Weird vibration

I have an 85 xj700n with 51000 miles. Great bike, low maitenance,great performance. I have experienced very few problems other than an occasional gremlin. Love it.
I got on my bike this morning to go to work and had a weird vibration coming through the seat when I accelerate. It only happens when I am applying throttle in gear. If I coast, it goes away. It almost feels like an out of balance drive shaft or a bad ujoint. Tires are bald beyond safe driving and have been for a little while now. The tire were almost completely flat when I checked them. I filled them back up to tire specs and I still had the feel. It almost feels like a flat. I am stumped. Please help my 23 year old work horse.

 

Drive shaft u-joint is easy to check. Put the bike on the center stand and with the tranny in neutral rotate the rear wheel. A bad u-joint will feel rough or binding.

 

If the tires are as bad as you describe, you may have a bubble forming on one of them.

 

I don't notice any binding. I do notice a lot of clunking going on under the bike. The harder I accelerate the worse the vibration. If I accelerate really hard, the vibration is so bad I can feel it all throught the bike. I am starting to question my fianal drive. Is there a way to check it with the tire still on the bike?

 

Pull the Big Rubber Boot away from the rear of the Engine and closely examine the Universal Joint. There should be NO Play in it as the Drive Shaft is rotated Left and Right.

If you hear a Clunk, clink, or something that sounds like a muffled bell ... the needles on the U-Joint Cups are run dry or have fallen out or deteriorated to such extent that there's movement.

Replace the U-Joint.
I've been through two of them on my 900. But, that bike gets shifted and down-shifted a whole lot. You have to expect to do maintenance on a U-Joint after time.

 

RickCo....Long time no see. Is the ujoint part of the middle gear. I went on bike bandit to order one and can not seem to find one listed for my bike. Can you also tell me the symptoms of a final drive going bad? I have crossed the 50k mark and am getting prepared to do the drive line on this thing but not haveing much luck determining what I should be replaceing.

 

The U-Joint is concealed by the Rubber Boot at the rear of the engine between the cases and the swingarm.

U-Joints go bad when they run dry from being exposed to moisture of any kind that attacks the grease.

I'd "Hand Check" that U-Joint before blaming it on the darn-near Bulletproof Final Drive.

Some Bikes have "Final Drive Dampening" at the rear wheel. The Rear wheel has "Split Pie-slice Dampers" that the Drive Mechanism fits into.

Those Dampers will Freeze with dust and dirt and need to be cleaned-out and lubed with silicone spray.

Before you go Blaming the Middle gear or the Diff ... check-out the U-Joint.

If there's a lot of moisture inside the Boot ... look underneath and see if the Boot Drain is open and cleared-out.
(On MANY Bikes it was never opened to begin with. Instead of the Drain Hole being OPEN ... a membrane of Rubber sealed the hole that was never opened at the Factory or during the pre-delivery ... so, the Drain Hole still has its virginity.)

It needs to be open to allow Moistaure to escape the ribbed Rubber Boot and keep the U-Joint from becoming contaminated with moisture.

I have seen some U-Joints so bad that there were no needles inside the Bearing Cups.

 

I was wondering where the ujoint would be listed in a parts manual. i like to just change questionable parts. I figure 50k is plenty to put on a almost 25 year old ujoint. i looked under drive shaft on bike bandit but it just list parts for the final drive. I can not find the ujoint in any of the parts list.

 

http://www.cmsnl.com/yamaha-xj700n-maxi ... partslist/

http://www.cmsnl.com/yamaha-xj700n-maxi ... /E-06.html



ref. no 37

Part # 31A-46180-00-00

Description: CROSS JOINT

 

Well, it is deffinately a u-joint. I finally got to check it today. One of the bearing cups broke into chuncks and destroyed the rear yoke. Any one have one lying around with the yokes and a good u-joint in it. Not even really concerned with the good u-joint. Need the yokes really bad. Not having much luck finding one local. Hoping to hear from charcal maybe.