'70 280SL rear brake caliper question

[Leester]

Hi all - I'm rebuilding brake calipers and encountered something I've not seen before. The rear brake caliipers have a post in the center of each bore and the piston has a corresponding larger post with a hole that allows the piston to slide on the post - up to a point.  In dry fitting the piston, it only goes onto the post so far then hits significant resistance, although the piston is not all the way in. It probably has a good 3/8 of an inch to go which means the pair of opposing pistons take up 3/4 of an inch and I doubt the brake pads will even fit in. 70's calipers I have rebuilt dont have this post, just the bore and the piston.  Should I install the piston, (after installing the inner seal) and press in with a C-clamp or similar? My concern is whether the piston will travel freely after pressing it on to the post?  It doesn't seem like the post arrangement will allow the piston to travel freely if it takes that much force to press it in.  If necessary, I could eliminate the post with my dremel but hopefully someone out there knows more about these calipers.  Any advice is much appreciated!

Lee

[Benz Dr.]

This set up sounds a lot like the ones I have on my 600. There's a small post that the piston slides over and the whole thing works on a spring that grabs on to the post. A set of spring plates at the bottom of the piston bore in the caliper are attached to the post and the whole thing pulls the piston back into place. As the pad wears the spring will slip a little bit to allow for that wear.
These are NOT standard 113 calipers.  Use a C clamp to push the pistons all the way into the caliper bores. If they're anything like I think they are the pads should have a small groove that slides over a head on the end of the piston. There should be a spring that pushes against the pads but it's not there to push them back or retract them after braking. It's only for noise suppression.

[Leester]

Thanks, I forgot to mention that the calipers are ATEs. You have described the inside of the bore and the inside of the piston exactly. I put a phillips head screwdriver in the hole in the pioston and there DOES seem to be a springy action in there. The outside of the pistons look like a standard piston and there wasn't any unusual hardware. Before I popped out the pistons, they looked like any other rear ATE caliper I've seen (not that I've seen THAT many). 

The car is a long way from being ready for the road (engine/tranny still needs to be installed) so I might just keep my eye out for a pair of correct rear calipers (I suppose I should check in the basement first).  Many thanks for your help.

[Bernd]

Hi Lee...
funy thing.. I JUST had that conversation on the phone with Dan, who responded to you. It is exactly as described. However, my car is 100%original and the calipers were never replaced and do indeed have the post as well. Therefore, I do think that they are standard 113. BTW..if you split the calipers (which everyone advises against), which I did 20 years ago when I started restoring my car (1968 280SL) nobody was worried about liablity issues with it as much, the little caliper seals are still available, but NOT from ATE or from Mercedes dealerships for passenger cars. I found them at an UNIMOG service place. They are the exact same seals.

Contact me if you would like. I have all the parts apart and can give you details.

Bernd

[Leester]

Hello Bernd, that's quite a coincidence!  I checked a number of years ago into getting the seals, never could find them so I have never split calipers before.  I usually work the inside of the bore with fine emery cloth and have actually polished the outside of the pistons with my buffing wheel.  I probably won't split these since I have done all the work in the bores already but I would be interested in knowing where to get seals. I know there is a dealer in Santa Fe NM - south of you, that I think does a lot of import stuff - is that where you got the seals?  Also, do you plan to follow Dan's suggested procedure of pressing the piston in with a c-clamp?

Nice to see another caliper rebuilder in the group! Its just so easy to do!

Lee

[graphic66]

The two best Unimog parts places in the US are http://www.expedition-imports.com/category/unimog_404_parts/    and http://www.eurotech-services.com/  The first place may be best because these sound like 404 calipers not U900.

[Bernd]

ok..I am NOT condoning splitting the calipers (liability blah blah blah), but for those who want to know what the seals look like...here they are:

http://www.eurotruck-importers.com/index.php?main_page=product_info&products_id=944

They are definitely cheap. and they are the right ones for ATE calipers.

If you want to see the calipers with post, attached is a picture too.

[Leester]

Yup - that's what mine look like! Maybe ours are the "special edition" rare models with the "post" calipers that are worth $zillions!