85 R80RT Vibrations

[franko]

I took a 400 mile trip on the bike today. About half way through the trip, a oscillating vibration set up. At first I was disconcerted and dropped my speed and it went away. It would reoccur like a switched turned on, but then fade away again. The speed and engine RPM stay the same unless I let them drop, so it is not a loss of power or slipping clutch. The vibration is felt in both the foot pegs and the handle bars. When stopped for gas, I felt the front hub-cool, final drive-warm, and transmission-hot, but I could keep my hand on it. With more riding, I could determine that below 65 MPH, the vibration was gone, at about 67 MPH it would start up again. As I am the type of person that hears hoof beats and thinks zebras, I thought I would ask for suggestions before I start draining oils and looking for particles. The bike is stock except for a Clearview windshield and the lower fairing removed. 58,000 miles.

 

[20774]

How new is this? Recent maintenance? Changes to tires, pressures, etc.?

 

[franko]

Tires are Avon Roadriders and more than a year old. All drive-train oils were changed a couple of months ago and swingarm greased. Fork oil was not changed, but they have good action. Tire pressure I will have to check later today.
Basically the bike is how I have been riding it all summer, except the ride yesterday was about twice the amount I have been doing recently.

 

[20774]

I would certainly go through the exercise of changing fluids and look for any signs. You might confirm that the bolts holding the driveshaft to the output of the transmission are still tight. With the bike on the center stand, try pulling/pushing sideways on each tire when the tire is held off the ground...feel for any looseness.

The steering stem bearings would have more to do with weaving, etc., but ensure that when the bike is on the center stand and the front wheel off the ground, the bars should move under their own weight from the center position to the stops on each side. They shouldn't clang off the stops. You have an RT...if you have the rubber boots around the forks, this might be a tough test to do.

 

[nickrides]

Since its related to speed, I wonder if the Wheels are in need of balancing, or the Tires are starting to come apart and are trying to tell you something.
Nick
1978 R/80

 

[stevenrankin]

Not enough information

For funny noises, it is hard to diagnose in a forum, we are not there.

Tires, bearings, gears, a number of things can change to cause funny noises. When was the last time valves were adjusted? A poorly tuned bike can sound or produce funny noises or act differently suddenly or gradually.

LOL, give us more information as you can, maybe we will be able to "hear" and feel what you do over time in your writing. St.

 

[PAS]

Check all the fairing mounts and motor mounts.

 

[nrpetersen]

Still not clear if it is engine contributed. I suggest you accelerate well above 67 MPH, pull in the clutch, let the engine idle, and coast down to say 50 mph...... Is the vibration with speed still there with the engine at idle? If so it is probably a wheel-balance or wheel uniformity issue.

 

[pglaves]

Still not clear if it is engine contributed. I suggest you accelerate well above 67 MPH, pull in the clutch, let the engine idle, and coast down to say 50 mph...... Is the vibration with speed still there with the engine at idle? If so it is probably a wheel-balance or wheel uniformity issue.

Or a driveshaft universal joint issue.

 

[Anyname]

I once had a similar situation my 86 80. It turned out to be one of the throttle cables was routed poorly and it would sometimes hang up causing a serious carb imbalance.

 

[franko]

I had time to start looking today. When I looked at the back tire, I could see that it had started to feather, no cupping, just feathering. I got the bike up on some wood blocks. For the most part the wheel felt good trying to wiggle it back and forth. Then i came upon a spot where it had perceptible play. I turned the tire a bit more and it was tight again. I took the wheel off and used the lug/studs to turn the final drive. I couldn't wiggle it, but as I turned it it didn't feel smooth. I pulled the drain plug and the new oil looked good and clear, but with a grey haze in it. The magnet in the drain plug had some grey fuzz on it but not over loaded. As the oil doesn't have but around a thousand miles on it, the amount of particles in it could be excessive.

 

[franko]

I changed the final drive with a used one. The vibration is gone and the bike rolls easier when I push it around. Not as easy as the Norton, but much easier that it had been. Turning the old and used final drives, the old felt very tight. the used one not so much. No backlash on the old. just perceptible on the used. So I still get to see fall colors and pick up apple cider donuts.

 

[Omega Man]

Always good to hear how a repair finished up.
OM

 

[stevenrankin]

Thanks

Glad things worked out for you, sorry you had to change the final drive to make it work out too bad it could have been easer and cheaper, LOL, at least you could do the work.

Big thanks for taking time to let us all know the outcome. St.

 

[bluehole]

Thanks for letting us know how this worked out. Good to learn from your experience.

 

[20774]

I agree...good to know how you made out. Will you be doing any investigation for the original final drive to see what the problem was? From your original post, it's not clear if this is the way the bike came to you or if it is something that developed over time.