So I bought some 4 pot calipers and when they arrived they were pretty much the rustiest brake calipers I had ever seen, pins rusted in, shims rusted through, they were bad, but I was fine with this as they were cheap.

Obviously I am gonna paint them, so I set about researching the best way to clean them, bearing in mind I needed to free off the pins as well.

Pentrating oil and wire brush was one method, but having used this in the past it is a pain, destroys many wire brushes, and is almost imposiible to get into all the nooks and crannies.

Electrolysis is good but reqires you to run power cables outside, setup sacrificial anodes and can kill power supplies. It also requires constant moving as the process is "line of sight".

Acid Bath - This is the easiest, slowest method, but it is quite safe, and all you need is a bucket of acid, a stiff scrubbing brush and a couple of days to allow it to work fully.

I decided to give the acid bath a try, and set about ordering some Citric Acid powder on ebay (the stuff in bath bombs and haribo fizzy sweet coating). 2 days later 5kg of citric acid powder arrived.

I mixed 2kg of acid powder into 10 litres of hot water, and dropped in the calipers. (20% solution) and set about waiting.

This morning I removed the calipers, rinsed, scrubbed and returned to the acid bath, the results were already looking quite amazing, but still a lot of rust in some places.

Tomorrow I hope to post pictures of the finished calipers, ready for paint. I think you might be surprised, and I feel really dumb for not taking before pics now.

 

It couldn't have been much more than surface rust. So a wire brush would have done it.
The thing is with the 4 pots, you'll never get a really smooth looking finish, so if you painted them with some hammerite, you'd have ben none the wiser to nooks and crannies you couldn't completely prepare.

Ian Godney shotblasts them I believe, and does a good job reconditioning those. But even then, they are never completely smooth looking because of the casting process in which they were made.

If they were as bad as you say, make sure the pistons are OK, as thats a problem area with older calipers.

Looking forward to some pics.

 

Well of course it is surface rust, it cannot rust inside the casting

But there is surface rust on a body panel and there is surface rust on an anchor at the bottom of the sea for 20 years, mine was closer the latter. (pics below are similar)

These will need new seals and pins, and I will likely fit some stainless pistons (some are bound to be pitted like you say) while they are off, but they are looking amazing.

Blasting with walnut sheels or sand or whatever is good, but this is something anyone can do at home for less than £20 (all I paid for citric acid powder, and I have 60% of it left and the liquid I have in a bucket can be stored and reused for which I have a 10 gallon plastic container).

I do have some nice new in box Goodrich hoses to go on with them as well, so some Godspeed discs and pads should complete the set.

Pics coming tomorrow.

 

That is after 36 hours, I reckon another 24 should see them completely rust free.

 

So after 2 more days soaking and pressure washing, the end result is...













Unlike Bead blasting, the solution acts like a penetrating oil so the brake pins dropped out, and as for the bleed nipples..



As you can see I havent been 100% removing all the rust as they are to be painted with rust converter, then etch primer and finally a Brake Caliper paint, black or blue I am thinking.

 

Good result there !!!

I`d replace the pots anyway, i had a 2nd hand set of 4 pots and the pots looked sweet, they still seized and warped my discs !

S/S pots all the way

enjoy the refurb bud

 

thanks galifrey,i know what im gonna do with my spare pair of seized 4 pots now ,

 

Yep gonna go stainless pistons, new seals and pins etc.

I will add the calipers are now coated with a very even coating of surface rust, the rust converter should deal with that nicely, then prime and paint

 

I used Bilt Hammer on mine with the same results, I had tried vinegar, but it was useless.

 

I was told that Bilt Hammer is mostly citric acid, hence why I went this route

deox-C powder I assume you mean which is £40 for 4kg instead of £20 for 5kg.

 

Good result, mate, well done.

 

Thanks, I didn't pay big money for them so expected to be rebuilding them, I bought them on here and they were very rusty so I am very pleased with the results so far.

Just waiting for spring to buy some SS pistons, seal kit and pin kit, discs and pads, then they will go on

Weedy brakes might be an advantage during winter

 

My intial glee has been shortlived as the pistons are still rusted in

Managed to drift 2 out (the ones adjacent to the pipe banjo) and move 2 others slightly, back in solutionto soak again, this time allowing the solution into the caliper to atatck the rust both sides.

 

Came across this via Locostbuilders:

http://www.locostbuilders.co.uk/foru...e=1#pid1394238



Not sure what came of it, but for really stuck pistons this usually works:

Put the pistons back in with the seals.

Close the bleed nipple.

Connect a grease gun to the banjo fitting (you'll need to get slightly creative with pipework - old brake hose (the grease will eat the rubber slowly) joined to some brake pipe, with the brake pipe flared to fit the grease gun.

Put a few old pads/sheets of metal etc between the pistons. Pump the grease gun to force the pistons out ("brake" onto the pads). Keep removing pads/sheets of metal until the pistons are far enough out to grab with your choice of wrecking implement. (usually once you've "cracked" the seal they move freely) Then do your cleaning.

You can also use an old brake pedalbox as your hydraulic supply. Attach caliper to the master cylinder, bleed, then scaff pole on the brake pedal and heave until the pistons move or you burst the rubber hose/demolish the pedalbox.

Where both stuck pistons are on one side, you'll need to make sure that the pad/shims stay central. Use a stack of M10 nuts or similar to space and support that pad.

You can also remove and discard the rubbers before dropping it in the acid solution (helps with access) and try some heat on the part to break the rust seal. (drop it in the oven at 250C then fill the pistons that you're discarding anyway with cold water to shock them free)

HTH,

--
Marko

 

Milkstone remover from your local farm shop - phosphoric acid - and cheap BTW.