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

[gtem]

Hi all,

I'm looking for a gut check as my rear brake woes seem to continue. Does the spacing and setup of my rear caliper bracket relative to the rotor, as well as the setup of all the rear axle components in terms of spacers look to be correct? It seems like the rotor gets notably closer to the right edge of the caliper bracket when I tighten the rear axle nut, even following all the directions as far as tightening it first and only then tightening the 12mm pinch bolt on the RH side. It feels to me like there is brake drag that shows up when I tighten the axle nut. With it loose and the axle "floating" the wheel definitely spins freer.

As far as the rear brake itself goes, I've got a fresh K&L master cylinder piston kit in my original M/C currently, brand new braided lines, a freshly rebuilt rear caliper with brand new SS piston and seals from brakecrafters. Bleeding the thing properly is still proving to be an absolute bear. I've got brake pressure but with long pedal travel. My suspicion is that I can't adjust the pedal travel rod very much at all, possibly due to the fact that I may(?) have this caliper alignment issue.

Any thoughts/suggestions/photos of what a "correct" setup looks like are welcome!

[DEEBS11]

Looks like the XS11 Standard collars. They look ok. The slide needs to be lubricated and free to move to be able to self center the caliper. The pedal should also be looked at for adjustment.

[DEEBS11]

..........

[gtem]

Yep the slide pin is well lubed, and I've been fiddling with the travel adjuster to make sure I'm not applying pressure to the M/C causing drag when the pedal isn't depressed. I swear I've never ever had this much trouble with a brake before in my life!

[bikerphil]

Yep, looks like you have the spacers correct for the Standard model with the 17" wheel....

[Larrym]

It feels to me like there is brake drag that shows up when I tighten the axle nut. With it loose and the axle "floating" the wheel definitely spins freer.

There's actually very LITTLE room/space between the rotor and the brake pads whens the caliper releases after pressure is removed. ( •_•)

On my own bike spinning the rear wheel freely while on the center stand BEFORE a ride doesn't spin PERFECTLY "free" and sometimes makes that noise indicating the pads/rotor are slightly and l i g h t l y making contact. (；☉_☉)

After the ride? (O_o)

Silence and smooth.... as during the ride everything wurky'ed back-n-forth and centered properly. (づ ◕‿◕ )

Just sayin'... there's a true difference between genuine brake drag (BAD) and what's coonsidered as nurmal operation. ヽ(~～~ )ノ

Bleeding the thing properly is still proving to be an absolute bear. I've got brake pressure but with long pedal travel.

Iffin' yur using the rear MC to pump the fluid and push the air OUT? (O_o)

The short stroke/pulse of the MC only "bumps" or "wiggles" the air bubbles back-n-forth at the high points (as shown in the pics below...) along with not providing enuf actual fluid FLOW to get the air bubbles to dive down and past the LOW point(s) also shown in the following pics. (￣ー￣)






HTH. (◕ ‿ ◕)

[bikerphil]

What about the spacer on the outside of the left side wheel bearing, is it in place? I know once I forgot to put it in, and the wheel would start to bind when tightening the axle nut.

Another thing to check is that the tip of the small screw on the inboard side of the caliper fits cleanly into the hole on the inboard brake pad. Sometimes that screw has been replaced and doesn't have a tapered tip like it should, or the hole on the pad is too small and requires drilling out. Otherwise, the pad can be forced at an angle and cause a binding issue.

[gtem]

What about the spacer on the outside of the left side wheel bearing, is it in place? I know once I forgot to put it in, and the wheel would start to bind when tightening the axle nut.

Another thing to check is that the tip of the small screw on the inboard side of the caliper fits cleanly into the hole on the inboard brake pad. Sometimes that screw has been replaced and doesn't have a tapered tip like it should, or the hole on the pad is too small and requires drilling out. Otherwise, the pad can be forced at an angle and cause a binding issue.

I'll double check the LH wheel bearing spacer, and that's a good point on that brake pad screw, I'll recheck that as well. Thanks for all the helpful suggestions!

[gtem]

It feels to me like there is brake drag that shows up when I tighten the axle nut. With it loose and the axle "floating" the wheel definitely spins freer.

There's actually very LITTLE room/space between the rotor and the brake pads whens the caliper releases after pressure is removed. ( •_•)

On my own bike spinning the rear wheel freely while on the center stand BEFORE a ride doesn't spin PERFECTLY "free" and sometimes makes that noise indicating the pads/rotor are slightly and l i g h t l y making contact. (；☉_☉)

After the ride? (O_o)

Silence and smooth.... as during the ride everything wurky'ed back-n-forth and centered properly. (づ ◕‿◕ )

Just sayin'... there's a true difference between genuine brake drag (BAD) and what's coonsidered as nurmal operation. ヽ(~～~ )ノ

Bleeding the thing properly is still proving to be an absolute bear. I've got brake pressure but with long pedal travel.

Iffin' yur using the rear MC to pump the fluid and push the air OUT? (O_o)

The short stroke/pulse of the MC only "bumps" or "wiggles" the air bubbles back-n-forth at the high points (as shown in the pics below...) along with not providing enuf actual fluid FLOW to get the air bubbles to dive down and past the LOW point(s) also shown in the following pics. (￣ー￣)


HTH. (◕ ‿ ◕)

Thank you for such a detailed and thorough reply Larry. The issue I had observed as that the drag was a bit more than what I would consider the "normal" drag on a disc brake on a vintage bike, enough that it stood out to me as a concern.

For the bleeding, I'm considering dismounting the caliper and setting it up high to hopefully prompt any air bubbles to make their way up to the bleeder. I had been doing the exact opposite of this, setting the caliper down low and trying for a "gravity bleed." I'd tried using my hand pumped vacuum bleeder after putting a bit of teflon tape on the bleeder screw but it never works quite right (is sucking a bunch of air at the bleeder interface).

Let's just say I'm glad I have another motorcycle to ride while dealing with this seemingly endless headache!

[DEEBS11]

gtem, after rebuilding a rear caliper, I do as you said, raise the caliper up with a bungee cord and let all the air bubbles enter the caliper before using the Miti-Vac. Works great.

[Larrym]

I had been doing the exact opposite of this, setting the caliper down low and trying for a "gravity bleed."

Actually.... that is generally a very sound idea/practice. (^_^)

I mean it recognizes that air bubbles don't really go UP but are rather air being displaced upwardz by the heavy(er) brake fluid going DOWN. (◕⍸ ◕)

It also recognizes that the MC not only pumps/pushes fluid but also, when at the highest point, gulps IN that displaced air and then "burps" the air outta the "spooge" hole. (´ ᴗ｀)

But then at the rear MC we gots the same issue that us Special owners mostily tear out our hair about-

There be a "high point/pocket" wheres the air bubble can get trapped and never make its way into the MC to be burped out. Even WURSE there's no amount of pumping the MC or agrressively "Mity-Vacing" at the calipers 3 feet below the MC than can make the bubble (and the problem...) go away. Yet the solution was/is simple as shown in the link below.

https://xs11.club/forum/idle-talk-forum/forum-how-to/884091-how-i-drained-refilled-the-front-brake-system-on-my-79-special?p=884115#post884115

In the REAR MC that "high point/pocket" is circled in red in a pic shown earlier AND the brake line has red tape round it. The rear MC design has this "air cavity" at a high point and the fluid reservoir positioned BELOW that air pocket.

Mebbe SOME of the air woulda made it up-n-over the air pocket "hump" and been burped outta the spooge hole... but that hump would still contain enuf air to make things spongy....

Solution? Suggestion? (O_o)

MoAr teflon tape so's you AIN'T got air leaking thru/round the bleeder threads, position the caliper UP like deebs says even iffin' it means temporarily removing the two brakeline holders/brackets, FILL the reservoir PAST the fill line, build the suction/vacuum in the Mity-Vac, and don't just crack the bleeder screw open a wee bit.

OPEN the bleeder screw a full turn or even 2 so's you can FORCE FLOW the fluid fast enuf to displace that pesky air bubble outta that high point.

BUT you gotta STOP the force flow before the fluid in the rear MC reservoir drops so low it's sucking air.

Have fun! (^_^)

[Radioguylogs]

I just finished installing new brake lines on my XS750 last night.

I packed the threads of the bleeders with red rubber grease. I only opened them 1/4 turn to bleed them. It worked well to avoid air leaks around the bleeders.

I had no trouble bleeding the rear, but I had big trouble with the front. I went away and came back and did the same thing as Larry- I moved the Special MC down the handle bar so the MC banjo bolt faced upwards. I was successful after that.

[gtem]

Awesome info Larry, thanks again! I just came back from some travel, having left the rear caliper set up high. Still no dang luck! I'm definitely having issues getting a good seal on the bleeder with my cheapy busted up harbor freight hand vac pump. I've long suspected that I've been having issues properly "priming" the master cylinder and that there *must* be air still trapped in it. I'm going to study your writeup in the other thread carefully and see if I can finally vanquish this soggy rear brake pedal!

[Larrym]

The "writup in the other thread" is fOaR the FRONT MC and like I said, a problem that I and mostily every OTHER Special owner gots to deal wit when doin' any work on the FRONT brake system. ヽ(゜～゜o)ノ

The REAR MC be the problem in yur situation so's I'd suggest starting with doing a "bench bleed" of the rear MC without any brakeline attached to it. （´＿｀）

A "bench bleed" whilst it's still mounted on the bike? (O_o)

YUP! (^_^)

https://xs11.club/forum/idle-talk-forum/xs11-xj11-discussion/38106-rear-brake-bleed?p=562245#post562245

I'd have a lotta shop rags pre-positioned to protect the paint and even mOaR in case there's any spray... ┐(´ー｀)┌

[DEEBS11]

The vac will not pull fluid if the threads of the bleeder are not sealed. I use Teflon. Either tape or liquid. Mike mentioned red rubber grease. Dry threads will leak air terribly and the tool will not work.