Brakes Why Won't The Brake Pedal Stay Up?

[stangboy]

I have a general brake question. If the MC, booster, and calipers have been changed and system bled 3 times, what would cause the pedal not to stay up? It will pump to bleed the system but it goes back down. It goes down faster when the car is running, I guess when the booster starts working. This problem is on a '96 Taurus wagon not a Mustang. I just figured brakes are brakes are brakes on a Ford. Thanks in advance.

 

[mikestang63]

vacuum leak
calipers on upside down
brake hoses old and spongy
MC not bench bled proper

My first guess is you have a leaky booster or a hose not on all the way, and vacuum is bleeding out.

 

[Grabbin' Asphalt]

one time my caliper hose was flipped and it touched my tire, 2 weeks later it rubbed a hole and i got no response at a red light!!! Thank goodness i was in the right turn lane making a right turn and no cars infront. Made the turn and coasted to a safe spot, pretty scary

 

[stangboy]

vacuum leak
calipers on upside down
brake hoses old and spongy
MC not bench bled proper

My first guess is you have a leaky booster or a hose not on all the way, and vacuum is bleeding out.

What do you mean "bench bled"?

 

[Mustang5L5]

What exactly does "staying up" and "going down" refer to.

I'm trying to guess what you mean by that terminology.

 

[stangboy]

According to my friend who is having this problem, the pedal will slowly fall back down to the floor without touching it. Does that help?

 

[84Ttop]

Honestly sounds like the seals in the master cylinder are gone, only thing I would imagine that could cause that.

 

[Mustang5L5]

I agree. Sounds like the seal in the piston of the MC is faulty allowing the piston to sink (due to gravity of the pedal) due to a leak.

Another cause is a VERY bad leak somewhere in the system

 

[mikestang63]

I agree. Sounds like the seal in the piston of the MC is faulty allowing the piston to sink (due to gravity of the pedal) due to a leak.

Another cause is a VERY bad leak somewhere in the system

I would have said that, but the OP said the MC was replaced, which is why my thoughts about the replacement MC not being bench bled properly. The fact he is asking what that means leads me to believe that may be the issue. If you don't properly remove all of the air out of the MC before you install it, you can bleed the system all day and night and never get the air out of the MC.

To the OP, was this a new or reman MC you installed. Here is a tool I use to bench bleed the MC

http://www.foxbodyworld.com/product...ign=shopping&gclid=CNCAgtyT8boCFRFo7AodbAwAPg

 

[Mustang5L5]

If the MC wasn't bench bled, then that would also be a cause.

 

[stangboy]

I haven't laid a finger on the car in question. I'm asking these questions for a friend that is the owner/person doing the work. When he asked me what could be the problem I didn't have an answer because he did everything I could think of. That's why I turned to you guys.

The MC was changed, so I guess I'll tell him about that tool, thanks @mikestang63, and tell him to bench bleed the MC. Now, since the MC is in the car already does it have to be removed to bench bleed it or can it be done while in the car? Sorry but this is the 1st time I ever heard of bench bleeding. I feel like such a newbie.

 

[84Ttop]

It can be bled in the car just easier to do it in the vise that's all. Two person job at this point but still can be done. Good luck with it!

 

[Mustang5L5]

Easier to take it out. Plus it ensures that you bleed all the air bubbles out. Also, brake fluid eats paint, so more reason to get the MC out of the car if there is a risk of spraying fluid around

I use a different method than that tool. I purchased a brake line from autoparts store, cut it in half and belt the open end into the reseviour so that pumping the pedal would push fluid through the lines and back into the MC. Couple pumps of that would clear the cylinder of air and i'd simply remove the lines and install.

 

[mikestang63]

Easier to take it out. Plus it ensures that you bleed all the air bubbles out. Also, brake fluid eats paint, so more reason to get the MC out of the car if there is a risk of spraying fluid around

I use a different method than that tool. I purchased a brake line from autoparts store, cut it in half and belt the open end into the reseviour so that pumping the pedal would push fluid through the lines and back into the MC. Couple pumps of that would clear the cylinder of air and i'd simply remove the lines and install.

Either way works fine. I also have some cut up old brake lines looped over as a tool. Depends on the MC. They also sell cheap kits that have plastic screw in adapters and rubber lines- I think Harbor Freight sells them.

 

[stangboy]

I talked to him again. He knew about bench bleeding. He said he did that. So, he asked me to go over to the house and look at it. The rear calipers were on the wrong sides. The line was above the bleeder on the rear calipers, he didn't notice. So he said he's gonna switch them when he gets off from work and see if that works. I'll let you know how it turns out. Thanks guys!

 

[mikestang63]

#2 on my list