currently I have the stock iroc 87 rear end(2:73, drum). I'm going to 3:73 disc. How would I know if I need to change my proportioning value?

any info would be great...

 

If you can, get the proportioning valve from the Disc set or buy a new one for disc brakes.

 

for disk rear you need flat sided machined aluminum PV

 

ok, I have had just about every rear in my car so I can say for sure whats needed. if you are using the iron rear disc setup then yes, you need a differant pv . having a machined aluminum one has NO differance at all. my stock drum one was and I am sure yours is. if you use the pbr rear brakes then you can use your drum pv even though it is not really the correct one it works fine. 84 and up use the bubble flare tubing and pre 84 use the standard double flare fittings. just to let you know

 

and you will also need the master from the iron disc setup

 

When I installed a BW 9-bolt Disc rear (1989) to replace the 10-bolt drum brake rear in my 87 IROC, the only Items replaced were.
1) Proportioning Valve with one from the 9-bolt.
2) Parking Brake cables from the 9-bolt.

That was it. No master cyclinder needed replaced. Just a straight forward swap.

 

well the part # for the master is differant