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Old 03-16-2010, 07:37 AM   #1
davemon OP
High Speed Airhead
 
Joined: Jun 2007
Location: NC
Oddometer: 107
Airhead tank slapper

Just did a 1200 mile ride on my 1977 R100S loaded with gear and camping eq. on the ride down road like a champ. Added my coat and riding pants onto the gear in the back and at 25 MPH the handlebars flapped like the tire was square. Repacked the load and same thing just not so bad. Was able to accelerate through the slap mode and cruised fine at highway speed. Made it home removed the load and same dance at low speed. Had the forks rebuilt about a year ago new rear schocks and new tires. Anyone else had this problem? Whats the fix?
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Old 03-16-2010, 07:55 AM   #2
jtwind
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My r80 with an S fairing did this. Not uncommon on airheads with handlebar or fork mounted fairings and windshields. On mine it was steering bearing adjustment that fixed it. But could as easily be the fork, tires, tire pressure, fairing or windshield attitude, poor shocks or loading/weight issues. I'd just work on making sure each one was right and then move on to the next if it doesn't seem to improve.

If you rode it similarily loaded before you did the forks, shocks and tires and it didn't do this, I'd start there.
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Old 03-16-2010, 08:00 AM   #3
Foot dragger
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The local BMW dealer is an airhead guy,he helped me put new races and bearings in the steering head on a R75/6 I brought back from the dead,he really stressed the adjustment on the steering head bearings. He used a torque measurement device suggested by BMW. He also said my forks would never work rt with out expert assembly and new stock parts.
Evidently the ft end on these older beemers is touchy about adjustment so maybe check all that over closely.
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Old 03-16-2010, 09:09 AM   #4
BKMLWR
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been riding a 77 R100s since I bought it new in 77, over 170k miles never had a tank slapper except for hitting washboard road once, riding includes 2up cross country trips

Check tire pressure and steering head brgs
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Old 03-16-2010, 10:20 AM   #5
Bigger Al
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15 years on an R90/6, and the only time the front wags is when the tire reaches the end of it's life span. Once the shimmy begins, I replace it and things go back to normal. This is irrespective of brand or tread.

Still a good idea to check out the bearings, though.
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Old 03-16-2010, 01:25 PM   #6
chasbmw
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low speed wobble is almost always caused by too loose steering head bearings, move the adjuster nut in small increments until the wobble goes away, but not so much that the bike feels as if you have wound down a friction steering damper.

Charles
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Old 03-17-2010, 10:49 PM   #7
pommie john
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Quote:
Originally Posted by davemon
.... Had the forks rebuilt about a year ago new rear schocks and new tires. ...
Dave

If the problem arose since the new tyres, it's worth checking they are on the rim true and properly balanced.

I had a very similar problem straight after I had new tyres fitted to my old Honda and they had not seated the front tyre properly.

Put it on the centre stand, prop up the front and spin the wheel. The tyre should run perfectly straight. Any wiggling from side to side, and that's likely the problem.
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Old 03-19-2010, 06:56 AM   #8
Beemerboff
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In my Brooklands Gold Portfolio of old Beemer tests they found that unequal loading of the panniers caused a wobble.

Wobbles were much more common 50 years ago when tires had a flatter profile, and I have found the more rounded the tire the more stable my airheads are.

So dont dick around with worn tires / flat profile tires.

Lasertechs or Distanzas both have a good round profile and work well on airheads.
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