Hard brake pedal
#1
Just an Olds Guy
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Join Date: Jul 2008
Location: Edmonton, AB. And "I am Can 'eh' jun - eh"
Posts: 24,525
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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.
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.
#2
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....
#4
Just an Olds Guy
Thread Starter
Join Date: Jul 2008
Location: Edmonton, AB. And "I am Can 'eh' jun - eh"
Posts: 24,525
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).
#7
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?
I have replaced booster and MC on the Chevy.
I wonder if the combo valve could do this?
#8
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.
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.
#9
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 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.
#12
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
#13
Just an Olds Guy
Thread Starter
Join Date: Jul 2008
Location: Edmonton, AB. And "I am Can 'eh' jun - eh"
Posts: 24,525
..... 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. 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.
Booster hose is in great shape, It was replaced as part of the rebuild.
#14
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!
Good luck with this. Be sure to post your success when it happens!
#15
Just an Olds Guy
Thread Starter
Join Date: Jul 2008
Location: Edmonton, AB. And "I am Can 'eh' jun - eh"
Posts: 24,525
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