Soft brake pedel

[Schurkey]

When I activate the dump valves with my scan tool the pedal acts like i think it should, pedal all the way to the floor for each of the 3 sections.

Doesn't the electric motor/pump push the pedal back up?

Maybe your motor is stuck. I've heard of other folks pulling the motor apart for cleaning and maybe new brushes. Not something I've ever done.

I believe the fountain that jets up when I press the pedal is the loss of the take up fluid for the low drag calipers.

There's always a pair of "geysers" in the reservoir; there's a bit of fluid that jets up from the cylinder into the reservoir before the passages between the two are covered by the piston seals as they travel forward.

If I jump on the pedal it feels hard but just steadily goes down, I think it is just the restriction of the hole on top of the QTU valve. Once the large piston passes the QTU valve port brake pedal.

How far does the pedal "steadily go down"? If it just keeps going until the pedal is on the floor, that's a sign of an external, or an internal leak.

If it's only dropping until the QTU valve is covered, I suppose that could be a failed QTU valve.

Have you verified that the calipers in front have pistons that move freely? If the pistons are stiff, the low-pressure/high volume section of the master cylinder won't develop enough pressure to move them. Then the high-pressure section has to flow enough fluid to push the pistons against the rotor, leading to low brake pedal.

 

[Dom2door]

The motor on the abs runs when bleeding and when function testing. during bleeding the pedal pumps back up some times and always on the final cycle. Function test pedal pumps up every test.
Calipers are free, moves nice and smooth.
Need to pull the reservoir to get to the QTU valve, that is going to be a pain.

 

[Dom2door]

How could it be the QTU valve if plugging the master cylinder out ports and have full pedal?
That's funny I was the one leaning toward the QTU.

 

[Schurkey]

Calipers are free, moves nice and smooth.

I'm not asking about the calipers sliding on the caliper mounting pins. I'm asking about the pistons moving nicely in the caliper bore.

 

[Schurkey]

The motor on the abs runs when bleeding and when function testing. during bleeding the pedal pumps back up some times and always on the final cycle. Function test pedal pumps up every test.

That's kinda suspicious...

 

[Dom2door]

I did not check the pistols in the calipers, I have been driving it and no pulling, stops fine . I don't think the brake pedal should be as low as the gas pedal.
The auto bleed function does seem odd, the fluid in the reservoir gets air rated with bubbles, knowing this I waited for the bubbles to disapat every time I did anything else whether it was bleeding or ABS functions,
ABS not bleeding, did the same thing with the other ABS that I pulled from t he junkyard.
If I holed the pedal off the floor it pumps up every cycle

 

[Schurkey]

The auto bleed function does seem odd, the fluid in the reservoir gets air rated with bubbles, knowing this I waited for the bubbles to disapat every time I did anything else whether it was bleeding or ABS functions

Either there's a heap of air in the system, and it's slowly being released into the reservoir as you do the automated bleed--in which case the pedal should be getting progressively better...


...or the pump and motor is putting air into the fluid somehow, in which case you can bleed it forever and it'll never get better.

 

[Dom2door]

Could be caveating, not getting better, ran the auto bleed a lot, and the test function.

 

[Schurkey]

There's a difference between "cavitation" and "aeration".

If it was cavitating, the bubbles would collapse almost instantly. I think it's more likely that there's a failed seal somewhere, and when the motor/pump runs, it's pulling outside air and mixing it with the fluid--which then rises into the reservoir.

My suspicion is that you need a different ABS unit that has proper sealing.

But as I said earlier; if there's a heap of air in the system the motor/pump may just be whipping that air into the fluid. As the air comes out of the fluid in the reservoir--or gets bled out the wheel cylinder bleeder valves--the pedal should be getting progressively better.

Remember, scan-tool bleeding of the ABS does not get the air out of the system, it just gets air out of the ABS unit. The air still has to be bled down to the wheel cylinders and then out via the bleeder screws.

 

[Dom2door]

ABS must be sucking air, pedal never gets better don't get worse. I will start looking for one or delete it.
Is there a rebuild kit for these?