engine and drivetrain Signs of a bad brake booster?

[beast02er]

So i'm still trying to diagnose my stuck brake problem. I have come to find that after sitting for a while, the front calipers will release their hold on the brakes. So when I go to push the brakes for the first time, the pedal goes really far down, then as I drive and push the brakes a bunch, the pedal firms up and goes down less and less. Then I come home, jack up the car and spin the tires and they are stuck. SO then I let it back down, depress the brake pedal a few times to release vacuum pressure and then check the wheels and they spin freely..... so would this point go a bad brake booster?

I tried the pedal pushing with the car off, and then checked wheel spin and it was fine, so it seems like the brakes won't stick unless there is vacuum pressure.. I also put my foot on the brake and went to turn the car on and there was no pedal depression when the engine turned over..

I'm no expert, but it seems to be brake booster, I just wanted to see what you guys thought before I spent $100 on one.

Thanks,

Bryan

red73

[Guest Anonymous]

When a brake booster goes out the brakes will get hard not soft. With the brake booster working it boosts your foot pressue to the master and the hydrolics. When you pump your brakes your building pressure in the system and it will work. take the clutch master on my truck its going out, to get the truck to the shop I will pump the clutch a few times and I can get it there. YES every time I need to shift I will do this. On yoru brakes this isnt an option. Have you been loosing brake fluid, if so where is it going?. Have you tried rebleeding your brake system?

Sam

merlin_m3_Racing AT yahoo.com

[beast02er]

No, what I said in my first post was the pedal DOES get harder, it stiffens up and the pedal travel gets smaller.

The only way to release the stuck brakes is when the car is off, and by pressing the brake pedal to release vacuum pressure......

Logically it seems that if vacuum pressure being relieved solves the stuck brakes, the issue lies where the vacuum is.... But that is why i'm posting cause I want to make sure. But you pretty much said what I described...pedal firms up..then its booster

Thanks though

[Bill_Riblett]

I do not think your booster is bad either.

What Sam is saying is that when you pump the brake pedal, you are in effect bleeding air out of your brake hydraulic system.

Your brake master cylinder is probably leaking internally. Your 73 has what is called a dual circuit brake system which means that your master cylinder is effectively 2 cylinders. I believe there is leakage between them and this is what causes both the soft pedal and the locking brakes. In effect, one circuit goes soft and the other hard.

[beast02er]

Would this still be the case even though the Master was just replaced and is brand new? Everything in the brake system is new except the hard lines, and the brake booster (and in the rear, the drums and shoes etc).

Thats what makes this hard for me to figure out....its all been replaced

[jonny]

This may not be the problem, but I thought I'd add an incident I had once re: "stuck brakes."

My rears would stick occasionally (12 years ago).

Solution: The linkage under the booster was RUSTY!!

If I reached down and physically pulled the pedal back 1/4"..they would release.

this may not be YOUR issue, but just thought I'd add my 02 cents.

I dumped 90w gear oil over the entire linkage and worked the pedal by hand about 500 times. Never had a problem since.

[Paul7002]

(nt)

[Durango_Dave]

You might want to try adjusting the rod between the brake pedal and the booster. Once I adjusted this rod to be too long, and as I drove the brakes kept getting on stronger and stronger until I thought that the front wheels were going to lock up! I'm thinking that I had it adjusted just to where the booster was beginning to acuate and causing this problem. If I recall correctly, you need to loosen the lock nuts at both ends of this rod to do the adjustment. Then turning it will lengthen or shorten the effective length of the rod. Try shortening it (more play and pedal closer to the floor, I think). What do you have to lose by trying? Good luck.

[c.d.iesel]

because:

your rubber brake hoses are 30 year old krap/colapsed internally?

replace them

bad vacuum booster? : rock hard high brake pedal / no vacuum assist

with motor off, pump the prake pedal 15 times and hold the pedel down with gentle pressure - start the car and feel if the pedal gradually falls to the floor - which it should if the booster and vacuum supply is good.

If the pedal does not sink down on start-up - look for a bad booster hose, backwards check valve, plugged check valve, or bad booster - or a booster that was once filled with brake fluid from a bad master cylinder - causing damage to the internal seals.

look inside the rear drake drums for rusted shoes not releasing and any slave cylinder leaks also