4th gear vibration and resonance question

drrags · 09-26-2006, 10:36 AM

Hi y'all,
I'm a new owner of an '04 R1100s and I have a strange vibration in 4th gear at 3200 RPM. At this RPM there is a paint shaker vibration that sets in, rising to earthquake level and then back down to paintshaker level. It does this resonance at about 2 Hz. It's only in 4th gear with the clutch engaged. If I pull in the clutch and keep the RPM's up, the vibration goes away. If I'm in a lower or higher gear at the same speed, there is no vibration. This seems to point to the tranny instead of the drive shaft, engine, wheels or tires. Does this seem reasonable? The TwinMax shows perfect sync at this RPM too. I've had two oilhead RS's and an oilhead GS before this one. The S vibrates overall much more than the others, but I understand that the engine is more rigidly mounted, no rubber handlebars, etc, and this should be expected.
Any ideas anyone?
Thanks!

SergioK · 09-26-2006, 11:36 AM

Only in 4th? Maybe that gear is starting to go. I had bad vibes but in all gears. Turns out not torquing some of the subframe/trans bolts was the culprit.

drrags · 09-26-2006, 11:39 AM

Interesting, and a good idea! I'm on it. Thanks!

SergioK · 09-26-2006, 11:42 AM

Don't overtorque them. Check the manual. A loose transmission bolt calls for only 14ft/lbs. Not sure what the other specs are but nothing was rated for over 40ft/lbs IIRC.

ErricZ · 09-26-2006, 12:28 PM

This is something many Boxer owners notice in all gears at around that RPM level, so just make extra sure it's only in the one gear.

Moybin · 09-26-2006, 04:17 PM

If you had X-ray vision you could check the synchronization of the U-joints in the final drive line. Just because it goes away when you pull in the clutch is symptomatic, but not definitive.

How many miles on the bike? Do you know if the previous owner ever had anything apart in the driveline? What's the condition of the rear tire?

R111S · R111S's Garage

Hopefully not a cracked left - rear engine mounting tab...

markjenn · 09-26-2006, 10:23 PM

The problem does seem to be worse in 4th gear. I don't have the slighltest idea why. My symptoms come and go with every tire change, throttle balance, etc., but when I have it, it's always in 4th. But it's been basically the same for 45K miles, so I wouldn't advise you start tearing into hard parts chasing a cure. I have just accepted it as one of the quirks of the machine.

- Mark

JimMoore · 09-27-2006, 01:40 AM

Mine does the same thing in fourth gear, or at least it did until I changed the torque arm to the short arm. Now it seems to have disappeared. U-joints at a different angle?

drrags · 09-27-2006, 11:35 AM

Quote:

Originally posted by Moybin
If you had X-ray vision you could check the synchronization of the U-joints in the final drive line. Just because it goes away when you pull in the clutch is symptomatic, but not definitive.

How many miles on the bike? Do you know if the previous owner ever had anything apart in the driveline? What's the condition of the rear tire?

The bike now has 16k miles on it. I know the bike as been at least dropped, and possibly at a low moving speed, judging by the little clues left.

What do you mean exactly by "syncronization of the u-joints"?

Indeed I'll try a GS arm. I've been looking for an excuse to do that anyway :-)

Thanks again for all the advice! There's some real good ideas here, and I appreciate it!

pdonnell · 09-27-2006, 11:43 AM

quirks of the motor for most owners. Not many things you can do.

jclark · jclark's Garage

Try out of round 4th gear. Many ( that would be lots! [ including me - 35k so far ] ) 1100's have them.
Do a search...

jeff

Moybin · 09-28-2006, 03:55 PM

Could also be the rubber bushings in the torque arm going south, which would explain why replacing with a shorter arm "fixes" the problem.

SergioK · 09-28-2006, 04:08 PM

Hmm... the bushings on my bike are 5 years old and have 60k miles on them. I should probably think about changing them out.

Moybin · 09-28-2006, 04:40 PM

I've been wondering lately if the rubber bushings in the torque arm should really be something more solid, again Nylatron is my first pick. What's the point of rubber bushings? The shocks make the bike ride smoother, not the bushings. And how did Der Enjineers miss putting roller bearings in those when they seem to think they are absolutely necessary in the pivots? WTF? The pivots don't sweep through any more arc than the torque arm, and the torque arm carries as much load... Again I say: WTF?

xk49 · 05-07-2007, 04:14 AM

I was actually searching this forum for throttle body info, when I came across your posting. I was just about to bring my r11 (2000 with 12k) in the shop with the exact same problem. Fourth gear has this nasty vibration that has a slight surging sensation at the same rpm’s you noted.

Did you ever find the cause?

BobP63 · 05-07-2007, 05:29 AM

This is fairly common; before you get too deep into this it make sure your throttle bodies are in sync at 4000 rpm. Tires can also have some effect here too i.e. type, condition, pressure.

Chris Canning · 05-07-2007, 09:04 AM

Quote:

Originally posted by BobP63
This is fairly common; before you get too deep into this it make sure your throttle bodies are in sync at 4000 rpm. Tires can also have some effect here too i.e. type, condition, pressure.

Ditto,good fuel,fresh plugs.