22 replies to this topic

[minimissionary]

Hi,
I've just taken my brake calipers off after problems with sticking brakes. I've stripped them of their seals, and removed the pistons, cleaning everything as I go. The pistons themselves were covered in degraded rubber, and a very small amount of pitting on the part that is frequently exposed to the elements. I have bought new seals and brake lines for the rebuild.
Question is; can I reuse these pistons? The pitted area is minute, and has smoothed off to touch, but I can still see it. Is this deep-set corrosion that is likely to come back and foul up my seals?

Ps. Does anyone know the correct torque for the bolts that hold the caliper together? I accidentally started to undo one when I was working under poor light. Never done brakes before!

Pps. It annoys the crap out of me that you can't buy standard pistons. £45 for a set is rather steep on a student budget.

Thanks.

[mike.]

Get a photo up if you can, will give a better idea of the pitting.

There is no published torque setting for the bolt you've undone because they're never supposed to be taken apart really. Although people have done it so someone may respond with a rough idea

[minimat]

Last calipers i bought from a local motor factors came with new bolts in so there must be a setting for them somewhere, calipers from brake engineering,looked as good as new and half the price that mini specalists want!!

[mike.]

These aren't the bolt that hold the calliper to the hub though, its the bolts which hold the calliper together.

[minimat]

I know!

[Cooperman]

I always use 45 lb ft. torque for those bolts and also use some Loctite. You MUST fit a new rubber 'O' ring between the two calliper halves.
Lubricate with rubber grease.
You really should fit new pistons as even stainless steel ones are not expensive and brakes are just so safety-critical.

[minimissionary]

I've not split the callipers, I just undid one of the bolts by accident (darkness, coupled with stupidity and lack of knowledge). I suppose brakes, along with tyres are the last thing I should be skimping on. New pistons it is.
Are these going to be as good as they say they are?... http://www.ebay.co.u...68#ht_836wt_858

[minimissionary]

Impatient bump with regards to the anodised aluminium pistons...
Edit: Actually, all good. Found a post on the subject on the forum.

Edited by minimissionary, 01 December 2011 - 10:53 PM.

[dklawson]

I don't know what it said in the post you found but I would not use anodized brake pistons on a street car. For that matter, I wouldn't use them on any car.

Aluminum is a very reactive metal. Anodizing is a thick oxide layer intentionally built up on the part to protect it and give it a hard surface. However, the surface is porous. Some anodized coatings are "filled" after the coloring step to close most of the pores. However, even that can develop pits. Once the corrosion starts on aluminum brake pistons (exposed to brake fluid, road salt, moisture, and heat) the corrosion will progress rapidly. Another attribute of aluminum is that it is highly conductive of both heat and electricity. Therefore, it will carry heat into the brake caliper (and fluid) better than a plated steel piston or a stainless piston.

For safety and long life, try and find a good price on the stainless pistons. If you plan on keeping your car for a while they will certainly be a good investment.

[Cooperman]

Always stainless steel ones for me.

[minimissionary]

Glad I bought stainless now. Got two pairs off jonspeed for £35 with postage. Not bad.
Thanks for the help, all.

[mike.]

I got mine off jonspeed too, cheapest I could find.

[bmcecosse]

Stainless is the way - but your original pistons would have been ok too - for a while.....

[Guess-Works.com]

When you buy a new pair of caliper bolts from AP, they come with a little bit of paper telling you the torque setting, but I'm buggered if I can remember what it is...

[bmcecosse]

They are supposed to be 'once use' only - but I never had any problems with a spot of Loctite on the threads - and just as tight as possible! They only have thin heads so it's not a great grip for the ring key. My sockets are probably a bit worn at the ends - and just wanted to jump off.