Brake pistons - Stainless steel vs steel

Hi VFRW, I'd love some advice from the knowledgeable/not so knowledgeable. I'm currently renovating/detonating my 30 year old Yamaha RD250LC. Ive been searching the net for different parts. I have come across replacement brake pistons (as the RD had been neglected by time). There are stainless steel brake pistons or normal steel ones. I cant seem to find any opinions other than 'stainless wont pit or rust around the seals'. I always thought Aluminium and stainless tend to react galvanically especially if the aluminium is not anodised - which it isnt in a caliper. Am I better off with just steel ones or spending a bit more on stainless?? Bearing in mind the bike wont be ridden as a commuter, probably every couple of sundays. Thanks for your input. Mark

 

Any idea what the S/S alloy is? This might be helpful;

Stainless Steel Aluminum Galvanic Corrosion

I generally use a product called "Sil Glyde" on all the moving parts or friction points.

AGS Company - Sil-Glyde® Brake Lubricant

There is probably some sort of equivalent product in your neck of the woods. You might try a place that specializes in trailer brakes. They usually have products that are made to help protect neglected or seldom serviced braking components.

Personally, I have no idea which pistons would be a better choice. I would think the S/S would be less inclined to seize over time, but that's more of an assumption than anything.

 

Thanks for the reply and the link.
Like you, I would have thought stainless would be less corrosive. But looking at the chart you supplied it looks like the mild steel is closer to Aluminium than all types of stainless. I suppose it doesnt matter what metal corrodes or reacts, the further they are away (galvanically) the bigger the reaction. Maybe once I get them back together I should check them every year or so.

 

If your using the bike as a sunday rider theres no need for special stainless pistons. Its not gonna see any harsh weather, and since you've got it apart you could swing for DOT5 brake fluid since it is silicone based and does not absorb water, further reducing corrosion issues.

 

Thanks for the advice Davis5g,
See this is why I love VFRW.
The Dot5 I will definitely use. I probably would have just followed the manual and put Dot3 in it. I ordered the plain steel brake pistons and seals tonight.
Thanks again for the info.
Mark

 

Glad I could help, post up some pictures of the old minger as she's coming along. Even at the age of 22, I love old bikes, my first ride was a 1975 kawi KZ400 that I think got more compliments than my VFR even if it was a little bit of a turd, it looked nice. I could pull the carbs off that think in about 15 minutes and the whole motor in under two hours...

 

Okay will do.

 

A note from the link on galvanic corrosion:

The piston shouldn't be in direct contact with the aluminum caliper, due to the rubber seals. And brake fluid isn't very conductive to begin with (internet digging shows about 400 ohms/meter vs. 10 ohm/meter for tap water and <0.1 ohm/meter for salt water). So, I really wouldn't worry about it too much.

As an aside, engine coolant seems to be about 100-150 ohm/meter, which further indicates that you shouldn't use tap water in your cooling system (just distilled + glycol) as it further reduces any corrosion in the cooling system (if there are any metals other than aluminum involved). I know the water pump in my Subaru uses a steel impeller, and the rest of the system is all-aluminum. I figure the same for the VFR. All aluminum cooling system, with perhaps the exception of the water pump having a steel impeller.

 

Thanks for the info.

 

If your gona make the switch to DOT 5 you might as well use it when you have the entire system broken down. If you go the other route you should flush the system free of your DOT 3 fluid thoroughly by giving it a DOT 5 enima, (read: MORE WORK) because the two are not compatible. I have an HD friend who went DOT 5 on all his old sport bikes with ok results. The only up side to going DOT 5 in MHO is that if you get it on your paint/plastic it wont fuck it up. Me personaly, I have re-built a few calipers and master cylinders in my day and went with the old DOT3/4 with great results.