1975 Mk. III Handlebar shake-speed wobble.

You didn't mention the isolastics. If you place the machine off the stand vertically, grab the rear wheel and pull it firmly from side to side, how much movement can you get? You have the stock head steady, right? Get a heim joint head steady or make your own if you have a workshop. What could be happening is that the engine/gearbox/swinging arm assembly is pivoting in the frame and this might only manifest at higher speeds.

The weave you mention can occur on other bikes. I had a Laverda Montjuic (500cc OHC twin) with the swinging arm mounted on rubber bushes and it weaved above 75 mph. This was a recognised problem solved by fitting bronze bushes. I only mention this because something is probably flexing more than it should.

A few things to try apart from replacing your stock head steady:

Pump up your tyres a few psi more than the pressures you usually run.

Move your weight forward.

What bars do you have? Flattish or cowhorn? This is only my opinion and I stand to be corrected on this, but I think that the weight is not sufficiently over the front wheel on a Commando with the standard, forward-facing footrests and anything other than flat bars. Try it with your feet on the pillion pegs, which will move your weight over the front end a bit more, and see what happens then. I do know from experience that moving the rider weight forward has solved speed wobbles on several bikes I have ridden, both modern and classic.

I assume your frame is straight and that your spokes are tight?

In addition to all that has been said, loosen the head steady at the head (the 3 bolts into the head) then sit on the bike, off the stand of course, and then tighten the head stead to the head for proper fitting.
Get the ISO's right, firm up the swing arm spindle and a set of Avons.

I, too, had a high speed wobble. After eliminating all the obvious it turned out to be the rear tire. I didn't find out until I replaced the rear tire after normal wear . Wobble disappeared.

Thanks for the replies.

New vernier isolastics were installed recently. Stock head steady; when I look at the two triangle plates, they tilt off in one direction; could the isolastics or the motor mounts be mis-aligned? After I re-did the swing arm, I checked for slop; there's none. Right now, with re-built forks, new steering head bearings, new Isos, oversized pin and spindle tube fixed; this is a tight Commando.

I'll try that loosen three head steady cap screws and retighten while on the bike trick.

As for frame straightness, the only time I ever crashed it was many years ago on a blind uphill 5MPH right where I hit some gasoline that had shot out of an uncapped cage tank - that's the only possible question about the chassis but it was a "step off" low side. The bike hit nothing, just slid on that gas. Spokes are tight, checked them last night while I was "stringing" the wheels.

New Avon AM-20 non DOT race tires have one track day on them, like new. They are a bit wide - 100-19 front 120-18 rear. Both on Borrani WM3s. It's a struggle to mount the wheels - let the air out and C clamp the tire to get the front tire between the fender bolts and to get the rear wheel into place. I can try giving the Avons a bit more pressure, especially the front.

Yes, wide bars with some pull back, good point about front-rear weight distribution. It's ironic; I can muscle the wobble, sort of, with those big bars but they might be the thing that's provoking it.

Has anyone cured the wobble with a steering damper?
How can one check whether the planes of the two wheels are the same?

xbacksideslider said:

Has anyone cured the wobble with a steering damper?
How can one check whether the planes of the two wheels are the same?

Click to expand...

Could I add a few more comments here? Again, just my opinion, but I think that a steering damper just masks the problem. I'm not suggesting you don't fit one, but you should aim to eliminate the weave without the damper.

The way I checked that the rear wheel was vertical in the frame was to remove the tyre and the rear mudguard, replace the wheel and nip up the spindle nut. I got a straight edge about 5 ft long and clamped it to the side of the rim pointing vertically. If you step back and eye it up. you can then see if the wheel is tilted from vertical. Mine was and it turned out that the swinging arm was very slightly bent. I think there was a thread about this recently.

Never did it with the front but I guess you could clamp another long straight edge to the front rim and eye up both straight edges.

Now that you say you had it on the track, this will tend to expose handling flaws that might not be so apparent on the road. Yes, could be that holding on too tight could exacerbate the weave but I feel that in addition to all you have done so far, a decent head steady, flat bars or clip ons and rear sets are the way to go for track work.

It would be interesting to hear from someone who has raced a proddie Commando.

Woolant said:

130/80/18 on the back.

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Tony,
How the hell did you get a 130 on the rear ?

I think I'm right saying; generally a shake is the front end while a wobble is the rear, grief you've got both.

Check the tyres are correctly and evenly fitted to the rim. There will be a little rib that runs round the tyre close to the rim, check the gap is the same on both sides and even all round, and check for buckles and ovality.

Dave.

I've had a few conversations over the years about handling with Norman White, a guy who know his Commandos on and off the track http://www.normanwhite.co.uk/, some of which I've even taken.

Gospel according to Norman:
Steering dampers - throw them in the bin, they can make things worse and are generally just masking a problem - quote "no Commando should ever need a steering damper", took mine off mostly out of embarrassment and had no problems. My excuse for fitting it in the first place was handling problems I later realised caused by a worn rear tyre and out of balance front.
Don't overtyre the bike, big section tyres ruin straight line stability he positively hated the 110 section I had on the back, he's into Bridgestones BT45's if you've got 18" front and back.

http://www.dinamoto.it/DINAMOTO/8_on-li ... bmode.html

This has been around on the web for years. It's useful to get the terms and the basic process. A few months ago the topic of hydraulic steering dampers came up on mc-chassis-design. They might turn out to be useful for headshake, useless for wobble, and actually contribute to weave problems. They don't react fast enough to do what you'd want them to do, apparently. Commandos are more sensitive to tire choice, profile, and inflation than any bike I've ever owned.
The trailer for the Cafe series captured it. "On a modern bike you're doing 140 and it feels like 80. On these bikes you're going 80 and it feels like 140." At this, Commandos can really excel.
http://www.ama-cycle.org/news/story.asp?id=2284

When I stand behind the bike and look at the alignment of the stock head steady, it is canted to the right side. That is, the engine seems to be offset to the left such that the two triangle plates of the stock head steady lean to the right.

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The whole power unit is mounted ~3/8" to the LH to gain chain clearance past rear tire. If you can fit a 130 rear then maybe someone has moved the gear box over
to LH a bit more as some racers like Ken Canaga have done. RH swingarm leg is angled different than LH to accommodate the power unit LH shift off center.

Bikes must weave to stay upright, it tire profile is off then they can magnify this on the fly. Dampers are dangerous to go fast on and expect to change directions fast to avoid stuff or recover from slips from grit to grease or flats. Also a drag to me just tooling down the road d/t the steering effort increase. As reported the top and front rods don't really solve much but do move the onset up higher in speed and frequency and suddenness of upset onset. Rear link is whole nother phenomena. Only loose stuff or cockeyed tire patch affects steady state handling.
If chassis allows non traumatic assembly its plenty good enough to ride hands off no wobble as good as perfectly straight Commando. Tire alignment same deal must be obvious bad at a glance off before you can detect anything but maybe a bit more easy to fling one way than the other but either side just as secure grip and line held. I've tested above in 2 Commandos but by crash tweaks and my own assembly fumbles, only discovered fault in tear down but nothing to alert riding.

Usually folks going 80 are at constant cruise steady states. I've had sloppy clutch and swing arm bushes resonate with triplex chain flop tugging on swing arm through rear iso pivot to jostle the front iso and cause forks to oscillate to compensate - causing wobble that wanted to escalate until I slowed way down.
Holding forks harder did little to control the wobble, which both angered and scared me, till checking chain tension and noticed same freg as felt on road.

Throw some more air in tires, leaving 2-3 less in front or throw money at new tires and see how it goes. If no help still get to use up the tires while wobble
down the hwy. Its also possible one shock ain't working as well as the other.
I've had that happen and felt it as wobble till bad or missing rubber mount replaced.

Ain't never gonna cure it if you ride fast!
Got mine to a reasonable level now, but fast bends are not too brilliant one up. 100-90-19 front, 1110-90-18 back, iso head steady. Was not perfect years ago when it had 4.10-19 tyres front & rear. I can go round corners up to about 80mph faster than I can on my modern bikes, but over that, the modern ones win. (Private roads of course ).
One thing I have always noticed is that it handles fantastic two up.

Thanks again for your thoughts.

Thanks Bob for this link -
http://www.dinamoto.it/DINAMOTO/8_on-li ... bmode.html

It adds definition and precision to the discussion and in those terms, what I've got is weave, as opposed to wobble. If it is weave, then, as I feebly understand it, a damper would be less effective and that may explain Norman White's opinion of steering dampers as related by Rich_j

This problem is not the "head shake" associated with wheelies; my Commando is not mis-behaving while under acceleration with the front wheel "light" or off the ground. The problem mode is in straight line operation and speed associated - 80 mph onset and at lower speeds when passing over freshly cut freeway rain grooves. It also got spooky when I went over a residential "speed hump" - I unweighted the seat and placed most of my weight on the pegs - I may have pulled back on the bars, don't know.

Flo said:

Ain't never gonna cure it if you ride fast!
Got mine to a reasonable level now, but fast bends are not too brilliant one up. 100-90-19 front, 1110-90-18 back, iso head steady. Was not perfect years ago when it had 4.10-19 tyres front & rear. I can go round corners up to about 80mph faster than I can on my modern bikes, but over that, the modern ones win. (Private roads of course ).
One thing I have always noticed is that it handles fantastic two up.

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Flo — before I bought my Commando, I was concerned about the handling of the "rubber Nortons". I happened to come across this story of racing an isolastic Commando:

http://jevans.com/norton/chapter9.htm

I emailed him to ask him about how his bike handled and how he set it up. He said there was always one corner on a race circuit, usually a 100 mph one, where the bike would weave while leaned over and he called it 'exciting'! He quoted Mick Hemmings who said that the way to stiffen up the plot is to add rubbers into the isos, to make a solid pack of rubbers inside the tube. Dave Jevans ran 18 inch wheels with Avon AM22 DOT race tires. He also won a race on this bike.

xbacksideslider — as Flo says, you may not be able to eliminate the weave completely but surely you could work towards minimising it, if you are willing to persevere?

Never got rid of the awful speed wobble until I installed a Dave Taylor head steady on my combat. I've had a steering damper on the bike almost its whole life because of the wobble and it does just mask the problem but can save your life. My symptoms were speed wobble if shutting off throttle abruptly at 80mph OR hitting a bump in a high speed turn. (I am not distinguishing between wobble, weave or whatever.) I had tried everything there was to try until the new head steady. Like night and day. I definitely don't need the steering damper on there anymore. I can ride the wheels off it now.

Controversial subject but it worked for me and several others on this forum. (Also one claims it made it worse????)

I notice this as my tires wear out. the more wear the more head shake or wobble. Also the wobble is worse at lower speed and smoothes out the faster I go. It really doesn't bother me because I am not one to just let go of the bars while riding?

My commando had head-shaking which was "solved" by the PO's installation of a steering damper. I took the damper off to discover this rather disconcerting tendency. I put the damper back on. Two years later I removed the PO's 18" wheels and much wider tires and installed oem 4.10s front/rear wheels and Avon RR tires. No more headshake; no need for steering damper.

Mike,

You may have had the same results with the 18" wheels and tires. I had a high speed head shake that I couldn't cure until I replaced the rear tire. Replaced a 110-19 Avon with the exact same size Avon tire. Head shake disappeared. I now run 120-18 Dunlop and still no head shake. I do think one should pay special attention to the mounting of the tires. Sometimes they don't seat correctly.

Made some progress, I hope. Got her up to 85 MPH once on my way to the DMV to renew her tags and my driver's license. Got 100 on both Cali's regular and MC tests.

Anyway no weave that one time but it was on newer smooth downhill section, not enough to know yet.

As suggested, I re-assembled the stock head steady while sitting on the bike. I tightened it from the top down, the rubbers first, then the lowers of the triangles, lastly the cap screws at the head.

Taking her to the Lake Isabella area this weekend for the Northern California BSA Owner's Club weekend ride so that will offer good tests.

I had hoped to build a head steady but ran out of time. Won't happen tonight or tomorrow before we leave.

Here's a pic of the Norton and the CBR loaded back into the Rampage after a day at Streets of Willow in June.



And here is a pic from earlier that day, I think its exiting Turn 3.

I spent the week end in the Lake Isabella area of SoCal with the NoCal BSAOC and had several opportunities to explore the weave.

On Saturday we had a run on brand new smooth asphalt on Hwy 395. If I sat in my typical "on the tank" forward position, the weave's onset was at 85 or 90 mph. I then shifted my weight toward the rear, the weave ceased. Disappeared.

On Sunday, on a straight empty stretch above the lake, at about 2700 ft elevation she indicated 110 MPH at 7000 RPM on a 20 tooth - no weave, stable.

So . . . . since I've established that the rear wheel is in line with the front, and since I can eliminate the weave with a weight shift, and since it goes away as soon as you turn in to a corner, I'm less interested in it.

Here's my hat in the ring... brand new iso's, set at .005", new Avon's 100/90-19 36PSIF & 42PSIR, fresh swing arm bushes and clamp mod. High speed wobble from 80 on up to 110. Head bearings are good.

Years ago I had the same problem. I went through everything, as you have. New Isos, shocks, headstock bearings, swing arm bushes. Still had the wobble. Eventually, it was time to replace the rear tire. I replaced it with the same Avon Super Venom I had been running. Wobble gone!. It could have been the way the tire was mounted. I guess if had the problem again I would try remounting the tire first.