W212M276

My brakes started pulsating, so I inspected the fronts and they appeared to be in good shape. The brake pads were evenly worn to 6.5 mm (>50%), and the outboard side of the rotors looked good, with only a very slight lip on the edges. I was sure that I had a warped rotor, so I took the front brakes apart. That's when I noticed that the caliper slider pins had seized. As a result, the inboard side of both rotors were badly worn.

Once I got the slider pins out, I was surprised to find that they were dry, without a drop of lubricant evident inside the boots. I was frustrated by this because the dealer replaced the pads and rotors when I purchased the car as a CPO. I can't complain too much, because I got 50,000 (mostly highway) miles out of the new brakes. However, I've noticed this is a common theme when I've had brake work done in the past: the shops don't lubricate the pins or the friction points in the calipers, resulting in premature, uneven brake pad and rotor wear. I almost feel like this should be a yearly maintenance check. I flush the brake fluid once a year, so this might be a good time to check on the sliders.

Anyway, I put a lot of lubricant inside the slider boots, but the pins still require a lot of effort to move. The calipers appear to be rebounding OK when I take my foot off the brake pedal, but I'm sure it's just a matter of time before they stick again. I haven't been able to find just the slider pins and boots for sale online, not even with the caliper rebuild kits. I hate to try to ream the holes out or try to reduce the diameter of the pins. I think this would just create other problems. I hate to have to replace the calipers, although the rebuilt ones aren't too expensive, once I get the core charges refunded.

Any suggestions from the group?

By the way, if you take a look at the photos below, you'll see that I had a stowaway I wasn't aware of. First time I've seen this in a brake rotor!

W212M276

As a last resort, I called a dealer and they informed me that they carry the brake hardware to service the caliper slider pins. A pair of sliders with two bolts can be had for only $229.00. Not a typo. Two hundred and twenty nine dollars. That's more than a new caliper! I don't even know what to say about that, so I'll say no more.

The rubber boots or "bellows" can be had for a more reasonable $7 a pair.

This gave me hope that I could find the parts in the aftermarket. I started calling around, and much to my surprise, I found the slider pins and bolts in stock for $7 a pair and the boots for $7 for a set of four at Advance Auto Parts, aka Car Quest.

I just wanted to post an update in order to potentially help someone out in the future.

W212M276

I want to close this threat out by posting my results. I was surprised by the root cause of the problem.

I thought there was some corrosion on the sliders inside the boots, or the rubber boots had swollen somehow. This was not the case.

It turns out that there was corrosion between the rubber boot and the caliper. This had built up to over 1 mm around the diameter of the boots, pinching the caliper sliders and causing them to stick. I literally had to hammer them out. Gotta love mag chloride! See the image below.

I scraped the corrosion from the holes in the caliper with a knife, and cleaned them with a battery post wire brush and a round file. I coated the outside of the boots with brake caliper grease, hoping to prevent at least some moisture from getting back in there.

The sliders were in good shape, so I reused them. I replaced the boots and lubed well them inside. Everything went back together as expected, and the results were great! The sliders move smoothly without a hitch!

I hope this helps someone troubleshoot their stuck calipers, as I have benefited from the posts of other members.

Happy wrenching!

CaliBenzDriver

I have just discovered your post about those dried out slider pins.
When my E350 was 10kMi my front brakes became noticeably harder. So I took them apart and discovered my pins where ridiculously dry from factory.

The lubricant of choice seems to be silicon based not petroleum grease because it swells up brake rubber components.

(fancy "Synthetic brake grease" is junk as well)
✌️