Brake piston dust seal

1981 KZ1000... I was cleaning up the front brakes today for paint, and squirted a little too much air into the hole try to push the piston out... so it popped all the way out. Now the bottom of the dust seal is still seated just fine, but after putting the piston back in I cannot get the top of the dust seal to actually sit in the ridge the same way that the other side is sitting. There's no metal ring holding the top in place on either brake, I don't see any difference between them, but it almost seems like the top of the boot was glued into the ridge on the piston? Is there some kind of trick to get the dust seal to properly seat into the groove?

What I have done, install piston boot on caliper end, lube piston , slide top half of piston boot over piston, get piston to go in partially, just inside caliper, install top part of piston boot around groove on top groove piston, "C" clamp piston back into caliper. DO not use brake cleaner on seals or boots, they will swell, use alcohol to clean. The boot maybe at its most expanded point with piston almost out, push in enough so piston boot stays into top groove of piston, while watching boot doesn't come out of groove on caliper.

Judging by your reply, I don't think I explained my problem very well. The bottom side of the dust boot is still in place, and the piston slipped back into the caliper with no problems. The specific problem I am having is the TOP side of the dust bot, where it seats into the groove in the top of the piston. On my other two assemblies, the dust boot is rolled inwards slightly, and sits nice and flat in the groove in the piston. However on this one, the top of the dust boot is pushed outwards, and is sitting at an angle in the groove. I can roll the dust boot with my fingers and get the top edge to sit flat in the groove temporarily, as long as I hold it in place, but as soon as I let go it just rolls outwards again. The groove in the piston is cut with square shoulders, so there's no lip I can see that the rubber seal is supposed to hook in to. I just don't understand how to get it to stay in place like the boot sits on the other calipers.

It may have been contaminated. Try putting in the freezer to see if it will regain it's shape.
Steve

I believe I understand. I had the same problem, I dont install piston completely, I start it into the caliper, then slide the upper part of the boot to below the groove on the piston, start pushing in the piston, then the lip falls into groove. I dont know why, well I can't see what problem you have. My bike is a gpz uses same piston as your bike, is the groove on top have debris in it? Hopefully I understood what the problem you're having.

OK, I got pictures! Focus is a bit off, but hopefully everyone can see what I'm talking about...

Look to the outside edge at the top of each piston. On the right side, it looks like another accordian fold, while on the left side the top of the seal sits nice and flat inside the groove in the piston. The left is the original position of the dust seal.


Same this here... the brake closest to the camera has the top of the seal pushed out. The brake further away is how the dust seals originally sat in the piston.


So what is the trick in getting the end to sit properly? Or is this just some weird thing that they do naturally over time? Is it even important that the top of the dust seal be completely snug to the piston, or should I not have to worry about brake fluid coming out behind the dust seal (under normal circumstances)?

What do they look like collapsed?
Steve

Pretty much the same. I closed up the pistons and then opened them back up again to see if they would seat, but it didn't change anything.

Did you try the freezer trick to see if it will shrink?
Steve

@swest: it's not stretched out, the rubber is still very pliable and sits tightly against the piston, so I didn't think that was the problem.

HOWEVER... I think I finally figured it out. I noticed differences in the pictures last night that I hadn't recognized before. After I took out my contacts, I got a good up-close look to compare the two brakes. One of them has had the dust seal replaced, so they are not the same between both brakes. And when I rolled out the lip of the seal that I thought wasn't seating correctly, I realized it actually has a flat inside edge set at an angle... the the seal really IS seating into the ridge correctly, it just looks very different from the other brake, making me think something was wrong!

So, apparently, crisis averted. I guess I'll go ahead and put them on the bike and just deal with problems if they occur.

Thanks everyone for the help.

Can't see it from my house. :lol:
Good luck
Steve

sometimes when calipers come apart like that, the inner seal which seals the brake fluid gets messed up, and it leaks.
if it were mine, I'd find a good used caliper or price a new one.