75 front caliper rebuild - ???? PICS

[estcstm3]

UPDATE*
Okay to retain history for others, I found the the seals once I got the pistons out now I have question about how to tell if my "rebuilt" caliper is functioning optimaley. I my brakes worked before I started this project, I am replacing my lines and M/C so I figured I would rebuild the caliper while I was at it.


Hi All,

I am rebuilding my brakes on my 1975 xs. I took my front caliper apart and I bought a caliper seal kit from 650 central. I only see where the one tiny gasket goes but the larger ring seals do not seem to fit anywhere???? What am i missing. I dont have an air compressor, so I am not sure how to actuate the piston.

Here is the kit...cant seem to figure out where these would go.
http://www.mikesxs.net/product/29-0019.html

Here are the pics.

 

[retiredgentleman]

Hi All,

I am rebuilding my brakes on my 1975 xs. I took my front caliper apart and I bought a caliper seal kit from 650 central. I only see where the one tiny gasket goes but the larger ring seals do not seem to fit anywhere???? What am i missing. I dont have an air compressor, so I am not sure how to actuate the piston.

Here is the kit...cant seem to figure out where these would go.
http://www.mikesxs.net/product/29-0019.html

Here are the pics.

You have 2 pistons and 4 rubber seals. So, each piston/caliper half gets 2 seals. You can't see where they go until you remove the pistons from the caliper halves.

You are going to have a struggle as they look quite rusted. You will have to use some type of penetrating oil or WD40 etc. around the edge of the pistons. Let it soak for a few days. I doubt air pressure will do any good. Air pressure works great if they are not rusted as bad as yours appear to be. Some lads report success by using a grease gun to build pressure behind the pistons.

Use caution if you use air pressure, because the piston can fly out as an air born
projectile and cause injury. Always have a pile of rags or some type of cushioning to catch the piston.

Once you get the pistons out you can inspect for damage. If you find a lot of pitting, they may not be re-usable.

 

[gggGary]

a bit of a trick for loosening pistons; after the rust buster soak grab a C clamp push the piston in, JUST A LITTLE, loosen the clamp a bit, apply compressed air. If it moves a little, push it back in a bit with the clamp, once it starts moving add rust buster, keep going back and forth til it comes out.
You can also bolt the two halves together but "butterflied" with the two bolts either side of the connecting port, this lets you use 2 clamps and work both pistons out.
Like RG says very careful with the compressed air the pistons can be deadly projectiles.
The grease gun trick is easier on the early calipers because you can find a zerk fitting to thread in the brake line hole.

 

[estcstm3]

Thanks all.

Since I am replacing my handlebars, M/C and lines, I hooked up my old lines on my old bars in a vise on my workbench. I then reconnected the Caliper to my old M/C, got some pressure in the line and was able to pump the handle and get the outside piston (the one with the yamaha label, right side) to come out, however my inside piston was stuck. I then followed the advice of another thread and hooked a grease fitting where the bleeder bolt goes and pumped the piston out with grease. To not mess up the otherside I c clamped a piece of wood over the hole that feeds brake fluid between sides on the caliper.

New Question
Okay so now I put the new seals in cleaned up the piston, not pitting at all, had to clean out the grooves for the gaskets, popped the pistons back in. I re-hooked everything up on my bars on hooked in the vise. Now both pistons definitely move, however the outside piston moves a ton more than the inside piston. Is it normal to have one piston want to more substantially move than the other? Both look to be in the same shape and cleaned the same way. I was thinking they should both move out the same amount when I squeeze the M/C handle? Any feedback from others? How did you check that your rebuild was succesfull, just wait until I hook my new lines up and bleed the system?

 

[gggGary]

No that's normal in a hydraulic system, ONE piston always starts to move a bit, then it's "keep moving" friction is lower than the stationary piston's friction.


Wow that sounds pretty believable don't it?

It is normal no worries. If you clamp the "mover" the other one goes, right?

 

[estcstm3]

No that's normal in a hydraulic system, ONE piston always starts to move a bit, then it's "keep moving" friction is lower than the stationary piston's friction.


Wow that sounds pretty believable don't it?

It is normal no worries. If you clamp the "mover" the other one goes, right?

Hi gggGary,

Yes the other will move, just not as easily as the outside piston. Its hard to for me to fully guage because I can put a block of wood inbetween but that still allows my outside piston to move which it does first, then meets the block of wood. Then the other caliper will keep moving after a lot of lever pulls. I went back and saw that I still have some grease in the channel of the back of the cylilnder that runs from the bleeder screw down to the the chambers that is behind the piston. I cleaned that out but havent tried to rebleed on my vise.

 

[gggGary]

If everything is just right when lightly lubed with brake fluid you should be able to push the pistons into the caliper with firm hand pressure (no brake lines hooked up). I typically light sand pistons and bores with very fine paper like 1000 or 1500 grit. then clean with paper towel and brake parts cleaner till the paper towel stays white. With the seal not installed, the piston should be a slide in fit to the caliper.

 

[estcstm3]

Thanks for that. With just a little brake fluid I can pretty easily push the piston to the bottom of the cylinder by hand (with the caliper apart dis-assembled). I didnt sand anything, but I elbow grease rag cleaned the pistion and cylinder walls (before I put the seals in) everything is pretty smooth.... I guess Im just being paranoid, I just dont want to pull everything apart again, because its a messy job for me. Not a hard one per say but messy.

 

[5twins]

Yes, using grease makes it a very messy job. I don't do that, only compressed air. I've encountered some pretty badly stuck pistons and haven't needed to reach for the grease gun yet. The C-clamp and compressor do the job.

 

[estcstm3]

Dont have a compressor....but really the grease isnt the messy part. Its so thick you just scoop it out the a red shop rag, then liberally shoot brake cleaner and its pretty much gone. The mess comes into play for me re-hooking up the caliper to test each time and bleeding back out. Enviably brake fluid gets on stuff...anyways.

on a perfectly clean caliper if you push the piston down by hand should you be able to pull it up by hand (not sure its possible), im guessing the rubber seals put enough resistance that you couldn't do that. If that is the case then without using a fluid the only way to get the pistons out (even if not seized) is using compressed air?

 

[gggGary]

Yeah pretty much, that or brake pressure from the MC. It sure is the easiest way.....It doesn't take much, a tire or mattress pump might do it.
One of those cheap 12 volt pumps you carry in the car for sure. I'd say blow on it but...
No; you don't want the moisture in there.
I think mikesXS used to sell a kind of pliers for getting the late model pistons out. But the early pistons don't have the groove to grab on

 

[estcstm3]

thanks all. now with the work week starting and I have a little one Ill update next weekend, or hopefully after work one night on the outcome. Thanks to all that helped guide me on this.

 

[gggGary]

Here's an idea I haven't tried cover the port and warm the caliper with a hair dryer or heat gun the expanding air inside might do it. And aluminum expands more than steel.

 

[roadstar06]

I am also trying to get piston free from caliper (front) , had it in vise and had some success but now it wont move out any further, it will spin but cant get it to move foward or back, have it soaked with wd40 overnight today going to try again with the compressed air deal..