electrolytic derusting

[news]

Can anyone say whether this method might work to free a rusted piston and caliper of a classic car? If so any tips to set about it?

AJH

[T i m]

It might (I've used it for general de-rusting with reasonable success) however you might need insure the process can 'see' any areas that are rusted so maybe not (even if you split the caliper).

This might give some good guidance:

This link mentions hydrogen embitterment towards the bottom:

However, think you might be better (to start with anyway) by soaking it in something like Plus Gas (or any other good penetrating oil, not just WD40) and maybe warm it up a few times with a hot air gun and re applying etc.

If you have tried something other than a penetrating oil or if you still have hydraulic fluid inside the caliper it might be best to wash it all out in some light spirit of some sort (panel wipe?) get it dry and then try the penetrating fluid inside and out.

Do you know where the rusting is? If the dust seal has failed on the outside it can be between the outside world and the seal or from water in the brake fluid on the inside and up to the seal.

Then you have to hope that when you do get the piston out that nothing is too rust damaged. ;-(

Cheers, T i m

p.s. I used an old PC PSU for the 12V. ;-)

[Peter Parry]

I've used it quite a lot. Washing Soda is the electrolyte to use (Sodium Carbonate) and for electrodes I used lengths of reinforcing bar.

If the parts are entirely iron/steel it has the advantage that it is quite difficult to harm what you are de-rusting (which is why archeologists like it). If there are alloy components that may not be true.

It takes a long time, typically days, but you won't harm anything leaving it for too long.

If you are concerned about Hydrogen embrittlement bake the part for about 8 hours at 190deg C (Domestic oven temperature - but wait until SWMBO is away). This bake should be done as soon as possible after removing the part from the cleaning bath, rinsing it off and coating it with a very thin layer (wiped on with a rag) of oil. I've never found it to be an issue except possibly with things like chisels as the parts you are cleaning have already corroded (Otherwise you wouldn't be cleaning them like this) and are already somewhat compromised.

[Roger Mills]

What sort of car is it? Have you checked on the availability of spares via enthusiasts' clubs, breakers yards, etc.?

[Lee]

Where I used to work, we used to use a company oop North that re-machined old calipers, inserting sleeves etc where necessary. Not cheap, but sometimes the only realistic option when something was NLA and nothing modern could be made to fit. Probably not much help that I can't recall the name of the company :)

[Dave Plowman (News)]

What make of caliper? Most are still available. And if the caliper bore is rusted, it's likely scrap, or will need sleeving.

[Capitol]

I recall a thread on this newsgroup some years ago which gave a reference/link to derusting drum brakes. I have lost the link, but maybe someone else has it?

[news]

It's my mate's mini cooper s

We're soaking it in diesel first and then will try to hydraulic it out with a grease gun.

The I'll see if he will let me use the electrolysis, thanks for the pointers Tim and Peter.

I have advised against splitting it for now.

AJH

[Jonno]

[e-mail] scribbled

Or buy new

[Kellerman]

Critical safety part. Buy a new one (pair preferably). If "originality" concerns you - put them in the boot when you sell it one so that somebody else can clean them up ans refit the originals.

[tabbypurr]

that's no reason to discourage someone capable of the job

NT

[Dave Plowman (News)]

No - but if it's so rusty the piston won't shift, the bore in the caliper will be pitted or damaged in some way. The piston can be replaced, but the only fix for a pitted bore is to sleeve it. And given the low cost of a new caliper, not worth it.

Typically, a complete new caliper costs about 2-3 times the price of new pistons.

[tabbypurr]

yup

Now we know what vehicle it is, before we didn't.

NT

[Dave Plowman (News)]

There are very few - if any - classic cars with disc brakes where calipers ain't available new. Low production cars - so rare - tend to use brakes from another more common car.