Kestas,

I believe the calipers are steel, not cast iron. Hard chrome plating the bore of a steel part is not that difficult and is regularly done on larger ball bearing housing bores to limit fretting corrosion. And hard chrome plating does look dull, a little frosty, not shiny like a bumper. The easiest way to tell is to leave a drop of water on it over night and if it is not rusty (orange or black stain) the next morning it is not steel.

The purpose is twofold. First, hard chrome plating is harder than typical cast or forged steel, and it is much more homogeneous than such steels in terms of hardness throughout the volume and grain size, which means it can be precision ground with greater accuracy. Next it serves to provide the necessary corrosion resistance, as well as abrasion resistance to stand up to the environment it will be in, which for a brake caliper is pretty aggressive.

The process has practical limits on thickness and is sensitive to contamination and other variables that can be difficult to control thoroughly. And, the base material must be compatible with the process as well, or the plating will not be homogeneous and tough. In which case it is not really useful.

Sleeving is generally only a good solution if it was engineered into the new part, as an integral part of the design. This way the dimensions of the sleeve, how it is installed and retained, and how it is sealed are not a compound compromise of necessity forcing a solution on a problem as a last resource. There may be a few instances where a part is designed with enough extra material to support sleeving as a repair method, but this is not a common practice these days, especially where it adds to unsprung weight.

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)

Hydraulic piston shafts are chrome plated, as are good shocks, for the same reasons. Considerable grit is aways present in dirty operating areas (as in under the car) and anything else will corrode away or scratch badly.

The experience of a friend of mine in the auto business is that "rebuilt" calipers should be approached with caution. In the US, he has found that nearly every one he installed has siezed eventually, so for customer satisfaction and liability reasons, he only installs new. Good working used is fine (although not for him!), but rebuilt he stays away from.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Jim,

Thanks for the explanation. It makes sense knowing that the caliper body is steel and not cast iron. I guess MB calipers are really an engineering gem, and it explains why they are expensive.

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95 E320 Cabriolet, 159K

Well, put it this way:

200,000 miles, no decent maintenance in the last ten years, and I have only had to replace the rubber on the fronts on the 280. Otherwise, they work fine. Not too bad for 32 years, eh?

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!