Re: stainless steel brake bleeder screws

[James Marriott <marriott@micron.net>]

Haudi,

Linus Toy wrote:
> 
> At 15:12 6/13/98 -0400, Huw Powell wrote:
> >> I don't know if you want this...unless your caliper is also made of
> >> stainless steel, you will likely experience even more corrosion from the
> >> dissimilar metals.
> >
> >No you won't.  This is a common myth peretuated by mechanics who don't
> >want to put S/S hardware on a customer's car.  Got S/S all over my car
> >(& truck exhaust!), doesn't corrode.  That's the point.
> 
> true, stainless steel does not corrode as fast as conventional hi-carbon
> steel.  however, the point at which the stainless and another metal meet is
> more susceptible to corrosion in the presence of an electrolyte (i.e. road
> salt, sulfides, etc), with the "lesser" metal deterioating faster.

Not necessarily true. While the standard electrode potential (usually
referenced to a hydrogen cell) does have some effect, the relative sizes
(area exposed to electrolyte) of the two materials is also important.
Since steel is lower on the chart than CRES (corrosion-resistant steel,
a more-proper name for nickle-chrome ferrous alloys), the plain steel
will tend to corrode preferentially, sizes being equal. However, in the
bleeder case, you have a large cast-iron blob (wheel cylinder or
caliper) and a small CRES piece. I posit that corrosion will be minimal
(if the right SS alloy is used). In the reverse case (small piece of
steel or, worse, aluminum; large CRES bit) corrosion of the non-SS piece
will be rapid and violent.

> Also, "stainless" steel WILL corrode, rust or stain if not maintained--go
> check out a rarely used boat in a saltwater marina sometime--for a "better"
> example, ask the engineers who spec'd the stainless steel fire fighting
> standpipes on several Washington State Ferries.

Used the wrong alloy. This "mistake" is made all the time (using 304/316
instead of the opposite). Losers . . .

cu
James
US Navy trained aircraft corrosion-prevention tech
Mech eng
'87 4kq (came from the east, plenty of electrolysis proof)
'89 200q (from the west, no electron-flow evidence noted)