Anyone have this happen?
After replacing the rear pads I can't seem to get a firm pedal.Was good before replacing the pads. Feels spongy, like air in the system. I've bled the brakes several times per Chiltons procedure for a 97 w/ABS RR, LF, LR, RF. Still Spongy, Never saw any air in the bleed. Bled thru about 24oz of fluid.
Anyone have a issue where turning in the rear pistons damaged the master cylinder? Thats where I'm headed next.

Thanks

 

A spongy brake pedal is an indication of air in the system. Incorrect bleeding technique can introduce air. Two mistakes can cause this:
1) The bleed screw was not fully closed when the "inside man" released the brake pedal.
2) The master cylinder fluid reservoir was allowed to go dry during the bleeding process.

Damaged hydraulic flex lines can bulge when the brake pedal is pressed, and this will cause a spongy feel, but not nearly as much as air in the lines. I cannot imagine how replacing brake pads damaged the flex lines, so I'll stick to the "air in the lines" theory.

 

Dan,
Thanks for your response,
I'm not concerned about the flex lines as much as the seals in the master cyl or ABS actuator.
Do you thing that the back pressure created by pressing (or in the case of the rears rotating) the pistons back into the calipers could damage the master cyl or abs actuator?
I'm concerned that the back pressure upset one of these seals, preventing the master from generating fluid pressure (the piston passes thru the fluid rather than compressing it).

I've bled it several times to no avail,procedure is correct. and pedal feel was ok prior to the pad replacement.

Thanks again

 

This is maybe a silly question... But after a brake job it sometimes takes 10-20 seconds for pressure to initially build up to firm the brake pedal. Have you tried driving slowly around the block while starting and stopping a couple of times?

 

I've never heard of a master cylinder being harmed by pressing caliper pistons into their bores. This procedure is commonly used for replacing brake pads.

There is some concern about sending old (and possibly contaminated) brake fluid upstream into the ABS actuator. Some technicians prevent this from happening by clamping the flex line and opening the caliper bleed screw. This method forces the displaced fluid out into a catch can rather than upstream into the ABS actuator. However, the idea of pinching a flex line frightens me and I won't do it. My preferred technique (this is for ABS systems) is to open the bleed screw, attach a hand-powered vacuum pump, and draw the old fluid out as the piston is gently pressed inward.

The ABS system performs a self-check at the beginning of each trip. You don't report the ABS warning light as being on, so there is no reason to believe the actuator is damaged.

 

Thanks again,
Actually I used the Hand powered vacumn pump to bleed them the first time (had to add teflon tape to the bleed screws to get a sufficent seal), then resorted to the old fashioned way when that did not seem to help.

No fault codes from the ABS. And I've also tried driving it a little to seat the pads, to no avail.

Do you know if there is a seperate bleed fitting for the ABS actuator?
How about the order of bleeding, the manual I have shows LR, RF, LR, RF.

Any other thoughts are appreciated.


Any other thoughts?

 

You have done all the right things.

My own car is not ABS equipped, so I can't look for a bleed screw on the actuator. The factory service manual doesn't show one.

Try pumping the brake pedal with the engine off. After 5-6 strokes you will have exhausted the stored vacuum. If the pedal then becomes firm, maybe you have a problem with the power brake booster. If the pedal is still spongy... much as I hate to resort to this... it may be time to turn this problem over to a professional.