The helmet strap wobble

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mikenixon
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The helmet strap wobble

Post #1 by mikenixon » Sun Feb 17, 2019 4:45 pm

All the larger Hondas develop a head shake when decelerating rapidly from 60 mph. We'll call it a "deceleration" or "helmet stap" wobble because it's most noticeable when you take one hand off the bars to check your helmet catch.1 Note that we're not talking here about wobbles of any other kind. Not shakes or wiggles in a turn. Not the weaves at steady cruise or during acceleration often found to be issues with tires. Not shimmies over highway rain grooves or railroad tracks. Just decel wobbles.

The decel wobble is not normal.2 The cause of the classic decel wobble is bearing races that have "floated" and become non-parallel. This results in torque forces in the steering which causes the fork to correct itself, with the result handlebar oscillation. The problem isn't bearing wear or looseness. Mere tightening will not correct the problem, and neither will replacement if the replacement is not properly adjusted. This special adjustment is the key, and what this article is about.

The following procedure is based partly on Honda Service Letter #126, with most of the augmentation you see here authorized by the factory verbally.3 Three tools are needed: a torque wrench, the special factory steering bearing nut socket (4) Honda part # 07916-3710100, and a good quality tubular 0-10 lb. spring scale.5 A floor jack or something similar to jack the front of the motorcycle off the floor will be handy, too.

Follow your service manual's instructions for removing the top clamp (Honda calls this the "bridge"), so that the pair of special castlelated nuts are exposed.6 The upper one is just a locknut. Remove it and set it aside, along with its special locking washer. Jack the front end up off the floor, and feel the bearings as you turn the bars each side from center. If the bearings are notchy or the fork has a self-centering feel, the bearings need to be replaced. Whether you replace the bearings or not, continue.

Turn the fork to full right lock, and with the torque wrench and special socket, tighten the bearings to 35 ft-lbs. The fork will be very stiff. Don't panic. This is only temporary. Now turn the fork lock-to-lock, repeatedly, at least twenty times. Bang-bang-bang-bang. You will probably notice the tension loosening up, indicating that the bearings have squared themselves.

Now turn the fork to full left lock and loosen the nut until it's just finger tight, then turn the fork to the right lock again and tighten the nut slightly, just enough to remove obvious looseness. Attach your spring scale onto one fork tube, using a piece of shoestring or something similarly soft so as not to scratch the tube. With the fork pointed straight ahead and the tire still off the floor, slowly pull the spring scale straight ahead until the fork begins to turn and the tip of the fender arcs one to two inches. Note the poundage on the scale. You're looking for a 5-7 lb. pull. There is no set number, each bike will be different.7 But start with 5 pounds.

Once at the 5-lb target, drop the special washer back into place, screw on the locknut, and tighten the locknut only snug, not so much that torque is added to the tensioning nut. Then bend the locktabs into the locknut to keep the two interlocked. Reassemble the rest of the fork per the manual, and test ride.8
If the test ride reveals that your decel wobble persists, repeat the procedure, adding another pound on the spring scale measurement. If on the other hand your test ride has the bike swaying side to side like a rowboat, this means the bearings are too tight. Repeat the procedure targetting a lower spring scale pull measurement.9

Notes:
1 When I test for a decel wobble I get to 60 on a level piece of road and snap the throttle shut and loosen my grip. If a decel wobble is present, the bars will wiggle slightly, then increase in intensity as the bike's speed falls through the 45 to 40 mph zone, then weaken again as the speed falls lower. That's a decel wobble. And it's easy to fix.

2 For many years Honda instructed its dealers to try to convince customers that decel wobbles were normal and not fixable. This didn't ultimately work and they no longer say this.

3 Factory Honda service reps taught this version of the procedure.

4 The factory special socket is long-discontinued by Honda but is available hit and miss overseas and reproductions are plentiful on the aftermarket.

5 Though not mentioned in the original Wing service manuals, later manuals include use of this spring scale, as do also some other manufacturer's service manuals. It's current best practice.

6 Wings have the two nuts, including the locknut, but some other Honda models do not.

7 The correct spring scale reading is variable because front end mass and dimensions vary. Different tires, suspension settings (resulting in attitude variances affecting weight transfer while riding), the presence of a windscreen, different handgrips, early vs. late brake calipers, different handlebars, even different clutch and throttle cables and their routing. All can affect the reading.

8 Tightening the bridge nut should not increase the spring scale reading. If it does the locknut underneath the bridge was over-tightened.

9 You might ask, why not simply torque the tension nut? The short answer is the spring scale method is much more accurate.

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Re: The helmet strap wobble

Post #2 by desertrefugee » Sun Feb 17, 2019 5:20 pm

Whoa! An extremely valuable addition to the real "Nixon Library". Thanks, Mike.

And very timely: My CBX has been suffering from this decel wobble and I've tried a couple of times to address it via the layman's "fork bounce" method. No joy. I will be employing this much more scientific technique soon! (As soon as I find my old <ahem> scale).

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Re: The helmet strap wobble

Post #3 by mikenixon » Sun Feb 17, 2019 5:56 pm

Thanks, Darrell! Hope it helps.

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Re: The helmet strap wobble

Post #4 by 77Gowing » Sun Feb 17, 2019 9:22 pm

Good article Mike
Here's some trivia from the study of phisycs.
Acceleration: a change in velocity and or a change in displacement as in angular acceleration. In phisycs you either have positive or negative acceleration. There is no deceleration, but rather negative acceleration
No worries though I'm not correcting you. But when it comes to the mathematics of such it matters. Just a bit of trivia.
BTW I've no idea if I have that wobble. First I'm too scared to try it and second my bikes are blocked by two huge mounds of dirt while my contractor install my dogs pool. Yet the weather is shamfully great here in West Texas.
Take care..y'all!

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Re: The helmet strap wobble

Post #5 by Track T 2411 » Sun Feb 17, 2019 9:58 pm

I guess I'll have to buy a scale, as my 1100 does this, most noticeably around 40 MPH. I too tried the 'bounce' method when I replaced the bearings...

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Re: The helmet strap wobble

Post #6 by mikenixon » Mon Feb 18, 2019 6:53 pm

77Gowing wrote:Good article Mike
Here's some trivia from the study of phisycs.
Acceleration: a change in velocity and or a change in displacement as in angular acceleration. In phisycs you either have positive or negative acceleration. There is no deceleration, but rather negative acceleration
No worries though I'm not correcting you. But when it comes to the mathematics of such it matters. Just a bit of trivia.
BTW I've no idea if I have that wobble. First I'm too scared to try it and second my bikes are blocked by two huge mounds of dirt while my contractor install my dogs pool. Yet the weather is shamfully great here in West Texas.
Take care..y'all!


Honda used to tell its dealers to tell customers, "Keep both hands on the handlebars!" Of course this was never a satisfying solution, as semi-logical as it sounded. Even today, on every bike I test-ride, whatever reason is is in my shop, including the first ride on a bike I bought for myself a couple years ago, I test for a helmet strap wobble. Set up a sudden decel through that 45mph zone with just the tips of my fingers touching the grips. About half of all bikes have it.

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Re: The helmet strap wobble

Post #7 by mikenixon » Mon Feb 18, 2019 6:54 pm

Track T 2411 wrote:I guess I'll have to buy a scale, as my 1100 does this, most noticeably around 40 MPH. I too tried the 'bounce' method when I replaced the bearings...


"Bounce" method?

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Re: The helmet strap wobble

Post #8 by 77Gowing » Mon Feb 18, 2019 9:27 pm

mikenixon wrote:
77Gowing wrote:Good article Mike
Here's some trivia from the study of phisycs.
Acceleration: a change in velocity and or a change in displacement as in angular acceleration. In phisycs you either have positive or negative acceleration. There is no deceleration, but rather negative acceleration
No worries though I'm not correcting you. But when it comes to the mathematics of such it matters. Just a bit of trivia.
BTW I've no idea if I have that wobble. First I'm too scared to try it and second my bikes are blocked by two huge mounds of dirt while my contractor install my dogs pool. Yet the weather is shamfully great here in West Texas.
Take care..y'all!


Honda used to tell its dealers to tell customers, "Keep both hands on the handlebars!" Of course this was never a satisfying solution, as semi-logical as it sounded. Even today, on every bike I test-ride, whatever reason is is in my shop, including the first ride on a bike I bought for myself a couple years ago, I test for a helmet strap wobble. Set up a sudden decel through that 45mph zone with just the tips of my fingers touching the grips. About half of all bikes have it.

Thanks Mike I'll give a good, whence they clear my drive.
Best regards.

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Re: The helmet strap wobble

Post #9 by Track T 2411 » Tue Feb 19, 2019 5:09 pm

mikenixon wrote:
Track T 2411 wrote:I guess I'll have to buy a scale, as my 1100 does this, most noticeably around 40 MPH. I too tried the 'bounce' method when I replaced the bearings...


"Bounce" method?

I don't recall where I found it, or the specifics, but basically, after the torque and re-tourque, the forks should freely move to either stop and bounce once... As said above, not very scientific, and there are so many variables...

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Re: The helmet strap wobble

Post #10 by mikenixon » Tue Feb 19, 2019 8:05 pm

Ahh. Interesting. Haven't heard of that. I'd rather not see the fork even hit the stop that easily on its own.

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Re: The helmet strap wobble

Post #11 by Track T 2411 » Wed Feb 20, 2019 4:02 pm

mikenixon wrote:Ahh. Interesting. Haven't heard of that. I'd rather not see the fork even hit the stop that easily on its own.

Which is probably why I have the death wobble, lol!

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Re: The helmet strap wobble

Post #12 by rcmatt007 » Tue Feb 26, 2019 3:10 pm

Every time I read one of your technical updates I learn something new.

Bravo!

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Re: The helmet strap wobble

Post #13 by mikenixon » Tue Feb 26, 2019 9:20 pm

Thank you. :)


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