Brake Issues-Lock up-Burn up

[ksbeatty]

Here is one of those posts that I hope will be good information for those who want to tackle. Her is where I started.

I had three cabs. One of which was a 1969 GMC 3/4 ton 2wd with power brakes. Second the original truck a 1970 Chevy 3/4 4wd with manual brakes. Third a 1970 1/2 ton with manual brakes. All of which were drum brakes. I took all of the parts needed for the conversion to vacuum assisted brakes. I still have all three cabs. I ended using the cab from 1970 1/2 ton because it had the most options and it was an A/C cab. So that puts the brake pedal from a 1970 1/2 ton drum brake. From what I can tell it should not matter. I am going to do some more research on that.

Second phase is the pieces from the 1969 GMC vacuum assist setup. I have replaced the vacuum boost and the master cylinder. I have replaced the brake lines with bendable green lines from NAPA but i am not happy with my work so I am going to buy some pre-bent lines not because the NAPA lines are bad but I don't like the way they turned out. My workmanship and patience.

I grabbed the proportioning valve from the 69 GMC also so we can be consistent. I think. Here is where we start having issues and where we start testing. Oh, the brakes calipers etc are from the original 3/4 ton 4wd. I have rebuilt all of the brakes and checked wheel cylinders.

I was driving the truck yesterday as a test drive and everything was going great. Then the last few miles the truck which has a nice new 383 was having issues keeping speed with the 700r4 in lockup. When I touched the brakes the left locked up. When I pulled into the drive way the driver side front brake was smoking. Therefore the title Lock up-burn up.

I followed one of the searches suggestions and followed this link http://www.classicperform.com/TechBo...hoot.htm#pedal
So without further adieu here is the research and testing that took place. It may not go anywhere but I thought a good account of what took place may help some one else.

This morning I readjusted my brake pedal. However it still seems that the push rod is too short. I have had to adjust it further out than I think it should be to hit my brake light which is adjusted all the way out. I started the vehicle and tested my vacuum and it measured about 17 inches of Hg. Which from the tech article is fine at idle. When I increase the rpms the vacuum increase to overe 20 inches of Hg which is still fine. I am now off to check the brake booster by specifications in the tech write up. My initial thought is because I did not replace or I am not sure what proportioning valve I used this may be the issue.

I hope that this write up helps someone in the future. If you have any comments or questions please let me know someone is reading this.