Brake Calipers

It came time to re-build my calipers, so I read every article on this website since I had never done it before. It seems that the biggest problem the members have had, was removing the inner piston. One solution I read was to drill the back of the caliper and tap the piston out with a drift pin, then either have the hole welded up, or tap the hole and put a plug in it. I didn't like that idea. Another suggestion was to use compressed air (he cautioned against too much air as the piston could explode out of the caliper) or grease. I couldn't figure out how this would work with the out-board piston removed, and if it was still in place, how I could keep the out-board piston in place while the inner piston moved out. I didn't have a compressor or grease gun available anyway.
Aha! I know. Since I've got new stainless steel pistons and don't care about the old pistons, I'll drill and tap them and screw a bolt into them and pry them out. So I pulled the outer cap off and, Dang! The existing pistons are stainless steel also. There is no way that I could drill and tap stainless with the tools I had at hand.
I managed to get the outer piston out and cleaned it. Then re-inserted it just far enough to rest on the rubber washer/gasket and replaced the outer cap. I found a 5/16 x 1/2" bolt and screwed a hex nut about half way on. I held the caliper horizontal and stood the bolt on the outer piston and balanced it there while I bolted a file to the original hole (with the original bolt) for mounting to the fork leg so that the file held the 5/16 bolt in place against the outer piston (the file passes through the caliper the same way that the rotor does). Then I re-installed the hydraulic line, added brake fluid and pumped the inner piston out with the front brake lever. Easy! Peasy!
In retrospect, I could have just used a hex nut if I had put the outer piston in backwards (flat side in). And after thinking about it for a while, I think a tool could be made that would get both pistons out. It would need to be about 4" long with a 7/16 hole at one end and a tapped hole (1/4 x 20 would work) about two inches away. But I'm still working on that.
I thought that this was a better way of removing the inner piston than anything I've read so far, and I thought you might like to hear about it.

Compressed air works fine, you just need to exercise a little care.

Place a piece of wood in the caliper so the piston can't come all the way out. Once it has moved a few millimetres it should be possible to get it the rest of the way out by hand or by gentle application of more air.

If the old pistons are original, they were chrome plated carbon steel.

You can pump the inner piston out with a pedal cycle pump using the Presta orifice:



Just cover the brake fluid holes with fingers, and pump lightly.
You can buy inner pistons complete with thread for later removal:



You can buy them from RGM: http://www.rgmnorton.co.uk/buy/caliper- ... t_2544.htm

Hi bucksfizz:

Now that I know more about the Lockeed calipers, I can understand the use of compressed air. Your post is a very good idea and the threaded piston is a great idea. Although the manufacturer shouldn't have stopped at just one. The outside piston could be made the same way, except threaded from the other side. It is odd though, that I spent two hours reading all of the posts concerning the piston removal and never came across yours. Thanks. I'm still going to make the tool that I have envisioned for those really stubborn pistons.

concours:

I just checked, and yes, a magnet sticks to them. So they're not stainless. They're pretty shiny though.

Personally i'm not a fan of drilling the back of the body. Lets face it this is life or death stuff, get it wrong and the consequences are unthinkable. Not saying that folks on here are not good engineers, but there are plenty that aren't.

What I did was to drill a small hole in the side of the piston which is exposed by the pad tang location slot. Then I dribbled some brake fluid around the piston, inserted a rod through the hole and wiggled it backwards and forwards until it popped out. If it won't wiggle warm up the caliper body and try again. If it still won't work, bend the end of the rod 90° pass it down through the cylinder then through that hole, and place the other end in a vice and pull - simples !!

There are now pliers available on EBay for removing pistons, e.g. these:
http://www.ebay.co.uk/itm/Sealey-Motorc ... Sws65ToELT

Once I had mine apart I found all the feed transfer and bleed ports full of what looked like crystallized brake fluid, so I boiled it out in an old saucepan. Once it cooled it looked much better, and I ran a 3mm twist drill through all the ports, except that the main inlet one was very restricted. I could just about get a toothpick through it, so as it's the supply I actually ran a slightly larger bit through that one (3.5mm). Has anybody else noticed that. I wonder if it was deliberately restricted?

Once reassembled I had no trouble bleeding it, so I wonder how many other calipers are in this condition? and if it may explain why some folks have a hard time bleeding their brakes.

While you have it apart, the is a very worthwhile (Ludwig suggested) mod you can do which will improve the brake efficiency. If you remove about 1mm of metal over 135° (7 and a 1/2 minutes to 6) of the circumference of the pad side of the pistons, you will get a slight servo effect and improved wear pattern on the pads by reducing the pressure on the leading edge of them ( the side facing the direction of travel) It is very important that these are correctly oriented when the pistons are reinserted though. For a MK2 with the caliper behind and on the right of the fork leg that would be the opposite side to the mounting lugs, but on the MK3 it would be closest to the lugs. I have some pics i can send, if anyone is interested p.m. me.












Cheers,

Cliffa