Rebuilding Calipers

[MrOwl42]

So I've been working on rebuilding the calipers on my 77 300D. The pistons were a bit stuck and it took some work with an air compressor to get them out, but they did come out. I cleaned them up a bit, replaced the seals, and removed some of the rust, but I'm not sure to what extent I should have them freed up... If anyone has dealt with this I'd appreciate some help

[Stretch]

If you over polish the pistons you can get to stage where they will suck in air but not leak fluid - but you have to be pretty unlucky to get there!

How much cleaning did you do?

If you live in a moist damp environment like mine the corrosion is usually too much to warrant even the thought of a reseal kit.

The pistons should be able to move freely. They should be able to do this for a long period of time - if they seize up in the next few days you didn't clean enough...

...it is a fine balancing act that is generally governed by the degree of corrosion.

[MrOwl42]

I pretty sure I didn't over clean them. I got them to move pretty freely, but when I put the rubber seal in it no longer moved freely. I'm assuming that's sorta the point but should it move freely with the seal in too?

[Diesel911]

There is quite a bit of Clearance between the Piston and the Bore. E
he main issues are if the Pistons are pitted in the Area the Seals ride on. Are the Bores deeply pitted and there can be no pitting in the sealing area where the Big Square O-ring Seal goes.
I am meaning no pitting where the outside face of the O-ring seats.

Also if you noticed the Pistons have a cut out area that has to be positioned in a certain spot when they are installed.
On the ATE Calipers the Heat Shields give you clue on that. I have no experience with the Bendix ones so cannot comment on them.

[Brian Carlton]

Originally Posted by MrOwl42

The pistons were a bit stuck and it took some work with an air compressor to get them out, but they did come out. I cleaned them up a bit,

There is no discussion about "cleaning the pistons up a bit". They must be perfectly clean without the slightest hint of corrosion or foreign material if they are to seal. The outside must appear to be brand new.

If you can't get to that condition, you're wasting your time rebuilding it.

[Stretch]

Originally Posted by MrOwl42

I pretty sure I didn't over clean them. I got them to move pretty freely, but when I put the rubber seal in it no longer moved freely. I'm assuming that's sorta the point but should it move freely with the seal in too?

Yes they should move freely in the seal - that is the point. But don't expect them to be as easy to move as they were before.

If you have the "technology" to test the calipers - apply pressurised fluid (gas is actually better for leak checks) then you can see whether the pistons move freely and are leak free. This is beyond the realms of most DIY mechanics though. However with a blocking device in the caliper (to stop the piston from popping out) and some compressed gas you might be able to get an idea of the condition of the new assembly.

PS - by over cleaning I mean it not only looks clean but you have polished the sealing surfaces so much that they no longer seal. If you can still see dirt then they're not clean - but if your cleaning erodes the sealing surface and they no longer seal then you've "over cleaned" it

[Carpenterman]

I used to rebuild calipers. Not anymore.

It's just not worth the effort when the cost of rebuilt units is so low. The last calipers I rebuilt were well stuck. It took hours to get the pistons out. There wasn't alot of corrosion--mostly staining. I cleaned the pistons with a buffer and jeweler's rouge, and the bore with fine steel wool.

A year later, when I went to replace the pads, the caliper was once again stuck. I ended up replacing the caliper anyway.

But Brian Carleton is right. If there is any corrosion whatsoever, the caliper is not rebuildable. And I believe that corrosion is mostly why they fail. So what's the point of rebuilding?

[Brian Carlton]

Originally Posted by Carpenterman

I used to rebuild calipers. Not anymore.

It's just not worth the effort when the cost of rebuilt units is so low. The last calipers I rebuilt were well stuck. It took hours to get the pistons out. There wasn't alot of corrosion--mostly staining. I cleaned the pistons with a buffer and jeweler's rouge, and the bore with fine steel wool.

A year later, when I went to replace the pads, the caliper was once again stuck. I ended up replacing the caliper anyway.

But Brian Carleton is right. If there is any corrosion whatsoever, the caliper is not rebuildable. And I believe that corrosion is mostly why they fail. So what's the point of rebuilding?

X2.

Just a little trick that I will never use again:

If ONE piston is stuck, firstly, do not remove the second piston.

Remove the caliper from the mounting flange but do not remove the hose. Remove the pads and clamp a block of wood against the SECOND (UNSTUCK) piston (after forcing it fully back into the bore).



Go inside the vehicle and press on the brake pedal. Use the hydraulic force from the vehicle to drive the stuck piston from the cylinder bore. If that won't do it, you're not rebuilding it anyway.

[Diesel911]

Originally Posted by Carpenterman

I used to rebuild calipers. Not anymore.

It's just not worth the effort when the cost of rebuilt units is so low. The last calipers I rebuilt were well stuck. It took hours to get the pistons out. There wasn't alot of corrosion--mostly staining. I cleaned the pistons with a buffer and jeweler's rouge, and the bore with fine steel wool.

A year later, when I went to replace the pads, the caliper was once again stuck. I ended up replacing the caliper anyway.

But Brian Carleton is right. If there is any corrosion whatsoever, the caliper is not rebuildable. And I believe that corrosion is mostly why they fail. So what's the point of rebuilding?

The MacParts rebuilders rebuild Calipers with big pits in the bores; I have seen them.
One of the reasons a lot of Members have complained about rebuilt Calipers leaking.

I rebuilt the Calipers on Mine years ago and there was some pitting inside. I have had no issues with them.
In Fact I have rebuilt the Calipers of all of the Various Vehicles I have owned and they all had some pitting in side.
Now if the Piston is pitted you either get a new Piston or replace the Caliper.

I think the Car Owner is actually more likely to do a better Job rebuilding the Calipers than the MacParts rebuilders.

Where I have had issues rebuilding Calipers it has been with the Caliper Kits. Dust Boots that fit poorly don't don't want to stay on the Caliper.

[Stretch]

Originally Posted by Diesel911

...

I think the Car Owner is actually more likely to do a better Job rebuilding the Calipers than the MacParts rebuilders.

...

nice one!

[Diesel911]

Originally Posted by Stretch

nice one!

3 years ago over on Benzworld someone received a single rebuilt Caliper that was for a W123 that one half of the Caliper was for a solid Rotor and the other half was for a what must have been a W126 vented Rotor.

[Stretch]

Originally Posted by Diesel911

3 years ago over on Benzworld someone received a single rebuilt Caliper that was for a W123 that one half of the Caliper was for a solid Rotor and the other half was for a what must have been a W126 vented Rotor.

Hmmm possibly for a semi-vented disc option???

[eatont9999]

Originally Posted by Diesel911

The MacParts rebuilders rebuild Calipers with big pits in the bores; I have seen them.
One of the reasons a lot of Members have complained about rebuilt Calipers leaking.

I rebuilt the Calipers on Mine years ago and there was some pitting inside. I have had no issues with them.
In Fact I have rebuilt the Calipers of all of the Various Vehicles I have owned and they all had some pitting in side.
Now if the Piston is pitted you either get a new Piston or replace the Caliper.

I think the Car Owner is actually more likely to do a better Job rebuilding the Calipers than the MacParts rebuilders.

Where I have had issues rebuilding Calipers it has been with the Caliper Kits. Dust Boots that fit poorly don't don't want to stay on the Caliper.

Same here. Make sure you get the right rebuild kit or you will be stuck. I learned that you should disconnect the rubber boot from the caliper before removing the piston so that if you have to reuse the rubber boot, it won't be torn when the piston shoots out. Keep your fingers away from the piston and let it hit against a piece of wood.

[Diesel911]

Concerning the Rebuilding Industry. One of their problems is getting Cores that are in good enough shape that they can be rebuilt.

In the case of Mercedes even if you include the Gassers there just is not and many Cores out there for them to try to rebuild. And, as time passes less and less of those Cores in are in good enough condition to be rebuilt.

so they are rebuilding a lot of marginal Parts that the give a warranty on but they are betting something will happen like you losing the Paperwork to return them, you sell the Car, like Me you might not even remember where you bought the rebuilt one from and so on. So the odds are on the side of them not having to warrant a crappy rebuild job.

Then on top of that they are sending those parts overseas to be rebuilt.
If the Overseas Rebuilder receives 5,000 items to be rebuilt the Rebuilder is going try to send all 5,000 back. That means they are not going to be so picky in deciding what they are actually going to rebuild.

Then there is the Overseas Workers. Likely taught enough to do the Job but might be getting only for each piece they complete.
I am pretty sure the Worker is not going to get blamed on some bad Unit He puts out since it is outside of His or Her country and not worth tracing back to the Worker.

Some Members have said that they won't work on the Master Cylinders or the Calipers due to safety. But, the training of the People who do the rebuilding in a Factory of those items is unknown.