It seems I frequently have to replace pads and rotors on my 85 300D. Not because they are worn down too thin, but because they wear unevenly and the disks rust.

I just pulled my front pads to to pulsing when braking. Disks and pads were hardly worn. However, on driver side, contact surface shows as a narrow band compared with the passenger side.

Why would the pads have full contact and keep the disk contact surface clean on passenger side but not the driver side? Different wear from inside surface to outside too.

Please excuse the fuzzy pictures (taken in dark!) - but they do show the differences in wear.

Driver side:



Passenger Side



No sign of any leakage or other problems on calipers. Hard to see how they could apply more force in some areas than others.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

A few ideas...

The RF caliper pistons move more freely,
The LF caliper pistons are sticky.
The pads on the LF are not moving freely in the caliper. I prefer to file the calipers clean where the pads contact, thoroughly clean the pins and lube the contact areas with caliper paste.

If you'd like to throw everything at it at once, replace or rebuild the caliper, replace the brake hoses and pads. Resurface the old rotors if within spec. It seems to me that used resurfaced rotors seem to hold truer longer. If this is true it's probably due to seasoning from many many heat cycles.

Before tearing anything apart use a heat gun to experiment, learn and compare. Additionally the bleeder screws could be broken loose soon after a drive to see if residual pressure is in the system indicating failing hoses

Out of curiosity are the calipers a matched set i.e., both Bendix or both Girling?

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

The calipers are the original ATE aka Teves. They have been rebuilt once by pro shop a few years ago. Disc's have little wear and pads <2 yr old. hoses replaced too. Lack of lube on pins due to winter use could be the problem. Or, perhaps pistons were installed incorrectly (raised C on wrong side. On my check list

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Pads on my 240D W123 used to hang up due to corrosion from road salt. It seemed to hang up mostly on the sides of the pad. I pulled the pads and used a file to clean the caliper then lube. Seemed to work well.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

I usually have to abuse an old Craftsman long handled screw driver to chisel the junk -combination of rust and corroding metallic (disc and pad) residue bonding to the guide surfaces of the caliper. When these become uneven and there is too little clearance. Applying the brakes can jam the pad metal backing surface that rides on guide surfaces into one of the protruding lumps as the drag from contact with the disc tries to rotate the pad as it is pushing it toward the disc. The result is the pad gets slightly cocked.

After I chip out all the lumps I always lubricate the pad surfaces with synthetic brake grease - green stuff in a tube - to try to avoid this issue. There is not much you can do with the rear discs. They don't do as much work and if you are light on the brakes they don't really do much of anything. With a 21:1 compression ration I didn't really ask for much from the rear brakes. Just taking your foot off the throttle about equalled their share of braking unless you were going heavy on the brakes.

Hope this helps!

Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

After removing one side's caliper & disk, I decided that even although caliper was not leaking, it needed a complete clean up and rebuild with new seals and heat shields. Mainly because of rust on exposed part of piston exterior.

I wasted a lot of time trying to find front ATE repair kits or Reman calipers. In frustration, I emailed a contact in the business, and he suggested I buy NEW calipers! This for my 37 yr old car that doesn't get any high speed use?? He did offer them at a good price. I was more interested in a DIY rebuild, but my wife said - You can't take it with you - buy the new ones!

So that is the plan. No core needed, so I will eventually rebuild the old ones, just out of interest. Someone may need them. That project will be added to my list that includes a CV axle rebuild

While I have the hubs off, I decided to remove the dust shields, get rid of rust and give them a coat of paint (along with nearby suspension parts.)

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

My initial vote was also to clean the accumulated gunk, this is IMO, a design problem .

Also , any time the brake fluid turns black you know it's time to flush and bleed the entire system before the caliper's pucks begin to drag .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

As mentioned, I decided to buy new calipers. For those of you in USA, you too can get them at a reasonable price (~$250) from EECESS. I paid C$325. These are ATE and come with hardware, but not pads.

While waiting , I decided to dismantle the problem caliper. I used air - I set compressor at mid point, but don't know just what the pressure was. Probably about 50 psig. One piston popped out immediately. The other did not budge. Tried increasing to 90psi but the other one would not move. I assume it was frozen and the cause of the uneven wear. I might try some penetrating fluid, but these calipers won't be used.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Thanx for the followup .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

On a 123 I always check to make sure the pad is free to move around a little. If not I take off the edges of the pad where they contact the caliper on my bench grinder until they are free. Much easier than trying to clean off the junk on the caliper.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

In our area, we couldn't get away with that. The surfaces inside the caliper that the pad backing slide on has to be cleaned. Small wire brush/small scraper/tooth brush plus brake cleaner. If pads are still tight fit (they often are), then trim them as you described.

You can get an idea of what we are faced with looking at the condition of calipers installed 8 years ago Pic a few posts back).

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Today I found out what a caliper should look like

or closer up


By the way, these ATE calipers may not actually be new, although they are sold as such. They could be from the ATE exchange program. But they essentially appear new. Not unhappy to get these ATEs vs remans from others.



Note: ATE catalog says Service Exchange Part for this part number. All a bit confusing, but calipers look good

https://web.tecalliance.net/ate/en/parts/3/24.9260-8029.5/detail?query=24.9260-8030.5&numberType=7&groups=78#@brc/search:Search%2520by%2520any%2520number%252024.9260-8030.5;query:24.9260-8030.5;page:0/detail:24.9260-8029.5;brandId:3;articleNo:24.9260-8029.5;query:24.9260-8030.5;numberType:7;groups:78

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Wow ~

For a Petrol Head like me, that's close to porno .

Sadly, M-B caliper cores are drying up, weird because I see them being tossed out constantly .

Peach {arts jerked me around for THREE MONTHS on my 300TD's front calipers, then they didn't want to cores .

I recently threw out a large boxfull of good un corroded weepy cores, I tried to give them to Peach Parts and multiple other vendors for FREE ~ no takers .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

I bought these because I had no luck finding remans here from usual sources. NAPA listed them, but they were about double what you would expect to pay for remans, so I didn't check availability.

As it is, my vendor threw in a set of OE pads at no extra cost!

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Interesting happening, I started to take a picture of the posted ATE package image.

A QR code link popped up and it took me to their website. Had not expected that.