Random wobble please help

[trevorwatson]

Hi I have a 1975 R90/6 and it is in great condition everything runs fine except for a random wobble that I experience. It comes and goes randomly at any speed and my handlebars start to wobble. It is pretty scary. I just cant seem to find the problem. Any help would be great thanks/
Trevor

[bikerfish1100]

more info needed- what have you checked so far? any recent changes to associated systems (tires, wheels, frame bearings, etc.)? condition of tires, air pressure? accelerating,decelerating or steady throttle?

[trevorwatson]

I have very steady acceleration.Iv checked the front fork for any play. The front tire could be replaced but nothing too serious. I did switch from the american bars to the euro bars recently. Iv heard people talk about the frame bearings being an issue.

[Stan_R80/7]

Since you recently changed the handle bars, and the wobble has occurred since that change, it is likely the change is due to the shorter bars. I expect the worn front tire may contribute as well. More dampening can be added to the steering by increasing the pre-load on the steering head bearings.

This is not that difficult provided you have taken the handle bars off and lubricated the bearings. If the the bearings have not been lubricated recently, that should be a priority and will probably fix the wobble. Good luck!

[trevorwatson]

Thanks I am recently new to all this and please excuse my ignorance but what are these bearings and where are they located.

[Polarbear]

Big NUT, right under the bars is the item to begin disassembly. First; The bars should fall over side to side with little effort. NOT just slap fall, but with a tiny degree of friction fall over to frame stop. ! This make sense? The steering head bearings are a likely culprit, but many items on the bike will/can be suspect. An old front tire is defintely a replace item, fork oil drain/replace and fork springs too can go in the trash. They are reletavely cheap, under a 100 bucks for both, total. The steering head bearings( clean up anmd regrease, MAYBE replace'em if needed) would be my 2nd looksee, as its fairly simple(cleaning and regrease), but some guidance would be nice for a first timer. My 3rd item is swingarm bearings adjust. Another easy task for those been there. IF you have some mechanical skills, the bike can become an easy learner fro ya. They are NOT complicated bikes. That was a PLUS for the older Airheads. NOW, go buy a "Clymer Manual" or otherwise at most book stores on your bike. A great idea for ya. These books WILL get you through most items of most difficulty to easy. We are here too. Airheads are still all about NAmerica in large numbers. Randy PS; LAST not least, Check ALL your spokes for tidyness/tightness. A DULL thud with a screwdriver indicates a LOOSE spoke. Make 'em all sound alike to the screwdriver.

[beemerPhil]

This would be a good time to make some new friends at your local Airheads chapter!

Wobbles can start in several places; your new short bars make it harder to control, but aren't the cause.

First, check the obvious and cheap solutions; tire pressure and wear. If the tires are worn badly or unevenly, chuck 'em- you should be sure of your tires' condition, whether or not this is actually the problem. Are they spoked wheels? Look for loose or broken spokes. Look for dented or bent rims.

Check for loose engine mount bolts. Check for loose bolts at the rear frame mounting points, under the seat and behind the battery box. Check the front fork clamping bolts and both axles and pinch bolts. Make sure you tightened all the handlebar mounts.

Check for smooth operation of forks & shocks; any oil leaks here?

I assume(!) that "frame bearings" means steering head bearings; these are definitely on the menu for any wobble issues, but their faults have some typical telltale behaviors. Loose bearings will produce a nasty wobble on deceleration; too tight, and the bike will weave at low speeds. Put the bike on the center stand, so the front wheel is off the ground, and slowly turn the bars from side to side- worn bearings will have a notch, or detent, in the straight ahead position. Anything but a smooth sweep from side to side (be sure it's not a cable catching somewhere) is indication that it's time to replace the bearings. (I never repack these; the bearings aren't that expensive, it's a waste of time IMO)

Check the wheel bearings; grip the wheel at top & bottom, try to wiggle it between the fork legs. Any detectable play here, or in the steering head, must be corrected.

Tip the bike forward on the center stand, check for play side to side at the rear wheel. Swingarm bearings are often neglected, play here or in the rear wheel or bearings can cause wobble too.

You said you're new to airheads; except for general inspection, you should have someone with more experience lend a hand. While preloading the swingarm bearing by the book is fairly straightforward, steering head bearing adjustment is definitely a hands-on, set-by-feel procedure. No special tool or manual can match experience, and learning by experiment can be dangerous.

[dwyandell]

Aftermarket windshields can cause some scary wobbles, but normally speed-related (worse at some speeds than others) and tend not to happen at slower speeds. Is the wobble predictable and reproducible?

[bikerfish1100]

dude- you really need to go back to the beginning, and get yourself one of these. http://www.amazon.com/Bmw-R50-Throug...r%27s+airheads
otherwise, you are going to be working blind for a very long time.
btw- Phil was spot on with his assessments and recommendations.

[lmo1131]

The front tire could be replaced but nothing too serious.

My wobble went away when I replaced the front tire.

Here's the fork/stem assembly with the tubes removed. The "big nut" on top of the upper clamp is obvious. What may not be so obvious is the "notched" nut under the top triple clamp plate (item #3 on the drawing; it isn't too clear in photo). This is the nut that preloads the stem bearings. If it gets loose you get wobble.

You should also check the swing arm pivot bearings to ensure that they are tight.





This nut is tightened with the spanner (at the far left), it's contained in your tool roll (or should be ... if you have the tool kit). It can also be tightened using a flat-end punch and a hammer if need be. Once tightened, the "big nut" will need to be re-tightened. There are torque-values for these nuts, but if you find them at all loose tighten them as best as you can and see if it makes a difference. We'll dig up the values later.

[trevorwatson]

Thanks everyone for the very useful info. I found that the lower nut (the notched one) was super loose so i tightened that one as well as the top big nut and no more wobble. I am still going to replace the tires though. Cheers and happy riding!
Trevor