Rear caliper drag (rebuilt, new ss piston, seals etc): axle alignment?

[gtem]

Great news guys: I *finally* got it!

It took a few things: as suggested, properly sealing the threads on the bleeder with teflon tape. Unscrewing the bleeder a bit more and really getting some flow through the whole system: sucking through most of a whole reservoir at a high flow rate finally seemed to have dislodged what must have been a substantial air bubble. Finally, and this was just as crucial in my case: with the latest K&L rebuilt M/C piston, it took turning the brake pedal travel adjuster rod almost all the way in to make sure the master cylinder piston was making a full stroke of the bore: prior to this, it just seemed like I couldn't get it to really pump/move fluid well.

I finally have a nice feeling pedal with minimal drag on the rotor. Well, pending some more test riding I suppose.

Thanks again to everyone who chimed in, this forum has once again proved to be worth its weight in gold!

[Larrym]

Alrightee then. ๑(◕‿◕)๑

I mean after alls you went thru to get the bike not just runnin'... but runnin RIGHT like a Super-Bike? (O_o)

The parts-n-stuff bout makin' a Super-Bike come to a CONTROLLED Staaaaaaahp be just as impor'unt. ε=ε=ε=ε=ᕕ(╯°□°)ᕗ

[gtem]

Another update after some test-riding: the rear caliper still gets hot to the touch on a 5 mile test ride (can put my hand on it for about 2 seconds before it is painful), but with the bike on the center stand, I'd say the amount of brake drag I feel is modest. So I'm very very close. By comparison, my front rotors are merely slightly warm after that same ride.

[LAB3]

The old timer that taught me the ropes in the garage used to say this little Diddy every now and again:

My bike is making a weird noise

Does it still run OK?

Yes

Then pull your chinstrap on your helmet tighter so you won't have to listen to it

In this case I'd give it a good 100 miles of riding before getting too upset over it. Remember, the caliper piston pushes outward but doesn't pull back inward meaning the pads are going to make some contact with the disk. Given a few miles the pads will wear in at this neutral position.

[gtem]

The old timer that taught me the ropes in the garage used to say this little Diddy every now and again:

My bike is making a weird noise

Does it still run OK?

Yes

Then pull your chinstrap on your helmet tighter so you won't have to listen to it

In this case I'd give it a good 100 miles of riding before getting too upset over it. Remember, the caliper piston pushes outward but doesn't pull back inward meaning the pads are going to make some contact with the disk. Given a few miles the pads will wear in at this neutral position.

That's what I'm thinking as well. One of those cases where I'm now hyper-sensitive to an issue because I've been messing with that sub-system of the bike.

[jetmechmarty]

That's what I'm thinking as well. One of those cases where I'm now hyper-sensitive to an issue because I've been messing with that sub-system of the bike.

The grooves in the piston where the rubber ring rides could be fouled, or did I miss the part where you cleaned that?

[gtem]

The grooves in the piston where the rubber ring rides could be fouled, or did I miss the part where you cleaned that?

It's a brand new stainless steel piston, new seal.

Retightened the rear axle using a screwdriver through the round hole in the other side for alignment/holding the axle. Just rode in to work, it's the least drag it's had yet. Caliper is still warm/hot to the touch but nowhere as hot as before. IE you can keep your hand on it for a good 5-7 seconds instead of barely being able to touch it.

[DiverRay]

The groves are in the caliper. If you did NOT scrape and clean the grove, that is probably your problem. I took a cheap, small, flat blade screw driver and bent it in a vice. I then filed the blade for a perfect fit of the grove, just to clean out the groves.

[gtem]

The groves are in the caliper. If you did NOT scrape and clean the grove, that is probably your problem. I took a cheap, small, flat blade screw driver and bent it in a vice. I then filed the blade for a perfect fit of the grove, just to clean out the groves.

Sorry that's what I meant to say, the caliper groove that holds that main piston seal, has been cleaned out.

[gtem]

Grr, I'm still getting a hot/dragging rear caliper unfortunately . Not smoking, but more than just warm (back to being too hot to touch more than 2-3 seconds after even a short ride to work), and even just rolling the motorcycle around or sitting on it in traffic I can feel the additional friction (doesn't roll freely).

A bit of info I hadn't shared before is that I'm pretty sure the rear rotor has a bit of warpage to it: when rotating the rear wheel with the bike on the center stand, there is definitely a tighter spot during about 90 degrees of rotation, and a freer rotating area the rest of the time. Nothing noticeable when riding the bike in terms of any uneven braking or anything like that. Looking at factory guidelines it looks like .15mm of deflection is permissible. No idea what my runout is currently, and frankly whether that is the root cause of my issues or not.

Another observation is when I push the caliper piston back with a caliper screw type tool I notice the M/C leaks some fluid past the seals, per my current understanding of how the M/C piston and seals work this is abnormal.

So on that note, What was the correct K&L part number for the master cylinder honing tool? I'm seeing they make an 11mm and 14mm 320 grit ball hone tool for aluminum cylinders but the rear M/C is a 1/2" bore.

And does anyone have a spare XS1100 rear brake rotor hanging around that they'd be interested in selling/shipping to me? Not sure of cross compatibility between standards and specials and front/rear in this case.
EDIT: seems like front and rear rotors on an XS1100 Standard are identical. I should be able to swap this rear for one of the fronts just to see if any of the issues follow the rotor to eliminate it as a variable in all this.

Part of me suspects whether it's possible that a piece of crud got dislodged in my latest round of bleeding and partially blocked the notorious "splooge hole." Only one way to find out I guess!

I've got my tour to the Mid Ohio Vintage Days planned for late July.... if the XS keeps this up I'll be riding either the Sportster or Bandit out there!

[DEEBS11]

..........

[DEEBS11]

https://www.ebay.com/itm/256894765392?_skw=xs1100+caliper+rebuild&itmmeta=01JXD2E6FABDD1XDKG1J2B9TX1&hash=item3bd01f0950:g:kX8AAOSwjdhn~sln&itmprp=enc%3AAQAKAAAA8FkggFvd1GGDu0w3yXCmi1fgB3GrKdeSj3KRTIeR2hJ75lwmoBltj6K6phI%2BW1vyPHx8Vc2U0Kmso0p%2F8AGGMuLv9dNTtg8CkseqQSiiR9qY32Kk6ssBgyYSPzKCXA%2F2QEToM6LbxEnda4bHk7AaypvlCYQgy9AX%2FWfYA61bw5RApt%2F706%2BGiCY6%2BR9jb6EEVuDCGjqPpmZRnFpg50rjWEeBCQInsw%2FJ37f2Grj%2BH1%2B71bIEHnO1ZTzZSzKy1isPpBvGgFrpM2Re%2FE8LyuJC6aXEnKLlcFut2SvAELI49r3BD%2FXbaLFSWzL28lCNjuKLjA%3D%3D%7Ctkp%3ABk9SR-jnuKLrZQ

[DiverRay]

Rotors can warp, and my guess from afar is that may be the problem. Almost ANY XS1100 rotor will work. Do be careful in unbolting it, though. Steel bolts into aluminum hub at 40+ years =trouble. I like to heat up the bolts with a propane torch, put a little ATF at the head of each one so it gets sucked into the threads, and then try and remove. Do run a thread chaser into the hub before re-installing any bolts, as the threads may be part aluminum oxide. We all know that is what sandpaper uses to cut steel.

[cajun31]

Just doing a quick search on Ebay. There are dozens of rotors for sale. Of course, you have to be careful on Ebay. They might be warped too. What kind of brake lines are you using? Original or replacements. If original they can get a build up of old crud over the years as well as breaking down. Best to replace them with stainless steel lines. I have taken a guitar string and brake cleaner and completely cleaned the old lines out and they have held up. When it comes to these old brake systems you really need to do a thorough cleaning top to bottom. They were never the best to begin with.

[gtem]

I'm going to try swapping one of the front rotors with the rear to see if the problem follows the rotor (hopefully my front rotors aren't also warped?) And I will take another look in that caliper groove just to make double sure.

Does anyone have a line on the correct model of K&L (or other brand) ball hone tool for a 1/2" bore? K&L's is specifically advertised as being for aluminum (320 grit), some of the other 1/2" bore ball hones I've seen on Amazon either don't specify, or look more aggressive (240 grit).