I have to replace my right rear caliper in my car; a 1978 300D. Do the calipers have to be replaced in pairs? If I do one, do I have to do both?

I will also be doing the right rear rotor, and the same question comes to mind. Do I need to do both if I do one?

I'll be doing both front and rear brake pads while I am in there. CARQUEST seems to show that the pads for front and rear are the same which doesn't seem right to me. I'm going to CARQUEST because of the Canada ~ USA shipping extra charges B.S. and because I have a good relationship with the guys behind the counter there.

Thanks in advance

The calipers don't have to be replaced as a pair. The rotors should be as you can expect the same amount of wear on both sides. Rear pads and rotors are replaced about 1/2 the frequency of front rotors and pads. I don't know about pads on a W123 but the front and rear pads on a W126 are different. The rear being smaller. Check Pelican Parts for the part numbers and see if they match. A lot of box stores like CQ screw up on MB parts and their systems do not reflect accurate exchangeable parts.

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1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
Monark Nozzle Install Video - http://tinyurl.com/ptd2tge

Thanks for that. I kind of figured that the pads would be different since the calipers definetly are.

You don't have to change calipers in pairs, but if one goes bad, there's a good chance the other isn't far behind, and they aren't very expensive or difficult to change, so there's a case for doing both at once.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

I bought the kits to rebuild my calipers on the 300SD. It's not a difficult task and if you have the time, it will save a few bucks. I'm still rolling on my home-rebuilt calipers.

__________________
1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
Monark Nozzle Install Video - http://tinyurl.com/ptd2tge