Odd brake issue
 

I just did a complete brake overhaul to my 69, lines , disc conversion , booster/MC even a new rearend. Bled the MC and the whole truck , all is good there. The issue is with the truck off I have a hard pedal but when I start the truck brakes go to the floor. I've checked the check valve and it seems ok, I get a small poof out of the booster when I take it out. It seems I'm at a wall with this one, anyone have any suggestions?

Re: Odd brake issue
 

What proportioning valve do you have? Did you use the little plastic centering tool for bleeding the brakes? Did you bench bleed the MC before you installed it? How about the rod length and how do you have your pedal setup?

I see your in Inman SC are you a member of our club?

Upstate GM trucks?:chevy:

Re: Odd brake issue
 

The prop valve is CPP and the booster/ MC is summit. Bench bled the MC and I used the tool and bled the truck 3 times, nothing but fluid coming out.The rod length is set up similar to my old one from measurements it took of all of it when I removed the old.

Yep I'm a club member.
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Re: Odd brake issue
 

Is this you Harry?:lol:

Re: Odd brake issue
 

yep. ;)

Re: Odd brake issue
 

How are the rear shoes. Are they tight on the hub when you install it? If not you need to adjust them to just barely rub to make them work.This needs to be done before bleeding.:chevy:

Re: Odd brake issue
 

Did that.

Re: Odd brake issue
 

Well as we spoke on the club page I would get a new prop, valve and start over.:chevy:

Re: Odd brake issue
 

In case you haven't fixed the problem: I had a similar problem on my truck and it turned out to be new defective brake master cylinder -actually two from same parts store. I finally got my money back and got a different brand. The difference between you're problem an mine is that my pedal would go down to the floor but not really fast. Turns out the master cylinder piston was allowing fluid to go past it.

I'm sure you already know this but for others that may not know, it's very important that you bench bleed the master cylinder according to the directions.

Re: Odd brake issue
 

Andy from what I have found a bad prop valve won't do what this one is doing.

68gmsee from what I have found it can be one of two problems, a bad booster or master. Changed out the booster this afternoon and no change so MC is next tomorrow.

Re: Odd brake issue
 

Hope the mc does it for you. If possible, try a different brand.

Other than lots of air in the lines and or really bad leak, there's not much else. Keep us posted on the fix.

Re: Odd brake issue
 

>>with the truck off I have a hard pedal<<
That pretty much rules out bleeding, shoe adj or Metering valve or Proportion valve, unless you had to pump the pedal to get that hard pedal.
>> but when I start the truck brakes go to the floor.<<
As it should, to a point.

A correct size and operating booster should allow three strokes of the pedal should the engine die and loss of manifold vacuum.

With the engine OFF, brake pedal depressed enough times to release all vacuum - while holding pedal down, start the engine. The pedal SHOULD drop.

If the pedal goes all the way to the floor, the booster is working, the MC is working. but you DO have a problem.

It sounds like one of two possible problems. Either the MC piston diameter is too small or the pedal-to-booster rod is mounted too high on the pedal arm.