Brake issue

I have drum brakes on rear and disc on front with Master cylinder being replaced 2x's now,all new seals ect. brake lines bled, apply brake and brakes pull almost to complete stop unless you pull brake pedal up with toe!
Any ideas??? At loss now with all scratching the ol' noggin'!!!

 

i think your saying your pedal is sticking down, do you have a return spring?

 

Do you have brake shoe springs? pedal springs? What car and brakes? residual valve?

 

Little more detail would be helpful.

What kind of vehicle?

What brakes?

Where's the MC located?

What's the MC, is it single or dual reservoir?

Does it have a power booster?

When did the problem start - did it work before?

Had you or anyone else changed anything else prior to the problem occurring?

If it's a power setup I'd almost say you've got some kind of vacuum valve problem inside the booster.

 

Did you change to m/c for front disks, or using a drum/drum m/c? Drum brakes have a small amount residual pressure, to keep the shoes up against the drums, if you use a m/c that has this residual valve, the front disks will drag and lock up.

 

the return spring on drum brakes will have about 25 lbs pull at 1/4" of travel, 10lbs residual pressure valves can not hold the brakes shoes from a total return, but i agree if you have 10lbs on the disk side then they could cause draging.

 

Budd, I'm not arguing with you because I agree with the statement, but your numbers (without explanation) are misleading. I say this because the it could be interpreted that you are directly comparing the 25# spring force against the 10 "lb." valve. The 10 "lb" valve is really a 10 PSI valve.

In this case the area is right around one square inch (not sure what size wheel cylinder we're talking) so that valve is actually placing around 10 lbs of force, probably a little more, but not more than the 25# in your example.

Call me a nit picker :-(

 

Sounds like a little free play is needed in the rod that goes from pedal to MC piston..

 

It is a 34' Ford ,the Master is a Dual Resovoir Systym off 80's Mustang,all brakes grab,no Power Booster,Manual Brakes,Master has been replaced 2x's, 2 different Mechanic's,they don't know. This has never had a return spring and never had this problem until recently.

 

Seb's got it right, I think

 

So what changed prior to this happening?

Are you sure which brakes are grabbing ?? How did you determine that?
Any chance you lost a pedal return spring?

 

3x - w/o a power booster