rear brake repair schemes for rusty mechanical piston

mikecoombs

Active Member
Has anyone had any experience in repairing the surface of the screw out piston on the rear brakes? I have a couple that are stuffed with the coating breaking off and rust pitting. I'm thinking of de-rusting them, removing whatever the coating is mechanically and electroplating them with a copper base coat to fill all the pits then Nickel and possibly chrome on top
 
I don't know how they're done, but rebuilt calipers seem to have repaired pad pistons so it must be possible. Most corrode in service and altough most can be reused they're not good enough to be used on a reconditioned caliper without work.
 
I've always wanted to try stripping the chrome off a piston and then trying a speedy sleeve. They are stainless and have a surface finish suited for seals, the only thing I wonder is can you get one long enough.

Yours
Vern
 
Just for interest that part is called a cup.

I wonder if it could be turned in a lathe and stainless sleeve fitted.

Colin
 
I've been thinking of speedy sleeves too and wondered if I can get one long enough...I've got one sitting in the lathe but getting it straight and centred is a real trial. so far i've only managed to get it close enough to emery cloth it. current thoughts are to make up an end piece to hold the pad end and use a small pipe centre in the tail stock to centre the other end without using the screw thread part. Which is why I'm thinking plating might be better as I can then emery the copper back to smooth without the need to centre it properly. problem then is to get the plating off first without worsening the steel.

in the back of my mind i'm also wondering if it is actually chrome plate as it is very white for chrome and not terribly shiny though one may be a product of the other...or it may be chrome sans nickel or nickel sans chrome
 
It's a "hard chrome" plate. The biggest difference is the object isn't polished to a high degree before plating, and the resulting surface roughness makes the chrome seem whiter. The chrome is also quite a bit thicker than the cosmetic version, which also affects the surface look.

Yours
Vern
 
I've found a Brush Chrome system, actually cobalt instead of chrome, and similar Copper kit can be bought for around $150AUS including the strippers and masking paint. I'm ordering it tomorrow. So I'll know if it works by the end of the week. Same people have a triple chrome (or cobalt) system for around ten times that but it is a dip tank affair so can do much bigger stuff, which I might look into later! I cleaned the part up tonight and it is in fact chrome on nickel, you can see where the chrome has not stayed in place, there is a distinct line between the good and bad areas, with no pitting in the good areas. I always thought it was the seal wearing the chrome that caused the rust and pitting but it looks like it was just a crappy job to start with
 
Hi, Chrome is porous so it's letting the moisture through to corrode the steel underneath. So a stainless sleeve might be better.

Colin
 
I spoke to the guy today, he doesn't think the brush kit is the way to go as it's alkali copper which you can't nickel over. So it's back to the big triple chrome process. So I might do a few more parts to make it cost effective or take a couple of pistons to a chromer and see what they can do. I had a whole bumper bar done for $660 so it shouldn't be too much...
 
I've found a local place that will fill and rechrome the pistons for $60 each which is a good price for just two. In extracting the second one I found out how to remove the screw thread from the piston sleeve. It is held in by a spring which presses against the inner case and stops against a ridge. Two levers either side forces both spring and thread block up and out. Allowing access to the inside of the piston. I might get the covers chromed at the same time...
 
Pistons came home this week. Finally finished assembly today and it was so much easier with the shiny chrome plating on the pad pistons. They turn with very little friction so can be turned by hand with fingers. I used Bendix Blue brake grease. i'll unbury the diff and put them on with the handbrake mechanism and pipework ready for a straight swap.
 
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