strange intermittent vibe at ~100km/h

Hey everyone,

My 85 Maxim X 750 has a strange intermittent vibration at 100k or above, almost a pulsing resonance at regular intervals. Only does it when cruising (doesn't do it if accelerating or decelerating). Seems to be coming from the rear end but before I tear everything apart just wondering if anyone else has encountered this before.....I went through the manuals and they didn't really have anything to say about it, and it seems to me wheel bearings or the final gear assembly would exhibit vibrations at all wheel speeds if that's where the problem was. My best thought right now is the driveshaft u-joint might be loose/worn out.

Thoughts?

 

That's about 60mph, or 5k +/- in 5th gear. All XJ's (from what I understand) seem to have an engine resonate frequency vibration at that spot.

I was worried at first too. It's nothing to be concerned about, but I try not to sit right at that RPM because vibration is bad for all kinds of things on the bike--bolts, wires, old exhaust, etc.

 

Good to know, I was having terrible thoughts of maybe having to try to find a new rear end.....you know it's going to be hard when Yamaha doesn't even list part numbers for those two gears.

That's also really irritating, most of the highway speed limits in my area are 100km/h.

 

Yeah, I really feel your pain--anytime traffic is at all a problem, people generally cruise at that speed. I tend to speed for this reason.

In Yamaha's defense, when the bike came out in the US, most speed limits were around 55 in my understanding, so that wouldn't have been a problem. (I end up generally speeding a bit to keep the RPM's over that vibe point.)

(I agree; I think this is my biggest complain about the bike, period.)

 

Have you checked all the exhaust connections and tighten all clamps and bolts? Mufflers can also have loose/broken internal baffles that vibrate at certian engine speeds.

 

put it in 4th!

Its not speed related, but rather around 4500-4900 on the tach.

thats when the bike is out of harmonic balance, just something that is how it is.

just speed up

 

Thanks guys! Yeah I checked all accessible clamps and bolts, especially around exhaust and wheels/axles, nothing loose. Not really that kind of 'dry' vibration though anyway. Guess I will have to just speed up. Think a cop would buy this as a valid speeding excuse?

 

Ha. I should have mentioned (though it has now been covered I guess) that when I had a loose left muffler (it was completely ripped off the exhaust pipe and suspended only by the rear left bracket that holds the rear left foot peg), the vibration was UNBEARABLE, so it makes a difference.