Caliper Piston Pits

[ZXDavid]

I have my 79 XS11SF calipers torn down and the pistons have some pits. What is acceptable to use and what is not? Since new pistons are not available for the front my only choice would be used pistons but they could very well be no better than what I already have so Iam kinda in a dilemma as what what course of action to take. I even had a guy tell me that he has turned the pistons around and put them in backwards in order for the seals to be on a unpited part of the piston but man I just dont know.

[Goin Commando]

I bet that Andreashweiss has a usable set to buy.

[Ken Talbot]

No, I don't think you want to put the pistons in backwards.

The thing you want to pay attention to is the location of the pits. Chances are the pits are on the outer part of the piston, the end closest to the pads that is normally outside of the seal. Out there, it really doesn't matter too much if there are pits or not. The part that matters is the part of each piston that rides in and out past the seal. If that area is in good condition, you will still get a good seal and good braking performance.

[HobbyMan]

Just make sure that there are no burrs. Sometimes I have gone over them LIGHLY with fine emmery cloth.
Never had one leak yet

[TopCatGr58]

Hey David, and KEN,

Aside from the pits near the pad contact surface which as Ken stated isn't much of a concern, I"ll be the pits he's found are near the cup end where the pistons fits deep into the caliper.

These pits are also inconsequential. The area of concern is right around where the rubber O-ring fits onto the piston, cause that's where it needs to make a good seal. As long as there are no pits at the Oring groove, then you can just emory cloth or wire brush the remaining pits around the rest of the piston.

The caliper housing being aluminum usually doesn't pit, just the spooge collects down deep in the housing. The water that can condense in the brake fluid gravity feeds down into the calipers and then sits there against the piston causing it to rust/pit! Another reason to flush/bleed your brakes annually to remove collected water.

Once you pull the square O-ring from the piston, you may find some corrosion in the groove that can usually be cleaned out with a flat blade screwdriver or other NON cutting flat scraping surface. Inspect the O-ring, as long as it's not damaged, you can clean it and put it right back in for your rebuild.
T.C.

[desert1]

stainless pistons

Was'nt someone offering stainless pistons for sale at one point? Maybe it was TKAT, dont recall.
Bruce

[John]

That was me selling the SS pistons, but they are all gone now.

[ZXDavid]

Originally posted by John
That was me selling the SS pistons, but they are all gone now.

Hey I have a machinist friend that might can make some. Would you mind sharing the info about yours? Did they make them to look exactly like stock ones?

[John]

I think I still have the specs. I look for them tomorrow. It cost $24 apiece if bought a batch of 20.

[ZXDavid]

Or, have you considered having another batch made?

[John]

I have to have a bunch of firm commitments before I go and lay out $480 on parts that I don't know if I can move them all. I had a hard time getting rid of the last batch. I will look around and see if I can find the drawings that a machinist made for me.

[John]

Special Front Brake Piston Dimensions

Originally posted by ZXDavid


Hey I have a machinist friend that might can make some. Would you mind sharing the info about yours? Did they make them to look exactly like stock ones?

I know the image is rather large, but this way you can read the measurements, and see the detail.

[Pat Kelly]

Pits in the piston don't hurt a thing, unless they go all the way through, then they're holes.
As long as the groove for the seal is in good shape the pistons should be fine.
Pits in the caliper bore are what could cause problems (leaks).

[ZXDavid]

I wonder if aluminum would work?

[TopCatGr58]

I wondered that myself? I know the caliper housing is cast alulminum, but the piston is under considerably more stress and also HEAT where the pad is being pushed towards the rotor, and aluminum gets soft as it gets hot. It also expands a bit more than steel, and perhaps that's part of the problem?

I thought I remember someone posting about this idea, but poo poo'd it because of the mushroom effect at the contact point.

HOWEVER, I was wondering if it couldn't possibly be made from SOLID aluminum, not hollowed out like the steel ones? Would that retain too much heat? Aluminum dissapates heat very quickly, and being solid would provide more overall strength for the part to possibly reduce or prevent the mushrooming effect on the friction pad end??

Any body else with thoughts? I've got a simple lathe, and so it doesn't seem too difficult to be able to make some solid ones out of stock T-6061 material?
T.C.