roger c
Well Known Member
Hello,
Problem: My brake pedal does not return to the correct height after driving a few miles.
It lacks about 1" returning to the rest position. I can turn off the motor & then pump the pedal 3 or 4 times & it gradually returns to the rest position, however with the engine running & vacuum to it, it will not return to the rest position.
While driving the car I can pull the pedal up with my foot, but as soon as I apply the brake, the pedal is 1" low again. If while driving I do not pull the pedal back up, I will loose all power assist to the brakes eventually. This has happened several times. I have driven the car with the vacuum hose disconnected & the brakes are hard to push but they work better than they do when they go out because of the low pedal with the hose connected.
There is no bind in the pedal linkage.
I replaced the booster & still the same problem.
Vacuum hose has been replaced with a non collapsible hose.
All brake lines hard & rubber have been replaced with new ones.
3 different new master cylinders have been tried.
2 new 7" dual diaphragm boosters have been tried.
I have adjusted the booster pin several times with no change in the problem, even used 1/16" shims this morning with no change.
Has a brand new proportional valve.
Discs on front & drums in rear.
It seems like the vacuum is causing it not to return. When I pull the pedal up to the rest position by hand, I can feel a slight resistance.
This is in a 56 Chevy with a stock OEM swing pedal. It does have the return spring on the pedal & the assembly works smooth & is free of any binds. If I disconnect the adjusting rod from the brake pedal, it returns to the rest position every time easily.
It seems to me that something is not right with the booster & not letting the vacuum equalize on each side of the diaphragm when the brakes are released.
I have been a mechanic for over 45 years & have never had or seen this problem before,
Is there any kind of adjustment to the rod that comes out of the booster on the firewall side? I did notice that it turns, but I didn't think it was adjustable. I used the rod that attaches to the pedal to adjust pedal height inside the car.
Any help would be appreciated.
Thanks,
Roger
Problem: My brake pedal does not return to the correct height after driving a few miles.
It lacks about 1" returning to the rest position. I can turn off the motor & then pump the pedal 3 or 4 times & it gradually returns to the rest position, however with the engine running & vacuum to it, it will not return to the rest position.
While driving the car I can pull the pedal up with my foot, but as soon as I apply the brake, the pedal is 1" low again. If while driving I do not pull the pedal back up, I will loose all power assist to the brakes eventually. This has happened several times. I have driven the car with the vacuum hose disconnected & the brakes are hard to push but they work better than they do when they go out because of the low pedal with the hose connected.
There is no bind in the pedal linkage.
I replaced the booster & still the same problem.
Vacuum hose has been replaced with a non collapsible hose.
All brake lines hard & rubber have been replaced with new ones.
3 different new master cylinders have been tried.
2 new 7" dual diaphragm boosters have been tried.
I have adjusted the booster pin several times with no change in the problem, even used 1/16" shims this morning with no change.
Has a brand new proportional valve.
Discs on front & drums in rear.
It seems like the vacuum is causing it not to return. When I pull the pedal up to the rest position by hand, I can feel a slight resistance.
This is in a 56 Chevy with a stock OEM swing pedal. It does have the return spring on the pedal & the assembly works smooth & is free of any binds. If I disconnect the adjusting rod from the brake pedal, it returns to the rest position every time easily.
It seems to me that something is not right with the booster & not letting the vacuum equalize on each side of the diaphragm when the brakes are released.
I have been a mechanic for over 45 years & have never had or seen this problem before,
Is there any kind of adjustment to the rod that comes out of the booster on the firewall side? I did notice that it turns, but I didn't think it was adjustable. I used the rod that attaches to the pedal to adjust pedal height inside the car.
Any help would be appreciated.
Thanks,
Roger