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  #1  
Old 10-19-2003, 12:02 PM
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Join Date: Jul 2003
Location: Alberta
Posts: 268
Brake caliper question - 190D

The right front brake caliper on my 190D has started to seize up occasionally, causing the pads to rub against the disc. I notice that a 'caliper repair kit' is available (for only $7.50), or I could replace the entire caliper with a new / rebuilt one for around $110.

Is the repair kit intended to fix this sort of problem? Does old caliper + repair kit = rebuilt caliper? Is there anything else I can try before going to the trouble of replacing/repairing the caliper? I notice that on this wheel, the brake disc set screw (that holds the disc to the hub) is missing - would this cause / contribute to this problem?

Matt

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1989 250TD Wagon 5-speed, 160,000mi ::: Dark gray metallic / black cloth
1984 190D-2.2 5-speed, 287,000mi ::: Silver-blue metallic / black MB-tex ::: SOLD
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  #2  
Old 10-19-2003, 12:16 PM
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Join Date: Feb 2001
Location: Canton,Texas
Posts: 987
A rebuild kit will work fine as long as you can get the old one apart (pistons out) and if the pistons aren't pitted with rust. If they are stuck too hard they are probably messed up anyway and you should just replace the whole thing.
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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k
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  #3  
Old 10-19-2003, 01:54 PM
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Join Date: Jul 2001
Location: Woolwich, Maine
Posts: 3,598
Matt,

If the problem you are experiencing is intermittent, I would presume the condition of the caliper bore and the piston is repairable with the kit. The intermittent nature indicates the parts are not locked together by corrosion products.

That does not mean when you take it apart you will not find lost of corrosion products. The braking residue left behind is a mixture of steel wear particles from the disc, carbon dust from the burnt pads, and road debris, including salts in places that use salt in the winter. This stuff is very aggressive and can make some very tightly adherent build ups that can also interfere with pad movement. The build ups can actually look like part of the caliper casting in some cases. You will need to chisel the stuff off.

This build up will occur in the piston and caliper grooves where the rubber boot lip is captured too. In some cases it will get under the chrome plating on the piston and caliper bore, causing flaking or pitting. If the corrosion extends into the cylinder bore beyond the boot lip groove, or on the piston past the boot lip groove, the caliper is likely not repairable. Removing rust or flaking chrome plating will adversely affect the function of the caliper as it depends on having a very precise piston to caliper bore clearance that is not practical for other than a brake manufacturer to measure and correct (would probably require replating and remanufacturing, anyway).

The piston seal to caliper bore is accomplished by an "O"-ring that is actually square in cross section. This seal has a high coefficient of friction and sticks to the piston under braking. As the piston moves forward a few mils to squeeze the pads against the disc, the seal deforms. When you take your foot of the pedal the seal pulls the piston back. There are no other parts or mechanisms to pull the piston back into the caliper, so, when this seal gets too old and stiff, it cannot store the energy needed to pull the piston back, and the brake sticks. This usually leads to rapid degradation of the seal from the heat, making the sticking brake problem worse, quickly.

When you go to put the new seal in, you will find cleaning the assembly thoroughly helps a lot. It is imperative that the reassembly be absolutely clean as dirt or other foreign materials will destroy the surface finish of the piston to caliper bore area. You will also find working the caliper reassembly on a bench much more comfortable, and the installation can be very frustrating. Remember to only use new, clean brake fluid as a lubricant and wash during reassembly. No other materials will be compatible with the parts.

I just did this on our 1986 190E 2.3-16. The brake was loaded with junk from nearly 18 years and 216,000 miles so cleaning was a chore. I used a lot brake cleaner, a chisel (and a Sears screwdriver), a hammer, wire brushes, a pie tin, a bunch of brake fluid, and lots of rags. After it was clean, I found the procedure of installing the boot very frustrating and it took more than twenty tries. What seemed to work best was arranging the piston and bore so the piston was being reinserted downward, along the vertical axis. I had to flush out any visible particles after each failed attempt so I used a pint of brake fluid flushing.

The caliper on my car was a single piston unit and that made getting a "C"- clamp on the piston centerline and caliper body to push the caliper in once the boot and seal were installed properly, relatively easy. Getting them apart was accomplished using the braking system before disconnecting the brake line. It took more than five or six pumps of the pedal to get the piston to pop out.

Overall, the procedure was well worth it. The repaired caliper has been fine for about 2,000 miles and the kit was only a few bucks. The other materials amounted to about $10 or so.

Good luck, and I 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)
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  #4  
Old 10-19-2003, 03:57 PM
Cazzzidy
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If you buy a replacement caliper instead of rebuilding --

Due to differences in wear and age, the mismatched new and old calipers will not be excerting equal braking pressures on the discs. The new one will function better than the old, and problems can arise. You should always buy calipers in sets of two, left and right.

Likewise, if you rebuild one, you might as well rebuild the other, too ... especially since the car will be down and out of brake fluid anyway.


My $.02

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