Hey, I picked up a 1991 Formula parts car, had a rear disk rear end, so I grabbed it.. I got the 2 dust shields with the caliper mount, and the proportioning valve from under the master cylinder.

Where my question comes in is... The rear end I got from the car is a 9 bolt POSI with a 3.42 gear.. I have a 10 bolt POSI with a 3.42 gear.. From what I've read, the 9 and the 10 bolt are not inter changeable..

So, What I was going to do was.. Remove my rear drums, and the dust shield, cut the wheel cylinder mount so it will fit the new dust shield with the caliper mount, and drill and tap 4 holes with 3/8 grade 8 bolts.. I was then going to run the new hard lines and install the prop valve.. Will this work, or am I barking up the wrong tree?

 

You can mod the axle flange, but since I'm lazy, I'd purchase the following parts from Ed Miller and bolt up:

http://www.flynbye.com/catalog/i30.html

BTW, a 91 shouldn't be equipped with a 9-bolt unless someone swapped it in. Does it have Delco-Moraine iron calipers or alum PBR's?

JamesC

 

Nothing, they're gone.. The cars vin checked out with factory 4 wheel disk.. I double checked.


How do you mean modifying the axle flange?

 

If I read you right, you want to convert your drums to discs. You can either purchase Ed's kit or do the following mod:

https://www.thirdgen.org/ls1reardisc

BTW, the only difference in the thirdgen 9- and 10-bolt, where brakes are concerned, is the backing plate. Check those out in the following link, post #20 (If your backing plates don't look like the ones there, which were made for PBR's, I'd guess the rear was originally equipped with 82-88 Delco-Moraine calipers):

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

JamesC

 

With the disc rear end you got with your find were both calipers positioned behind the axle or were they staggered??

If they were both in the rearward placement (PBR) i'll tell you what I did....

 

i have a 10 bolt rear like yours wih 3-23 posi with drums..i wanted to keep the rear end because the posi unit is new,,,so i did what most people here on 3rd have done,,,i bought a set of brackets for pbr calipers from ed miller ...bolt on ..now i have rear discs and it was quite easy...hope this helps.

 

They were both positioned behind the axle.

 

Don't mean to hijack, but along the same lines...
I have a 91 10 bolt with 3.42 gears & Drum brakes... I was looking at Ed's conversion kit and I emalied them, but no reply...
Can I use that and still fit disc brakes into a 15" wheel? I have them & there is no problem with the front... so does this kit keep the same stock spacing??? Thanks,

Rafael