Weird brake problem

[ScoobyDoo]

This is my first post on your site, nice site too I might add. Has alot of great info.

I have a 69 930 (1 ton) that is suffering from a weird brake problem and am unable to nail it down.

The problem is the rear brakes provide almost all of the braking and when its wet out the thing is just a nightmare to drive.

The master cylinder has been changed and all the lines bled many times so air is not the problem. It will also brake straight so a bad flex line is not really an option as well.

I took a picture of the booster master cylinder set up just in case what is on there is not what it should be.

Thanks a bunch


Jason

[Geno]

Does the booster have a leak? If it did your idle would fluctuate when you pressed on the brakes. Also what about the slave cylinders on the drums.

[krue]

Did you do anything with the shoes on the front brakes? Are they adjusted correctly, are the adjusters installed correctly? How do the wheel cylinders look?

BTW Welcome to the board from South Mississippi!

[Longhorn Man]

Sounds like the front shoes need adjusted.
A bad booster is out of the question, and on the daul diaphram booster, you'd more likely idle funny, but still have power assist... I lost an engine to a bad booster on my one ton due to that.

[70C10Toejam]

How old are the front brake hoses? They could be swollen almost shut. Even though they bleed, just not enough volume getting through.

[ghip]

incorrect proportioning valve?

[ScoobyDoo]

All the front brakes are new and have been adjusted,checked and checked again.

Idle is good and like was mentioned the booster itself should not cause troubles with the front but not the rear.

The flex lines are one possibility but the only thing is both front wheels provide the same braking force. (will check to see if there weather checked and may just replace them to rule them out).

The proportioning valve is the thing i keep looking at.

Can anyone tell me if that valve in the picture I provided is what should be used on this vehicle or has someone installed the wrong unit?


Thanks for the replys


Jason

[71SWBChevy]

That prop valve looks nothing like the one on my truck but since my truck has discs up front that probably doesn't help you.

[ScoobyDoo]

I am 99% sure that the set up for disc/drum is different for drum/drum.

Jason

[john]

That is a distribution valve on your truck, and is the right one for your truck if you have drums all around. . It separates your front and rear systems and houses the warning light. Disc brake systems use a prop valve to proportion front to rear balance.

[OLDIRON69]

maybe stupid....what about the valve on the side of the booster?Also, can the distribution valve be bad?? My '69, before I replaced the rear drums pulled hard to the right, found the right front wheel cyl. was leaking. FIXED right?? Nope! Not until last week when I swapped my rear axles to five lug and put NEW drums on. My rear brakes would also lock up on me if I had to make a hard stop,before I replaced the rear parts I mentioned. I would check your adjusters on the rear,mine were nearly all the way out,even with new shoes the PO had put on. Some machine shops will turn them even if they are past the safe zone...