LC MotorSports

When they check the ECU (as I understand it) they scan is not of anyone specific module (newer cars) but of the whole unit, which contains the data for each module (ABS being a separate node inside the ECU, that sends data down to the main ABS controller circuit module)... And the Flash for the ABS would be inside the ECU... Is it not likely that when the read the ID's and dates they would see the ABS being of a newer model then that of the car. Lets say the scrut then over reacts and DQ's you because of it.

Maybe I worry about the little stuff way to much.

LC MotorSports

Now lets take the seals issue on step further.... The psiton seals on the calipers could be getting worn out and reacting to the higher heat by allowing blow by during heavy braking...
The Bearings being worn could create slop that pushes the caliper piston back into the caliper... Thus, soft pedal! Many of these little problems can have numerous root causes

onefastviking

Exactly, my point.

2BWise

The way to confirm or rule out any of these is with a standstill test. Any slop should be taken up in one or two pumps of the pedal and it should be rock solid. If it still sinks to the floor it can't be bearing slop, and if its not leaving a pool of brake fluid on the ground it can't be the piston seals. If there is no fluid being removed from the system (reservoir never needs refilled) there must be an internal issue with the system. Could be crud in the lines that is creating a restriction and slow pass thru of fluid, could be master cylinder seals (but it appears that has been replaced with a known good one), could be ABS unit valves letting pass by,

onefastviking

Easier to check the wheel brgs IMHO and besides sometimes one problem causes another. Say his wheel brg was bad and creating enough heat to heat up the caliper and pad on one wheel after a few laps. Then you have knock back AND air in the lines all of sudden.

By the OP's 3 initial complaints you are correct in assuming it would not be a wheel brg issue. But with cars I have come to NEVER assume because it's always what bites me in the a$#

2BWise

No assumption in crossing off potential root causes. Just starting with the most likely culprits for the problem and tests already run.

onefastviking

It would seem that he already checked the most likely culprits tho and ruled them out. I've found whenever the most likely things all check out ok then you go back to all the basics and usually find something really silly or weird. But that's just my personal experience.

mdrums

If no PWIIS how can you cycle ABS then?

onefastviking

A few ways. #1 Durametric should also be able to do it. #2 depending on what car we are talking you could hot wire the ABS pump relay to run all the time. #3 although not the best, turning on the key from off to on with most of the cars will trigger the pump to run momentarily, if doing this while manually bleeding it will trigger some air out of the pump if it's an issue. #4 Just drive the damn thing and make sure you engage ABS a few times so the pump runs. By cycling the abs pump a few times it will pump any air out of the system into the brake system.

Obviously the best and most sure way of doing this is to use the computer to cycle and run the ABS pump.

LC MotorSports

We use the Durametric software to cycle the module....
The test drive to activate the system to double check.

Viperbob1

Thanks all for suggestions. Wheel bearings are good. One of the first things I checked. If standing still car off car has rock solid pedal. Start car and pedal is mush and will sink to floor. Temp strips on calipers were normal, no abnormal pad/rotor wear on any corner. Even in a bleed pretty much zero air off any bleed screw. Piston seals were replaced in March as well as dust seals. No fluid at all on any part of the caliper.

So with all this, I ordered an ABS pump. Strange with ALL the stupid diagnotics everywhere in the car, a bad pump can cause you to lose almost all braking and yet not even set an error light. Still think it is odd.

I also use the Durametrics software to cycle the pump...

LC MotorSports

Glad to help

jakermc

I have a Durametric but never used it to do this. What is the sequence of the steps when bleeding/cycling the module? Cycle then bleed or bleed then cycle?

Nordschleife

there is a lot of stuff in here

http://www.bosch-motorsport.com/cont..._Manual_en.pdf

even if you do not have the M4 unit, some of the diagnostic techniques/software analysis etc, plus bleeding wizard may be helpful

R+C

2BWise

Well, its likely not the pump but the valves (all contained within the same unit so by replacing it you replace everything). Diagnostics would have found a faulty pump. If the valves are either slightly damaged or worn you can get seepage where the fluid is sneaking past the outlet valve. The diagnostics may not find a valve leak if it is small enough. The problem is that any leak will cause a falling pedal.