i have an '86 bonneville that i just replaced all brake lines on. also replaced wheel cylinders. front calipers are still fairly new. no leaks detected in master cylinder, which is probably original. after replacing lines and wheel cylinders, i bled the brakes. i bled them by having one guy working the pedal and one opening the bleeder screws. the process was a as follows. pump the brake pedal then hold it down. while the pedal is held down, bleeder screw is opened and pedal drops to the floorboard. with pedal still down, bleeder screw is closed. we repeated this process on all 4 wheels until no air comes out. With the car off, the pedal is high and firm. however when the car is turned on, the pedal drops to within an inch or two of the floorboard before it stops. when the pedal does stop it is firm and the car stops quite well. This seems to happen on all cars that i bleed brakes on so im not sure if im doing something wrong or not, thats why i tried to include most details of how i bleed the brakes. my question is, how do i get the pedal to firm up where its supposed to, closer to the top of the brake pedal's travel? any suggestions would be helpful to this extremely frustrating problem.
Brake bleeding problem, low pedal
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Bleeding brakes
Been there done that. It seems that at the proportioning valve there is this rubber knob that has to be pushed in and held while the system is bled. This is mentioned in my GM manual.
Been there done that. It seems that at the proportioning valve there is this rubber knob that has to be pushed in and held while the system is bled. This is mentioned in my GM manual.
i haven't tried holding in the proportioning button before. however, i put rear brake shoes and adjusted those manually, just to where there was slight drag when spinning the drum.
i found some info that said the proportioning valve needs to be held in while pressure bleeding the brakes, but does it need to be held in for manual bleeding as well?
hitting the floor isn't good, but it's not the root cause. what i've found works well is to pressure bleed everything, then just uncover the resevoir, open the farthes bleeder first and let it gravity bleed for awhile. then do the others. i don't know why exactly, but it does work.
you don't say if the reservoir was emptied when you did your brake work but if it had then you need to bench bleed the master. As for bleeding the brakes you don't mention what corner your doing first but you need to start off with the wheel furthest from the master. I use speed bleeders on my vehicle and they make bleeding the system alot easier
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