I searched and couldnt find info. will a '85 9 bolt-posi-disc bolt in place of a '91 ten bolt-open-drum. im buying this 9 bolt tommorow at a junk yard, it has 3.08:1 gears and i need to know tonite if it will bolt in. also do i need a proportioning valve off the donor car because it has rear disc? how can i tell the gear ratio on my 91 vert 305 auto ten bolt without pulling the rear cover?
Thanks

 

Yes it will bolt right in.

Expect to have no rear brakes, since the 85 9-bolt will have the crappy Saginaw cast-iron calipers. You will need both the combo valve and the MC, as they are different for the crappy calipers.

Easiest way to tell what gear it is without pulling the cover, is to pull the cover. Anything else is just a guess.

Odds are, it's a 2.73.

 

Yes, the 9-bolt will swap in, but you'll have issues with the parking brake cables (IIRC, 90-92 cars had a self-adjusting parking brake while the earlier modes were adjustable).

Personally, I'd take the combo valve and master cylinder.

No, real way to know without pulling the cover.

JamesC

 

okay wil grab the mc and combo valve for now what calipers would you suggest for future upgrade and will the 85 mc and combo valve effect those upgraded calipers?

 

I went to 1LE's all the way around (but there are many options). You'll require a new combo valve and a drum master cylinder. A search will provide most of your answers.

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

JamesC

 

One other thing to note is the thread pitch is different on a 91 proportioning valve compared to an 85 one, so you'll want to grab the brake lines that run between the master cyl. and pro. valve off the 85 also.

 

I have been all over the junk yards and cant find the front brake line that goes between the mc and combo valve, mine was missing from the car when i pulled the parts. does anyone know where to get a new line?