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Opinion on Deceleration Headshake aka death wobble

Stasch

Member
Member
While I understand where they come from, there are several recurring comments on this topic that I disagree with as being the fundamental source in most cases, of the typical 50-40 mph deceleration headshake on C10's, C14's, Goldwings and other heavier bikes.

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Disclaimer: My opinion is based on my experience. I am not an engineer. While I do hold a Motorcycle Mechanics certificate from the State of Michigan, the test wasn't that difficult. Its a cool thing to me to have and maintain for $20 per year to the state coffers.

I am not a professional mechanic nor am I broadly experienced across a wide range of bikes. I do all my own work on my personal bikes. I have worked on other C10 owner's bikes, but I know them and am usually working alongside them (but not always).
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LEGEND: SHB = 'steering head bearing'

So here we go. Comments most often posted on threads (on this and other forums) asking about this issue include:

'wheel bearings'
'tire imbalance'
'uneven tire wear'
'just don't take your hands off the bars'

It is possible to have the first three issues which do need to be resolved if they exist. However, I think in most cases, the decel headshake is simply due to improper SHB adjustment and can coincide with any or all of these other three issues.

I am not claiming that wheel bearings or tire issues can't cause some degree of headshake and its always a great idea to keep tabs on the health of your tires and wheel bearings.

However, if you have a headshake, it makes the most sense to me to first check the steering head adjustment. Its free to do, and is necessary for the long term health of your SHB's anyway.

Headshake severity varies depending on how loose the SHB adjustment is and / or how grooved the SHB's races are. (See attached photo below). Some bikes (even within the same model) are worse than others.

I test for it often on all my road bikes. To do so, I allow the bike to decel from 50 or 60 mph down to 35 or so in a safe situation, with both hands on the bars. Once I let off the throttle, I loosen my grip slightly and pay close attention. At any hint of a shake, I tighten my grip.

If you test, you do so at your own risk, but hey, you're on a motorcycle and probably already know if you have some headshake anyway. Don't simply let go completely to test. In more severe cases you could find yourself in an uncontrolled death wobble tank slapper that you can't recover from šŸ˜§, which on some bikes with severe mal-adjustment or severe SHB wear can happen quickly and violently if you are no handed, or fail to tighten your grip back up.

What can make diagnosis a bit obscure is that it is possible for a new tire to temporarily eliminate the headshake phenomenon if its relatively minor. However, the headshake will return if the fundamental cause of improper SHB adjustment is not addressed.

This is pure speculation on my part, but I think a new tire can have uneven wear introduced to it by too loose of SHB adjustment which is why I think new tires only hide the headshake for a short time.

Personal Examples:

My first (and current) 2000 Concours ZG1000 has 106,000 miles on it. I bought it in 2003 with 9,800 miles and it had the decel headshake on my test ride. After a new front tire change from the old stock Dunlop, it temporarily resolved the issue only to return about 1,000 miles later. Finally at 26,000 miles, the proper adjustment of the SHB was done. I have not had any headshake since, having run multiple brands of front tires through their wear life.

I had to adjust the steering head again at 81,000 miles after a slight clunk over bumps showed up, but never had a headshake. That bump clunk adjustment only required 1/8 turn. Since then, all has been well.

I owned a 1999 Voyager XII ZG1200 which also manifested the decel headshake issue. Fresh front tire resolved it temporarily, but it returned. Once the SHB was properly adjusted, the issue was finally resolved, lasting through several more front tire's wear lives until I sold the bike.

I have also owned another dozen C10's which I have brought back to life. Every one of them had the decel wobble to some degree. Most of these were from situations where they had been put up for several years or weren't consistent on the maintenance, but still - EVERY ONE.

Some were able to be tuned out, but two were downright violent requiring SHB replacement, such as my current project, a recently acquired 2003 C10. It will be a very nice bike once gone through and tweaked up. It even has the SISF 7th gear mod and overflow tubes / 2 minute mod! But I digress.

The headshake on this one happened VIOLENTLY, all the time at any road speed, not just on decel or in the 50-40 mph range.

This fairly common decel headshake occurs on multiple brands of heavier bikes when the SHB adjustment is too loose. Many older bikes used to have a knurled rubber knob on top of the top triple tree to allow for 'on the fly' adjusting. My 1971 Suzuki T500 Titan, my younger brother's 1970 Suzuki GT350 and my dad's 1968 Yamaha 180 (all 2 strokes twin road bikes) all had it.

Decel headshake can happen after new SHB's are installed and settle in. Even new bikes can have this issue shortly after taking ownership as this adjustment probably doesn't receive adequate attention from the factory, dealerships at assembly or at dealership maintenance service intervals.

I get that the recurring comment of 'just don't take your hands off the bars' has a safety sentiment to it, and I don't discount that. I am the last person to say, 'yeah, just run down the road no-handed, what could possibly go wrong?', nor will I hold your beer while you try it!

Do I do this myself? Of course I do in certain situations, but that doesn't mean you should. I am confident in my bike's adjustment and test often. I don't do this in the potential 50-40 range just out of common sense, unless I am testing using the method described earlier.

However, if there is a headshake that is only kept from manifesting itself because your hands are always religiously on the bar at all times to knowingly prevent it, it still means your SHB's are too loose and there is probably damage being done to your steering head races.

Test for it and take action.

Only tighten 1/8 turn at a time. Yes its a bit of work to disassemble and reassemble again to readjust if necessary, but you will be happy once you get it right.

If you adjust too far, the steering will become vague and 'wandery' meaning the adjustment is too tight. You will know the feeling almost immediately on a test ride at normal speeds, even before you get out of your neighborhood. The difference between too loose and 'wandery' is not that much, its that much of a fine tune.

If you can't adjust it out, I would check the health of the SHB races. If they are grooved you will need to replace them. (see attached photo below)

Only then would I look to the wheel bearings or tires (which you've been keeping an eye on anyway right?)

GroovedOuterRace.JPG
 
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bobct

Member
Member
Totally agree, and nice writeup Stasch.
I got my C10 with around high teens or low 20K mileage.
As soon as I got it running on my first ride I perceived the deaccel wobble. Hands off long enough I think it would end up a tank slapper.
I got rid of the aging 2nd set of Dunlops that were on the bike when I bought it.
Definitely got less wobble but it was still there.
I thank COG for pointing me in the steering head bearing check.
The only thing I can add to your writeup is get the front end off the ground and the front end shouldnt turn to one side on its own and bounce off the steering stops.
I tightened it up, probably more than a half a turn before I got to where if you had an old type fish scale it would take a pound or so to drag the bar end to the stops. Very close to too tight. Check for a notchy feeling full the range of back and forth bar motion, if you feel it then it is either a new bearing is needed or the bearing race has the notches and needs to be replaced.

Thanks to COG and member recommendations my C10 with ZRX front end (larger fork tube, better brakes, wider rim), SISF tuned carbs, ZZR rear shock, non stock windscreen, I know this bike rides better than the day it rolled off the factory floor.
 

Stasch

Member
Member
The only thing I can add to your writeup is get the front end off the ground and the front end shouldnt turn to one side on its own and bounce off the steering stops.
I tightened it up, probably more than a half a turn before I got to where if you had an old type fish scale it would take a pound or so to drag the bar end to the stops. Very close to too tight. Check for a notchy feeling full the range of back and forth bar motion, if you feel it then it is either a new bearing is needed or the bearing race has the notches and needs to be replaced.
bobct - Nice addition to the adjustment process.
 

Cra-z1000

Member
Member
bobct - Nice addition to the adjustment process.
Totally agree, and nice writeup Stasch.
I got my C10 with around high teens or low 20K mileage.
As soon as I got it running on my first ride I perceived the deaccel wobble. Hands off long enough I think it would end up a tank slapper.
I got rid of the aging 2nd set of Dunlops that were on the bike when I bought it.
Definitely got less wobble but it was still there.
I thank COG for pointing me in the steering head bearing check.
The only thing I can add to your writeup is get the front end off the ground and the front end shouldnt turn to one side on its own and bounce off the steering stops.
I tightened it up, probably more than a half a turn before I got to where if you had an old type fish scale it would take a pound or so to drag the bar end to the stops. Very close to too tight. Check for a notchy feeling full the range of back and forth bar motion, if you feel it then it is either a new bearing is needed or the bearing race has the notches and needs to be replaced.

Thanks to COG and member recommendations my C10 with ZRX front end (larger fork tube, better brakes, wider rim), SISF tuned carbs, ZZR rear shock, non stock windscreen, I know this bike rides better than the day it rolled off the factory floor.


When I was a dumb young kid (now a dumb old man) my 550 four always had that notch . I just got use to it and rode on...lol . Between that and the cheap Cheng Shin tires I'm lucky to be alive šŸ˜‚ .Now if I sense anything wrong at all with my bike I'm on it .
 
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