Front Brake piston

[MikesBike]

Hi, I'm a new member to the forum but have
been searching and reading the posts for quite
a while. I used to own an 850 triple, bought
it new off the showroom floor but sold it just
before my first child was born. Now that almost
21 years have passed, I'm ready to play with
motorcycles again (must be one of those mid
life crisis things).
I've bought myself a '79 Special, an '80 Special
and parts of a third . It looks like the '80 Special
will be the bike to be restored with the other two
as organ donors.
One of the first things my son and I did was to
tear down and clean the front brakes. We used
the best calipers out of the bunch but noticed
several small pits in the metal of the piston.

Having said all that, I guess my questions are:

Are the front pistons still available anywhere?

Has anyone repaired the pitting by welding or
brazing and re-shaping or turning the piston?

I understand the piston is made from stainless steel.
Could a replacement be turned from plain steel or
aluminum?

Thanks for a great forum and any help that can be
offered.

Mike

[strom]

A friend used aluminium for new ones...
Try to polish em first. If that doesn't work, get new ones. Whatever they're made of, be sure that it doesn't corrode with brake fluid around and doesn't stretch too much under HIGH temps.

LP

[Snow]

Partsnmore.com sells new ones for XS11 - I'm not sure if they are the same between the Special and the Standard though. I *believe* one of the members, maybe even T-kat himself, was making new ones for awhile.
The partsnmore caliper pistons are $29 each.

[MikesBike]

Thanks for the reply Strom and Snow!
I took a look at the pistons at PartsNMore. The description
indicates it's for the rear on the Special. I dug around in
my garage and found a couple chunks of Aluminum large
enough to turn a couple of pistons from. I'm just not sure
if Al will be OK to handle the heat and stress.
Mike

[ratbyk]

Caliper pistons

Mike, I know that caliper parts can get hot but aluminum should work OK. Remember that there are rubber seals in there and they don't cook up. It should not get hot enough to cause trouble with aluminum pistons. I would not turn them down to the maximum outside diameter. Maybe a few thous. under the max. so that the extra expansion from the aluminum does not cause them to hang up in their bore.
Ken/Sooke

[TopCatGr58]

Hey there Ken and MikesBike,

When I did my rebuild of my front calipers, I, too, found pits in my pistons, so I deburred and ground them relatively smooth with a simple wire brush bit on a drill. The pistons were only pitted on the actual cup surface, deep inside the caliper chamber, and maybe a little along the sides, but no where near the front lip or rubber seal and not in the groove where the seal sits!

The rubber seal is what actually seals the pistons inside the calipers. The pistons themselves were not that tight of a fit without the seals, and after deburring them, there wasn't any rough edges to scratch any grooves into the aluminum caliper walls. I put my pistons back in, and they are working just fine, no leaks, no lockups, etc.!!!

I am in the medical prof., and have seen old time glass syringes, where the tolerances were so close that the fluid being drawn up into the syringe was enough to make the seal between the syringe case and piston, and so if the brake piston/cylinder tolerances were that close, then I could see being worried about some small pitting. However, modern syringes use a rubber cap/o-ring design to seal the plunger/piston within the syringe case, and this seems like the same situation with these brake calipers and pistons and O-ring seals.

Nice thing about the aluminum caliper cylinder, they don't seem to get pitted or corroded with the presence of water inside the chamber, just the steel pistons!!

So, this is just an observation from a shadetree survivalist, perhaps I could be wrong, but if so, then please explain why!?
T.C.

[scalded dog]

I have some pistons, that are stuck inside the caliper, what is the best way to remove them, I have tried pliars, locking pliars. screw drivers in the grooves, they move so far and then stop. TIA, Later , 'Dog

[TheDjost]

Dog: the easiest way is to use hydraulic pressure. Just hook them up to the m/c and pump away. They should come out pretty easy. In fact put a piece of wood in the caliper to keep the pistons from shooting too far because if there is any air in there, they will want to go a long way. Put the whole thing in a bucket to keep the mess to a minimum. You don't want brake fluid everywhere.

-Justin

[steelcat]

I've used compressed air. Have to be careful, about 30 psi & not let the piston fly out.

[MikesBike]

The wood suggestion is a must and make
sure you have your fingers out of the way!
Both of ours came out with a POP using
compressed air . I've been watching
for leaks from the calipers and other than
a bleeder that was a little loose, have seen
none. I'll keep an eye on it and if the pits
cause a problem, I'll turn out a pair from
Al.
Thanks everyone for your help!
Mike

[sixtysix]

I use compressed air, need to put a thickly wound rag on the bench under piston to insure it des not get damaged. If ones flies completely across the garage and slams into the door, it will probably be OK to reuse (don't ask how I know ) I have heard of guys using a grease gun and just pumping it full of grease. I guess they come out slower that way.

[scalded dog]

Thanks everyone, this is a great source of info. Later 'Dog

[pathfinder]

Caliper pistons

I would not use aluminum as like materials tend to gall (IE piston will tend to stick to the wall of the bore). Use 410SS, 4140HT or 4140 Aircraft if you can find it.
Just my 2 cents

I can get these made here in Houston if there is enough demand. I need three myself for a 78 Standard. Taking a poll let me know via email @ delzell@iname.com

[Geezer]

Re: Caliper pistons

Originally posted by pathfinder
I would not use aluminum as like materials tend to gall (IE piston will tend to stick to the wall of the bore). Use 410SS, 4140HT or 4140 Aircraft if you can find it.
Just my 2 cents

You are correct on that point but I have seen aluminum caliper pistons but they are always plated with some unknown alloy. Another issue is the level of polish. If after turning you can get a mirror finish on it with out distorting the shape, it would be worth trying. Throwing on a copper plate to prevent galling is pretty simple. I don't think it's worth the effort on a non-racing machine. It's a lot less trouble to cough up $30 for a replacment.

I don't think the stock pistons are stainless but rather hard chromed steel to keep the friction down. If you've ever seen one badly rusted it's obvious that they're not stainless.

Geezer

[pathfinder]

Pistons

Geezer, I guess I should have read the whole thread (Partsnmore.com) I guess I'll order a set. I forgot all about them having these.
I just said s/s because they definatly would never rust. The reason I need new is because the rust pits are all around the piston just below the groove. I've tried the JB weld trick but with little success. Now that I think about it I probably only need the square o-rings in the bore because the pits are between the groove on piston and the o-ring. The pistons should never go in that far. Glad you got me to thinking which I normally don't do untill I've spent allot of time or $$$$$