The Airheads Beemer Club is a non-profit club reclaiming the 'Legendary Motorcycles of Germany'

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1 week 2 days ago #6899 by 10665
HIGH SPEED WOBBLE was created by 10665
My 1984 R100RT with about 29,000 miles showing, has developed a vibration at around 80 mph, going into a wobble that would eventually lead to tank slappers as speed is increased. I have balanced the wheels, checked tire pressure, lubed and reset swingarm bearings, with no improvement. I have not touched the front wheel bearings yet, and would like to get some opinions before I tackle that job. Any advice would be welcome. Thanks!

J. E. "Pete" Peterson
Lillian, AL

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1 week 2 days ago - 1 week 2 days ago #6900 by 8166
Replied by 8166 on topic HIGH SPEED WOBBLE
How long has it been since the steering head bearings were serviced/replaced? If they're loose, the grease has hardened, or the races are Brinelled, you'll get oscillation in the handlebar, typically at multiples of 40 or so MPH.

How old are the shocks? If they're the originals, they're probably shot. If the rebound damping in the rear is gone, it'll wobble.

If the front tire is worn unevenly or badly cupped, it'll wobble.

I wouldn't mess with front wheel bearings unless I could feel slack in them. Put the bike on the centerstand and use a jack to loft the front wheel. Grab the wheel at 9 and 3 o'clock and apply opposite pressure with each hand in an axial direction to look for any play. Might as well do the rear wheel, too, looking for swing arm play.

Tire pressure could be an issue if you're trying to go by the original BMW recommendations in the owner's manual. Tires from those days had much stiffer sidewalls and didn't need as much pressure to keep lateral flex to acceptable levels. Modern tires need more pressure, sometimes much more. Manufacturers sometimes publish inflation recommendations for our airheads on their web sites, but I've also had good luck calling them and asking for a recommendation.

Start with your steering head bearings and let us know what you find out. Above and beyond everything else, though, be very careful around those speeds until you have the problem identified and remedied. You don't wanna have anything to do with a genuine tank slapper. Body surfing down the road isn't my idea of a good time. DAMHIKT.

8166 Scot Marburger, This email address is being protected from spambots. You need JavaScript enabled to view it.
Last edit: 1 week 2 days ago by 8166.

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1 week 1 day ago #6902 by 8053
Replied by 8053 on topic HIGH SPEED WOBBLE
There is 1 other thing that can create instability. Check for a cracked weld on the rear sub-frame at the cross brace where the fender bolts to it.

James Strickland, IL. Airmarshal

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1 week 1 day ago #6904 by 10665
Replied by 10665 on topic HIGH SPEED WOBBLE
Thanks for the advice. The wheel bearings seem tight, but I don't know the history of the steering head bearings. The rear shocks are after-market Koni's, but, again, I have no idea how old they are; however, they seem to be working properly; I don't feel any slack in the swing-arm bushings, The front tire is new. For starters, I'm going to increase the tire pressure in both the front and the rear, and if that doesn't work, I'll attack the steering-head bearings. Thanks a million for the "check list." It's appreciated.

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1 week 1 day ago #6906 by 10665
Replied by 10665 on topic HIGH SPEED WOBBLE
Thanks, James. Based on your advice, I checked all frame welds and can't find any cracks or breaks; of course, internal cracks could be present, but all feels tight. I'll try the tire pressure increase first.

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1 week 1 day ago #6909 by 2752
Replied by 2752 on topic HIGH SPEED WOBBLE
Really. Follow Scot's advice and do the steering head bearings. If you don't know the history of the bike's service, that bike is 36 years old and even under ideal conditions, the grease in the head bearings is like glue now (assuming it has not been serviced in the past 20 years, which seems likely). You do not want that tank slapper.

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