2001 Dakota Sport. While the brakes will stop me the pedal goes almost to the floor. Then I have a
hard pedal. With the motor off and I pump up the brakes I have really good pedal, but after starting the pedal goes allmost to the floor.
Local shop (brake specialist, so they say) install new shoes, drums and adjust rear brakes. Allmost $700 and I have the same pedal travel as before.
Take it back and they re-check and rears are properly adjusted (they say). And then they pinch off the rubber hoses on the front and the pedal is now normal height evan after starting. They say I now need to (have them of course) replace calipers, pads and rotors and want another $600.00 to do that work. They think that for some unknown reason that when the fronts are eliminated then the pedal acts as it shoud, evan after starting the truck.
There is no sign of brake fluid leakage. Anywhere.
Could the combination valve be causing this?
I just bought this truck and the car facts say the front brakes were completely replace not very long ago. Rotors look and feel really good.
So, any ideas?
Thanks a lot, Tom/Idaho

 

Bleed the front brakes first....... before doing anything else. In fact, I would flush the entire system, and see if anything changes.

 

The system was flushed on the first visit. The front bleeder screws have been cleaned off, so, I assume they bled the fronts.
My big problem is mobility as my right leg was amputated 4" above the knee in July as the result of an auto accident. Otherwise I could do the work myself. I will have someone help me bleed the fronts as soon as I can.
Thanks, Tom/Idaho

 

Sorry to hear, Tom.

So here is my input from the hydraulic side of things. For a given swept volume (pedal travel), there is a pressure increase.

V1P1 = V2P2
Volume 1 = master cylinder swept volume
Pressure 1 = master cylinder pressure

Volume 2 = swept volume w/ fronts blocked
Pressure 2 = pressure with fronts blocked

Volume 2 is lower, therefore the pressure would be higher to keep the equation balanced. However, there is a maximum pressure in play since the brake calipers and wheel cylinders can only extend so much. As a result, the pedal does not travel as far.

In other words, less volume to fill equals less swept volume required to fill it, hence a shorter pedal when you block off 1/4 of the hydraulic system. What's funny is that there is no soft line to block off both front brakes, only one side at a time, unless they are pinching off both sides together.

They are using hydraulic principals and your lack of knowledge to sell you on a bogus remedy.

Also, $600 is wayyyyyyyy too much to service both sides! Much less $700 to do the rears. They're bending you over firmly, or shop rates are wayyy higher up there than here in DFW.

Does the truck have 2 wheel/Rear only ABS, or 4 wheel ABS? 2 wheel/RWAL has a pair of solenoids right next to the master cylinder, 4W ABS has a control module under the battery tray. RWAL was standard, 4W an option.

It is possible the front soft lines have bloated, and now hold more fluid than was designed, making the pedal drop some.

When I removed the RWAL and combination valve on mine, I noticed a slight improvement both times. I don't recall much difference when I swapped to stainless steel braided front brake lines, but maybe there was.

 

It has 2 wheel/RWAL. I'm pretty sure they pinched both lines at the same time to come to their conclusion.

It is possible the front soft lines have bloated, and now hold more fluid than was designed
If this happened wouldn't the pedal travel be less due to the extra fluid in the lines?

I have to order the tool to center the combination valve before I can bleed the front brakes.

Thanks for your assistance, Tom/Idaho

 

Interesting problem. Please let us know what you find tlcvac.
I know you said the lines were bleed , but that does sound a lot like bubble compression.
I don't suppose a it could also be a faulty seal in the master cylinder could it?

Unrelated, This reminds me of a problem i once had with a different vehicle with unusual peddle travel. The front rotors looked pristine and the outside brake pad looked new , but the back side of the rotor was grooved and glossed over and the inner pad was almost completely worn out. Turns out the caliper was putting uneven pressure on the rotor because there was a slide pin (guide pin) issue.

 

that sounds like the same mine was doing firm hi pedal with engine off and to floor with running also pedal was slow to return (couldnt evan pump brakes)..it ended up being the master cylinder was bad after i replaced calipers and hoses on front...

 

A tool to center the combination valve????? I always just cracked open a bleeder, to get the valve to move in the desired direction.... I have never used a tool for that purpose.

 

Front brakes bled...no difference.
New (as in brand new) master cylinder and front bled again. Still the same as before, no change in pedal action.
Could not detect any air when bleeding.
Motor off and the pedal is solid about an inch or so down. Start the motor and it sinks rapidly down to about 1 inch or so above the floor.
Can not pump up at all when the motor is running.
No leaks anywhere.
Rotors and pads appear to be pretty new.
Any and all suggestions are welcome.
Thanks, Tom/Idaho

 

If there is no leak, then I'm thinking master cylinder issue, but I'd be checking really hard to make sure there really is no leak.