front end wobble at 80mph

Hello all, I recently bought a 73 Commando, its it great condition runs great with awesome torch looks cool and I am super happy. I have an issue however with the ride.
When I am on the highway my norton will start doing the cha cha at about 80 mph and i have to let her slow down and she will stop around 70mph... then I can cruise stable at 70 - 75. but if I go up over 80 it gets hairy again... whats the possible cause? Any suggestions what I need to do. Are any of you guys using fork stabilizers on yours? I need top speed!

Expatcommando said:

Hello all, I recently bought a 73 Commando, its it great condition runs great with awesome torch looks cool and I am super happy. I have an issue however with the ride.
When I am on the highway my norton will start doing the cha cha at about 80 mph and i have to let her slow down and she will stop around 70mph... then I can cruise stable at 70 - 75. but if I go up over 80 it gets hairy again... whats the possible cause? Any suggestions what I need to do. Are any of you guys using fork stabilizers on yours? I need top speed!

Click to expand...

TIre balanced?

Wheel true?

Fork oil in forks?

Could be anything from front tire patch to rear tire patch with lots of stuff in between. Suspect tire profile wear and air balance between f/r, shoot for 2-3 lb lower in front. Fork striction like say rusted up springs in stanchions might amplify other things like loose swing arm buses to worn out clutch wobbling gear box bushes that can then jostle back into cradle isolastics. A good C'do does not have a top speed handling limit in bee lines as the land speeders have assured me more than once. Double check rear hub and dummy axle are stable.

I'll definitely start with new tires, the ones I got with the bike are wrong, the previous owner put an oversized Honda tire on the back wheel... perhaps thats the cause... hope so...
Thanks for the help!

One more question... the back brake is a bit weak in its stoping power, do you think that is normal? I don't want to lock up the back wheel but need some help on the front brakes sometimes, we have alot of bad drivers here in Norway!

Expatcommando said:

I'll definitely start with new tires, the ones I got with the bike are wrong, the previous owner put an oversized Honda tire on the back wheel... perhaps thats the cause... hope so...
Thanks for the help!

One more question... the back brake is a bit weak in its stoping power, do you think that is normal? I don't want to lock up the back wheel but need some help on the front brakes sometimes, we have alot of bad drivers here in Norway!

Click to expand...

Back brake worthless? Perfectly normal. Get an updated master cylinder for the front and you'll be fine.

Expatcommando said:

I'll definitely start with new tires, the ones I got with the bike are wrong, the previous owner put an oversized Honda tire on the back wheel... perhaps thats the cause... hope so...
Thanks for the help!

One more question... the back brake is a bit weak in its stoping power, do you think that is normal? I don't want to lock up the back wheel but need some help on the front brakes sometimes, we have alot of bad drivers here in Norway!

Click to expand...

Properly setup (which it isn't in 99% of commando's) you should be able to lockup the rear brake with modest effort.

'Vintage brake can get you better pads, and if you like they can completely setup the rear to work very well

http://www.vintagebrake.com/products.htm

You can get back brake to point its a bit grabby to lock up, which I like. Much clean up the surfaces w/o solvent, detergent and/or sanding, best crossways to the motion and adj the cable for slight drag or you will have to stomp and stand on brake to get much action. Check rear drum for heating after a short ride to make sure not dragging too much.

I've got both the resleeved and factory front m/c and now think most the benefit of resleeves is that they all remove the factory tiny pin hole restrictor in the end of the big rubber boot inside. i ran a cherry hot nail through mine, like 6 penny or over 1/8" OD. ABS like over 40 but need some caution back off or locks up below that, perfect to me.

One neat trick with a rear that's easy to lock up is to lock it up going 30-ish and drift diagonally to side of road to park steering just like in a parking lot up right.

If you are dumb enough to use trail braking, that is braking while leaned instead of all of it bolt upright, and front snaps out from under- you can stab the rear and hi side up to get bolt upright straight, then use front again as its mean too. You are talking Norway aren't ya, I'm talking Ozarks and all this can matter suddenly out the blue.

Its the rubber hinge!

Rubber hinge only shows up on braking when front locked up a few yards to bike lengths and in held powered sweepers it'll creep up one ya but still some reserves left if you have your wits about you and don't screw up with much trail braking leaned.

Expatcommando said:

Hello all, I recently bought a 73 Commando, its it great condition runs great with awesome torch looks cool and I am super happy. I have an issue however with the ride.
When I am on the highway my norton will start doing the cha cha at about 80 mph and i have to let her slow down and she will stop around 70mph... then I can cruise stable at 70 - 75. but if I go up over 80 it gets hairy again... whats the possible cause? Any suggestions what I need to do. Are any of you guys using fork stabilizers on yours? I need top speed!

Click to expand...

Tires, tire pressure, alignment, isolastics and headsteady all work together and all should be addressed to make the ride stable.

Tires, tire pressure, alignment, isolastics and headsteady all work together and all should be addressed to make the ride stable.[/quote]

I agree. Here in California we have rain grooves on the hiways which play havoc with stability.
But yeah, what he said.
It's K81's for me thank you very much

Having only one rear view mirror or a rubber mudflap on the front mudguard can cause instability at speed.

So canm a bruised sidewall / delaminateing . finger on sidewall spinning tyre or good examination for bubble .

The Dreaded Isolastiques . Adjustments . vou le vous . Er . There Is A Procedure , wher For Starters . You get the sucker CENTRAL .
Throw all the gookey bits ( friction washers ) out , and shims .
Measure the TOTAL clearance at the rear , at one side , with the powertrain levered over . Pry Bar . CAREFULLY . No Hammers !
Then the other side , rear .
for starters .

Then at Ea position , You check the side gap at the front , with the ' consumables ' out .

What ' WE ' are trying to do , is see if it will take EQUAL shims Ea side, Both ends . We need a pencil & a piece of paper here .For the Arithmatic .
The idea is If Everything Is Straight . ! The shim width will be the same ( within a gnats D... ) Ea . Side . Then Ea Third reshim , do the right too .
To keep it neutral .Check the thrust washers are the same thickness too . Thats what they Are , Side Thrust washers .
The Check above will let you know if sombodys been bouncining it off the kerbs , Chevy Novas , or fitted a side car .
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Indeed , made for TT100s or V c V . The old Jap ' Nylon ' ones wernt trusted in the wet. Differant story now im told . See if you can get American TT100 ' R 's with the
flash caseing . Solo a lot ( of Poms) prefered 3:60 19 front , with the 4:10/25 rear . Or for getting dramatic , your better with a 4:25 18 rear & 4:10 front .
Or a 327 compound 3:00 19 KR76 front , with either rear , if ones ' obtainable ' ( the hard compound , of three , was Sh.t )

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Set as above , you should be able to run the iso's at 3 or 4 thou , + or - 1/2 though .Id found no hinge evident when set under 5 thou. Just the light frame in evidance
when you were stupid enough to change up on the overrun , haveing got it down to 80 for a sweeper . A gentle rock / rock / rock (3) That was @ 5 thou.
Set the bitch to 2 after that , took a few runs of 10 miles out and back to free off the extra 1/2 thou tight . Didnt break anything though , took it easy till it was all
ISO lated Again .

Intresting going round a off camber right into a stop onto a main road in the rain and cold , keeping a bit of throttle on , with the front brake for etc , shed understeer front , overster rear .

Expatcommando said:

Hello all, I recently bought a 73 Commando, its it great condition runs great with awesome torch looks cool and I am super happy. I have an issue however with the ride.
When I am on the highway my norton will start doing the cha cha at about 80 mph and i have to let her slow down and she will stop around 70mph... then I can cruise stable at 70 - 75. but if I go up over 80 it gets hairy again... whats the possible cause? Any suggestions what I need to do. Are any of you guys using fork stabilizers on yours? I need top speed!

Click to expand...

First thing to do is get wheel balance properly checked................

Actaully, the FIRST thing to check is whether your SPOKES are properly tightened.

...and it's FREE!

Just chock up one wheel at a time, then go from one spoke to the next (starting at the air valve), tapping them with a screwdriver. They should all produce a very similar tone "tink".

Any "thunk" indicates a loose spoke.

http://www.google.com/url?sa=t&source=w ... jg&cad=rja

This is a good video on the general topic of wobble and weave. Longwinded though.

http://www.google.com/url?sa=t&source=w ... eA&cad=rja

This is an explanation of the physics along with an animation that shows what's going on. It's unusual to have wobble at 80mph, that's normally weave. There is a school of thought that steering dampers only work for headshake and can make both wobble and weave worse.

A link type headsteady really is a good place to start with to improve handling, after you've cleared all the usual culprits; loose swingarm, headstock bearings, worn or improperly inflated tires, shot iso's, ect.

rpatton said:

http://www.google.com/url?sa=t&source=web&cd=1&sqi=2&ved=0CBoQtwIwAA&url=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DfvsDIq3WwVA&rct=j&q=wobble%20and%20weave%20%20youtube&ei=j_uBTtC2L8XYiALYvLWODQ&usg=AFQjCNEMBx-Hzc5_pxi6sufTQSV_-pbfjg&cad=rja

This is a good video on the general topic of wobble and weave. Longwinded though.

http://www.google.com/url?sa=t&source=w ... eA&cad=rja

This is an explanation of the physics along with an animation that shows what's going on. It's unusual to have wobble at 80mph, that's normally weave. There is a school of thought that steering dampers only work for headshake and can make both wobble and weave worse.

A link type headsteady really is a good place to start with to improve handling, after you've cleared all the usual culprits; loose swingarm, headstock bearings, worn or improperly inflated tires, shot iso's, ect.

Click to expand...

According to the 2nd link it is indeed a weave thatr I feel affects my norton.... I thank you all for your imput and will look carefully at the culprits you have directed me to.

It's a puzzle to me, I've got the weave but I can tame it by sliding my weight/butt to the rear. If my weight is forward it provokes the weave. I suspect it is related to overwidth tires but that doesn't explain anything. Playing with air pressure helps too but I haven't been diligent enough to find the right pressure combination and even if I did, it wouldn't explain why either. Good point about one mirror.

Postby dave M » Sun Sep 25, 2011 10:56 pm
Having only one rear view mirror or a rubber mudflap on the front mudguard can cause instability at speed.

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Ugh good point, I'd over looked a lost mirror or the mud flap. Even if imbalanced aerodynamics are not the cause of the webble wobbles it sure can trigger it off or just plain faster magnify the upset. I have had my jacket flapping or wrapper/cover of luggage get loose or long asymmetric things like a 2 ft chainsaw sticking out to make air eddies oscillations that'd trigger off my 1st un-restored C'do following traffic, but a fully fettered C'do will only feel this the same as any wind gusts ie: a wiggling that don't upset lines or handling or confidence.

A link type headsteady really is a good place to start with to improve handling, after you've cleared all the usual culprits; loose swingarm, headstock bearings, worn or improperly inflated tires, shot iso's, ect.

Click to expand...

Amend to the various links Bob but not that many are installed world wide and a C'do w/o links should feel quite secure and steady up to quite thrilling speeds and corner loads.

Those were wonderful URL's on weave and wobble references, especially the very last race video example of weave/wobble combined. I'm always amazed how bikes can self correct after spitting the pilot off or even with pilot still hanging on then climbing back on to finally grab bars to carry on, even with a messed seat. In that cyclic video the bike repeatedly saves a low side by automatic straight steer into the lean direction then as lean and rear are about to flip a hi side the other way so does the forks, sorta like a sail boom does in a tack change. There is a lot of gold to mine in almost crashed video's.

I think that's what you sense on your linked C'do that's stable enough to let it fall into a turn so doesn't need fork effort to do so, just relaxed dampening the innate fork wobble.

There is a check list for isolastic vibe adjustment that goes by car lights patterns in mirrors after dark, but the list does not cover the wevil wobbles. There is no diagnostic test other than plain checking-replacing-adjusting > loose/wore/missing/bent/tight items from tire patch to tire patch. That can even include the gearbox innards effect on clutch basket loose wobble and chain slack flop.

So we all await the last shoe on your weaving centipede to drop...