850 Rear Brake Repair - AGAIN - Tips

PeteB · Post by **PeteB** » 22 Nov 2022, 19:18

I read FireFox31's thread about painting his calipers and I'm shocked by the rust that he's battling. Was also
surprised by how bad some of his rebuilt calipers looked. You'd think that these companies would inspect the
cores coming in and reject them when they are so badly rusted like the ones he and I both showed. I'm lucky
to live so close to FCP so that I can return or inspect them when I pick them up.
It's been on my mind that if one could find reasonably clean or even new calipers and somehow strip and then
plate them, this might be a solution. I'm not sure if there's anyway to plate cast iron but have not researched it much.
I saw the problems with rust that he's having on the caliper pistons and thought that electrolysis might be a good
way to clean them up in the case where the rust has not gotten down into the part where it matters. This video
at 15:00 in shows how to treat parts with electrolysis:

PeteB · Post by **PeteB** » 22 Nov 2022, 19:27

It does seem to be possible to zinc plate steel so this might be an option for the caliper pistons.
It might be best to just do the part outside of the boot in order to avoid altering the dimensions of
the working part that goes inside the caliper.
I'd probably remove the rust with Oxalic acid, and then plate with Zinc.
This guy shows how to do DIY Zinc plating but notice that he's also trying to sell a kit to do it. I have
several bench power supplies so I'll watch some other DIY videos to see how to do it:

Post by **abscate** » 23 Nov 2022, 00:44

My caliper rust problem has been solved as my 6th car in my fleet becomes the latest to ride the FreeCP train of free replacement parts. The Centric calipers seem to be lasting 5 years plus on my P80s, but once they seize they get a trip to Milford for new ones. I keep a new set on my shelves so I can flip a car in a day, and return them the following week.

PeteB · Post by **PeteB** » 23 Nov 2022, 10:04

Thanks, yes, the current calipers are from FCP and I'll probably just do the free replacement but it sure
would be nice to NOT have to do this every 3-5 years.

I had a sort of Deja Vu thinking about these rear calipers and pads, thinking why do these look so familiar
and why do I have the feeling that I was annoyed by them in the past. I think that my 1979 Alfa GTV4
had the same brakes, that I worked on in the early 80s. I sold my last Alfa about 10 years ago but my
brother still has them and he said yes my GTV4 probably had them.
I've also seen pictures of Porsche 911 ATE calipers that at least looked similar with dual pistons (one on each
side, not floating) and squarish pads.

PeteB · Post by **PeteB** » 23 Nov 2022, 17:48

@abscate Do you know if cast iron can be Zinc plated? I looked it up and it seems cast iron is just iron with
low Carbon content whereas steel has a higher carbon content.

Anyone?

Post by **abscate** » 23 Nov 2022, 18:09

I don’t know that , but am pretty sure you cannot galvanize cast iron.

850oldschool · Post by **850oldschool** » 23 Nov 2022, 18:48

A lot of this information on restoring vintage Porsche calipers probably applies to Volvo ones:

https://pmbperformance.com/pages/the-ul ... tion-guide

This shop has them zinc plated, as Porsche did from the factory. It should be noted that zinc electroplating is different from hot dip galvanizing of the kind which is used on things like hand railings, which wouldn't be appropriate at all.

Personally, if I were going to have my calipers plated I'd probably opt for nickel, since it would provide good wear resistance in the bores, as well as very good corrosion resistance.

Post by **scot850** » 23 Nov 2022, 19:25

I had looked at painting my re-con calipers, but the supplier said if I did it voided the warranty.................! Have to now wait a year to do that.

Neil.

850oldschool · Post by **850oldschool** » 23 Nov 2022, 19:32

abscate wrote: ↑23 Nov 2022, 00:44 My caliper rust problem has been solved as my 6th car in my fleet becomes the latest to ride the FreeCP train of free replacement parts. The Centric calipers seem to be lasting 5 years plus on my P80s, but once they seize they get a trip to Milford for new ones. I keep a new set on my shelves so I can flip a car in a day, and return them the following week.

Tell them you're not paying for the ones you keep in inventory until you pull them off the shelf and install them.

PeteB · Post by **PeteB** » 24 Nov 2022, 06:51

850oldschool wrote: ↑23 Nov 2022, 18:48 A lot of this information on restoring vintage Porsche calipers probably applies to Volvo ones:

https://pmbperformance.com/pages/the-ul ... tion-guide

This shop has them zinc plated, as Porsche did from the factory. It should be noted that zinc electroplating is different from hot dip galvanizing of the kind which is used on things like hand railings, which wouldn't be appropriate at all.

Personally, if I were going to have my calipers plated I'd probably opt for nickel, since it would provide good wear resistance in the bores, as well as very good corrosion resistance.

This is great to know! If I had a fairly newish pair I'd probably zinc plate them everywhere but in the bores
Edit: That article says to plate the bores - they probably know better!
since in my experience they never rust being bathed in brake fluid. I wonder if the Porsche versions are a
direct fit into the 850?
Really, the most important spot to plate them is where the pads ride to avoid the growth.

850 Rear Brake Repair - AGAIN - Tips

Re: 850 Rear Brake Repair - AGAIN - Tips