Rebuilding brake calipers and carriers

[SteveSarre]

Hi all

I am rebuilding some front brake calipers (normal V70 ATE) and carriers (in fact two sets).

Using rebuild kit from BiggRed
https://www.biggred.co.uk/product/br...-brkp10/BRKP10

I have dismantled the calipers (removed the bleed screws, pistons and seals), degreased/washed then I have used phosphoric acid (about 80%) which eats the heavy rust away in about 24 hours.

Then I rinse and wire brush the black slime/deposit and wire brush again. Rinse and repeat as necessary.

Then place in a hot domestic oven to dry out. A thin layer of rust forms - as expected.

I want to paint, probably using Halfords Silver spray paint.

Shall I paint straight onto that final rust, or wire brush it first? What about using Fertan rust converter?
https://www.fertan.co.uk/product/fertan-rust-converter/
Would that convert the rust into a protective layer or am I better off without that?

Suggestions welcome.

If this process works, I have some rear calipers which I would rebuild in the same way

Steve

[ITSv40]

I haven't used the exact same technique, but I have used Por15 on many parts. Very similar process. They actually tell you to ignore any surface flash rust that may form before painting. I always just give it a wire brush as it makes me feel better before applying the paint.

[Luxobarge]

I've got quite a lot of experience with rusty parts, having restored several cars and a tractor. Personally I'd get as much rust off as possible (ideally sandblasting) then paint/spray with etch primer, which does as the name suggests - it bonds to the steel better than anything else ever will. Then paint over with your top coat of choice, if it's cellulose based (e.g. an aerosol of caliper paint) then so much the better. Several thin coats, allowing each one to go tacky before applying the next.

[SteveSarre]

Hi all

The phosphoric acid is very effective at removing rust. And unlike spirit of salts, or muriatic acid or various other chemicals, it doesn't attack the iron, just the rust.

I should have taken some photos.

These brakes were very very heavily rusted.

I considered electrolysis but preferred to remove the rust rather than convert it back into iron.

Steve

[ITSv40]

I know it is not brake callipers - they are quite difficult to clean up without sandblasting. I repainted the servo after it had suffered years of careless topping up of brake fluid and had gone quite rusty below the master cylinder. I cleaned off all the paint with stripper and a wire brush. First attachment. Then treated with the POR15 phosphate and washed off - that got into the pits that the brushing could not. Second attachment. Then brush painted the top coat of paint on - two coats, it is very self levelling so the brush marks soon spread out leaving a smooth finish. Third attachment. That was done five years ago and still all good.

[SteveSarre]

Well, I didn't expect this!

Two front sets - the 4 calipers, 4 carriers - derusting, painting and caliper rebuilds went fine.

Assembling everything back onto the car ....

The caliper slider pins (Allen H7 key), silicone greased and threadlocked through the new slider boots, didn't seem to be threading in correctly.


Taking things apart, I can see now that those threads in every carrier have turned to dust. They must have been heavily rusted and the phosphoric acid has eaten the threads away completely.

Obviously I should have checked that earlier in the process, but I have never encountered that problem before.

New carriers for the 280mm discs are still available from Volvo for £47.76 inc vat each
Part number is 8251156. Delivery from Sweden is 4 - 8 weeks

I wonder if one can safely use thread inserts in the 4 carriers? (All 8 holes have the same problem). But there is not a lot of metal around that hole.

Or I could find a better used carrier and think twice before derusting it!
Or find somewhere that can sell me at least two new ones quicker than my local Volvo dealer.

Comments and suggestions welcome.

Steve

[Simmy]

short term answer get some from a breakers and then do a search for some new ones at your leisure try volvo main dealer for a base price then all the usual places ecp gsf and auto doc. parts for volvo ect

[Martin Cox]

Interesting.

If the threads on the carriers were that heavily rusted, there can't have been much remaining strength in them anyway. Far better to find out now albeit rather frustrating.

I have to say it's not something I'd ever considered.

Martin

[ITSv40]

Originally Posted by Martin Cox

Interesting.

If the threads on the carriers were that heavily rusted, there can't have been much remaining strength in them anyway. Far better to find out now albeit rather frustrating.

I have to say it's not something I'd ever considered.

Martin

Yes sounds like a lucky escape.

[SteveSarre]

Those sets were ones that I had picked up from cars being broken.

I derusted the carriers because they were particularly bad.

Just bought a couple more (calipers and carriers) off ebay, so will inspect them carefully.

Thinking about the danger if the slider pin threads had failed completely - I am pretty sure that the pads would still retained by the rest of the carrier. Will have a think and probably send photos.

Steve