Brake Calipers - PeachParts Mercedes-Benz Forum

dieselman · #1 10-30-2002, 02:23 PM

Someone please help!!!!! I have changed my calipers twice on the 80 300sd and both times they have been stuck. What am I doing wrong with the calipers

rickg · #2 10-30-2002, 03:08 PM

What ya mean "stuck"? If you mean the pistons are stuck, check your brake lines for crimps, kinks, and otherwise blocked. I had this on an old '67 230. The steel line going over to the passenger front wheel was clogged with rust'n'stuff to the point fluid could get thru when I hit the brake pedal and there was enough force/pressure to get the fluid thru, but was clogged enough that it wouldn't release the pressure for awhile until it finally bled back thru. Made it impossible to drive.
Just an idea. good luck!

dieselman · #3 10-30-2002, 04:43 PM

Well the pistons are stuck. The car is in very good condition with very little rust and I have taken very good care of it. they will not budge when it comes time to replace the pads. It may be the lines, I will replace them. If I replace them will that cause the calipers to loosen up. Thanks for the help!!!

Dinosaur · #4 10-30-2002, 05:01 PM

Dieselman
I recently had this same problem with my 83 300tdt. I had to disconnect the caliper from the brake line. Carefully remove the rubber dust seal and using compressed air in the (brake line inlet) push the piston out. Next I cleaned out the crude(not very much) in the caliper. The piston has a square seal ring you need to take care with also. Clean all the crud off the caliper housing using brake cleaner or carb cleaner. To put the piston back in the caliper, I had to freeze both pcs. and press the piston back in using a large C clamp. Be carefull to line up the piston and the caliper. Use some brake fluid to lubricate.

This should work if the calipers are still in good shape. Mine were not rusted at all. Change brake fluid once a year and you will not have this problem.

Mike

I hope this helps. This is my first post so I might have left out some info.

#5 10-30-2002, 08:08 PM

I also changed rear calipers because they were locking (grabbing) - and because the seals caught on fire from the heat! I also had to swap rotors after dumping water on them to put out the smolder

The replacements also grabbed. I tracked it down to a bad master cylinder.

dieselman · #6 10-30-2002, 08:36 PM

I had a 82 300sd that caught on fire once. I set the idle to high and while comeing of a steep hill in WV they stuck and caught on fire. It had 298,000 miles on it. That 126 leaked really bad I prefer the 116 over the 126. I currently have a 84 300SD that well compared to the 116 feels like a crown victoria or something like that. I also have had several of the 240 models and currently have a 75 115 240 manual transmission. It still runs pretty good but it uses a quart of oil every 150 miles. I think my next diesel will be a 300cd or 300td I have not made my mind up yet. I am going to pick up the oil filter housing gasket tomorrow for the 116. That is my only leak. Man I love this site!!!!!!!!!!

Thanks again for the replies!!!!!

#7 10-31-2002, 06:49 AM

When replacing pads in dual piston calipers such as on the Benz, change the pads one at a time. That is, remove one pad, push the piston home, put in the new pad, remove the other pad, push the piston home and then put in that pad.

If you remove both pads, then push one piston home, the pressure will often extend the other piston to a point where the seal folds and cannot be pushed back into its bore again. It has to come apart and new seals installed.

Good luck,

psfred · #8 10-31-2002, 09:13 PM

If replacement calipers didnt' fix the problem, it is either master cylinder or hoses/lines. The hoses can delaminate, and the lining will break loose, acting as a valve. Pressure goes in fine, brakes work, but don't release when you take the pressure off the pedal.

The test is to get them tight and open the bleeder valve. If the pads relax, the hose is shot. Any doubt, replace all of them. They are inexpensive and easy to replace, usually. Best to get line wrenches that fit (11 mm and 14 mm on the 280 SE, who knows on yours), then tap firmly on the fittings, then blow them out with compressed air, especially the one on the line with a free "nut" going over the line. Spray with penetrating oil after you get the dirt off -- several taps with a mallet and lots of compressed air is good here -- then let soak a bit and remove fitting. Have a care not to round them off.

Will work wonders for the brakes.

If the calipers have been overheated, replace the piston seal and dust boot -- kit is cheap, easy job, just make sure you get the pistons back in at the correct angle.

Peter