Help! Brake Pedal Sticking in the Down Position......

[Katmandu]

I just picked up an 81 Rabbit Diesel that had been sitting for about (2) years.

 It had a broke RR brake line when I bought it and I just repaired it and  cleaned up the rear brakes (appeared fine). The fronts looked OK as well. I bled the brake lines out as well. The brake pedal feels good and firm (when the car is off).

 Anyways, the brake pedal STICKS in the down position (Not to the floor) while the engine is running. I have to stick my toe under the pedal to pull it back up into position and release the brakes.  :banghead:

 When the engine is off, the brake pedal feels normal and comes right back up to position.

 What's going on here ??  :confused:

[Katmandu]

Anyone ??

[RabbitJockey]

could just be something wrong with your pedal cluster, or ur mastyer cylinder, or a slave, basically it could be any part of ur brake system.   good luck

[greggearhead]

Bleed your brakes.

[jtanguay]

Sounds to me like a slave cylinder problem.   I'm pretty sure there is a spring in the actual pedal and the master cylinder though...   If you were able to bleed the lines with the brake pedal, then your master/slave cyls should be ok.

it could also be the power brake assist screwing up.  I believe it uses  vacuum.  Maybe you have a vacuum leak somewhere?  If the car has been sitting for 2 years... there must be a lot of little gummed up things on it.

[Katmandu]

Bleed your brakes.

 Did that already.  

[Katmandu]

it could also be the power brake assist screwing up.  I believe it uses  vacuum.  Maybe you have a vacuum leak somewhere?  If the car has been sitting for 2 years... there must be a lot of little gummed up things on it.

 How does one diagnose the brake booster or the vacuum pump  :?:

[Katmandu]

Here's another reply I got from some one .......

 

It sounds like your brake booster or the valve that is on it have a leak.

 The brake booster is a round black thing that is located in the back of the engine compartment on the drivers side. It forms a vacuum inside of it, and when you press the brake pedal, it opens a valve that allows outside air to come in on the opposite side of the vacuum (there is a diaphragm that separates the sides) while sealing off the other side so air doesnt enter the vacuum.

 This causes the side that the outside air just entered to have a higher pressure than the other side that has the vacuum, and that gives assistance in pushing the brake pedal and engaging your master cylinder. The booster has a rod that is attached to the brake master cylinder so when you get this assistance it pushes the pistons in the master cylinder, which then causes the hydraulic pressure in the brake lines and that then engages your brakes.

 Then when you let off the brake pedal, the valve on the booster is supposed close, sealing off the outside air and at the same time reopening the rest of the booster to the vacuum, and that is when the pedal returns to its original position.

 Since the car is a diesel, there will be a vacuum pump that is providing the vacuum for the booster since diesel engines dont produce vacuum.
The vacuum pump is not active when the car is off, so the brake will feel firm because you have no assist from the booster.

 My guess is since when the car is off you have no outside air (higher pressure) fighting the return of the pedal it just goes down firm and comes right back out. But when the car is running, you get that outside air pressure in the booster when you press the pedal down, and i think the reason the pedal is not coming back up is because you have a leak in the valve that is supposed to seal off the outside air, and since the air is not out of the booster it is holding the pedal down.

 Idea ?

[LeeG]

Is the a return spring on the pedal pivot broken or missing?
Is the pedal pivot assembly rusty?  After sitting 2 years, there may be enough drag on the pedal pivot that the spring can't overcome it when the booster is assisting.  I think I would start with the pivot point and make sure its free.

There should be a check valve on the brake booster so it holds vacuum when the motor is off.  Usually after you shut off the motor, it will take 3 or 4 brake presses until the vacuum is used up....you will feel the pedal get firmer once the vacuum is all gone.   Turn motor off, does it still stick the first couple times you press brakes, but then stops sticking when the stored vacuum is used up?  When the vacuum is used up, does the pedal come up quickly or slugishly?

Boosters are pretty bullet proof, if yours is shot you can probably find one cheap used.

A problem in the hydraulic side should not affect the way the pedal returns.   Not sure what people mean about slave cylinders here, wheel cylinder?  Caliper?  Nothing in those can make the pedal stick.  Nothing in the master can make the pedal stick either, the connection between the 2 is only a push rod, master can't pull on it.

[RabbitJockey]

i wouldn't think theres a leak, because when there is a leak or something ur brakes just get very hard to push, like when my vacuum pump went out

[745 turbogreasel]

I put a wire on mine to pull it back up with.

Later I dissasembled the pedal pivot which was all seized with rust, cleaned and lubed.  It workded on that car, but I have also seen the master cylinder pack with rust between the piston and circlip preventing it from returning all the way.

[hillfolk'r]

ive had boosters fail many different ways,,on one i would hear an air leak when pedal was depressed,and it would only give you one good power assisted stop with the engine off,,,,,,,,id be lookin into the booster,possibly