Zinc Plating the Brake Calipers - How To?

[Pawel66]

I wanted to ask (sorry for my ignorance) - when you zinc plate the brake calipers - what do you do with the surfaces of the cylinders in which the pistons are moving? They will be zinc plated too. Do you have to grind/polish them then?

[wwheeler]

I pondered this same question when I thought about doing mine. I ended up painting them gold as the plating route seemed too difficult. My guess is on new parts, they plate the housing and then do a finishing bore. For old calipers, you could plate them and then send off to be sleeved. New calipers are clear zinc plated with a tint of blue. So if you are wanting yellow cad/zinc, that won't work either. No one said restoring was easy....

[450sl]

Electroplaters plug the holes with a standard conical Polyurethane plug.

[Shvegel]

The pistons are a very loose fit by design. When not loaded they actually float on the seal. Since the pad is retained there isn’t much side load either.

All Ate calipers were plated from new so as long as you strip of any remaing plating in the bore you should be fine.

Make sure you can get the small square cut o-rings between the halves before you take them apart. 

[Pawel66]

Thank you!
I thought there was some catch there...
You mean: strip off remaining plating in the bore - before plating it now? So that the plating is even? And then you just insert seals and pistons?

[Pawel66]

Yes, thank you for the point on the seals too. They are present in some of the rebuild sets. I will give the calipers to the rebuilders - they have all that is needed.

[Shvegel]

Removing any remaining plating from the bore would be safer but I doubt you would have to worry since Zinc/Chromate is very thin.

[wwheeler]

I would imagine however that the surface of the caliper bore has to have a very specific surface finish (RMS or um) for the seal to be zero leakage. I cannot imagine that a plated surface would suffice for that. I can't speak for the piston clearance, but I can for a zero leakage seal surface. Same deal as your piston bore in your engine. The finish has to be right on. Messing with the seal on the brake system is not something I am going to leave to chance.     

[Pawel66]

Wallace, this is exactly what I was afraid of.
My mechanic is saying what Shvegel is saying and I suppose Shvegel did a couple of those rebuilts. I will talk to the rebuilders - see what they say to that. I will be coming back on this topic.

Thank you all for your kind advise.

[doitwright]

PMBPerformance restores ATE calipers. Email or call them if not sure what to do. Their YouTube videos seem to indicate no plating inside the bore. Perhaps they block it somehow from the plating.

[Pawel66]

This sounds like a good call Frank, thank you!

[wwheeler]

Yes, I am not saying that it can't be done. I am just saying that the inside finish concerns me and I personally didn't want to manage that. If there is a company who rebuilds them and knows what they are doing, should turn out fine.

[Pawel66]

Wallace, this is what I hope for. When you have stuck calipers, or rusty, when they re-build them, they have to be able to finish the bores' surfaces. Similarly here, I suppose.

[Shvegel]

Wallace,
the seal is a square cut o-ring that is fixed in the bore.  The finish of the piston is the important part. 

[wwheeler]

Wallace,
the seal is a square cut o-ring that is fixed in the bore.  The finish of the piston is the important part.

Oh boy you are right! Thank you for the correction. Not sure what I was thinking and a good reminder not to go off of memory. So I guess it is ok as long as the surface of the bore is uniform. Given that, you could probably use a hone to finish the bore if you suspected it needed it.

[Pawel66]

Here is response from PMB (very helpful guys, actually):

"All bores on all ATE calipers are plated. It’s the most important part actually. Once the plating wears off the bores, they can rust and the calipers begin to stick.

The bore is not as critical as you make it out to be. It has never been machined smooth. The “bore seal” is (obviously) the sealing surface not the bore so, things like bore sleeves and hones are smoke and mirrors for these calipers so...

...bottom line; it more or less opposite of what you’re thinking.

Hope that helps.

Eric S. Shea
PMB Performance"

And what I was thinking was the concern I had expresed before.

That confirms, I guess, what we hear from Shvegel...

[Benz Dr.]

It gets a bit more interesting than this. The seal around the piston/s is square cut but the grove it sits in has a bit of an angle to it at the bottom of the bore. When you apply the brakes the seal will lift slightly on the trailing edge and when you release the brakes the seal will fold back into its seat pulling the piston with it. The cross springs also help to move the pads back on ATE brakes while Girling's rely on the piston seals.

[Pawel66]

Thank you Dan, good learning for me.

My plating process was held for a week. The wave of -20 degrees C frost caused the plating people some unplanned holidays. They said they could not keep the proper temperature in the room they do the plating in, so they had to stop the processes... 

[wwheeler]

I found this on the PMB website FAQ - See attached picture. That should end the debate about what color the calipers are from the factory. Not sure if this is a Mercedes assembly line, but it is using ATE calipers. Below is from the FAQ:


The zinc plating we offer "is" the original appearance the calipers would have possessed as your car rolled off the assembly line. We've torn apart thousands of calipers from ATE and every single unit has a nice coating of yellow zinc on the mating surfaces that have never seen the light of day. Included is a picture from the factories front suspension sub-assembly area. Notice not only the color but the variation of the zinc finish on the new calipers.