Hey everyone, having a freakin blast over here with the caliper rebuild.... hah

Diesel911 I was trying to follow your advise about being sure to align the pistons like they came out, but unfortunately I messed that up... Now I'm using the pictures I took and the wear on the brakepads to position the piston correctly. This really isn't working out though. I've seated one in perfectly with the boot around it, but when I went to put the other side in, it became stuck as I tried to compress it in with a c-clamp. I'm trying to be sure to slide it in perfectly straight, but this is quite difficult. I cannot tell you how many times I've had to pop each side out with the compressor. What a PITA...

Do the pistons only fit in the side that they came out of? I'm starting to think this may be part of the problem. I can't seem to get one of the sides to compress enough so that I can even attempt to put the boot on it. Also, if there is a way for me to know for sure how it should align, then please let me know. I feel like I'm missing something here.

I've gotten to this thread late, but I would have suggested making a little cardboard triangle that represents the angle of the notch to the caliper pad slides so you could align the pistons correctly upon re-installation.

At any rate, if you are trying to install the pistons with the heat shields still on, I don't see how you are going to fully seat the dust boot that resides underneath it. Of course, Mercedes makes a special/expensive tool for seating the dust boot, but I was able to do it with patience, finger tips, and a soft piece of whittled wooden dowel. Be careful you don't push too hard with something too sharp as it is easy to tear the thin rubber when it is pushed too hard against the brass retaining ring inside the boot.

You may be better off just removing the heat shield, installing the piston correctly, fully seating the dust boot, then re-installing the heat shield. Mercedes makes a tool for this, as well, but most of us just carefully seat it slightly below the face of the piston. There is a spec for this distance, but I disremember what it is. There are some good threads on caliper rebuilding that should contain the value. It's in the FSM, as well.

Added: I am sure that each piston is the same size. If not, there would have been a left and right version of the seals in the rebuild kit.

Sorry I'm also late with this thread - I was rebuilding my ATE calipers yesterday evening in front of the TV!

According to my ATE repair kit there are two sorts of pistons that fit in their front calipers one is set at 20 degrees and the other is set at zero degrees...

Did you buy ATE parts to fit in your ATE calipers? Do you have the same information as me?

Apparently, you missed this piece of information from the OP:

Hydraulically speaking, it is critical that both pistons be the same size, at least as far a diameter goes.

After I tried to press the piston once with the heat shield I ended up removing it. Thats when I realized I hadn't previously marked the position of the piston. I'm lucky that the orientation of the piston is marked onto the old pads, or I'd be completely screwed.

I have some picks that I ground the ends off of for putting the boot on. They are rounded, so they don't puncture the boot itself. I'm about to go and try to get these aligned right again. I'm still apprehensive about how hard I should be torquing the c-clamp when I'm pressing them. I don't want to damage the piston.

Thanks for the continued help guys.

15 minutes later.... I can't believe how a millimeter can be the difference from it not moving at all, to being able to slide it in by hand. I ended up putting the piston on the old brake pad in the exact place it used to be, and then slid it into the caliper that way. Then I just used the orientation of the one I seated to align the other side. Worked like a charm. I used a bench vise and a crow bar to seat the piston rather than the C-clamp. The C-clamp was just too hard to get in that narrow space while being sure it went in straight. Thanks guys, this forum rocks!

edit: It seems like the boot should sit on the recessed part right under the lip of piston, but I can't imagine how it would stay there even if I could get it that low. I'm just putting the heat shield on, and having it push up against that. Sort of like Carpenterman was saying. I'll post back if this turns out badly.

The new brake lines I have seem to have more threading than the old ones. The top of the nut doesn't sit flush with the calipers or the hard lines. I know that these types of fittings seal at the mouth, but its strange. I'm gonna bleed them to see if they leak, but maybe I got the wrong part number? If anyone has changed their brake lines out and noticed the same thing without any adverse affects, I'd appreciate hearing from you.

That is the way it should be. It is easier to seat the boot to the piston with the piston partially extended (ie: not fully retracted.)

My right rear caliper is completely seized. No amount of compressed air will force it out. The pad was almost warn down to the metal. I'm going to go pick up a new one tomorrow.

But in the meantime. I was wondering if any of you noticed the threading on your brake hoses is longer than the original ones? I'm not sure if this is going to affect anything. I can see the way the hard lines attach to the master cylinder that they stick out a bit there.

Edit: So after replacing all of the brake hoses I bleed them all and jumped in the car. The brakes felt spongy, and I could tell there was air in the system. What I failed to do was bleed the Master Cylinder. An easy way to do this, is to top off the brake fluid. Put a pile of rags right under the master cylinder. This process is very similar to a normal brake bleed. You crack the last line on the MC and have your assistant step on the brakes and hold it. You want to hold a rag right near the line to catch the fluid that is going to poor out. It's not going to be a ton, but that's why you put the pile of rags right under the MC. Then you tighten the line. Have your assistant let the brake peddle come back up. Loosen the line, have your assistant hold the brakes down... etc, etc.

You should only have to do this 4-10 times to be sure there is no air in the master cylinder. Then you can start the normal bleeding process. Right Rear, Left Rear, Right Front, Left Front.

I hope this short thread helps some people in the future. Its pretty easy to rebuild a caliper if you keep everything clean and marked well. I would have rebuilt the rear caliper if it weren't completely seized up. Thanks for the help guys/gals.

Brake lines seat at the end, both double flare and ISO bubble, the length of the thread on the nut has little bearing unless the seat in the part is recessed. Premanufactured brake lines usually come with a long nut on one end and a short on the other.

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1984 300 D runs, interior
1984 300 D light hit in front, RUST, mint/perfect dash, decent interior (see above), parts car
(hate to kill one)
1998 Dodge diesel

Chomp, Thanks for posting this thread. I replaced my rears last year with rebuilts and was not impressed with the quality.

So, yesterday I rebuilt the fronts with kits (ATE's). The job was a lot easier than expected. I did not see a need to split the calipers as I could get to everything relatively easy. There was some serious gunk collected on the bottom of the pistons and in the bottom of the bores. But, they cleaned up beautifully. Any longer and things would have been ugly.

I replaced all 4 rotors, the pads and did a bleed job. The car has never stopped that good! The fronts were obviously sticking and not working properly. It stops with authority now.

Thanks to everyone else for posting photo's, diagrams and posting other advice. Especially D911 for posting that "Piston orientation diagram". I marked one side as I took it apart. But, I forgot to mark the other side and had to come in and search to find it.

Regards, AJ

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AJ

1985 300D (SOLD)

The brake pads on the 300D are so easy to remove that I have been pulling them off every 8 monts or so and scrape off the rust and scale on the sliding surfaces which inevitably builds up and make the brakes drag. If the pads are even half worn, I get a free set of pads from Autozone and replace them (lifetime pads- I'm on my 3rd set now and Autozone don't seems to mind they are not worn down). I put a little grease on the slides and bleed all 4 wheels till clean fluid comes out. My brakes work great and I haven't had any problems since starting that regimen. I used to let it go till the very end like metal to metal or brakes pulling before I would service it and I like servicing it every 8 months no matter what much better.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

That reminds me... I used cheap aftermarket pads too (PBR). I had to file down the edges off the pads to keep them from hanging up in the caliper. Too much paint on the edges of the pads.

You are correct about the crud and build up. I replaced my rear calipers about 6 months ago and they were full of crud when I pulled them to replace the rotors and pads. There was so much crud that I had to use a screwdriver and a wire brush to get most of it off. Then a follow up with Brake Kleen.

I'm seriously thinking about finding a 300D junk yard car that still has the original rear calipers, pulling them off and re-building them myself. These rebuilts really suck.

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AJ

1985 300D (SOLD)

Has anyone found a local or online source for the ATE brake pad spring clips? They are a cross shape and mine are pretty rusted. They are important to keep the pads in place and not drag.

Too bad they don't make pads and calipers out of stainless. Is it a matter of strength? i.e. stainless is not strong enough?

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked