Caliper Piston Material-what is it?

[falling]

So, I got some 6-pot Sumitomos for a smokin' deal. Problem is, the P.O. Had them powdercoated blue which, by itself, isn't a problem.

The problem is that he/she removed the old pistons by grabbing the outside with pliers. This wrecked them pretty good.

Parts for these calipers are non-existent.

I am planning to machine some new ones but do not know the material for sure. They appear to be SS. They are magnetic, so I am thinking 304.

Does anyone know better? Any ideas on tempering?

Thanks.




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[jfeagins]

As long as the damaged areas do not engage the seal area of the calipers when fully collapsed, I don't see why you can't simply smooth it off a bit (cosmetic reason only), and reinstall the cup as is. Of course, if the plier marks contact the seals........the cups' gotta go.

 

[falling]

Some have actually been deformed and are oval, looking from above. Several gouges contact the dust scraper.


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[dannymax]

+1 It appears that the damaged area is well clear of where the seal seats. Why not chuck it up and turn a slight chamfer to clean the ends?

 

[falling]

Yeah, these must have been fully seized. The guy grabbed them with vice grips after eating his Wheaties because they mic out of round. Trust me, several are unusable.


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[dannymax]

Didn't see your post #3 when I posted....yeah, sounds like they're toast.

 

[falling]

I happened to have an R1 caliper lying around. I figured what the hell and popped out the Pistons.

The small R1 Pistons are dimensionally identical to the large 6-pot Pistons.

The small Pistons from the 6-pot are ok...so i am back in business!


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[Fire-medic]

Well that piece of info may have an appropriate location in the stickies, I would say. Some clear shots of both sides of the 6-piston calipers, and maybe micrometer measurements of the pistons, to assuage the curiosity of the machinists and tech junkies probably would be helpful.

 

[falling]

I installed the R1 caliper on the rear so I don't have the dimensions handy. I did order 8 new R1 Pistons though and when I get them, I'll post photos with measurements.

Attached is a photo of 6-pot piston on the bottom, R1 on the top.


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[falling]

Okay. Here are the measurements:

These are the four Pistons out of the R1 caliper. They are marked V6 (large) and V4 (small). The fifth piston, marked 4 is a large piston from a 6-pot Sumitomo.


Here is the Outside diameter of the 6-pot piston. Sorry about the digital caliper. It was too hard to get the barrel of my micrometer to focus in the camera. It mics the same as the caliper. I know, I don't trust calipers either...but here it is.


Here is the O.D. of the R1 small piston.


Here is the length of the 6-pot piston


Here is the length of the R1 piston


Here is the bottom of both Pistons. The 6-pot is shinier because I spent hours trying to polish it back to useable. The length is off by 0.06mm. It looks like the bottom thickened part is slightly different. I'm calling it close enough.


I still have no source for the small Pistons on the 6-pots. I got mine clean enough but they are pitted and will go to hell in a couple years. If I had a source, I'd replace them. They are marked "3" and measure: 25.4mm O.D. X 21.6mm length.



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[[email protected]]

Great info to share with the group!

 

[falling]

Finally got the calipers done.

8 new pistons
4 cleaned up pistons
All new seals
Fresh powdercoat
New EBC HH pads







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[mugello74]

Oh wow! I´m planning to get YZF 750 R 6 pot Sumitomos and refurb them. Then i found out that actually ONE piston with seals is actually around USD 50,-! Aftermath reveals USD 600.- for just the pistons... - i can´t believe it or am i just on the completely wrong webshop?

 

[Fire-medic]

A complete Sumitomo caliper is $799 so the pricing for the pistons you've found doesn't sound out of sorts. 1994 Yamaha FZR1000F Front Brake Caliper | Ron Ayers

In this time of supply side economics and interrupted supply chains, if you can find it, I suggest you buy it.

 

[mugello74]

Ok then - A price for 2 calipers with all new gaskets and refurbed pistons of €380,- sounds like a bargain...

 

[mugello74]

...even if the brake pads are not included...