I need rear calipers for my 1980 300SD. Just wondering if anyone has
any recomendations as to which rebuilt brands are best? I see 3
A1 - Cardone
Autospecialty - (TRW Company)
Reason I'm asking, I replaced these about 3 years ago and they failed
again. The original ones lasted 20+ years, which is pretty damn good.
The rebuilt ones are shot in about 3 yrs/20K miles. I'm not sure
which company the rebuilt ones came from. The failure mode is the
retaining rings for the rubber boot seals around the pistons came
loose, allowing the boots to come out, water to get in, you know the
rest. One has seized, the other is still working, but the boots are
already out on that one too. This looks to me like something was
clearly done wrong when they were rebuilt, as these boot retaining
rings should not just come out.
Any suggestions as to which ones are best?
I have one rebuilt caliper and still have it... 11 years. The thing about
rebuilt caliper is you have to buy the one you replace unless you replace
both side... meaning if you have a Bendix there, you must replace it with
Otherwise you need to buy a pair to match the calipers... like switching to
I buy my parts online but have not bought rebuilt caliper since then.
I disassembled the caliper to take a better look at it. This is an 80
300SD with Bendix rear calipers. The rubber piston boots are held on
by a thin split ring that goes over the boot and holds it to the
caliper. Somehow, all 4 of these are off both calipers. And they
must have come off fairly early, as the boot was still folded back.
If you open it up, the rubber in the folds looks brand new.
I tried putting the boot and split ring back on just to see how well
it holds. This doesn't appear to be the greatest design. The ring
sits on top of the rubber boot and relies only on the tension to hold
it to the lip of the cylinder. If you imagine slipping a rubber boot
on the end of an 1 1/2 pipe and fastening it with a thin split spring
ring that sits at the very edge of the pipe, that's the idea. It does
seem tight, but not a great design. If the ring somehow moves 1/8
inch, it will just slip off.
I see as replacements there are also ATE and Girling calipers
available. Does anyone know if these handle securing the boot
differently? I'm left wondering if the split ring wasn't installed
all the way on or if there is some other mechanism at work, like
expansion/contraction with heat that works it loose? The originals
were Bendix too and they lasted 20 years, so I'm leaning toward the
rings not have been done properly by the rebuilder.
One thing for sure, this time I'm going to take a close look at the
boots before I put them on. The last ones came loaded, so it wouldn't
have been obvious if the rings were not on right.
They all hooks on the same way regardless of brand... I have seen them. Like
you said, it is all tension strength... the ring should have been hard to
remove... you have to coax it out with big screwdriver.
You can try a bit of red loctite to make it stronger. The boots simply slips
on with notch and tension strength.
Logical, but the discs were brand new and are still fine. I unfolded
the boots and most of the boot area, ie in the folds, was clean and
brand new. They never extended much at all and it looks like they
must have come off early on. I'm going to check the new ones prior to
putting them on.
Another interesting thing I learned. According to the shop manual,
the pistons have a high side and a low side. Depending on the type of
rear suspension of the particular model, the high side is supposed to
be rotated so that its at the top or bottom of the caliper. The only
thing the manual mentions this is for is to reduce squeaking. I never
checked the rebuilt ones I put on last time, as they were loaded.
Taking them off, I see the pistons were rotated so the high side was
vertical, which wasn't right for any model. Probably had nothing to
do with the boots, but they did squeak when I backed up. This time
I'm gonna watch that too.
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