Last year was fun. After a long build in the garage my car was able to see the light of day and stretch its legs. But there's a problem:

The car has PWR Disc front brakes / Drum rears. All new or rebuilt components for the stopping system. I kept as much OEM (and restored) stock as I could. When I installed the new Power Brake Booster (from The Right Stuff) and completed the brake rebuild I bled the system. The brake pedal had just the right amount of pressure - not too hard, and extra play. Needless to say I was pleased. That was 9 years ago. Now to the heartache....

The brake pedal is hard again, although the car stops but requires the force effort likely of a non power disc brake car. Naturally I immediately suspected the power brake booster, and ordered a new one from The Right Stuff. Installed, and - no joy. Still a hard brake pedal. I've bled this system 2x, all new hoses, lines, calipers rebuilt to specs.

What am I missing? My first thought was to overhaul the calipers and see if the power piston is stuck, or if the slide pins are not working as designed. These brakes are really simple, but trouble shooting them is turning into a PITA.

 

Hi Allan, Maybe the master cylinder itself has stiffened up? I would think it was the booster also but you've replaced that, so what else would make a hard pedal? I'm not sure but seems logical... Good luck....

 

Are u getting vacuum from the engine to the booster

 

Thought of that too and replaced the Master after bench bleeding it.

Yes sir, I did test that - and have a solid 20" of vacuum. This car has its original non rebuilt engine and was built with PDB. No aggressive cam. It was a stock L32 that was changed to L34 (2bbl to 4bbl).

 

Allan, Check the push rod from the booster. My pedal was very soft, so a buddy of mine put a longer rod in, and it's been fine since then. Maybe yours is too long?🤔

 

Dave, I set the pushrod length to the same as the original. Also used the original clevis to attach it to the brake pedal (in the proper cutout)

 

I have a Chevy that does this and two Olds that don't and would like to know, too. It stops, just takes some foot.

I have replaced booster and MC on the Chevy.

I wonder if the combo valve could do this?

 

Poor stopping power, high, hard pedal: Brake hose(s) plugged. I've owned multiple vehicles that have done this. If the proportioning valve were blocked, you'd have the same effect. If the brakes bleed normally, this ain't the problem.

Same symptoms, brakes bleed acceptably well. Seized caliper piston(s). Just today, I had the front calipers of my Trailblazer apart to clean the pistons so they move freely. On most vehicles, you'd need to assure that the caliper floats properly on it's mounts/pins.

Poor stopping power, normal-height, hard pedal: Failed booster. I've had two FWD vehicles that have done this.



Of course, glazed or deteriorated pads/shoes with low friction coefficient will require extra pedal effort, too.

 

Have you driven the car much in the 9 years since you worked on the brakes?

The reason I ask is because I had a similar issue and found it was due to the caliper pistons not moving easily in the bores. Apparently some surface oxidation occurred while the car sat idle. Probably not what you want to hear since you already went through those parts.

 

The booster hose can collapse if is has softened.

 

I will look at my calipers, that's a good idea.

 

Make sure that you aren't stopping with only the rears, proportioning valve plugged or calipers not moving. Doubtful if it is the calipers though it would be strange that both sides would seize up at the same time....Just a thought...Tedd

 

That's the plan, pads are new so not glazed or worn and so are hoses/lines.

Kenneth, that's one of the first things I wondered too. When the brakes were freshly rebuilt they were exactly as they should be after a fresh rebuild. And you're right - the car never turned a mile in those 9 years so that's a definite possibility. Hard to think that 2 boosters would fail without turning a mile either so you're speaking my language right now.

Booster hose is in great shape, It was replaced as part of the rebuild.

Checked with the car up on jacks. The rears stop properly and when the fronts are rotated by hand and brake applied they also stop. I don't think this is the proportioning valve either, especially since the brakes will bleed.

 

Just a SWAG, you mention bleeding the brakes, but not replacing the fluid (complete purge of all brake fluid). Speculating here, but moisture in lines or bad, incorrect fluid type.

Good luck with this. Be sure to post your success when it happens!

 

The fluid is all new as of last year. I ended up replacing the master cylinder and then bled the brakes. No worry about having any old fluid or wrong type either. But thanks for that thought.