master cylinder disc drum

[aussieta]

i have always had poor brakes on my 1978 TA, with disc/drum
it has aftermarket master cylinder and combination valve
is there a way to diagnose if these parts are the correct part for my car
i am particularly interested in the 10lb residual valve
i went through this about 20 years ago and was never really satisfied with brake shop answers
some told me residual valve was in mc, some told me was in combination valve, some told me was a separate fitting in rear brake line, some told me was not required
i want to get these brakes correct, i have bought a pressure test gage set and plan on the next few weeks sorting this out for once.
thanks
andrew

[jonathonar89]

Start with the basics first.  Test the vacuum if the booster is holding vacuum.  If no one has blead the brakes, make sure to bleed them out.  Make sure the rear drum shoes are adjusted out properly. 

[aussieta]

thanks jonathon
all of the basics are ok which is why i think either mc , combination valve or both are incorrect
rears lock before fronts in the wet with average braking
with panic stop in the dry all 4 seem to lock around same time

[firebirdparts]

I had a 1977 driver that never had any brakes, and I wonder if it was because of the orientation of the MC - air can't get out, and that's why everybody bench bleeds.  Of course it's hilly here, and I could have vented it just fine on a suitably steep incline, but I never did try that.

My 78 redbird has great brakes, and from the original owner's records, you can see that he had the MC replaced over and over.

Generally I don't like working on them, because the booster isolates you from the MC, and the pushrod length dictates everything that's going to happen, but you can't even access that.  You just know if you run out of boost before you get any braking, that you're not going to be able to stop.  I don't like them.