I had four tires put on the 300e last weekend, and the tire guy said that my passenger side rear brake pad is shot and I need to get it fixed pronto. He said he suspected a frozen caliper.

Now, I bought this car about 30,000 miles ago, from my dad, and he replaced the rear brakes right before he sold it to me. Is it possible he goofed something up and that's why this one pad wore out so fast? The front pads and driver's side rear are all in better shape.

I am replacing all four pads anyway (none of them were in that great a condition). What's the easiest way to tell if the caliper is no good? Also, what exactly is involved in rebuilding a caliper, if I find that it is necessary? should I just buy a rebuilt one (about $80)? How do I check if the master cylinder is still good?

I already did a search on this, but surprisingly I found little info on actually diagnosing a caliper problem and rebuilding it, only info on changing the pads.

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headrivenoise... listen.

Sounds like your on the right path, but I wouldn't worry about the master brake cylinder yet!

Also, when was the last time the brake fluid was changed? Should be changed every year, or two. Look at the brake fluid reservoir and see what the color is. If it is clear it's been changed recently, but if it's yellow, or amber, or darker, it's old. My guess is that it's old and has moisture in it which has corroded your rear brake cylinder causing it to stay extended thus wearing pad.

Let us know what you find.................BB

A classic sign of a sticky or stuck caliper is that one of the two pads is much more worn than the other. Likewise if as you say the pair of pads is much more worn than the other side of the car, it's probably stuck.

Otherwise, if you see any brake fluid on/around the caliper, it's most likely shot. Replacing a caliper is not too hard, but it can be a PITA to get the old flex lines off without munging them up, and likewise, when you are trying to get the thread started on the flex line into the new caliper by rotating the caliper, it can also be a PITA - those calipers get heavy with one hand holding the caliper and the other the brake line while you are trying to get the thread started. But overall not too difficult of a job.

Rebuilding a caliper is somewhat of an academic exercise IMHO, as today you can get "loaded" rebuilt calipers from most parts houses for reasonable money. It can be a pain to pop the piston(s) put in new seals, and hope the bores are in good shape to continue with, not to mention cleaning all the accumulated gook.

I won't lecture on the fact that you should probably change the pair of calipers rather than just one, but it'll work with just one new one.

And changing fluid every other year is very good practice. Get a Motive Power pressure bleeder, it makes the job very easy, far easier than the ol' Mitey Vac.

Rgds,
Chris W.

from your descriptions of what I should do, it seems that there may be a chance that the caliper is just stuck from corrosion, and therefore I can just free it up by cleaning it, and it may not even be broken. Is this a possibility? For some reason I thought that a "frozen caliper" meant new caliper time, but I know little about brakes, other than what I have read perusing this forum.

Thanks much for the quick replies!

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headrivenoise... listen.

Go for a 20 minute drive. Stop and hold your hand next to the disk that has the faulty caliper. It will be very hot from the pad constantly dragging on the disk.

Happened to my '92 124. Replacement is the way to go. Not a big project, but you do need to pressure bleed the brakes after the replacement.

Steve

Some MB cars use "floating" calipers and some don't. Floating calipers have one half fixed and the other can move. If the caliper is corroded externally it may be difficult for the caliper to float. You may free it up by a good cleaning, wire brushing, etc.

Otherwise, if the piston is stuck, it's normally because the seals have gone and the cylinder bore is corroded. Time for a new/rebuilt caliper.

Rgds,
Chris W.