R1100RT

[Dave Parry]

Hi all,

Just changed the rear pads on the R1100RT and because one of the pistons was a bit stiff and wouldn't go back with just thumb pressure, I decided to use my small "G" clamp,pushing a hole in the surface of the piston, not knowing that the piston was hollow & made of plastic! Usually I would have just levered between the old pads but as i'd already taken them out and the clamp was near at hand I decided to use it. (as I regularly do on car brake pistons) Anyway, I don't think it will cause any problems as it's the outside edge of the piston that puts pressure on the pad and the pad backing plate has holes in that position anyway. Just wondering if anyone has done this before and can confirm that it won't cause any problems. (this is one of those cases where we use the term "numpty"!)

Dave.

[Caerleon]

I have always used the old or existing pads as the tool to push back the pistons. I shall be renewing mine in the next few weeks as it has a MOT due.

 

 

[wheeliepup]

When servicing the calipers (whether its new pads or a brake bleed/flush), Its a good idea to exercise the pistons and seals by pushing them all the way in to bottom of cylinder...(make sure your fluid reservoir is low or it will overflow with the displaced fluid).

 

Personally I have never heard of plastic brake pistons and I'm very surprised that BMW would even use plastic pistons in there products!! If your "C" clamp punched a hole through the piston, then it is no longer serviceable and will need to be replaced. Your piston will leak break fluid through the hole!!

[Boffin]

The pistons are steel cups, with the open end sealed with a plastic disc. This goes toward the pads and helps to limit heat transfer into the fluid.

 

The brakes will still work fine with a hole in the disc. BMW do sell a calliper rebuild kit which has new pistons and seals in it.

 

Andy

[Dave Parry]

Your piston will leak break fluid through the hole!!

-----------------

Thanks for reply but I don't think that can happen because the seal will keep the fluid behind the piston, besides which I have pressurised it with the brake pedal and there's no sign of leakage,

 

Dave.

[Dave Parry]

Thanks Andy, that makes sense now, I thought it was a bit odd to have plastic pistons!

 

regards,

 

Dave.

[oldyam]

Hi Dave

I use exactly the same equipment to push back my rear caliper pistons , never had that problem though, must be a larger head on the g clamp I use.

 

But a good point to watch out for.

 

I'll be more carefull in future, did mine last friday.

 

Note to self wash bike more often ......so I spot pad wear before it gets down to last millimeter of pad .....

[Dave Parry]

Hi Nigel,

Yes, the G clamp I was using did have a very small head on it, added to the fact that the piston did take a bit more pressure than usual to push back, I usually find just thumb pressure is enough, in fact it was on the first one. Probably always best to push back with an old pad in place,

 

Dave.

 

[Matt, Kazoo]

I did that on my LT a number of years ago. No leaks. Works fine. If I ever buy the bike back I may replace it.

[Dave Parry]

Good to hear i'm not the first to do it Matt!

 

Dave