98 mountaineer brakes working poorly

[hollerg]

When I jump quickly to the pedal, the pedal feels like I am pressing on a shock absorber (~1 sec of poor braking) then it feels more normal and braking improves some. If I depress the pedal at a normal speed the sensation is less pronounced. Braking is not as good as it was before the shop replaced the front rotors and pads. They overfilled the master cylinder somehow. Fluid also has squirted out of the master cylinder around the cap.

Since then the master cylinder has been replaced twice, front pads and rotors done, rear pads okay, no leaks, have had fluid flush, and booster replaced.

One guy speculated there might be a leaking valve on the ABS unit and stated that there was no way to test, besides replacing it (costs $1000). Any idea on how to test? Is the proportioning or bypass valves a cause?

 

[96eb96]

When I jump quickly to the pedal, the pedal feels like I am pressing on a shock absorber (~1 sec of poor braking) then it feels more normal and braking improves some. If I depress the pedal at a normal speed the sensation is less pronounced. Braking is not as good as it was before the shop replaced the disks. They overfilled the master cylinder somehow. Fluid also has squirted out of the master cylinder around the cap.

Since then the master cylinder has been replaced twice, front pads and rotors done, rear pads okay, no leaks, have had fluid flush, and booster replaced.

One guy speculated there might be a leaking valve on the ABS unit and stated that there was no way to test, besides replacing it (costs $1000). Any idea on how to test? Is the proportioning or bypass valves a cause?

There could still be air trapped in the master cyl, sometimes they are a pain to bleed. Was it properly bench bled when level? Another trick is to inject fluid into the cylinder with a syringe and rubber bushing at the end.

Are all your hoses ok? Sometimes they can swell.

How was the system bled? is it possible there is still air in a caliper? When bleeding its good to tap the calipers with a deadblow hammer.

There is a simple way to test for what that guy thinks is wrong. Plug off the ABS unit (you have to find adapters) and see if you have a firm pedal after bleeding the M/C.

The ABS unit itself has a special procedure to bleed, then you can bleed the system again, maybe that is worth a try. You do need special equipment for that. Usually though you would get air after an ABS activation if that was the issue.

 

[my98nnj]

Since then the master cylinder has been replaced twice, front pads and rotors done, rear pads okay, no leaks, have had fluid flush, and booster replaced.

Lets rule out brake components, basically everything is new.

Trapped air would give you a spongy feel, not what your describing.

What pads did you install when the brakes were done? Initial bite (or lack there of) sounds like what your describing. Depending on what type of brake pads you have, that could be whats causing it.

I would find out what pads your running and research them. The pads play a huge role in how your brakes respond when you hit the pedal. Some people like a nice initial bite or grabby pad even when cold. Some brake pads don't have that feeling, but will perform better once heated up.

 

[BK_89iX]

Lets rule out brake components, basically everything is new.

Trapped air would give you a spongy feel, not what your describing.

What pads did you install when the brakes were done? Initial bite (or lack there of) sounds like what your describing. Depending on what type of brake pads you have, that could be whats causing it.

I would find out what pads your running and research them. The pads play a huge role in how your brakes respond when you hit the pedal. Some people like a nice initial bite or grabby pad even when cold. Some brake pads don't have that feeling, but will perform better once heated up.

That is an excellent point and very good advice!

Along the same lines, some pads really benefit from a formal bedding in and heat cycling process to get an even transfer of vital pad material onto the rotor surface. Stoptech has some great descriptions if you visit their site. Usually this is something we only think about in performance vehicles, but brakes is brakes for the most part. Regular stop/go use does not always get the job done.

BK