Brake Pad Screw Up (W123)
 

OK. I need some guidance friends.. I attempted my first brake pad change (the '85 300D) and I think I am under water...

My first mistake was removing both pads. I then retracted one of the pistons to get the new pad in. The other side of the caliper is now very close to the roter and I am unable to get it retracted.

So I am stuck...

I don't what to create more problems but not too sure how to proceed.

First thought is to remove the caliper and get a better perspective on the situation. No problem identifying the 19mm bolts to remove (Thank you Gordon for the CD on brake rebuild) but the brake line removal seems tricky for some reason.. I can;t remove the line from the caliper because of twisting and the 17mm at the juncture of the metal brake line and the housing does not seem obvious...

Friends, I've got other issues in my life right now (minor) but this one is kicking my a$$ right now.. I need some mentoring... :)

humble and forcing a smile...

Mark

Open the brake fluid reservoir and then push the caliper back with a large flat screwdriver. It takes some time and effort to push it back. Be careful not to damage the rubber.

I'm concerned about damaging the rotor.. How do I get leverage?

I used the handle of another screwdriver as a leverage. Or use the rotor and spin it every-time after each push.

It won't budge.... What is the next step?

Maybe starting the engine will pull it back...I'm afraid I can't help you any further.

I had to use a lot of force to push it back.

Good luck!

On a non-Mercedes car (a Subaru) I had the same problem. The piston would not budge. I cracked open the bleeder... and the piston could then be moved with finger pressure.

Your mileage may vary...

On stubborn caliper pistons I usually
use a large C clamp and a piece of
wood.
You can put more force on the piston
this way.

Louis.

I always found it more difficult to allow the brake fluid to go all the way up to the reservior. I always take off the pad holding clips. Then the spring plate for the pads. Stick a large screwdriver between the pad and the rotor. Then open the bleed screw ( a tube and container to catch the fluid is helpful) and push the screw driver slow and steady to force the piston all the way back into the caliper. Using this method the piston will not go to far into the caliper and cause a leak to start. The pad may be damaged by the point of the screwdriver but I'm replacing them, so who cares. Once the pad has pushed the piston all the way in. I close the bleed screw. Now remember, when I do this I always bleed the system to eliminate any air and to refresh the brake fluid.
Doing this thru the caliper opening designed for installing and removing the pads means you don't have to remove the calipers.
But this method does requier a bleeding of the system.

Dave

If the piston has extended itself and you cannot pry it back into its bore, you will have to take the caliper off and use a C-clamp, as others have suggested. You cannot take the brake hose off the caliper until you remove the brake hose from the connection at the end of the brake line. This connection is not too difficult. Just use two wrenches. One wrench goes on the brake line and the other goes at the end of the tubing. In fact, if I remember, there is a steel plate that prevents rotation of the tubing. Once you have separated this connection, you can take the caliper off the vehicle and work on it. Much easier than trying to deal with it on the vehicle. When using a C-clamp, be very careful to ensure that the C-clamp is providing even force against the piston and is not trying to cock the piston. The clearance between the piston and the bore is very small and, if the piston is forced into the bore while is it slightly cocked, you are hosed :mad:

Thanks all.. I'll post back with results

Just a quick followup..

In usual fashion, I did the "premium" fix but glad... Here's the scoop..

The Front caliper piston was hyper-extended and I was unable to retract it so, of course, I replaced all 4 calipers. I bought new ATE from fastlane along with new rotors and brake lines.

I also got a power bleeder from Performance products and it works great. Attachment screws on in place of the brake fluid reservior and you build up 20 lbs of pressure. Then open each bleed line until air is out. Simple and painless.

The rear brakes were real easy and all in all a positive experience. There is a real handy cd from repairflix.com on doing brakes on the 123 and 126 chassis. They also have one on bleeding brakes which is were I learned about the power bleeder.

regards

Mark, Brakes are pretty important to the long term enjoyment of our old cars.... so I think your premium fix is well worth the peace of mind....

I agree
 

I just did discs, calipers, etc all the way around.

Much better performance and I feel alot safer. Maybe 27 years is long enough for discs/calipers, the original ones I replaced, at least is was in my case.

JCD

appreciate the comments.

I did notice that the pad wear on the front right was uneven and the rotor was rusting. I expect to get better wear on the pads and noticed that the PO was replacing pads every 15-20K miles or so.