2001 Dodge Dakota Sport, auto, 4 x 4, 4.7. (153,000 miles) After extensive brake repairs this problem still exists.
Motor off and push down brake pedal, pedal goes down about a inch or two and then is rock solid.
Start motor while still pushing on brake pedal and the pedal goes nearly to floor.
Pumping the pedal while the motor is running does not help.
Pedal will return when driving, but goes nearly to floor without any resistance when applied.
It will stop the truck, but makes me wonder 'if' every time I hit the brakes, as the pedal stops about an inch off the floor.
Rear brake shoes, drums, front calipers, rotors, front brake lines, master cyl all replaced.
Brakes bled many, many times.
Had this problem when I bought it 2 years ago.
Any advice is welcomed.
Thanks, Tom/Idaho

 

If you have 4 wheel abs, may need to have the abs controller bled as well. Need a good scanner to do so.

 

4x4 abs? How can I tell? Where does one find the scanner you mention?
Will doing that restore my brake pedal?
Thank you sir,
Tom/Idaho

 

Look under the hood. See if you have the motor/controller, or the dump valve. If you have the motor controller, gonna need a pretty high zoot scanner to run the bleed procedure. Probably have to take it to a shop to have it done....

 

if the rear brake drum to shoe clearance is excessive...you will have a deep pedal...the mc has to move a lot of fluid for the wheels cylinders to take up the gap.

 

There are two aluminum units by the master cylinder. Both have brake lines and an electrical connection.
One is larger than the other.
Which one do I need to replace and what are they called?
Rear brakes were adjusted when the new shoes and drums were installed. New rotors, calipers and brake lines installed on front.

As I said before, motor off and brake pedal when pushed goes down about 1 inch, stops and is solid.
Start the motor and while pushing the pedal the pedal goes straight down and stops about 1-2 inches from the floor.

Why does it do that?
Thanks again for any advice.
Tom/Idaho

 

long story short, it means your brake booster is working properly. You don't have enough strength to move the plunger in the master cylinder by yourself, but with the aid of the vacuum booster, there is enough force present to move the plunger.

 

I understand the brake booster's part in this process.
What I don't understand is when I start the motor push down on the brake pedal an it sinks nearly to the floor and will not pump up while the motor is running. Turn off the motor and I am able to once again pump up the brakes. Start the motor and the pedal sinks nearly to the floor when I push on it and will not pump up while the motor is running.
What am I missing?
Thanks once again,
Tom/Idaho

 

The pedal doesn't come back up because the booster is holding it down probably. I bet you can pull it back with your foot?

In which case that indicates that there is indeed air in the system, assuming nothing changed with regards to the master cylinder itself. A long pedal is usually more synonymous to having too small of a bore for the amount of volume in the brake system, needing a bigger bore to reduce the swept distance (pedal travel). But given a stock master, that's not a given change.

1. Master Cylinder is leaking internally (would have fluid coming out at the booster connection)
2. Caliper piston seal is leaking air but not brake fluid
3. Wheel cylinder is leaking air but not fluid
4. ABS plunger is not closing all the way

 

The pedal doesn't come back up because the booster is holding it down probably.


I don't think I am explaining the problem well enough, so I will try again.

Motor off. push down on the pedal and it goes down about 1 inch and stops solid indicating 'good brakes'. remove foot and pedal comes back up as expected.
Push pedal down and hold (as before) and start motor. pedal sinks nearly to the floor and will not pump up, evan though it comes all the way back up and goes all the way back down and up when pumped. Nothing keeps the pedal from moving up or down. Pedal goes down (with pressure applied) and comes back up (when pressure removed) it just will not pump the brakes up.
With the motor running the pedal goes nearly to the floor every time it is pushed down and freely returns and will stop the truck.
I'm just not sure how quick it would stop in a panic situation.


New rear shoes, new wheel cylinders, new drums and adjusted
new front calipers, pads and both brake lines. Rotors in near new shape
New master cylinder (New, not a rebuilt one)
No fluid leaks anywhere
In the 'old' days if I had this same problem I would change the master cylinder and be done with it.
Not now!
Thank you again, I truly appreciate your assistance and patience.
Tom/Idaho