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Low speed vibration R80RT

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Richard W
(@wobbly)
Posts: 2546
Member
 

Posted by: @16077

On my 1986 R80RT (new to me) I get an up/down vibration that is most noticeable at 35 to 40 mph. Not a nice feeling. I've tried a ton of things to make it go away.  

  • New tires and careful balancing and mounting
  • Checked and rechecked the tire pressures

• 1) Unlike "wobbling", "weaving" or some other side-to-side movement, "up/down" vibration almost has to be generated by something mechanically loose and allowing movement up & down, OR something spinning out-of-round. 35MPH is almost too slow to be balance, but balance could exacerbate mechanical free play, such as wheel bearing issues... or some other similar combination.

2) And, what you feel in the handlebars could just as easily be coming from the rear wheel. So that whatever you check on the front... MUST also be checked on the rear. Kudos for checking the rear shock.

For many reasons, the primary cause of up/down is almost always 1) incorrect tire mounting or 2) tire balance, in my experience. Incorrect tire mounting is almost always the tire bead NOT being fully "popped out". This is easy to check by allowing your finger nail to ride on the rotating bead of the wheel rim, while you "feel" the 0.02" high indicator ridge molded into the tire's sidewall. That indicator ridge MUST be the same distance from the rim all the way around BOTH sides of the mounted tire.

?

If not, then the bead of the tire is not fully seated on the rim correctly, a condition usually caused by too little tire lubricant and too little air pressure during mounting. 1) Both the rim and the tire's bead need to liberally coated in lubricant. 2) Momentary air pressure for seating may need to go as high as 60psi !!

• Please describe the balancing method. Owing to the presence of wheel bearing grease, roller bearings, brake drag AND grease seals, static wheel balancing of Airhead wheels MUST be done on an independent set of bearings. I keep a separate set of new bearings in my tool box just for this occasion.

• Please describe the air pressures used when you "rechecked" them.

 

Posted by: @14724

Richard, do you have a preferred procedure for fork alignment?   St.

As described throughout this thread.

This post was modified 2 months ago 2 times by Richard W

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 04/06/2024 05:25
Peter Lehman
(@16077)
Posts: 69
Estimable Member
Topic starter
 

Hey, thanks for your interest. I think this is a great discussion... Will try to answer all the questions. 

Did the fork oil replacement. Initially had difficulty finding 7 weight fork oil, but Cycle Gear had the Bel Ray. They also had 5 and 10 weight, but 7 seems a perfect compromise. I poured in 320cc per the book for a 1986 R80RT, but drained quite a bit less. I'd say around 500cc for both legs. And it was dark and clearly not fresh. I should take it for a ride but we had snow this week in Boston. Curious if that will help. I'll report back later this week. 

Then I moved on to the wheel balance. Attached is my jig. I can't remember where I bought a really nicely machined balance axle, you fit the parts on either side and place it on two jack stands. Image attached. It's pretty close, maybe needs a few ounces. Dead nuts N and E, but it moves a little S and W. Just a little. I watch a local guru do this (on this wheel) and I'll try again when I'm fresh tomorrow morning. Really not out by much. 

Also attached is a video of the tire (against the R90 backdrop). This should be really smooth. I don't get it. Again. I'll balance the wheel/tire. Fork oil is fresh. It should ride super smooth. 

Cheers

 

 

 
Posted : 04/06/2024 15:22
Peter Lehman
(@16077)
Posts: 69
Estimable Member
Topic starter
 

Doesn't like the movies

 
Posted : 04/06/2024 15:26
Steven Rankin
(@14724)
Posts: 197
Estimable Member
 

I may be seeing things or not seeing things but when I zoom in on the picture right about where Classic ends on the side of the tire, and under the Tubeless logo, to me it looks like the tire is not fully on the bead?

LOL, it just could be the angle of the picture.  St.

Beware! I do not suffer fools gladly! St.

 
Posted : 04/06/2024 16:23
David Elkow
(@4949)
Posts: 304
Reputable Member
 

Any progress on this issue?  I’ve been reading with curiosity… what could it be?

 
Posted : 04/13/2024 05:56
Peter Lehman
(@16077)
Posts: 69
Estimable Member
Topic starter
 

Tons of rain, that thing called work and I've been very slow to do this: 

  • Balanced the tire again. Added 5 grams. (best balance job I've done)
  • Found the forks were not to the correct level of oil. Added 7 weigh Bel-Ray in the book amount
  • Was low on tire pressure (in the high 20s). Went up to 36 psi

I know, it's taken a long time but promise to take a good test ride tomorrow morning and will report back.

Place your bets. 

 
Posted : 04/13/2024 10:15
Peter Lehman
(@16077)
Posts: 69
Estimable Member
Topic starter
 

WTF. Not much difference. Just rode about 40 miles and here's what I find. There is still a noticeable up/down vibration at 35-40mph. Front end, felt through the bars. As the speed increases it can be felt but becomes less present. Then at highway speed it cannot be felt, the mirrors are clear and I can take it up to 5,500 rpms and it feels great. 

I think I'm being too fussy, but am planning to bring the wheel to Wheel Repair Service of NE out in Auburn. 

thanks

 
Posted : 04/14/2024 08:41
Richard W
(@wobbly)
Posts: 2546
Member
 

Posted by: @16077

I think I'm being too fussy, but am planning to bring the Wheel to Wheel Repair Service of NE out in Auburn. 

thanks

Anything they can repair you should be able to see right now. Tape a 6" length of mechanic's wire to the front fender or fender stay. Bend this wire so that it points to the different portions of the rim and then slowly turn the wheel. The machined portions of the rim (around where the tire sits) should be perfectly round, with zero deviation.

 

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 04/16/2024 06:31
David Elkow
(@4949)
Posts: 304
Reputable Member
 

I’m feeling your frustration. Hope you get an answer from the wheel place. 

Reading your plight jogged my memory. Nearly an eternity ago, I had a significant wreck on my ‘78. I was young and foolish, riding way over my head. The wreck tweaked the forks somehow. I was still able to ride the bike to my dealer, however, once rolling it would begin to quiver.  The quiver peaked under maybe 40 or so, then it smoothed out at higher speeds. I think the wheel was fine, as it turned out, the issue was in the fork/front end alignment. Now, my case was severe - but it makes me wonder if your front end might be slightly tweaked. 

Is your balancer from Marc Parnes?  I have one as well. It does a perfect job - I enjoy balancing my own wheels - much better than the shop. 

 
Posted : 04/16/2024 06:43
David Elkow
(@4949)
Posts: 304
Reputable Member
 

Reading your initial post, I see that you replaced the steering bearings. I just did mine, as well. Boy, they were shot. Anyway, so you had the fork tubes out, I presume. Were they reinstalled in the same orientation (not rotated) in the lower clamps?

Just thinking out loud here. If I were in your shoes, while the front wheel is off, I would remove the brake calipers, undo the nuts at the bottoms of the sliders (there goes your new fluid), and then remove the sliders. I would come up with a way to gage the parallel-ness of the tubes. They should be dead on parallel. Then, I would find a chunk of glass or something absolutely flat to lay against the tubes, being at least square. There should be no gaps, no rocking motion possible. Then I would feel that the forks are straight and fine. 

I’d also check the front axle on the chunk of glass to be sure it’s dead straight. Again, just thinking out loud. 

This post was modified 1 month ago by David Elkow
 
Posted : 04/16/2024 08:00
David Elkow
(@4949)
Posts: 304
Reputable Member
 

Oops - just occurred to me, your forks are newer / different than mine. So, not sure how your sliders drop off. 

 
Posted : 04/16/2024 08:21
Peter Lehman
(@16077)
Posts: 69
Estimable Member
Topic starter
 

Getting back to it. Driveway has been blocked by construction… 

 
The wheel place wouldn’t take a motorcycle wheel despite having that on their website. Any suggestions? I’m in the Boston area. 
 
But I think it’s actually the front end fighting with the back. So I tried adjusting the mono-shock full H (hard) or full S (soft) and in between. It's new and really nice - from Tom Cutter. Thought it might feel a little better on hard, but not really. It’s still up/down vibration around 35 to 40 mph. So weird. Also strange is up at highway speed it’s quite smooth. As someone mentioned, that’s not usually how it works. Things normally just get worse or happen at some multiple of the bad speed. 
 
Next step I’ll bring it out to Duncan Beemers, sometime in the next few weeks. Attached is a shot of the bike today. 
 
thanks
 
Posted : 04/21/2024 14:50
David Elkow
(@4949)
Posts: 304
Reputable Member
 

Hello Peter. I have been curious about your issue. Any determination?  (Also feeling your frustration.)

 
Posted : 05/12/2024 06:47
Peter Lehman
(@16077)
Posts: 69
Estimable Member
Topic starter
 

Was waiting for a tech day. They suggested go back to wheel balance. I did - no luck. Then I asked Duncan of Duncan's Beemers to bounce the front end. He started laughing and called another guy over just to try it. The springs were very, very stiff. Theory. Very stiff springs are transmitting every tiny imperfection instead of absorbing the bumps. 

I'm in process of replacing with a proper weight, progressive springs. I also cut the pre-load spacer in half, but am going to 10 weight oil. Both adjustments suggested by Duncan. 

Interesting trick to hold the (very stiff) spring down to get the son-of-bitch circlip out of the top of the fork. A strap, a punch, then much fiddling with the circlip. 

Not done yet. Will report soon. 

 
Posted : 05/13/2024 04:48
Steven Rankin
(@14724)
Posts: 197
Estimable Member
 

Thanks for keeping us updated, I am glad you are making progress.  St.

Beware! I do not suffer fools gladly! St.

 
Posted : 05/13/2024 05:56
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