my brakes are working to dam good

Hey guys I've got a under floor power booster set up in my 57 truck was working great but found out today if i drive the truck all day the pressure in the booster builds up and the brakes drag bad were my truck is barely moving I pulled over and pulled the check valve from the boister and release the pressure and it was back to normal any idea what would cause this? Any help greatly appreciate. Thanx guys

 

Oh yeah forgot to mention the pedal was hard and well I had no pedal like it had 1/2 inch of travel when pressed

 

Make sure there is free play in the pedal. The rod that pushes the piston in the mc has to have free play or it will do just as you described


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In my experience,

Most common - push rod between the brake pedal and booster not set correctly, also can be booster rod to master piston.

Sometimes - flexible brake hose is old and not letting pressure bleed off after letting go of the brake pedal.

Least common - bad master cylinder.

 

Yup. Hopefully the rod is threaded and you can just crank it in an 1/8th of an inch to start.

Bob

 

Something to check is the weight of the pedal ass. it could be lightly pushing the rod while driving and causing this. May need a light return spring.

 

Needs a return spring if you don't have one.

 

Buddy of mine had a similar problem. His exhaust ran VERY close to the brake lines. I think the lines were working like a heat soak and boiling the fluid creating pressure. Whatever the reason, moving the brake lines cured his problem.

 

I'll try them all my exhaust is 1.5 from the line. The rod is threaded I had it adjusted but it had little pedal in the morning drive so i moved it out there is a sleeve between the pedal and booster ill adjust it from

 

Oops adjust it from booster side first hopefully it will fix it thanx guys

 

And if you get it real close to the exhaust, the brake line becomes porous and you can actually see it boil out. The pedal goes to the floor.

Bob

 

i adjusted the rod from the master cylinder to the sleeve. so far so good. hopefully that will work. thanx guys

 

I first learned about this after putting a new master on a '66 Impala back in 1976. Success really teaches you nothing.

Bob

 

Great line - I should be freaking Einstein by now then!

 

funny thing this happen once before to me and i didnt realize till i was lying under the truck looking up at it. LOL

 

Return spring, wrong rod?