how to get brake piston inside the piston boot

[matt_gs450]

Hi All,

Does anyone have a neat trick to getting a brake piston re-installed (for a 1981 GS450)? I'm having a hell of a time trying to get the piston inside of the piston boot and then back into the bore.

I assume the boot must be installed first, so I did that. But, it's very difficult to get the mouth of the boot to wrap around the piston. I don't have enough fingers to pry it open wide enough while trying to guide the piston in... The previous rebuilder had a neat workaround for this... They simply didn't install the boot. As a result I had a lot of cleaning to do when I took it apart.

I'm thinking I have to construct some sort of paper clip contraption to hold open the boot. Any advice or tips is appreciated.

-Matt

[DimitriT]

the boot has two places where it needs to seal:

in the cylinder, near the top
on the piston, near the top

the problem is that its very hard to get the boot
in with the piston already installed and its very
hard to get the piston in with the boot already
installed...

solution is to do both at once:

0. lube everything lightly with brake fluid

1. put the boot on the piston but wrap the piston
seal around the lower end of the piston so that the
seal which goes into the cylinder extends below the
piston

2. insert the part of the boot that goes into the
cylinder where it needs to go while hold the boot over
the piston - to make sure the cylinder seal went in
correctly, rotate it: its should rotate smoothly

3. push the piston down into the caliper - as you
push the piston in, the boot will ride up until it snaps
into the groove on the piston

4. push the piston in all the way

If you still have a tough time visualizing this, I can
put together some pictures showing how it's done.

[hampshirehog]

It's a fiddly job but DimitriT describes it well. One other thing to check if you've got pattern rubbers - test them in the cylinder first without the piston - sometimes they don't fit and you've save yourself a lot of time finding that out later.

[matt_gs450]

Thanks guys. Actually now I remember last time I did this I installed the piston first and then somehow got the boot installed (it was on a different bike, that brake is still doing fine). Lots of fiddling I bet

Another question. How much pitting is too much? The current piston has a very small amount of pitting around where it contacted the o-ring. I don't mind paying $17 for a replacement piston, but I really hate waiting a week or more to finish such a simple job. On the other hand I want the brakes to work for a while...

[p_s]

Another question. How much pitting is too much?

Really, any. The Suzuki ones I got are now stainless, which is nice. A week is pretty good. Mine took two weeks because they were only in some distant warehouse. Just be thankful you can still get them.

[matt_gs450]

OK. So I ordered another piston set from bikebandit. Better safe than sorry. Also I ordered the "pad shim" which sits between the pad and the piston. That was also missing when I took apart the brake. Any idea as to how critical that shim is?

So it's a couple more weeks without brakes.

[49er]

Another method. You can fit up the new boots to the caliper, then lightly lube the sealing edges with brake fluid. Now place the piston up against the seal and use compressed air through the bleader oraface to inflate the boot until the sealing ring expands past the piston surface. You need to keep adequate force on the piston against the sealing surface to make this work.

[matt_gs450]

I was able to finally get the piston in the boot using a couple of wooden barbecue skewers and a dental tool.

I held the boot open with the skewers, got the boot around about 40% of the piston, and used the dental pick to pull the boot around the rest of it. It took about five minutes with that method.

49er. Thanks for that tip. It's time to get an air compressor.

[simon kuether]

I think the shim you are talking about is supposed to stop the brakes squeaking.Cheers,Simon.:-D

[DPage]

Dental pick method-caliper boot

The dental pick method is a great way to get the piston through the upper boot. I just rebuilt 2 front calipers this way. The air pressure method probably works well too, but my compressor is outside and it's COLD in Chicago right now. Here's what I did to make it work. First, get a cheap $3 (Dentek) dental pick, not the fancy ones used by real dentists. Clean both grooves inside the caliper - I used an Xacto knife and piano wire. Wash the whole caliper out with solvent to get it squeaky clean and let it dry. Pour a little brake fluid in both the upper and lower caliper grooves and on the two seals for lubrication. Put the lower seal in first, it goes in easily and is usually just a press fit if the groove is clean. Don't put in the piston yet. Using a small screwdriver, work the upper seal/boot into the upper groove. The last bit will be the toughest, it pooches out a little, but if you keep working the seal all the way around the groove with the screwdriver, eventually it will relax and you can get the whole seal in. (The lower seal took me about 1 minute to install, the upper one 5-10 minutes). Now for the hardest part, getting the piston past the upper seal. Put a little brake fluid on the piston and push it through the upper seal as best you can, starting at the back. Then use the curved dental pick to pull the boot/seal over the piston, slowly working your way around. The rubber in new seals is surprisingly strong, so don't be afraid to pull fairly hard with the pick - it's unlikely to poke all the way through the seal. It will probably take several tries, but be patient, eventually it will work - it took me about 10+ minutes to get coordination and luck running my way. When the upper boot is all the way around the piston, it's easy to then push the piston past the lower seal to the bottom of the caliper, no tools needed.

[Nessism]

I use DimitriT's method; install the boot on the very bottom of the piston, install the lip into the caliper body, and then push the piston down into the bore. Very easy process. One thing I do is to keep brake fluid away from the very bottom of the piston or the boot may want to slip off. As long as the caliper seal is well lubed with brake fluid, the piston will slide in easily enough.

Using sharp objects like picks can cause to punch a hole in the boot. Not worth the risk when the other method works so easily.