Commando steering shake.

Hi All,

I'm looking for advise to cure my head shaking Commando. I see the problem has been touched on in numerous threads e.g. Steering Dampers, but so far as I've found, none have directly addressed the subject.

What I've found is that there's a consensus that "Commandos just do that". But mine never did in the 5 years I've owned it, until last month. One day nearing the end of a ride it just started shaking it's head at (the usual?) c. 35-45 mph. I haven't had the bike over 60 or so since it started. No tank slappers and it's controllable with a firm grip on the bars. Movement is maybe +-3" at the bar ends. It happens going straight. No cornering or surface disruptions are needed to initiate the bad behavior and it does it consistently, not just now-and-then.

So far I've;

Checked the steering bearings - no play or notchy-ness. (I've only checked by feel, turning the steering with the front wheel suspended)
Replaced the isolastics Ft. and Rear with new, vernier types
Re-balanced the front wheel
Made a feeble attempt at truing the front (steel) rim
Removed the front tire and re-mounted it 90* off
Tried tire pressures Ft. and Rr. from 26 psi to 50 psi.
Realigned the rear wheel a few degrees
Checked the ft. wheel bearings (by feel, installed). They might be a little notchy but there's no discernible play.
Confirmed the (factory type) head steady rubbers are not torn.
and maybe a few other things.

I can move the real wheel a bit relitive to the frame a little but I don't have another bike available to see how much movement is "normal". Also, I don't feel any clunks or play on the swing-arm fitting. Tires are Avon AM26s with maybe 1,500+ mile on them. The front looks new and the back is showing some scalloping. Shocks are 4+ yr. old, stock length Hagons. No steering damper, UK style bars... a pretty stock '71 750.

Any and all suggestions of what I should re-confirm or look at next, deeply appreciated.

Thanks


-Danny

I have never had scalloping on a rear tire. Maybe checking that front and rear wheels are parallel with each other.

lazyeye6 said:

I have never had scalloping on a rear tire. Maybe checking that front and rear wheels are parallel with each other.

Click to expand...

Yes me too.
Try this : Obviously you now need new tires. When you install them over inflate even more to seat them fully on the rim , then let off air to tire specs.

My buddy and I bought two new identical 69S models when growing up in Toronto .( 18 years old ) I rode mine hands off often , if I rode his , hands off at the lower 30-40 mph speed , it would shake bad enough that you had to grab it right away . That stopped the shake.
his would do it every time .
never did find the problem , but we were young and stupid .
we often would go along the 401 flat out , side by side for a few miles . I think we could get them up to 110 - 115 mph , hard to tell as everything was shaking . At night the exhaust was shooting out sparks , carbon I guess .
cool thing is I still have both bikes and he and I are best friends still .

Knucles said:

My buddy and I bought two new identical 69S models when growing up in Toronto .( 18 years old ) I rode mine hands off often , if I rode his , hands off at the lower 30-40 mph speed , it would shake bad enough that you had to grab it right away . That stopped the shake.
his would do it every time .
never did find the problem , but we were young and stupid .
we often would go along the 401 flat out , side by side for a few miles . I think we could get them up to 110 - 115 mph , hard to tell as everything was shaking . At night the exhaust was shooting out sparks , carbon I guess .
cool thing is I still have both bikes and he and I are best friends still .

Click to expand...

Does "his" still shake?

lazyeye6 said:

I have never had scalloping on a rear tire.

Click to expand...

Nope me either, but I did have scalloping on a front tire (Avon venom or super venom) and replacing it made the head shake go away.

GTCarlos said:

The front looks new and the back is showing some scalloping.

Click to expand...

I run Avon tires on all my bikes and I always find them hard to get seated properly. I bet your rear tire did not properly seat. If you change it (you should), look carefully at both sides. There is a ridge in the rubber that must be equidistant from the rim all the way around on both sides.

All m

maylar said:

Nope me either, but I did have scalloping on a front tire (Avon venom or super venom) and replacing it made the head shake go away.

Click to expand...

all my Avon RR's have scalloped on the rear wheel.

Putting the rider's weight (and luggage if applicable) a bit further forward helps a lot.

We'll need a number.
"I can move the real wheel a bit relitive to the frame a little but I don't have another bike available to see how much movement is "normal"."
1/8"
1/4"
3/16"
???

Mine has always nodded the head a bit.... Not too bad, but a nuisance if I've a light grip at around 50 mph. No scalloping ever.... just a slight squirm.

GTCarlos said:

No tank slappers and it's controllable with a firm grip on the bars.

Click to expand...

It's counterintuitive but try relaxing your arms when it starts to wobble to see if it gets better. There is a off chance that you trying to stop a slight wobble is causing a larger wobble.

What you feel to be at the front, often comes from the back. You might have destroyed an internal part of a rear shock absorber, or an iso adjuster might have moved. The fact that the shake has suddenly just appeared indicates that something has changed.

mine wiggles a bit as i slow to around 20mph but is steady otherwise

Mine is steady until I load it up with luggage , the small Chihuahua wife too. We camp a lot on the Norton. Small wobbly issue leaving Toronto , you have 2 choices , the 401 big trucks and grooved concrete sections , or the 404 north choice , no trucks allowed. Both are aggressive drivers situations so I keep to the right lanes or collectors and deek off of hell to countryside A.S.A.P. Since Covid hit I see less and less Police enforcement , It's winter now though. Upgrade time and maintenance.
Even loaded up for a camping/fishing trip I can stop any wierdness by moving forward and hugging the tank at speed. Everyone should ditch stock headsteadys and upgrade to the Heim joints type if you intend to RIDE , not be a trailer show queen for display. Move weight forward I say.

My thoughts exactly. I put in new Isos SINCE the problem began so I can rule that out. I'll swap in some other shocks, buy a new tire and figure out a way to measure the rear wheel play and alignment.

Meanwhile, THANKS for everyone's ideas and suggestions.

Torontonian said:

Mine is steady until I load it up with luggage , the small Chihuahua wife too. We camp a lot on the Norton. Small wobbly issue leaving Toronto , you have 2 choices , the 401 big trucks and grooved concrete sections , or the 404 north choice , no trucks allowed. Both are aggressive drivers situations so I keep to the right lanes or collectors and deek off of hell to countryside A.S.A.P. Since Covid hit I see less and less Police enforcement , It's winter now though. Upgrade time and maintenance.
Even loaded up for a camping/fishing trip I can stop any wierdness by moving forward and hugging the tank at speed. Everyone should ditch stock headsteadys and upgrade to the Heim joints type if you intend to RIDE , not be a trailer show queen for display. Move weight forward I say.

Click to expand...

The steering shaking began while riding solo and without luggage. That configuration accounts for about 90% of my riding and I have only ridden that way since.
A year or two ago I got a NOS Dave Taylor head-steady from a friend. It's a simple design but it never seemed to sit properly on the bike as the instructions illustrated. Any way I mounted it (and there aren't a lot of options) it had tensoin on the head or on the joints. I nonetheless tried it and rode with it for about 100 miles. It made the bike feel worse. Hard to describe exactly how but maybe less steering feedback or less stable steering. In the end I bought new rubber for the factory head-steady (early type, no springs) and all was well - or at least back to normal. In ay case, the D.T. didn't induce head-skaking and there weren't any at the time to try to correct.

It;'s Officially winter here in California too but that just means we dress a little warmer to go riding. Sometimes I think some enforced down-time to work on the bikes would be a good thing but really I know I'd hate it.

Best regards,

-Danny

GTCarlos said:

The steering shaking began while riding solo and without luggage. That configuration accounts for about 90% of my riding and I have only ridden that way since.
A year or two ago I got a NOS Dave Taylor head-steady from a friend. It's a simple design but it never seemed to sit properly on the bike as the instructions illustrated. Any way I mounted it (and there aren't a lot of options) it had tensoin on the head or on the joints. I nonetheless tried it and rode with it for about 100 miles. It made the bike feel worse. Hard to describe exactly how but maybe less steering feedback or less stable steering. In the end I bought new rubber for the factory head-steady (early type, no springs) and all was well - or at least back to normal. In ay case, the D.T. didn't induce head-skaking and there weren't any at the time to try to correct.

It;'s Officially winter here in California too but that just means we dress a little warmer to go riding. Sometimes I think some enforced down-time to work on the bikes would be a good thing but really I know I'd hate it.

Best regards,

-Danny

Click to expand...

That you had problems mounting the DT head steady and the scalloped rear tire seems to indicate an alignment issue.

swooshdave said:

That you had problems mounting the DT head steady and the scalloped rear tire seems to indicate an alignment issue.

Click to expand...

Humm... Maybe I'll try to mount the Taylor head-steady again now that I have new isolastics. And replace the rear tire. I moved the rear wheel alignment a lot by eyeball, I'd estimate at least 2° or 3°. No discernible difference. I have to build some kind of rail to see if they wheels are actually aligned. Twists are a bit harder to measure but again, I haven't *found* anything broken causing the sudden onset of symptoms, so it seems unlikely to be a twist problem.

Use a 4' fluorescent tube to check.

gortnipper said:

Use a 4' fluorescent tube to check.

Click to expand...

Clever! And I actually have one. I can see some difficulties but it's worth a try!