Stainless brake pistons or not?

[JonB]

Per viewtopic.php?t=53680&f=42&start=0#p391604

I’d be interested in opinions on this comment that chromed steel is a better choice for brake pistons than stainless steel.

The background to this is my resto, where I’m about to overhaul the callipers. I’ve been advised by a good and knowledgeable friend to fit stainless, but StressCraxx’s comment has me thinking.

I’ll kick it off with a (rhetorical) question. Do we believe that today’s chromed pistons are good enough (meaning by that, is the chrome plating thick or hard enough, when compared to original)?

[JohnP]

I think we have been there before Jon (at least once).
viewtopic.php?f=42&t=49478

[JonB]

Yes, sorry! I realised it after I posted.

** Move along, nothing to see here.. **

[Elan45]

I'll make just one comment. I do consider galvanic differences, although I do not have a table to hand. Mi bigest concern was attaching aluminum panels to the mild steel tubing of my Lotus Eleven S2 LeMans. I used monel Cherry rivets and over 30 years later, everything seems to still be tight and corrosion free.

Before the Eleven project, my Elan SS required a new chassis. Corrosion in the front turrets. cracking at the location where the rear "Y" is formed to the backbone and other negatives. I restored the Elan completely, including works chassis and rebuilt calipers. I had replaced the rear calipers about 1976-77 w/ NOS Girling boxed at that time. And now about 10 years later, time to rebuild them again. It was complete in Sept 1985 and I decided on synthetic DOT 5 fluid, and I did my 1st vintage race in that car at the filler race for the Columbus 500 IMSA race.

Driving the SS to my high school reunion at a state forest lodge 2009, I hit a big buck LF corner, so time to go back down to the bare frame again, to check for frame damage. There was no frame damage, but engine out and a refresh and change the 2.5 1st gearbox for its original 2.9 1st box. Seemed like a good time to drain, clean and rebuild the brakes and get away from DOT 5 fluid. Girling plated pistons had some corrosion, but the USA made SS pistons were cleaned and reused. My pre-airflow FHC is going together now and my experience led me to cad plate the calipers and fit all new SS pistons.

Case closed for me!

Roger

[bitsobrits]

If your intent is to keep the car for decades, I would say go stainless. If your plan is to just keep it for a few years, then it doesn't matter. These cars don't get used much these days, and whomever owns the car will be replacing brake seals sometime in the next decade, so really it doesn't matter. Nothing lasts forever. At least not without proper maintenance and the the occasional rebuild.

[Quart Meg Miles]

My rear calipers are the originals and when the pistons seized with rust a few months after being "overhauled" by a Lotus dealer I bought some stainless pistons from an advert in Exchange and Mart. Fifty years later and over 200,000 miles they are still satisfactory though I have replaced the seals a few times. I'm not sure what's in the front calipers, certainly not the original pistons.

On another brake-related subject: I had always been rather casual about changing brake fluid because the brakes were working fine. Feeling guilty, some time in the 1980s, I changed it using new Girling fluid. Not long after that my brakes became progressively and dangerously soft (though passed the MoT tests) and I replaced all the caliper seals and even the master cylinder, without improvement; until I remembered the flexible hoses. Bingo, problem solved and I am still using their reinforced replacements.

It was too much of a coincident and since then I've only replaced the fluid when I've had to detach the calipers to overhaul them.

[UAB807F]

I've had stainless pistons in the rear calipers for something like 40yrs now and the only snag is that because they don't corrode or seize then it's very easy to just ignore them. But as well as brake fluid replacement the Lotus manual also mentions replacing the seals at intervals;

Brake Seals, Hoses and Fluid
The brake manufacturers recommend that at intervals NOT EXCEEDING 40,000 miles
(65,000 km.) or 3 years, whichever is reached first, that the braking system be completely
overhauled and all washers, seals and hoses renewed. Hydraulic servo units should be
stripped, all old seals discorded, component ports cleaned and examined and, if in good
condition, the unit rebuilt with the appropriate service kit.

Now how many of us ever do that every 3yrs then ?

Well, I don't for one but at least I'm aware of the potential problem. The seals do wear and I've overhauled cars where the fluid inside the caliper body has been black and the seals so soft & swollen that they wouldn't easily go back even if you wanted to.

So my take would be to fit stainless pistons without question but be aware that you should have some planned maintenance on the seals and not just forget about them.

I am certainly not convinced by claims of fretting corrosion (huh ?) and the superiority of chrome plating. It's just been cheaper in the past to machine a mild steel piston and flash chrome over it to give the required surface finish/hardness than it has to machine and grind stainless steel to the same spec.

Brian

[smo17003]

I have almost zero knowledge regarding material specifications for caliper pistons, but reading this (and the other current topic) made me curious enough to see what is available out there. Via Ebay I found a company called Bigg Red Ltd and they offer (for the Elan) pistons that are "steel and electroless nickel". Bigg Red do appear to have a very good reputation for caliper rebuilds etc. I just wondered what opinions or knowledge others have on this "third" material type?

Mike

[2cams70]

Yes it’s interesting that Big Red are now offering plated pistons as an option. Perhaps they know something we don’t. Nickel instead of Chromium - hmmm. No doubt Chrome is an issue because of environmental regulations.

[2cams70]

Just a bit further on this topic. My cat pissed in the kitchen recently. Some of it hit my stainless steel cooker. Boy oh boy. If you ever want to test something for corrosion resistance let your cat piss on it.

[UAB807F]

Drifting slightly off topic of the value (or not) of stainless pistons, I do think that chrome plating will get either more expensive or harder to source correct quality items. I think the key problem is "quality" because there's hard chrome and decorative chrome plating, basically hard chrome is the industrial version for wear, corrosion resistance, etc and is significantly thicker than decorative chrome which is just there to look shiny.

We all know that the chemicals used in chrome plating are carcinogenic and there's ever tighter controls on what you can & can't do. As an aside, the HSE issued a report on nickel plating last year so it wouldn't surprise me if the cost of Ni plating follows Chrome plating.

As UK costs rise it's easy to see how imports from countries with lesser costs take over and there's the problem we face. I would have no idea it the piston in the box was hard chrome or decorative chrome, if it had an intermediate layer of copper on the base steel or not, but one is going to last far longer and was probably the original spec back in the day.

On the topic of Ni plated pistons, I overhauled the calipers on my Elise last year and was surprised to find a black coloured piston. My first thoughts were "nickel plated steel" but it felt too light and I think now that it was hard anodised aluminium. I did a bit of digging and found that AP Racing (basically the Elise calipers) fit either stainless or aluminium pistons and so I think I've got Al pistons in those calipers.

Brian