Brake caliper rebuild - piston issue

[JHZR2]

I had a prior thread discussing the seized piston on my 82 MB 300CD.

Finally tonight I was able to remove it and take it apart. I used compressed air, and one piston came out easily, the other not so much.

This piston came out easier:

What do you think?

One:

Other:Ed

Now here's the catch... when removing the seal, I found thi:

They're under the lip of the seal, don't think they're a mating face of any kind.

Is this done for? Btw, the side with those damage marks was the side that popped out easily with compressed air. The other side has the smooth piston that didn't want to come out.

 

[97prizm]

If there are that Deep of gouges I'd look for new pistons

 

[maxdustington]

I'd run them. The plating on those is decent and if that gouge is not on a sealing surface you are probably OK. I'm going to assume new parts will be difficult to find for that car so I think it is worth a try.

I got some calipers from the yard and rebuilt them intending a quick swap. My calipers were in much better condition that the ones I rebuilt, to my dismay. It was difficult to find calipers that had pistons that did not have flaking chrome or rust.

 

[928]

https://www.rockauto.com/en/catalog/mercedes-benz,1982,300cd,3.0l+l5+diesel+turbocharged,1193554,brake+&+wheel+hub,caliper+piston,1724

 

[demarpaint]

I think I'd replace them.

 

[DuckRyder]

As long as that nick is not on the sealing surface I'd run those.

 

[Donald]

I would probably run those. But how much are new pistons? I wonder how the gouge got in there?

 

[supton]

Originally Posted by Donald
I would probably run those. But how much are new pistons? I wonder how the gouge got in there?

Casting defect? Maybe no one noticed it, or they did and it was known to not matter (an allowable defect).

 

[JHZR2]

Originally Posted by Donald
I would probably run those. But how much are new pistons? I wonder how the gouge got in there?


Ive yet to find these pistons available. The link above for rock auto has them listed but "not available".

Originally Posted by DuckRyder
As long as that nick is not on the sealing surface I'd run those.


They were there when I pulled the pistons, under the dust boot. On full thickness pads it's not clear if they would be interfacing with seals.... I think...

 

[WyrTwister]

What do the caliper bores look like ?

I know just about nothing ab a MB , but I would probably use fine steel wool or emery cloth to polish them , and the caliper bores , if needed .

 

[DuckRyder]

Pull the seals out, clean the bores up and clean the pistons up drop the piston in the bore and see if the nick is above the seal groove, it looks like it is, but be sure.

 

[JHZR2]

Originally Posted by WyrTwister
What do the caliper bores look like ?

I know just about nothing ab a MB , but I would probably use fine steel wool or emery cloth to polish them , and the caliper bores , if needed .

 

[spasm3]

If it was not leaking, then it's probably not going to. I would make sure there are no sharp edges, if so touch just that area with a fine round file or emory. Then i would clean it with brake cleaner and JB weld it. I'd fill it with jb weld epoxy and sand over so its smooth. That way you don't damage a new seal when installing.

If there was any evidence of leaking, then i would replace the piston or caliper.


Not familiar with MB, but whats the difference in the ate calipers and the bendix?

 

[maxdustington]

The dust boot seals inside of the rusty part on those right? That's why they're so bad?

It might make it a bit hard to get a brake hone in there if that rust groove is the same diameter as the inner bore.

That bore looks a little rough, but I'm no expert.

 

[JHZR2]

The bore inside of the seal is smooth. There's a little bit of wear on the bore and piston, but these are 37 years old and 163k miles.

I pulled out the FSM. It says to lube the inner seal without ATE brake lube. Worked great to press the pistons back in.

 

[JHZR2]

I guess it all works. Is there a better way than this to test?

 

[barryh]

Those pistons are in good shape for their age. The nick is of no consequence, if it had been there would already have been a brake fluid leak.

The pistons went back in with brake fluid to lube the seal. Now the important part is to lubricate the part of the piston that lies outside of the seal. Brake fluid is the worst thing you could use as it just attracts moisture. There are dedicated brake greases compatible with the rubber seals, either red rubber grease or silicone based brake grease. This will ensure the pistons stay free from future corrosion.

 

[JHZR2]

Originally Posted by barryh
Those pistons are in good shape for their age. The nick is of no consequence, if it had been there would already have been a brake fluid leak.

The pistons went back in with brake fluid to lube the seal. Now the important part is to lubricate the part of the piston that lies outside of the seal. Brake fluid is the worst thing you could use as it just attracts moisture. There are dedicated brake greases compatible with the rubber seals, either red rubber grease or silicone based brake grease. This will ensure the pistons stay free from future corrosion.


Thanks!

I didn't use brake fluid for any of it. The factory manual said to use ATE grease, so that's what I did.

 

[BlueOvalFitter]

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