Can I swap calipers?

[debi]

Would a caliper off my '71 250 fit my '72 220D/8? I need a right front caliper (actually I need all four, but I'll start with the one that's broken).

Are these the same calipers and interchangeable?

[psfred]

If they are both W115/114 chassis and the same piston diameter, yes. If not, no.

What's wrong with the bad caliper? If the piston is just stuck, they can usually be fixed by using compressed air to remove the piston (very carefully) or by using the brake pedal (much safer), then cleaning and replacing the piston seal and dust boot.

Peter

[debi]

Peter, tell me more. I thought these were absolutely disposable, not fixable. If it can be a stuck piston, I'll go at it from that angle. But, could you give more info on it. Especially, how to use the brake pedal to unstick a stuck piston.
Any info is more than I have now.
debi

[psfred]

Debi:

What's wrong with the caliper you want to replace? The pads are throw-away, but to replace them all you need to do is remove the cap on the master cylinder and push the piston back into the caliper.

If it won't move, it's stuck and the brakes were dragging. To use brake fluid to remove the stuck piston, you remove the caliper but leave the brake hose attached. Hold the other piston in place with a C-clamp and pump the brake pedal until the brake fluid forces the piston out. Messy but effective -- when the piston comes out, all the brake fluid will spill on the floor.

I can be of more assistance if you tell me why you think you need a new caliper.

Peter

[debi]

The caliper is blamed because very suddenly the brake pedal went "spongey" then it sank to the floor with pressure; braking ability was greatly reduced. But, I still had some brake left.
I stopped as quickly as possible to check and there was evidence of brake fluid having flowed down the tire and onto the pavement a little brake fluid "puddled". I drove home slowly, by way of back-roads.
Checking at home showed the brake line to be dry. Both front brake lines were replaced just last summer.
My conclusion: caliper is main culprit
because that's only thing left? Right?
I've asked some mechanical friends who felt caliper was likely to blame.
I ordered the caliper repair kit from FastLane. Hopefully, everything will go well.... Someone else with brake-work experience will do the actual work. He has never actually done a caliper overhaul so I will gather instructions (from Peter!) and pass them on to him.

So Peter, your information is so very critical because I don't know anyone or any place else to get the knowledge you are sharing with me.
Many thank yous!!!
debi

[psfred]

Debi:

I've posted this a couple time, so you can do a search to check that I don't leave anything out.

Here's what you do:

Remove caliper from car by removing fluid line and the two large (19mm I think) screws on the back. You may need to push the pads back a bit to get the caliper off, but you don't necesarily need to remove them on the car. You can pull them first if you like.

Once you get the caliper off, all the fluid will drain out of the master cylinder. This is no big deal, you want to change it all anyway, but you do want to have a container to catch it. It will probably look like dirty motor oil rather than being water clear like it should be.

Clean the caliper with brake parts cleaner and a cloth or brush. You must remove all loose dirt, or it will find it's way into the bore, causing the piston to stick.

You have two (really three) choices for removing the pistons from the caliper -- compressed air (low pressure, please!) or the brake fluid, or you can pry them out with two screwdrivers. The air works better, especially the pistons are only leaking, not stuck.

Pry the heat shield off one side -- it's a thin metal peice. It fits down into the piston. Make sure you have the replacement handy, they two sides are different. Do only one side a a time. Not the exact position of the piston, the face is not symetric and the heat shield must fit over the piston so that the raised part of the rim fits into the slot in the heat shield. Should be obvious when you look. There may or may not be a tab on the bottom edge to hold the brake pads. There is a portion of the circular edge cut off, so you can use it to position the piston going back in.

Pry off the dust boot. It is a press fit on the outer rim and fits into a slot in the piston. Likely it is torn. Discard.

Clamp one piston down with a C-clamp or similar, the apply air to the line fitting with a blower nozzle (such as one would use to blow dirt or chips -- if you have compressed air you know what I mean). Do not press the tip into the fitting very hard, you only want enough pressure to push the piston out. If very much pressure accumluates, the piston will depart explosively, and this can generate more than enough force to break bones. It is entirely possible to be killed by a flying brake piston hitting you in the head.

If it won't move, reconnect the brake line and pump the pedal. This should generate considerable force. You may need to add brake fluid to the master cylinder, or bleed out the air if it drained. The advantage, other than coating the garage floor with brake fluid, is that a stuck piston can be forced out with several hunderd psi of pressure, but the brake fuid doesn't expand, so no explosion when the piston finally comes free. Messy, though.

Once the piston is out, you need to clean it and the caliper with lots of brake parts cleaner and a lint-free cloth. No abrasives except maybe some scotchbrite on the caliper bore above the seal only. None on the piston at all. However, if the brakes were working before, they will clean up nicely with just hte cleaner and a rag.

Use a wooden or plastic stick to pry out the piston seal in the caliper bore -- it's the only part in there. Make sure the slot is clean, then coat the new seal with fresh brake fluid and install it in the slot. It's square, so make sure it isn't twisted and is fully seated.

Lubricate the seal and piston with fresh brake fluid, then insert the piston into the bore. Make sure it is at the correct position, as it will not rotate unless you have the fancy piston rotating tool. Put the caliper on a surdy surface (I use the floor) and put a small board through the caliper on top of the piston. Press down and slighlty rock the piston until it goes past the seal. Go gently, as you must not roll or "nip" the seal. If it doesn't stay exactly square, it will leak or drag. You will be able to tell when you get past the edge as the piston will drop smoothly down. Bottom it out completely, it saves on bleeding time.

Check for the correct position. you can use the head shield as a guide. If it isn't correct, blow the piston out and try again.

If it is right, install the dust boot into the groove in the piston, then force the spring clamp down around the outer edge. Start in the hardest to reach part. Make sure it is down all the way -- you may need to use a flat stick and a hammer to tap the last bit down.

Align the heat shield and press home with the board. You have to get it right the first time, it won't come back out in usable condition.

All this is easier to do tha write -- if nothing goes seriously wrong, you can do both calipers in a hour or so. If someone ran the rotors too thin so that the pads touch the antirattle spring across the top, expect the pistons to be stuck. If so, just clamp the one that will more and use the master cylinder to force out the stuck one (usually the outer one) before you remove the brake line.

Do both sides at the same time -- in fact, I'd do all four. If one was dead, they all are.

When finished with the rebuild, reinstall the calipers. Attach brake line, fill master cylinder, the bleed.

Make sure you pump the brakes up before driving the car!!!! Takes quite a few stabs at the pedal to get brakes if you don't!

Peter