Brake Feedback

[kafn8d]

I recently completed the 6 to 5 lug conversion using the disc brake setup and rear end from a 1971 on my 67. I was told that the donor trucks brake booster was gone but did get the master cylinder and prop valve. The donor MC was later found to be bad and a new "corvette" style was the replacement for a 71 per the local parts house. I was wanting to know what type of braking performance should I be expecting, because the disc/drum combo seems no better maybe even worse than the original 67 drum/drum. I was concerned that maybe the original 67 brake booster was not a good choice as far a producing enough pressure, so it has been replace with a new 71 booster from the parts house. Still no dramatic improvement. Are my expectation too high? Could the prop valve be bad? Are the brake lines bad? Any feedback would be greatly appreciated. Thanks!!!!

[truckdude239]

soft or spongge pedal? if so air in lines i'd change the prop valve if you've got an new mc and booster

[crazy longhorn]

I run a manual disc (front), & drum rear on my 69, & have no issues with stopping. All of my pcs came from a '75 C10 parts truck(all match). you should have much better braking with the disc front, than you did stock. I dont have a bunch of thoughts, but just be sure all the pcs are a match, & there is no air still in the system. best of luck..... L

[RainFade]

Originally Posted by kafn8d

I recently completed the 6 to 5 lug conversion using the disc brake setup and rear end from a 1971 on my 67. I was told that the donor trucks brake booster was gone but did get the master cylinder and prop valve. The donor MC was later found to be bad and a new "corvette" style was the replacement for a 71 per the local parts house. I was wanting to know what type of braking performance should I be expecting, because the disc/drum combo seems no better maybe even worse than the original 67 drum/drum. I was concerned that maybe the original 67 brake booster was not a good choice as far a producing enough pressure, so it has been replace with a new 71 booster from the parts house. Still no dramatic improvement. Are my expectation too high? Could the prop valve be bad? Are the brake lines bad? Any feedback would be greatly appreciated. Thanks!!!!

This new 'corvette style' MC, what diameter bore does it have ?

[kafn8d]

Brakes are not soft or spongee. They feel just like they did with the drum/drum setup. They have been bleed several times and seem to have good fluid. Unsure of the bore of MC will have to find out and let you know. I know it was just an upgrade from 67 to 71 technology, but others on the board have reported that they had gotten a pretty dramatic increase in braking performance. The only issue that I have noticed is that since I've updated the booster with a 71, I had to get the firewall to booster bracket from the junkyard. With everyting re-installed the booster and MC appear to be pointing downward toward the front of the truck not real bad but definately more than the norm.

[truckdude239]

did you change the prop vavle when you switched from drums to disc? if not then you need to get an prop vavle for disc brakes because the disc brakes take alot more pressure then the drums so the drum vavle isn't letting eoungh pressure though just my $.02

[kafn8d]

The prop valve was swapped with the 71 donors when the 6 to 5 lug was done. I do have concerns that the prop valve and original MC isn't from a 71 C-10 as was told by the junkyard because it doesn't look like any I have seen from various pics. I will try to get a pic of the prop valve posted for all to view. Maybe you guys could post some pics of your prop valve for me to see.
Rainfade had asked the size of the MC bore. I believe it to be 1".

[kafn8d]

Come on guys! I need a little help here.

[VetteVet]

If this article don't answer your questions then nothing will.

http://www.hotrodheaven.com/tech/bra...kes1_index.htm

[Killavee]

I had this exact same problem when I swapped out disc brakes out of a 78 1/2 ton chevrolet. I tried everything imaginable. Brand new booster from a 1971/72 era truck. Brand new disc/drum proportioning valve from Classic Performance. Brand new brake lines. Re-built calipers. New rear wheel brake cylinders. I also added a Jegs vacume cannister (about 16" of vacume). All to no avail. The truck would not stop very well and was down right scary under panic braking. The pedal would resist your input and not let the pedal travel at all under panic braking. Under normal braking the truck would stop but it was just sub par. Also, the brakes would not lock up no matter how hard the pedal was depressed. A definite step backwards from the drum/drum brakes I had just replaced. I eventually retrofitted a booster and prop. vavle off of a 1995 chevy truck. It was a major pita to do and I wouldn't recommend it to beginners. The booster rod had to be shortened. This modification alone would constitue another thread. But it looks real slick cause the booster is mounted directly to the fire wall with no brackets pointing the booster/master cylinder down towards the ground. The truck brakes very well now. I can lock the brakes up with minimal pedal effort. As a side note, I read somewhere that a bad rebuild (I rebuilt the calipers myself) could cause the problem I was experiencing. I might replace the calipers at a later date.

[kafn8d]

I finally fixed the problem, but not sure how. I just re-adjusted the rear drums, adjusted the pedal linkage to remove some slop and re-bled all the brakes. Marked improvement. Thanks for the help!!!!!!