[superhero]

I have a 85 monte carlo and changed the rearend to a ford 9" with disc brakes. The original brakes were drum on the rear. I changed out the proportioning valve to a disc-disc valve. The stock m/c does not seem to be working well and pedal travels almost to the floor. I think this is due to more volume needed from the m/c for the discs in the rear. What m/c should I use (part # please) and also will I need adapters for the lines going in to the m/c (where do I get these)? Any help appreciated. I need to get this darn thing on the road.

[Triaged]

What kind of disc brakes? What calipers? Bleeders pointing up? Did you bleed all the air out? Is the e-brake hooked up and working properly? With your quick take-up master cylinder I highly doubt it is a volume problem.

[superhero]

bleeders are up, discs are 11" with hats from speedway motors, calipers are pre-metric mid size gm. I was told from other so-called knowledgable people that the m/c from a disc/drum setup could not be used as it would not push enough volume. I am ready to set fire to this project if I can't figure something out on these darn brakes. Also, no e-brake and I have vacuum bled them time and again.

[Triaged]

So you are using front calipers in the rear (what make/model/year exactly)? Do you still have stock front brakes?

[406 bug]

I believe the original mc port that connected to the front flowed more than the rear (drum ) port. Now, the rear needs the higher volume so you may try reversing the lines at the mc. Also you may investigate and determine if chevy offered a 4 wheel disc option in 1985; if so, maybe you can find the mc that was used for this option.

[Triaged]

The rear calipers should be smaller than the front calipers. The front calipers are low drag calipers (which is why he has a quick take-up master cylinder) that retract the pistons more than older designs. The rear should never need more fluid than the front. GM would not have used a different master cylinder for rear disc brakes anyways. The rear port on the master cylinder goes to the front brakes from the factory.

[406 bug]

Originally Posted by Triaged

The rear calipers should be smaller than the front calipers. The front calipers are low drag calipers (which is why he has a quick take-up master cylinder) that retract the pistons more than older designs. The rear should never need more fluid than the front. GM would not have used a different master cylinder for rear disc brakes anyways. The rear port on the master cylinder goes to the front brakes from the factory.

Good point. I was thinking he had an aftermarket system like a 4-piston wilwood rear as I have, wich do require reversing the ports on the mc I am using.