Front brake pistons with 21mm height (2000 M900)

[ian48th]

In the process of removing the pistons from the front brakes so as to replace the seals and clean things up, I managed to scratch two of the pistons and I'm having a hard time finding replacements.  The pistons on my 2000 M900 have a height of 21mm, while everything I see online has a height of 16mm.  This is a P4 30/34 caliper.  Any idea where I could get some replacements?  Gotham Cycles doesn't have them (and said that a lot of people have asked for them) and the set that I got from OPP Racing includes pistons with a 16mm height; seems that there is more than one kind of P4 caliper.

I called my local dealer and was told that the whole caliper unit is no longer available.  He said there are a couple of outfits in England that might have what I need, but didn't recall their names.

I have replacement seals and just need one 34x16mm piston and one 30x16mm piston.  Thanks

[ducpainter]

Unless the scratches are extremely deep, I wouldn't worry about it too much. The piston doesn't really touch the bore. It's all about the oring.

That said...you could try to find the dimensions of these pistons... https://store.bevelheaven.com/Brake-Related-Parts/Brembo-30/34-Piston-Seal-Kit/

[ian48th]

Well, that's the question I was afraid to ask - could I try to smooth it out and reuse the pistons.  The scratches aren't bad.  Maybe given the situation, I'll give that a try; if they leak, I'll get a used caliper.  I'm slow, so it may take a little time, but I'll report back and let you know how it goes.

[stopintime]

 

[Howie]

Lots of different P4 calipers.  Memory fails me, does your 2000 have 45 or 60mm spread?  1 pin or 2?  I'm not sure if the piston height matters.  I think not, but again I'm not sure.  I would want the same size pistons in both calipers.

[ducpainter]

Lots of different P4 calipers.  Memory fails me, does your 2000 have 45 or 60mm spread?  1 pin or 2?  I'm not sure if the piston height matters.  I think not, but again I'm not sure.  I would want the same size pistons in both calipers.

I agree. Piston height shouldn't matter. All it will do is allow a larger volume of fluid behind the piston.

Since you can't compress a liquid it should make no difference.

[ian48th]

This is a 65mm P4 with 2 pins.  I wondered about the importance of the piston height.  As long as it can't get pushed out too far, like beyond the seal, then I could use a shorter one.  I'll try to get things reassembled today.

Any tricks for getting the old seals out?

[ducpainter]

Might be helpful...

[stopintime]

OPP have both 30 and 34 mm pistons in 21 mm depth. $5

[ian48th]

Thanks for the video - that was definitely helpful!  So, making progress, but the bolts that hold the caliper together were super tight.  First caliper is reassembled and back on the bike, but one of the bolts on the other caliper was crazy tight and now the head is stripped.  Might have to go shopping in order to get it out.

OPP does have a 34mm x 21mm piston listed.  Not in stock, would have to contact them to see if it's actually available.
https://www.oppracing.com/product_display/14429468-brembo-racing-piston-aluminum-34mm-dia-21mm-long-20539870/

[ian48th]

Had a battle with the stripped bolt, but with some help from a friend I got the dang thing out, replaced the seals, put the shorter pistons in one calliper (16mm vs. 21mm of height), got it all together and bled the system and had a good test ride.  All is good!

So unless you hear from me later, using the shorter pistons is not a problem.  I've kept the slightly scratched pistons, just in case.

Love that bike...