4th gear vibrations

[Koboldwrangler]

Hello--

I've been having an odd vibration on my '85 gl1200a, 64k miles. When merging on the highway, I've been feeling this very abrupt vibration mainly at high rpms in 3rd, all through 4th gear, and sometimes 5th, usually when I start getting near 75-80 mph. Its not something that happens at slower speeds in any of the gears, nor does it fades in or out -- if I'm in 4th, its fine until the rpms start ramping up, then like a light switch being flipped on everything starts vibrating. It kinda feels like something is running out of balance in the drivetrain. When its vibrating I can pull the clutch and it stops, so I dont think its my wheels out of balance. My guess is either a bad u joint, or maybe something with the clutch basket. Thoughts? Anything I should check?

[Whiskerfish]

make sure to check the rear wheel bearing. the 1200 had a known issue with the bearing wallowing out the area inside the hub of the wheel. If it is not snug in there it could be causing your issue when under a load.

Otherwise yes inspect/lube the teeth for the final and the ujoint

[Koboldwrangler]

make sure to check the rear wheel bearing. the 1200 had a known issue with the bearing wallowing out the area inside the hub of the wheel. If it is not snug in there it could be causing your issue when under a load.

Otherwise yes inspect/lube the teeth for the final and the ujoint

ive read about that issue, itd be strange if the bearing was bad and only showed up in 4th gear.

I'm trying to do research on peoples experience with bad u joints, and the people who change them rarely say what the bike was doing that made them come to that conclusion.

looking at randakks blog, I've got 2 of the 3 warning signs for a failing u joint -- excessive driveline slack and harsh vibrations. The slack, it feels like theres a bunch of gear lash when accelerating and decel, and, I know goldwings whine, but man, compared to my '78, its suuuuper loud, especially in 3rd and 4th. Harsh vibrations, i would say whats happening in 4th gear falls under that.

I'll squeak the boot back and take a look and see if I notice anything out of place or damaged with the u joint. Does the lube need to be a moly paste, or will regular moly grease work?

[Sidecar Bob]

Re spline grease, see this thread (particularly post #15)
http://ngwclub.com/forum/viewtopic.php?f=1&t=46048

When I bought my '77 GL1000 I had never had anything with a U joint so I did not know how it should sound or feel. A few months later I was on the way home from a long day out on the 'Wing (now with sidecar); I had just gone up the QEW from St.Catharines and across Toronto on Hwy 401 and was northbound on Hwy 404 when I just had a feeling I'd had enough of that and needed to get of onto secondary roads so I took the off ramp at Bloomington Rd. About half way around the ramp I suddenly had no drive. Fortunately the ramp sloped downhill in the direction I was going so I was able to coast to the end of it.
It was quickly obvious that I wasn't going to be able to get it going again so I looked for a house with a light on and asked to use their phone (this was before everyone had a cellphone in their pocket). I ended up taking a taxi home and we came back with my wife's van to tow it home the next day.
When I got it apart a couple of the the loops of one yoke were worn right through and the rest were badly worn so this must have been developing for quite a while.
I didn't notice any different sound or vibration before it let go but it could have been doing that for thousands of Km and I didn't know or I could have subconsciously picked up on some subtle change (hence the feeling I had to get off of the highway).

[CYBORG]

The driveshaft is different on the 1200. Still could be the U-joint, but there are splines on both ends of the actual shaft. One end into the rear end, and the other into a separate U joint unit, which also has splines to the engine side. Three sets of splines that need lube. Any one that was dry can wear enough to cause a vibration

[Koboldwrangler]

The driveshaft is different on the 1200. Still could be the U-joint, but there are splines on both ends of the actual shaft. One end into the rear end, and the other into a separate U joint unit, which also has splines to the engine side. Three sets of splines that need lube. Any one that was dry can wear enough to cause a vibration

well, if the splines were chittering and have wear, wouldnt they be bad at this point, or would grease help that? im still trying to think what would cause a harsh vibration at higher speeds / hard acceleration, but be fine in casual use. Id hate to go through the hassle of grinding all the stakes on the u joint, changing it, and that was not the issue. Hm.

[dontwantapickle]

...Thoughts? Anything I should check?

Interesting issue.
Have you run the bike in gear on the center stand and pulled in the clutch?
Any Noises?

Or when up on the center stand, just put bike in gear and try to spin the rear tire back and forth by hand,
you should be able to feel if there is a whole lot of slop in the u joint or splines.

I can't think of too many places in the engine that could cause vibration that goes away when the clutch is pulled.
Maybe:
Actual clutch issue?
Engine output shaft?
Loose alternator Nut?

Or driveline issues that others have already suggested.

[Koboldwrangler]

...Thoughts? Anything I should check?

Interesting issue.

Have you run the bike in gear on the center stand and pulled in the clutch?
Any Noises?

Not on the stand but i have pulled the clutch while sitting on the bike, and held it, no abnormal noises.

Or when up on the center stand, just put bike in gear and try to spin the rear tire back and forth by hand,
you should be able to feel if there is a whole lot of slop in the u joint or splines.

ill have to try, but i feel like trying to spin the tire while in gear wont say much due to the gear lash between the rear drive and the transmission.

I can't think of too many places in the engine that could cause vibration that goes away when the clutch is pulled.
Maybe:
Actual clutch issue?
Engine output shaft?
Loose alternator Nut?

Or driveline issues that others have already suggested.

ive been also thinking about clutch issues. it definitely isnt slipping, but i thought about it chattering; however, if that was the case, id expect that to be caused by load and replicatable at low speeds, not high speed, high rpm, only in certain gears.

if the alternator nut was loose, id expect there to be a multitude of other issues following that. speaking of, i do need to start another thread on that -- ive got the typical light dimming issue, but now they are starting to pulse. yay...

[Sidecar Bob]

The alternator rotor (= flywheel) is held on by a bolt that you can access by removing a cover that screws into the alternator cover. That's right, the one you use to turn the engine with a wrench.
If it comes loose this happens
viewtopic.php?p=723837

[dontwantapickle]

IDK why I said Alternator Nut.
I think just speculating on what there is at the back of the engine would/could cause a vibration while under load.

I will be interested in finding out what the issue actually is.

[redglbx]

One thing that comes to my mind reading this is that years ago I had a 92 mercury marquis with a 4.6l that would shudder vibrate badly under load in the higher gears, it ended up being the spark plug wires believe it or not. Change the wires and it would go away until the next time. Strangest thing I ever encountered. So may be something worth checking. This was before they went to the coil-on-plug setup.

[Koboldwrangler]

One thing that comes to my mind reading this is that years ago I had a 92 mercury marquis with a 4.6l that would shudder vibrate badly under load in the higher gears, it ended up being the spark plug wires believe it or not. Change the wires and it would go away until the next time. Strangest thing I ever encountered. So may be something worth checking. This was before they went to the coil-on-plug setup.

yea, this isnt a misfire. ive ridden with torn slides, and the power drop off even with one torn slide is huge and very noticeable.

[Fred Camper]

If the wheel bearing were not changed the last time it got tires, I would look there first.

[Sidecar Bob]

Are you saying that you replace the bearings every time you change the tires or do you just mean "if the bearings haven't been replaced recently"?
FWIW, It's been 27 years and about 107,000 Km since I put Mr.H together (engine from my wrecked 1000, most of the rest an 1100 that sat outside for years). I've only changed the wheel bearings once and that was when I was trying to make it handle right with the sidecar. It made no difference (I did eventually get it figured out) so the originals probably would have been OK for many more years.
I know the 1200s had a wheel/bearing issue but surely the bearings should last longer than the tires....

That said, checking wheel bearings isn't a bad idea if the vibration happens at a certain speed. It wouldn't hurt to examine the tires too.