bought the bike with seized brakes so I am going through the brakes top to bottom.
4 brake pistons are very difficult to move.  one piston ends up moving then you have no air pressure to move the remaining.  gets even more fun when you get 2 out and run out of fingers to plug the holes as you blow in air.
Ended up scratching the pistons to get them out with pliers.  Now I know why they sell the repair kits with 4 new pistons.
Its almost impossible to get all 4 brake pistons out of this 4 pot caliper with out damaging the pistons.

I prefer the old 2 piston brembos like the rear brake on this LT.  The dust seal on the 4 pot is very tight, gets dirty and gets tighter.
regards,
Jerome in Portland Oregon

A week later and I have overcome the challenge.  I did not want to split the calipers and splitting would not have solved the problem of getting a stuck piston out.  OSHA has limited the pressure in air blow guns to 30 psi so i used a tire chuck and an old air valve to get a good shot of pressure into the caliper and move one more piston out.  Another piston would not budge so I resorted to the nuclear option:  broke out the plastic center of piston and epoxied in a short bolt, after epoxy set up I had something to grab, twist and pull to remove the last piston.  Epoxied bolt can only protrude about 1/4 inch or you wont get the piston out after it is free.
Motorworks web page recommends not splitting these calipers and you dont have to split them to rebuild, it just makes cleaning bores a little harder.  I sawed off a toothbrush head to get in the piston bores to clean.
Hope this helps someone get the job done quicker.
Now to replace caliper bolts that previous owner could not use the correct size allen wrench on

Jerome in Portlanld

attitude wrote:. . . one piston ends up moving then you have no air pressure to move the remaining.  gets even more fun when you get 2 out and run out of fingers to plug the holes as you blow in air.

The thing is that you could remove them two-at-a-time. 
Technique always looks easier on video though; take Miracle Knives for example. 

Hydraulic method is better. IIRC the braking pressure is 300psi; you won't get that with air pressure. Also, as shown, it's controllable - I have serious doubts about compressed air and flying pistons. I've used a similar method (i.e. the master cylinder and calipers were still on the bike!) and used a spanner of suitable thickness to stop the pistons from coming all the way out rather than an old brake pad.

That's a really old CB750 m/c he's got on the bench...

I had just been thinking Dai knows his onions..... 

Thanks Olaf

Kr4mo wrote:

I have used a grease gun and fitting for this before. wrote:

attitude wrote:. . . one piston ends up moving then you have no air pressure to move the remaining.  gets even more fun when you get 2 out and run out of fingers to plug the holes as you blow in air.

The thing is that you could remove them two-at-a-time. This man didn't need fancy equipment. He was resourceful, and a similar technique could be used with air pressure.


Technique always looks easier on video though; take Miracle Knives for example. 

That's fine for one sided pistons on the calliper but does not work as well on a 4 pot. 
You can use a spanner across the pistons but they will only come out an extra amount as the spanner is thinner than the disc plus the thickness of the pads.

warmshed wrote:That's fine for one sided pistons on the calliper but does not work as well on a 4 pot. 

The Miracle Blade is not for everyone, either. 

warmshed wrote:That's fine for one sided pistons on the calliper but does not work as well on a 4 pot.

From experience I'd disagree. BMW recommend removing the pistons without splitting the caliper and to push the point, will not sell you the small o-ring that seals the two halves (stupid idea - available in bags of 50+ from ebay. I digress). My Bandit also had four-pot calipers and in both cases, a bit of jiggery-pokery with the thickness of the spanner/steel bar allowed me to get all four pistons to the point where I could wiggle them out with my fingers. The Nissin calipers on the Bandit were very reluctant to give up a couple of their pistons. Even if you have just one piston of the four that wants to come out,

- stop it from moving with a bit of steel braced against the other side
- get the other two moving
- put a bit of steel between them when they finally decide to meet in the middle so that the bit of steel also covers the other two pistons
- remove your original bit of scrap and start pumping
- the easy-move one will hit the steel bar pretty quickly and you may need to apply some hand pressure to prevent the bar from rotating out from the other two pistons
- eventually the last one will move

I have never had a caliper seal burst yet but I guess it's not beyond the realms of possibility that it could happen if a piston is corroded enough. I've also never been beaten by a corroded piston yet but having said that, I'm not looking forward to doing the next one because... you know... Murphy's leprechauns and all that.