brakes Stainless-steel caliper pistons - are they really so good?

[jbenajes]

Hello,

I made an error and ordered standard caliper pistons instead of stainless-steel ones. The pistons I got are not chromed but have a matt dark grey finish that is supposed to be less prone to pitting. I could send the pistons back and change them for the SS, but twice shipping costs and VAT between Spain and UK is going to be expensive, I guess more than 50 pound.

Are SS pistons so superior and recommendable? My TR3A is driven only very occasionally, and brakes components stay still during weeks.

Thanks for your responses.

Jesus

[RogerH]

Hi Jesus,

the SS pistons are very good if used in wet conditions etc.

Having said that, rust from the calipers can build up and stick to the SS in the wrong conditions.

 

The standard pistons work just as well but are prone to rusting in very wet conditions.

The ones you have with the grey coating may last better than standard - even in the wet.

 

I would stick with what you have and consider an upgrade in 10 years time.

 

Roger

[jbenajes]

Thanks Roger for your advice.

 

Really, I drive the TR3A very, very little. At the ast rates, in 10 years I will have drive less than 3000 miles. With climatic conditions in this region, probably I will never drive in rain or on wet roads. So, if the main issue is splash water onto the calipers, those standard pistons would last forever.

 

I am more concerned for the long periods of stillness.

 

Jesús

[RogerH]

Hi Jesus,

remaining still should not be a great problem.

The normal brake fluid DOT4 (or 3) is a good lubricant . Not sure about the silicon DOT5.

 

Roger

[ctc77965o]

Hey Jesus,

The piston is protected if the pads are not worn heavily, it is only exposed to the elements when the dust covers leak whilst the pistons extended...of course you must keep your brake fluid in good order no matter want piston.

So I say stick with what you have....probably 20 years before any corrosion sets in and by then the rubber components a due replacement.

[Fireman049]

Regarding Roger's doubts (and mine) regarding Silicon DOT 5 brake fluid.

There is an excellent and very informative article covering this matter in the May issue of

the 'E'-type Club's magazine. I shall definitely be using DOT 5 in both my 3A and 'E'-type.

 

I wonder if the TR Club could request permission to copy the article from the 'E'-type Club?

 

Tom.

Edited August 5, 2015 by Fireman049

[stuart]

Regarding Roger's doubts (and mine) regarding Silicon DOT 5 brake fluid.

There is an excellent and very informative article covering this matter in the May issue of

the 'E'-type Club's magazine. I shall definitely be using DOT 5 in both my 3A and 'E'-type.

 

I wonder if the TR Club could request permission to copy the article from the 'E'-type Club?

 

Tom.

I have read that as well, dont believe everything you read on the internet.

Stuart.

[AndrewP]

For what its worth, if you already have the grey type, then its nothing that wasnt used originally...and they have lasted a good few years! Rebuild with a smear of red rubber grease, fresh brake fluid and a good quality seal rebuild kit and they will last for years

 

I use SS in all my rebuilds though as all the calipers Ive re-conditioned that have had coated/chromed steel pistons end up with a rust ring above and below the caliper seal. This stops the piston moving freely in the caliper and can cause uneven braking and pressure on the pads (in the same caliper).

When you brake, the piston only moves a matter of mm in and out and adjusts and moves as the pads wear.

Problem is, classics tend not to be used as much as daily driver, so the pads dont wear as quickly and so the piston stays in the same place for long periods of time.

Brake fluid is hygroscopic and so will always have some level of moisture in. Hold that moisture against something steel for long enough and it will start to rust.

 

As others have said, regular changing of the brake fluid reduces the moisture in the fluid, but it will happen...eventually.

 

Correct grade SS wont rust, and therefore wont develop the rust ring and prevent the piston from freely moving in and out. The problem with SS is cost...they are nearly double the price and as SS is harder than mild steel, the finish is often more abrasive that on mild steel and so can wear out the seals quicker (same goes for brake master cylinders that have been re-sleeved with SS).

A pain, but it will be the cost of a reseal kit rather than new pistons and seals.

 

Just my 5c..

Edited August 6, 2015 by AndrewP

[Eddie Cairns]

Andrew

 

Which grade of SS does not corrode?

[stuart]

Andrew

 

Which grade of SS does not corrode?

If you can put a magnet to it and it doesnt stick.

Stuart.

[AlanT]

Don't think you need stainless steel in Spain.

 

It's funny stuff stainless. It's not like Lead or Bronze which really don't corrode.

 

Its steel protected by a surface coat. In the normal outside environment the surface coat repairs itself.

In some enclosed situations it does not.

 

Milk tends to eat away at stainless tanks for example.

[jbenajes]

Thank you all for your interesting and useful comments. I will use the standard steel pistons and change the fluid. I used initially DOT5.1 and will stick to it.

 

This all started because some jerky braking at low speed. When restoring the TR3A I used the original discs (rotors) and some NOS pads. I cleaned the calipers, the chromed pistons and put new seals.

 

Now I plan to install new discs, new green-stuff pads and the said pistons with a new seal kit. Hope to get a better and uniform braking.

 

Jesus

[Alec Pringle]

Throw the green stuff in the bin now, and save yourself the effort of having to take them out again and do it later . . . . .

 

Cheers

 

Alec

[AndrewP]

What Stuart and Alec said....

 

For what its worth, If you can get the old Ferodo pads (H&S dont like them as they have a small amount of asbestos) off eBay or similar, they are my pick of the bunch after trying a few types. Bendix ones locally here in Aus were pretty good off the shelf jobbies in my opinion as well.

 

SS doesnt necessarily mean corrosion resistant. Different grades have different properties and some have better resistance to corrosion.

 

I try to source 316 Grade pistons, which is generally known as marine grade so has excellent corrosion resistance (it needs to be as its often in contact with salt water) , but if Im honest I tend to use what I can get hold of and not get too hung up on it.

Good thing is even with SS that 'rusts' the rust tends to be surface discoloration and easily cleaned off using a brillo/steel wool.

 

Bit of bedtime reading here:-

http://www.brownmac.com/blog/what-is-stainless-steel

Edited August 8, 2015 by AndrewP