I was hoping someone here could have some suggestions about a quirk I'm having with my front brakes.

THe brakes are 1970 SS disc, the car is a 71. I did put the 2 proportioning valves from the 70 on, but did not change the third that looks like it distributes between the sides of the front brakes.

The problem is nothing major, just a minor annoyance. The car seems to stop fine for situations I've encountered, but the front brakes never get enough pressure to actually lock up (perhaps a good thing?).

Since I came from worn out drums, I have been satisfied with braking quality but I'm wondering if there might be a gremlin preventing it from being as good as it could be. I've heard stories of these old model discs being able to "throw you through the windshield" and my car is far from doing that.

While braking is good I know if i ever get stuck behind some jackass in a new car who decides to stop from 50 or more theres a good chance I'm going through HIS windshield.

Could this be a vaccum problem or something like that? The brake booster is from the 70 too, the master cylinder is new. I'm unsure if a dif MS could be it, I dont know if my dad remembered to tell the store the cylinder was for a 70 brake system.

Maybe you have a vacuum source that is not good enough. If the brake booster shares a vacuum port with the pcv valve, then the signal to the booster is not strong enough. I do not know of any problem that would cause the booster to underperform-- they usually work well or not at all. If you are locking the rears, but not the fronts, then you need to take a look at the proportioning valve.

thanks, but no the back don't lock either

when we first did the conversion it was pretty jerky and it slowly fell away (so slow I didnt really notice it until it a few situations occured they should have locked)

I guess the first step should be to test vaccum

The 70 brake system uses 1 proportioning valve and 1 distribution block. The distribution block is down on the frame and the only purpose it serves is to send the fluid to all 4 corners. The valve up top delays the fluid to the front so that car doesn't nose dive. Have you bench bled the master cylinder and bled all the air out of the lines? Also make sure the rear drums are adjusted properly.

Yeah I discovered the 70 had differences in an issue of Super Chevy about brake systems that came the month after I did a nose dive into a ditch Dukes of Hazzard style when I got a brake warning light instead of a stop...

The casting number on the lines between the sides of the front looked the same best i could see so we left it and added the proportioning valve that goes under the master cylinder and the one that was forgotten at first is the one that goes above the rear axle to adjust the pressure and make sure the back lock before the front. I'm beginning to think I should have just bought a 71 style valve instead of splicing the line for the 70 system.

Yeah the brakes are bled fine and adjusted so I'm guessing from the information given here the booster may be weak since its from the 70 model car, or perhaps one of the prop. valves is damaged?

I do know that the master cylinder my dad bought looks different than the factory style bigblock one. Could this be the problem? I have a small block, but maybe the system still needs the other style master cylinder?

I think I'm gonna cruise over to parts plus pretty quick and get a master cylinder, mine is leaking and if I pick it up I can be sure to specify that it is a 1970 power disc even though the car is a 1971 that had drums...

If this doesn't fix it I'm out $14 and get a leak stopped...if it does fix it I might not rearend someone due to weak braking

plus I'll actually be able to get a roast out of about 24 in. tread on my new BFGs, right now it just pushes the car forward slowly graemlins/angry.gif

if i ever hit a patch of dew or anything they get enough slip to start spinning without moving the car

i hate brake work more than electrical work