1975 Mk. III Handlebar shake-speed wobble.

Hi- I am new to the Norton Commando Forum. My name is Steven Lawrence, am from Alamo, CA. USA. Interests are vintage vehicles of all types. My 1975 Commando has a bad speed wobble. Anytime I let my hands of the bars, it starts. Seems to be so bad I don't really want to let it develop. Stops with hands back on bars. The bike is in generally in good shape, and is original. I have checked the head bearings they seem to have no play . Swing arm pivot also seems OK, and I took some clearance out of the front isolastic. Twin springs above cylinder hear are at 1.5". Any advice on this problem? Something is really wrong, but I can't seem to figure it out. I also have "european" style handle bars- shorter and lower than US spec.
Many thanks!

Welcome to the forum.

The symptoms that you're describing are not unknown and they can get to the stage where there is no pleasure whatsoever in riding the thing.

The Commando is a bike where many things have to be in good order, certainly the basics like tyre type, condition, run-out etc.

There are also possible misalignment problems which should be checked for.

There is often a suggestion that smaller lighter riders suffer more problems and this reflects my experience. I came to the conclusion that my problem was effectively a low-frequency vibration induced steering shake. Maybe a heavier rider damps things out ?

My difficulties were sorted by installing a rose-jointed head steady, after trying everything else. There are a number of threads on the forum which will give you chapter and verse here. I fitted a Dave Taylor type.

If the head steady is not doing its job then there can be a vertical misalignment of the wheels and that is clearly not a good thing at all !

Good Luck

Ten years ago I had a head shake above 90 mph. Went through everything. Added a steering stabilizer. Still had the shake. Eventually it was time to replace the rear tire. Replaced it with another Avon Super Venom, same as I had been running. Voila! No more shake.

Does Your Grandmother Dance?

First, welcome. I'm new here, too, but have been around motorcycles for over 45 years; started working on Nortons in the early 70s and have forgot more than I'd care to admit, but I am working on a '75 Mk III and have had a first hand opportunity to see what 35+ year old isolastics look like (mine had 6300 miles).

Your Isos are junk, unless they have been replaced recently (you didn't mention that, only that you adjusted them). Here is what I'd do to kill your handeling gremlins:

1) Replace your Isos, when you see what they look like when you push them out, you'll know how bad they are.

2) Check the age of your tires! If they are older than 5 years get rid of them, or put me in as your beneficiary. There is a date code on the sidewall (Google it, if you can't locate it) that tells you the year and the week of production. There are too many people out there that think tread wear is the ruling indicator of tire life! For those of you committed to this BS indicator I have two TT 100 Dunlops for sale with 95% tread showing (1981 vintage!) that I haven't thrown out yet...they make great fire starters for wet wood (EPA not withstanding)

3) Check and true your wheels.

4) Re-torque your steering head

5) Change your fork oil, no one seems to do this

6) If you rear shocks are original, lose them

7) Lastly, make sure that your rear wheel and front wheel are running in the same plane, or at least in parrallel planes.

Additionally I suggest that you change out the rubber insulators that comprise your head steady.

Best wishes with your Norton

Tiers and/or spoke tension/looseness.

Many thanks for the replies to my post. I will replace the isolastics, rear tire. Also will do an alignment after this. Will report upon completion of the work.
Thanks Again,
Steve

1968 motorcycle article, slight flutter of handlebar if the hands are removed from grips. By 75 the poms perfected it and turned it into a violent flutter. A rod type head steady stoped mine,may be some one with an isolastic type could tell you whether they have the same effect.

as for a Tyre selection I WOULD NOT recommend the TT100 or any other Tyre that has a straight center groove. the Avon AM26 is a great Tyre especially if you are running stock wheels.

windy

I agree with all RoadScholar's points, and especially tyres. I inherited my Commando with Avon Roadrunners of indeterminate age, with plenty of tread. I junked them and fitted new Avon Roadriders and straight away the bike steered and cornered better and felt more planted. The classic low speed wobble, with hands off the bars, also disappeared when I fitted new rear shocks, and rear sets, which shifted my weight forward. I have the same bars as yours. A rod-type head steady would be no harm but I would first check/replace the standard rubbers and also isos.

LJK Setright wrote a technical article about motorcycle stability in a 1976 issue of Bike magazine, citing the Commando as an example. The Commando's low speed wobble could be inhibited by careful adjustment of the steering head bearings, and by simply shifting the rider's weight forward.

In addition to going through the checklists posted above, steering head bearings can develop a notch in the straight ahead position, which interferes with the smoothness of the steering and the self-correcting action of the wheel when deflected, and which can cause a weave.

Good luck in solving your problem and let us know what did it!

When I put my bike together, I put on fresh TT100s, and I don't think I'll do it again. That tread design, with the slightly undulating groove down the middle, makes going over drawbridges a harrowing experience. It feels like the grating on the draw section of the bridge just fits into the groove, making both wheels jog side to side a bit, often in different directions.

I, too, have a high-speed wobble, and am in the process of making a heim-joint head steady to see if it helps. Everything on the bike is new, and replacing the swing arm bushes and shocks (the only things I did not do on initial assembly) raised the wobble from 70 to 85 MPH.

More places to throw money

One point I failed to make earlier is the front fork springs; they may be as old as you!

The more the front springs sag the less trail you end up with. When your trail gets close to 4 inches you are in Ducati territory without the benefit of a trellis frame and Olins/Marchocci suspension. Ideally you should have a sag figure that is between 25-30% of your suspension travel with your weight onboard.

Progressive has a nice set for under $80 (US) that will give the average weighted rider back the stability at higher speeds. Also watch how much pre-load you crank on to the rear shocks.

As mentioned a few replys back, do check your steering head bearings for a notch. Raise the front end and see if the front end sort of "clicks" into a specific position; this occurs when the bearings have been allowed to get loose and then pound themselves against their races brunnelling the bearing. If your steering heads likes a specific position ("clicks" in) you will have a built in wobble.

I found an OE fork rebuild kit on E-bay for $54, it included bushings, seals and damper rod gaskets. If your sliders are exhibiting lateral play (check with springs removed) please have a look at your bushings. I rebuilt my forks and filled them (5 oz) with 10 weight oil. My intention is to run this light oil so that the bushings can break in gently; when I do the 500 mile service I will replace this oil with 20 weight whilist checking the set of the steering head.

I agree that TT100 Dunlops have no place on a Norton, I was thinking about donating my 30 year old examples to the local pub for wall hangers.

In rebuilding my MK III that I have I had CNW drop the rear tire size to 18 inches, which further adds trail to my front end. They fitted Bridgstone BT 45 "V" rated tires; I expect that my Norton will have longer legs then I do...

Can't say enough about Fork maintenance...Don't forget folks that shocks and springs don't last forever..most Nortons are riding on 35+ year old suspension..Widow Maker stuff!

RS

lotus15racer said:

Hi- I am new to the Norton Commando Forum. My name is Steven Lawrence, am from Alamo, CA. USA. Interests are vintage vehicles of all types. My 1975 Commando has a bad speed wobble. Anytime I let my hands of the bars, it starts. Seems to be so bad I don't really want to let it develop. Stops with hands back on bars. The bike is in generally in good shape, and is original. I have checked the head bearings they seem to have no play . Swing arm pivot also seems OK, and I took some clearance out of the front isolastic. Twin springs above cylinder hear are at 1.5". Any advice on this problem? Something is really wrong, but I can't seem to figure it out. I also have "european" style handle bars- shorter and lower than US spec.
Many thanks!

Click to expand...

I HAD THE SAME PROBLEM WITH MY '71....
CHECKED EVERYTHING, COULDN'T FIND THE PROBLEM, IT CAME OUT ORIGINALLY WITH 4:10's FRONT AND BACK [MORE COST CUTTING BY THE POMS ?] ANYWAY I REPLACED THE 4:10 ON THE FRONT WITH A 3:60 AND HAVEN'T HAD A SHIMMY-SHIMMY-SHAKE-SHAKE SINCE.....

Fit Avon road riders and will behave like a Norton should. :lol:

Tires can make a big difference and often solve the problem. Rake and good springing and control front and rear are also necessary. Of course isolastics, bearing, swing arm buses, etc also have to be good.
On Honda Goldwing and certain BMW models this is often cured by fitting roller neck bearings instead of ball bearings. Roller bearings can give you a bit of the same effect you get from a damper.
I'm not sure how involved it would be to fit roller neck bearing to a Commando. On certain BMW models it is quite difficult to find a working substitute as they are not a common size, same for wing swing arm bearings.
On my old Commando when I got the shakes it was usually cured by new tires, and once by cranking up the Konis on the rear a bit. They must have been sagging a bit at that time as they were easily ten years old.
Have any of you folks fitted roller neck bearing to these old ones? I think both of my Commandos had ball bearings but that was years back.

Hello
I too have the exact same problem, a bad head shake from 80MPH up, however at 50MPH that I can take my hands off the bars without a problem, the bike will track straight with no wobbles.
I have replaced or rebuilt: forks including springs (progressive), rechromed the Tubes, rebushed the sliders etc with 15W oil, new rear shocks (Hagon), tyres (Avon Roadrunners) Iso's to mKIII and rechecked, fitted a Dave Taylor Head Steady (this shifted the woblle up 10MPH), replaced all wheel bearings and neck bearings with tapered Ball & Race, new swing arm bushes and pin. As part of the rebuild I centred lined both wheels through the centre of the crankcases and they were within 1.5mm of straight and perfectly vertical.
Does anyone have an opinion on tyres, I am running a 100/90/19 on the front and a 130/80/18 on the back. I realise the back is slightly over tyred but that was all I could get at the time.
Any help will be greatly appreciated
Tony

Woolant said:

Hello
I too have the exact same problem, a bad head shake from 80MPH up, however at 50MPH that I can take my hands off the bars without a problem, the bike will track straight with no wobbles.
I have replaced or rebuilt: forks including springs (progressive), rechromed the Tubes, rebushed the sliders etc with 15W oil, new rear shocks (Hagon), tyres (Avon Roadrunners) Iso's to mKIII and rechecked, fitted a Dave Taylor Head Steady (this shifted the woblle up 10MPH), replaced all wheel bearings and neck bearings with tapered Ball & Race, new swing arm bushes and pin. As part of the rebuild I centred lined both wheels through the centre of the crankcases and they were within 1.5mm of straight and perfectly vertical.
Does anyone have an opinion on tyres, I am running a 100/90/19 on the front and a 130/80/18 on the back. I realise the back is slightly over tyred but that was all I could get at the time.
Any help will be greatly appreciated
Tony

Click to expand...

Tony, when you switched over the headstock bearings, do you mean tapered rollers? Did you get rid of the spacer? How did you set up the preload? Have you rechecked it after putting some miles on it? It's common for the bearings to settle in and need tightening up.
The engine isn't a good thing to use for alignment because it's not centered in the frame. The backbone is the best bet.
My bike has always been sensitive to tires as far as low speed wobble and high speed weave goes. Inflation and tire profile being the biggest issues. That, or having a lot of weight and a passenger on the back can affect the stability and handling.
The NOC tech section and BritIron archives have quite a bit online if you search 'Commando Wobble'.

Hi Bob
Yes I do mean tapered rollers, it is over a year since I reassembled the bike now, so I am having difficullty remembering the the spacer, however I do not recall installing a spacer, only one way to find out I suppose!!!!!!! Yes I have constantly rechecked the neck bearings and in fact have retightened them a couple of times for the reasons you state. It is a strange one as the bike handles and rides perfectly in every other aspect.
The reason I used the cases was the fact the swing arm mounts on the engine if the cases are not straight in the frame the swing will be off line, in saying this everything measured up very well for vertical and parellel straightness. Baffles me.....
Thanks for replying and I will look up those links you suggested.

Thanks
Tony

When I switched mine I took the spacer out....??

pelican said:

When I switched mine I took the spacer out....??

Click to expand...

Thanks
I'll have to check!!! I'm getting good at getting the forks out!!!!!!!!!!!

Woolant said:

Hello
I too have the exact same problem, a bad head shake from 80MPH up, however at 50MPH that I can take my hands off the bars without a problem, the bike will track straight with no wobbles.
I have replaced or rebuilt: forks including springs (progressive), rechromed the Tubes, rebushed the sliders etc with 15W oil, new rear shocks (Hagon), tyres (Avon Roadrunners) Iso's to mKIII and rechecked, fitted a Dave Taylor Head Steady (this shifted the woblle up 10MPH), replaced all wheel bearings and neck bearings with tapered Ball & Race, new swing arm bushes and pin. As part of the rebuild I centred lined both wheels through the centre of the crankcases and they were within 1.5mm of straight and perfectly vertical.
Does anyone have an opinion on tyres, I am running a 100/90/19 on the front and a 130/80/18 on the back. I realise the back is slightly over tyred but that was all I could get at the time.
Any help will be greatly appreciated
Tony

Click to expand...

I feel like I wrote the above.

I've had a wobble too.

Rebuilt forks with stiff springs, new steering head bearings, good Konis, new AM20s.

Still wobbled but I rationalized it - the swing arm spindle pin tube was loose.

So, last week I welded nuts onto the swing arm spindle pin tube and then had the spindle tube and swing arm bushes reamed to fit a new oversized swing arm spindle pin. Happy with the fix. Now I can crank down the new bolts that go through the nuts to clamp the pin.

Still wobbles.

So, last night, on a level floor, I put the bike/frame on two bike stands, so that both wheels were off the ground and the forks were free to turn. Set up taught strings on some heavy jack stands and established that the thing is straight - at least in the lower 1/3 of each wheel where I was able to get a straight shot of string - the two wheels are in nigh perfect alignment.

I can't say, however, that the wheels are in the same plane - how would you suggest I check that? What method?

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.

Other than a heim joint head steady, ideas?