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Old 09-11-2014, 11:00 AM   #1
CanadaBiker OP
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Axle, left lower fork tube, caliper drag, issue

On my new-to-me '87 R80RT, I pulled the wheels and tires to sand the inside of the rim; they were leaking air. I put the front wheel back on and noticed that on the left, the outer portion of the caliper body was hitting the disc. It took me a while before I realized that there is substantial play and flex in the left lower fork tube that allowed it to slide in and out on the axle. Even with the fork brace bolts good and tight I was able to use a large screw driver wedged between the back of the tube and the disc to pull out the tube on the axel. This allowed the caliper to centre over the disc.

(On the fiche, it seems to show the axel going in from the right side, but on my bike, it goes in on the left.)

Before I found the movement, I had loosened the fork brace bolts. Obviously, this allowed the tube to slide even more easily. Am I missing something? I have the 'small top' hat spacers in place, and on their correct sides. Is this just part of the design? If this is the case, I can understand why the single disc models have the disc on the right side, as when the end cap and bolt on the axle are tightened, it lines up the caliper, as there's no play allowed for the lower tube on the axel.

I looked through the Clymer manual and didn't find a procedure to make sure the left tube is set in the proper spot to allow the caliper to be centre over the disc, prior to tightening the axle pinch bolts.

Thoughts?
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Old 09-11-2014, 04:09 PM   #2
garthg
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Quote:
Originally Posted by CanadaBiker View Post
On my new-to-me '87 R80RT, I pulled the wheels and tires to sand the inside of the rim; they were leaking air. I put the front wheel back on and noticed that on the left, the outer portion of the caliper body was hitting the disc. It took me a while before I realized that there is substantial play and flex in the left lower fork tube that allowed it to slide in and out on the axle. Even with the fork brace bolts good and tight I was able to use a large screw driver wedged between the back of the tube and the disc to pull out the tube on the axel. This allowed the caliper to centre over the disc.

(On the fiche, it seems to show the axel going in from the right side, but on my bike, it goes in on the left.)

Before I found the movement, I had loosened the fork brace bolts. Obviously, this allowed the tube to slide even more easily. Am I missing something? I have the 'small top' hat spacers in place, and on their correct sides. Is this just part of the design? If this is the case, I can understand why the single disc models have the disc on the right side, as when the end cap and bolt on the axle are tightened, it lines up the caliper, as there's no play allowed for the lower tube on the axel.

I looked through the Clymer manual and didn't find a procedure to make sure the left tube is set in the proper spot to allow the caliper to be centre over the disc, prior to tightening the axle pinch bolts.

Thoughts?
Did you reinstall the wheel in the same direction as it came out?

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Old 09-11-2014, 04:29 PM   #3
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Originally Posted by garthg View Post
Did you reinstall the wheel in the same direction as it came out?
Yeah I did. I even took pics prior to removal just to make sure. (and I just triple checked my pics) The right caliper lines up perfectly centred over the right disc.
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Old 09-12-2014, 09:41 PM   #4
Wirespokes
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Are the calipers on the front or rear of the slider?

I think they're supposed to be on the front, and have the idea someone might have switched them around.

It also sounds like a spacer may be missing, but that's just a guess.

Another thought is one or both of the fork tubes may be bent.

The slider shouldn't just slide on the axle - although it will if not tightened down. There are two pinch bolts I believe on those forks.

One of the sliders is held captive between a spacer and the nut. The other is free to find parallel on the smooth end of the axle.
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Old 09-15-2014, 09:44 AM   #5
CanadaBiker OP
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Quote:
Originally Posted by Wirespokes View Post
Are the calipers on the front or rear of the slider?

I think they're supposed to be on the front, and have the idea someone might have switched them around.

It also sounds like a spacer may be missing, but that's just a guess.

Another thought is one or both of the fork tubes may be bent.

The slider shouldn't just slide on the axle - although it will if not tightened down. There are two pinch bolts I believe on those forks.

One of the sliders is held captive between a spacer and the nut. The other is free to find parallel on the smooth end of the axle.
The calipers are on the front. I had considered flopping them around until I realized the axle was off centre and it would slow the steering.

I double checked the fiche and I have all the spacers.

The left slider only moves when the pinch bolts are loose. But it won't find the correct spot over the left disc on it's own. I need to pull the slider out a few millimetres before I tighten the left pinch bolts. I just eyeballed it for centre, and that seems inexact compared to most things BMW.

I am considering removing the left disc and caliper altogether. I know that sounds crazy, since most people here would rather go to two discs. But I wanted to lessen unsprung weight, and reduce overall complexity. I would upgrade my lines to SS, install the best pads I can find, and maybe install a floating disc. I've since turned the bike from an RT to a naked R80, and I've lost a lot of weight. I also now have a solo seat and won't be riding two-up...

Maybe the single disc would be plenty.
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