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-   -   Sticking caliper or bad brake booster? (http://www.subaruoutback.org/forums/81-wheels-tires-brakes-suspension/20382-sticking-caliper-bad-brake-booster.html)

mhardiman 09-14-2009 05:57 PM

Sticking caliper or bad brake booster?
 
Hi all,

I recently took my 2000 Outback to Sears Auto for a tire warranty replacement, and to get my brakes looked at due to a grinding from the left-front wheel.

They basically told me I was worn down to bare metal, needed new front pads, and 2 new calipers since one was sticking (why two when only one was sticking? not sure...). I didn't like their price quote, being around $400 USD. Since the car has 213,000 miles on it, I figured it was time to try a D-I-Y... what's the worst that could happen?

Bought new pads and 2 calipers, set to work first on the grinding wheel (left front). Found the outer pad was like-new, and the inner pad (that is in contact with the caliper pistons) was down to bare metal. Brake pad box mentioned this is a sign of a bad piston.

Turns out, AutoZone gave me the wrong calipers, so I had to work with the old ones for now. Replaced the pads, retracted the pistons with a C-clamp, and everything seems fine. No more grinding, no squeal or anything. The car still stops, and the ABS still works (hard stop on gravel).

If I had a sticky piston, wouldn't I hear grinding or squealing even with the new pads?

For the past several months, I've noticed my brake pedal makes a wooshy airy sound when pressed down. Also, this car has always seemed to have "mushy" brakes compared to other cars I've driven (rentals)... you have to press a good ways down before getting the brakes to respond. I have heard that the "wooshy" sound can be a sign of a bad brake booster and that this, too, can lead to uneven wearing of brake pads.

So the final question becomes... do you think the new calipers are even necessary?

FWIW... I have not yet checked the right-front brake pads (ran out of time). If it is a bad brake booster, then should I expect similar uneven ware on those pads?

Thanks for your help,
-Mike

CNY_Dave 09-14-2009 06:18 PM

I can address some of it-

If the caliper piston retracts without having to go nuts with the C-clamp, the caliper is fine.

Inner pad worn, outer pad fine (or vice versa) is caused by either the caliper pins sticking (easy to check with the caliper off) or the pad binding up where it sits in the pad holder. This binding can be caused by the pad backing plate being slightly too large, or the metal of the bracket under the stainless shim rusting and bending the shim in ever so slightly.

The brake booster has nothing to do with how the pads wear.


Dave

mhardiman 09-14-2009 07:12 PM

Depends on what you mean by "nuts" ... the pistons (dual-piston caliper) did not offer noticeable resistance. Twisting the clamp seemed no worse than with nothing in the clamp at all.

I track gas economy rather closely... and noticed a huge drop-off several months ago... from average 26 mpg to 22-23. Not well enough timed for "summer gas" to be the cause... perhaps from increased rolling resistance/friction from the pad sticking?

CNY_Dave 09-15-2009 07:48 AM

Quote:

Originally posted by mhardiman
Depends on what you mean by "nuts" ... the pistons (dual-piston caliper) did not offer noticeable resistance. Twisting the clamp seemed no worse than with nothing in the clamp at all.

I track gas economy rather closely... and noticed a huge drop-off several months ago... from average 26 mpg to 22-23. Not well enough timed for "summer gas" to be the cause... perhaps from increased rolling resistance/friction from the pad sticking?

If the piston slid back easily, it's fine.

gas mileage- could be- or that other caliper might actually be sticking.


Dave


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