fork shake at 80

[Guy]

I have a shake in the fork at 80 mph.
82 xj purchased in Nov 2003. Had the original back tire at 15,000 miles and previous owner self mounted a cheng shin backwards on the front. Replaced the rear with michelin commander. I think when I first took the bike on the interstate it smoothed right to 80 with no problem, I know it did at at 5K rpm. I replaced the yamaha fairing with a vetter five and lowers. But now at 80 the instruments shake real bad and looking down the forks they move front to back what looks to be about an inch. I had the front tire turned around and balanced, very small weight, no change. Had the shop check over the front end. They thought the steering might be a little tight, it doesen't flop from side to side, but found no problem. So I replaced the front tire with the matching michelin commander. Allowing about 50 miles to seat the tire, it still has the shake, maybe only slightly less. I have tried different damper settings and several presssure settings.
Surely this can be corrected. Where do I start.
Guy

[TopCatGr58]

Well,
Even though you have a new tire, they can be bad! Also the rim might have received some damage from the PO. You may want to check the tire for evenness of round as well as the rim. Support the front of the bike/frame so that the front wheel is off the ground, then spin it and visually inspect the rim for a wobble, out of round movement, like a cam lobe, but hopefully not that pronounced! Also check the profile of the rubber tire for same. Is the tire's bead truly seated evenly all the way around the rim?

You may also want to inspect the bearings for excessive wear. Will the tire spin freely for many revolutions, or does it slow down very fast due to brake pad drag? Are the brake disc's true, or warped, that combined with drag could accentuate things!? Just throwing out some ideas, perhaps the "Real" gurus can chime in with more!?
T.C. ......shadetree survivalist

[TheDjost]

Is the steering head bearing just a little tight, or is it worn? Just a little tight should not be a problem, but too tight can. If it dosen't flop to one side when the front wheel is off the ground, i'd take it apart, just to make sure. Clean it, repack it and reinstall it with the correct torque setting.

What is the torque on the front axle? The pinch bolt?


-Justin

[Geezer]

Re: fork shake at 80

Originally posted by Guy
I have a shake in the fork at 80 mph.
82 xj purchased in Nov 2003. Had the original back tire at 15,000 miles and previous owner self mounted a cheng shin backwards on the front. Replaced the rear with michelin commander. I think when I first took the bike on the interstate it smoothed right to 80 with no problem, I know it did at at 5K rpm. I replaced the yamaha fairing with a vetter five and lowers. But now at 80 the instruments shake real bad and looking down the forks they move front to back what looks to be about an inch. I had the front tire turned around and balanced, very small weight, no change. Had the shop check over the front end. They thought the steering might be a little tight, it doesen't flop from side to side, but found no problem. So I replaced the front tire with the matching michelin commander. Allowing about 50 miles to seat the tire, it still has the shake, maybe only slightly less. I have tried different damper settings and several presssure settings.
Surely this can be corrected. Where do I start.
Guy

Look at the seating ring on the tire and make sure it’s even all the way around and inflated to the PSI indicated on the sidewall. Next make sure both fork tubes are the same height in the clamps. If one is higher than the other, you will have handling problems. Make sure all the fork bolts are properly tightened. Others have already mentioned the steering head bearings but I’ll toss my 2 cents in anyway. Put a jack under the engine and raise it up so the bike is resting on the center stand and the jack. The forks should turn smoothly from left to right with no for and aft shake. I prefer to adjust them with the top clamp off to get a better feel. Adjusting tapered roller bearings is an acquired feel, not to loose or too tight. Also change the fork oil. Unequal amounts of oil from one side to the other will make it act a little wonky.

Geezer

[Guy]

Thanks
We did the raise the bike and rotate and check the wheel and tire with the first tire at the shop. They said the same "maybe it's just a bad tire" The ching shin is not an expensive tire.
I will check it again and take the bike out without the fairing. Then guess I will get into the bearings.
Thanks
Guy

[Dennyz]

check your fork fluid. You may need to replace it.

I experienced a similar problem. I found my fork oil old and thick. After a good cleaning and new fluid, the problem went away.

[Jerry]

Check the rotors for warpage. Replace brake pads. Make sure calipers are not 'hanging up' and are retracting OK. Check the brake bleeders to make sure the 'spooge hole' in the master cylinders is releasing all brake line pressure.

Many front end problems do not originate in the front end. I would check the rear tire for run-out and correct balance, and check the swing arm to make sure it does not have play in it. Finally, check the shocks. If one has lost fluid or has a different damping setting (black thumbwheel on top of shock) the uneven performace will show up as front end vibration. Note: the XJ shocks are air adjustable, try 24- 28 psi in them. If they don't hold air, replacements are in order. (Max pressure is 57 psi.)

[Guy]

Well here is the end of this adventure.
After changing fork oil, trying all settings of damping and air pressure in the front fork. I loosened all calipers so they did not drag, and still shakes. Replaced the steeering bearings too. I spun the rear tire on the stand at about 3k the whole back end would shake. I went back to the shop with my findings,, they rebalanced the front tire to the same place and weight. No difference. I couldn't believe I'm telling them the rear tire shakes and they redo the front? Enough of this, to the shop down the road, pull the rear and have it checked. They say the balance is off and turn the tire on the rim to get a balance. Spins up great and some of the front shake is gone. Well lets redo the front too. It's not off as bad, but now is much smoother.
It's amazing, the problem must be in my bike, not in their equipment. Guess their balancer needs to be calibrated.

[pathfinder]

Shaking front end

I bought a new Metzler tire about 8 years ago that I swear was square. It hopped all over the place. Took bike back. They removed tire and remounted with equivelant of a 6 pack of weights. Still felf square. Removed tire and changed to another Metzler they had in stock all problems went away.

[Guy]

follow up

This adventure started with the Cheng Shen tire on front and did not notice the problem. I put a Michelin on the rear then changed the front to Michelin and t;hink thats here the problem started. Now many miles later I have Avon Venoms, needed to work out tire pressure but they work fine no shake no wobble. Riding used to be fun but now ilt's a pleasure. The Avons run true and no road snakes.
I mounted the CS tire on the front 81 XJ650 that I was working on for my wife, then added a CS rear tire, and you know what? Those tires do really well , not even bad on the snakes. Just after the 82 XJ1100 the 650 feels like a bicycle.

Guy

[LoserShoes]

Those Michlins weren't radials by any chance were they? Never tried it, but radials aren't supposed to work too well on the older bikes.

Steve

[Guy]

Radials??
No, I don't think so. Michelin Commander. I would think a radial tire would have too much sidewall flex to be used on a bike.