brakes go to the floor when car starts.

[maliblue]

Ok ive been riding on the floor for a while now. i have replaced rotters, calipers, flex lines ft and rear, all steel lines everywhere. A good proportioning vavle out of wreckers, wheel cly, sring kit and yes i adjusted them back out after, new drums and then bleed the whole system several times and systen holds pressure great! as soon as i start the car they drop rite to the floor!! i cant lock the front wheels in the rain! HELP
Thanks
81 malibu, 350, turbo 350 shift kit, 308 posie but no brakes!

 

[Blake442]

Well, you've replaced everything but the master cylinder... I'd start there.

Make sure you properly bench bleed it before installing it.

 

[monte olrac]

i'm almost sure you need to adjust the back brake drums, use the adjuster and make them where they start to drag, that should do it

 

[Phoenyx]

I didn't notice 'pads' or 'shoes' in your list.

 

[maliblue]

of course i used new pads and shoes.
I will adjust the drums till they drag and try that.
thanks

 

[dan2286]

Well, you've replaced everything but the master cylinder... I'd start there.

Make sure you properly bench bleed it before installing it.

X2!

A good way to check if it is the master cylinder is to look for brake fluid running down the brake booster. The pedal probably only goes to the floor when the engine is started because the booster is appling more pressure to the brake system than you can do by yourself without the car running.

 

[megaladon6]

it's the booster, or the vac supply to the booster (theres a minor poss of a master needing to be bled--just gravity bleed the brakes). if it was anything else the brakes would also have problems engine off.

 

[flip66]

it's the booster, or the vac supply to the booster (theres a minor poss of a master needing to be bled--just gravity bleed the brakes). if it was anything else the brakes would also have problems engine off.

X2

 

[TURNA]

it's the booster, or the vac supply to the booster (theres a minor poss of a master needing to be bled--just gravity bleed the brakes). if it was anything else the brakes would also have problems engine off.

When a booster goes bad doesn't the pedal get harder to push down?

And a large vacuum supply problem like that would make the car stall when the brakes are applied, wouldn't it?

I had brakes pump up just fine with the car off and as soon as you start it and the vacuum assit kicked in they go to the floor as well.

Either it was a pinhole, air or the master.

Or since you changed everything you may need the brakes power bled.

after you get done adjusting the rear brakes check the proportioning valve switch in the front under the rubber cap. Make sure it is pushed in. Sometimes if you do not have the proper brake pressure the switch will pop out and needs to be reset.

Does the brake light come on at all?

 

[maliblue]

Ok the rear drums are adjusted out till they drag, bleed the system out really good and when you start the car they still go rite to the floor.The proportioning valve switch is a good one, i forgot about that. Thier has never been any visable leaks on the booster fittings or anywhere and im not loosing fluid. the brake light has never come on.