I have a set of 10 bolt plates here to compare with, so we can see if the 10 bolt plates can be modified in any way.

 

i found my backing plates for 89 9 bolt rear, and i scanned some images of one of them if someone wants to compare to the ten bolt ones, or wants to try to make their own, there are mesurements in inches too. if it is usefull to anyone i can do the other one too.
pics

 

Are you sure those measurements are right? The measurements for the flange bolt pattern should be trapezoidal.

 

your right its not 2.90, i dont know why i wrote that, it is 3.125. i changed the pic. i checked over the others and they seem ok. i know the pic suck and i wish i had a better way to show the layout,

 

That's somewhat different from the 10 bolt plate then, which has this pattern:

<img src="http://www.precisionbrakescompany.com/precisionimages/12bchev.gif">

Is there any difference in height between the flange mounting surface and the caliper mounting holes?

 

there is verry little offset looks like less than 1/16 of an inch, doesnt look like enough to cause a problem, if it does im sure washers or a shim can be used on caliper, or it still may be easier to modify the 10 bolt plates by drilling.

 

Ok, the height difference is about the same on the 10 bolt plates then.

 

Ok I have a 87 Trans Am GTA and it has th 9 bolt rear end. Can the 89 brake seetup be swapped over as in a bolt on swapor would there be some fabrication envolved?

 

As long as you can find the right backing plates it's a bolt-on, but they're no longer available from GM.

 

You can get the backing plates for the 9 bolt BW rear from Baer. THey sell backing plates for the stock size (11.3? or 11.6?), 12" and 13.25". THey are $100 a piece. The plates are 1/4" zinc coated pieces.

Part # E2GF11415A02 for the Left Bracket
Part # E2GF11416A02 for the Right Bracket