ATE caliper pistons...

[cosmikdebriis]

I don't seem to be able to find pistons for ATE calipers (in the UK).

So, I'm making some up out of stainless. If all goes to plan would anybody else want any?

Not sure of a price yet but may depend on how many people are interested.

[arvo92]

Hi,

Motorworks does supply them: BRC37256 - just google this code and youll find them.

They are a bit pricy though with almost 40 pounds each. i just finished total rebuild of my brakes but since they were a bit too pricy for me at the moment, I re-used the old but not in perfect condition ones.

I might be interested if you get the self-made pistons work for yourself!

Arvo
R65 in Cumbria

[Mike V]

This subject of producing caliper pistons always interested me.  Seems simple enough to obtain some quality round stock and turn to OEM configuration on a lathe.  The more I learned about this (which is minimal) the more I discovered the importance of the piston finish being hard and robust  in nature through a process called Centerless Grinding on special machinery.

Just wondering if there's any qualified and experienced Machinist's out there that can elaborate on the process and if this is essential towards safety and reliability towards the brake system.

...

[Barry]

I'm no machinist but I have worked with a lathe.  The ground finish of the OEM items is not going to be reproducible with a normal lathe cutting tool.  If I was making them I would turn the best finish possible then polish with 600 grade paper.  A good turned finish probably wouldn't  leak but a polished surface would be easier on the seals.

[georgesgiralt]

With 600 grit paper you won't match the smoothness or the roundness of a centerless grinding machine.

[cosmikdebriis]

FYI...

Mine are being ground to size and then cut to approx length by a friendly engineering company then I will be finishing them off.

Don't worry, I had no illusions as to getting the sort of finish I require on my lathe (even if it is quite a nice one)

I'm not sure of costs but if I can't beat forty quid I'd be amazed.

One of the advantages of stainless (apart from the obvious one) is that it's harder than mild steel*. Perhaps not as hard as chrome but hard enough. (of course stainless steel contains chromium which is what makes it stainless).

*To be exact, there are different grades/alloys of steel so it's not quite that simple, but for our purposes Stainless is more than adequate. (IMHO).

[Tony Smith]

With 600 grit paper you won't match the smoothness or the roundness of a centerless grinding machine.

You certainly will not. but after using the 600grit (personally I'd use 800), some polishing  rouge (or even a good automotive "cut" polish) will produce a result more than satisfactory for brake pistons.
 
It is much easier to do this using a polishing mop in a bench grinder, even easier if the person making the pistons leaves a "tail" on the inside so that you can hang onto them with a drill chuck. Spinning the piston against a polishing mop with lots of rouge on it will quickly produce a mirror finish on the pistons - the secret is that the mirror finish is more important than the last 10/1000 mm roundness accuracy.
 
Now a lot of people wont have a bench grinder to mount a polishing mop on, and sadly I suspect that most machinists will not think to leave a small "spire" on the inside of the piston so that they can be chucked in a drill (and I hold my hand up, the first four I made didn't, so I made more).
 
But given that total roundness is not required, a buffing pad in your drill (or angle grinder if you own one) will quickly achieve the required finish. My suggestion would be to wear gloves and hold the piston lightly and allow it to turn slowly as the mop works on it. If it starts getting too hot too hold you are using too much pressure, back off and go slower.

[Tony Smith]

FYI...


Don't worry, I had no illusions as to getting the sort of finish I require on my lathe (even if it is quite a nice one)

If you have a lathe, you are cooking with gas - Crocus paper to start (say around 800 - 1200grit) followed by toweling cloth and polishing rouge.

If you have an old and well worn speedo cable, you could linish the pistons with that, but crocus (in long belt like strips you can work against the rotating piston) will be much, much faster - linishing is really only used on cranks and big ends, the theory being that the process lays the edge of the grain over and makes the bearing surface more durable. FWIW I have linished bearings and I have polished bearings with crocus and rouge and I have had cranks finish ground - I think the results were about equal over all, with finish grinding requiring the least effort from me because I paid someone else to do it.

[Rob Valdez 79 R65]

Justin made a set.  We need his input.

[Mike V]

Is chrome plating an option (I wonder)?

It would be interesting to see those pistons that have been privately turned and manufactured after 5 or 6 years of service.

[cosmikdebriis]

Well the R65 is a relatively new bike for me. my main hobby is British stuff back to 1920 so, as you can imagine, owning a lathe and other workshop machines  goes with the territory.

Although I could spend hours getting the right finish, it's just so much easier getting it done by someone with the right equipment. A lesson I learned over many years of spending hours trying to achieve something it takes only minutes to do if you have the right kit.

I should have these done in a week or so so will post some pictures.

[Ed Miller]

I posted a link somewhere on this site to a guy here in the U.S. who advertises them for sale, in stainless.  I haven't bought from him yet.

[Tony Smith]

Justin made a set.  We need his input.

So did I, well actually I made 2 sets but for reasons discussed above, I tossed the first set.
 
There is no magic whatsoever, if you know what you are doing with a lathe you should knock out a set of 4 in under an hour.

Bear in mind my comment that when removing metal from the back of the piston, if you are polishing them yourself, leave a central "spire" so that you can chuck them in a drill.

Alternatively, you could turn a length of round stock to size, polish and then part off the individual pistons, the risk you run doing that is marking the surface when you chuck them to "hollow" the pistons.


Last comment - someone mentioned chroming the pistons. - Firstly ATE did that to the originals and the reason we are having this conversation is that it didn't really work out so well. Secondly, the chroming would have to be hard chroming to be worth doing at all and that is expensive.

Take it on faith that a nicely polished set of stainless steel pistons will give a long and trouble free life, by the time they need replacing (say 35 years from now, which is kind of how long the originals lasted, most of us will be dead and the R65 models fitted with them will be 70 years old. (and doubtless worth a King's ransom).

[Luca]

I'm with Tony.  A well polished set of stainless pistons should be plenty smooth (as he can vouch) to seal the piston and allow it to retract.  I wouldn't be overly concerned about the piston seal wearing out the piston either.  While I've seen a rubber radiator hose abrade an aluminium valve cover (on my lost-love W123 Benz), the piston in the ATE caliper has no wiggle room and the steel should be hard enough to wear the seal out first.

P.S. Tony, I'd imagine you could use an inside-jaw chuck in the "hollow" of the pistons to secure them in the lathe for polishing.  You could save a few pennies by not using the extra stock to leave a "spire" on the piston  [smiley=2cents.gif]

[Tony Smith]

P.S. Tony, I'd imagine you could use an inside-jaw chuck in the "hollow" of the pistons to secure them in the lathe for polishing.  You could save a few pennies by not using the extra stock to leave a "spire" on the piston  [smiley=2cents.gif]

Due to loaning a couple of bits and pieces to a friend the only chuck I had at the time was my trusty 4 jaw, it was too big and cumbersome (it was made for a much bigger lathe than mine) for me to be bothered to reverse the jaws to hold the original set of pistons I made from the inside. Which is really why I decided to bin them and make a second set.
 
The second set I simply left a 8mm "spire" or column cut off slightly below the level of the back side of the piston so that I could chuck them in a drill.  I was also a lot smarter in making the second set as I first turned to size, then polished with crocus, then machined out the hollow and then parted off, then repeat 3 more times, they took me about 5 minutes each. It didn't take much at all to get a mirror finish on the polishing mop.

But, as I, and others (you) have said, a perfectly adequate result can be achieved using hand tools only.

In fact, I reckon that I could make an alloy piston of more than sufficient accuracy on a wood lathe, cathode anodise it and polish and it would last nearly as well as a stainless steel one. In fact when I start on the R100, which I know needs new seals on the rear Brembo, I might even try it......