Caliper Piston Pits

[COOL TOM]

Caliper size

Does any one know if the standard and the special are the same size? John are these figures for the special or standard? How about the XJ calipers are they the same size? And is the back caliper the same as the front? I am going to check with a friend about making some for me and was wondering what kind of material to use also. Let's hear from some of you metalurgist people.


Thanks Tom
82 XJ DAILY RIDE
78 XS1100E FIXING UP
79 XS1100F PARTS BIKE
82 XJ IN THE ROUGH

[John]

The Special caliper piston is a larger diameter than Standard caliper piston. The Standard use the same size caliper pistons all around, and the rear caliper on a Special is the same size as those on a Standard. The Standard piston can be purchased at MikesXS, as the 77-84 XS650 uses the size piston as the XS11 Standard. The drawing I posted is for the Special piston. The material used was 303 Stainless. I have some xj11 calipers, I'll check to see what size they are, but I think they are the same as a Special front.

[John]

XJ calipers

I just checked and it appears the XJ uses the same size pistons as the Standard calipers, so new pistons can still be had, and I would assume that the rebuild kits would be the same for both bikes.

[AlanB]

Hi Guys,

I built an XS650 a few years ago, and I fitted early TZ Yamaha calipers. I am not a metallurgist, but the pistons were VERY light, but felt "hard"- I am guessing aluminium with an anodised coating?
The caliper bodies were amazingly light, took a nice polish, but went white and "fluffy" quickly- I guessed at ally with a lot of magnesium?

If it is tough enough for racing, it should be OK on the road, But I would worry about corrosion on an aluminium piston- Unless it does not rain where you are!

AlanB

[DeanR]

Have my rear caliper apart and clean. Is there any lubrication to be done when reassembling or does everything just go back together clean and dry? (such as the square o ring)

[DeanR]

Forgot to ask if there any of those pesky spooge holes in the calipers that I may have missed. Didn't notice anything.

[randy]

Dean,

Lube everything with brake fluid.

[DeanR]

Brake fluid it is. Thanks Randy
Any spooge hole in there? or in M/C only?

[randy]

NO, only M/C have spooge holes.

[planedick]

Almost solid...

You could make them in Aluminum, don't bore the hole so deep, and screw a steel plate on the bottom outside to prevent the mushroom affect. I could turn a few too and I probably can get material as cut off or "rem" from the local supply yard who is a customer of mine. I'll check into it. Maybe even come up with some stainless.

[TopCatGr58]

Hey Dick,

There's not much room on the contact end of the piston, with the Sealing dust cover and such, plus the steel plate would take up more thickness needed for clearance of new pads, rotor?

If you did hollow out the center for weight, probably just wouldn't need to make it so thin for the sidewall, leave a much thicker rim, and I would think that would be sufficient to prevent the mushroom effect against the large flat brake pad metal backing plate!?!?

Wish I had the facilities to do Anodizing!?
T.C.

[ZXDavid]

A machinest friend of mine made me a couple of caliper pistons out of stainless steel. Thanks John for the drawings. I also use a brake assembly lube made by Raybestos to assembly the caliper pistons and seals. Its a clear glycerin looking type of lube and lets the pistons slip right in very easily with little effort. Ive used this product for years when rebuilding automotive calipers.

[fredintoon]

I'm with Pat Kelly

the piston surface don't matter. The sealing surfaces are the piston groove and the caliper bore. The groove will clean up with a narrow strip of emery cloth tape and the caliper bore will clean up using a brake caliper hone.
For myself on this, an aluminum piston should work OK. Aluminum is a better conductor than steel and should transmit heat to the caliper faster and therefore should cool itself more quickly.
Fred Hill, S'toon.

[SG-Olli]

Objection

The groove in the piston has nothing to do with sealing. It is for the dust boot.
The square o-ring is in the caliper bore and seals against the piston surface.
Pits in the piston surface don't matter as long as they are not in the area of the piston travel.
On Ebay there are stainless steel pistons from seller "taunusrainer". He ships and sells in the US as well.
I just bought quite a few for the german XS650 community.

[mason79]

wouldn't the solid chunk of aluminum displace enough volume in the caliper to render a different hydrolic ratio from master to slave,

the multiplicaiton of force would change wouldn't it?

thereby needing more pressure xscertion to acomplish the same amount of work? or less? or not enought to make a differance

would this new ratio be a good compensating factor in offseting the too sensitive stainless rear brake line conversion?