Brake Caliper Frozen and more


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I'm here for confession...
I've neglected my (77 and 72) XS650(s) to the point where the F brake caliper is frozen, and, the brake lever/cylinder doesn't pump anything, AFAICT. I will get to fix it this coming Spring, after a long hiatus (divorce and...) away. Next year, 2023, is going to be my XS650 year again. So, I am starting the process now. I might re-coat a tank too, or I might just slight surface derust the other, not sure.
I'm not sure how much of the work I will do or farm out.
Suggestions ?
Should I buy a new caliper and F master cyl or try to rebuild ? Or maybe just ride slow :)
Is it possible (how much $) TO REPLACE A f DISC WITH A DRUM SYSTEM ? oops.
How can a previously coated tank be recoated ?
If I were to coat the non-coated tank, how do I do this or what do I use ?
FYI, if I work on it, I do not have compressed air, and I have 2 (at least) grease guns but neither work. IIRC they both need new orings or ? This is what happens when you get old :) This is why I prefer drum brake, on my cars too. I drive (usually) a 69 Chevy.
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Can you provide some info on your bike? What year is it?
Two ways to free a stuck caliper... 1. compressed air. Be careful with this though as they come shooting out with major force.
Option 2, use grease from a grease gun through the bleeder screw. I have not done this but reports are it works well. It just leaves quite a mess afterwards.
I revised the post. Not sure if I could get it unstuck with grease even. Are there many sources of used parts ? Maybe I could buy a rebuilt caliper ?
I really would like to get rid of the disc front end anyways and put a drum on it. And I want to buy a plastic gas tank, which woudl work for maybe 1000 years. Don't tell me, I know, blah blah. Most people don't know almost all cars since 2000 have plastic gas tanks.
Most people don't know almost all cars since 2000 have plastic gas tanks.

While that is true, most people also don't know how long it took to get the materials and blow-molding process right to get a plastic fuel tank to work and stay together when filled with gasoline. It ain't as easy as it looks.

As for freeing up that frozen caliper - I can only support the words to be cautious with compressed air. That piston has a fair bit of area and with 100+ psi behind it, would make a good sized dent in your forehead if it came shooting out.

When I do that, I usually mount the thing in a vise and apply the air while slowly opening the vise jaws. The enables me to monitor the progress of getting the piston to move.
Yes :)
I would never try air anyways for those same reasons. Grease is the ticket.
I've seen the piles and piles of plastic tanks that come out of cars at a junkyard. I see they get run over and don't even crack. IMHO they're better and safer than steel or AL for a MC. I'll bet I could get as many as i want for free. If only I could shrink one !
To free up a stuck piston in a brake caliper and get it moving, put a big C-clamp on it. Once you break it free, you can use air or grease to get it out the rest of the way. I use air and place a small piece of plywood in front of the piston so it won't shoot out. I also wad rags in around it. It can be done safely.
Yes, I have done that before, but not the grease part. I'm not sure if the caliper, even though it is AL, will have too many small holes to be useable. I'm looking for a spare caliper, among other things !
Spray brake cleaner in hose hole... Bottom out the piston with a C clamp. With a pick.. you can work out the outer square O can just barely see it... remove the complete 0 ring... wrap caliper in a small towel... loosely mount in a vise.... replace bleeder screw and hit the hose hole with compressed air... piston may pop out quickly or slightly move.. repeat... C clamp.. air.. it'll come out... Use a wire wheel Dremel to clean..clean..clean the bore.... then use a 90-degree pick and clean clean clean the O ring channels in the corners... use a mirror.. you'll be surprised how much crud is there... it has to be removed to properly sit the new 0 ring.... assemble with new brake fluid. I also Dremel the piston.. and finish off with 600 sandpaper.. 😎 After I assemble it.. I use brake grease..... brake grease... to coat the exposed outer cylinder bore.. this helps prevent moisture and related problems ... I also coat the back of the pads to help prevent brake squeal... 😎


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Mine were at least as bad as the ones shown above. I pushed the pistons in with a C-clamp and they still wouldn't come out using compressed air. The grease gun pushed them out easily, but it is a pain to clean up all that grease. After using a dremel with a wire brush and a dental scraper to clean out all the rust and gunk they were in surprisingly good shape, seems like the worst damage was confined to the pistons. I made new pistons out of 316 stainless so nobody will ever have that problem again!

Great job. I'm contemplating taking the caliper and master cyl off (how do i get the electrical connector off ?) and sending them to someone who has the facilities to do a good job. Anyone want to offer ? We have plenty of time, as I have until next May to get it running.
BTW - using stainless, does that make them cylinder and piston differing materials, which would promote rust ? This makes me wonder, are the orig pistons steel ? Why not make them out of AL so the piston matches the caliper cylinder ?
I used grease on several - it works well - make sure you get all the grease cleaned out before rebuilding though.
Yea, that sounds sensible. But it makes me curious, what if there is some grease in the fluid area ? What if there's a lot ? Is grease compressible ? I'd say no. This makes me wonder, why not fill the entire caliper with grease instead of brake fluid to slow rust down ? that would make the next owners brake bleeding quite interesting :)
The housing on the twin piston calipers is cast iron so yes still different materials but I don't expect there to be a problem. I have read that this style caliper on the Yamaha racebikes (TZ350, TZ750) were aluminum but those are pretty rare. The original pistons are chrome plated steel IIRC. I believe modern aluminum pistons are hard anodized to keep them from wearing too quickly which is a bit out of my wheelhouse. If I had a cheap source for that I probably would have considered aluminum. As it was, I had the stainless in my pile of odds and ends and had never made anything out of stainless so that's the direction I went. From a purely practical point of view it wasn't worth all the time since replacement steel pistons are fairly cheap but it was a good learning experience and a nice upgrade.

I didn't bother with the pressure switch in the junction block so I can't speak to that. I replaced the original master cylinder with a 1/2" master off a Honda Shadow for lower lever effort and made up a single braided stainless line to replace the original multi-piece lines. The only thing left to do is make up a small harness to connect from the original brake switch to the new one on the master cylinder.

I have some pictures but haven't posted to my thread yet. Someday soon when I get a Roundtuit...
Huh, my Dad used to be a great machinist. He used to make pistons for my Hodaka, CZ, chain saw, anything. But he was too busy runnign away from Mom to keep up with it all and have employees (besides me that is).
When I get back to TN, you'd only be a few hours north of me, Cookeville. I could drive the parts up quicker than do it myself. Isn't Cleveland where the Vintage MC races are ? My Son and I went there, 10 years ago, shoudl have bought that 72 XS650 but I had no way to get it home, didn't really need another. The prices are too high now, I won't go.
Replacement stainless pistons are available. They cost a few dollars more than the steel ones but it's well worth it I think. Pitted, rusty original steel pistons are about the only problem I've encountered when rebuilding these.
If you are interested, I have this caliper I will sell for $50 plus shipping. The seals are nice and pliable but make no guarantees on their condition.

Or another option is to buy a new reproduction from HVC Cycle. They also sell repop master cylinders.
I used grease on several - it works well - make sure you get all the grease cleaned out before rebuilding though.
What size greese fitting did you use?
I used grease on several - it works well - make sure you get all the grease cleaned out before rebuilding though
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