High speed wobble problem ?????

My 06 SD developed a high speed wobble just over a year ago. It kicks in at around 115-125mph and is totally uncontrollable. Shade will vouch for how mad it looks as when it kicks in and he's following me, he drops back 100yrds just in case Here is what I have tried to do to get rid of it.

I first noticed it after swapping my top yoke for a nice black one that Bic very generously gave me. My thought was the head bearings had been released and were possibly shot as she had done nearly 32k miles and London speed humps must be murder on them. I didn't actually get that fixed for a while though and waited till the autumn and at the same time got my forks rebuilt by MCT and the SDR shock that I had bought in August had developed a oil leak and went back to Redline for a rebuild. Bike was put back together and the problem appeared to have been cured.

Recently it has come back again. I really noticed it after fitting a new Power Pure fron to replace my totally worn Racetec. I'm thinking the sharp profile of the tyre showed the problem up again. I decided to swap back the top yoke as just perhaps there is a problem with the one Bic gave me. Went to undo the top nut to find it just finger tight instead of the 25nm it's supposed to be. So I swap it back and torque up to correct setting and head out up A1. Hit 110 and off she wobbles Bugger!

So I swap yoke back again and repack the bearings and again this makes things a bit better but it's still there. If I give the slightest input at high speed into the bars I can make it wobble like mad.

Had a new Power Pure fitted on the rear and while there got the guys in tyre shop to see if head bearings, wheel bearing and swing arm bearings felt ok. they said they could feel no play. I though perhaps running around with head not torqued up properly might have fooked bearings again. I had also been doing a few stoppies

Next I decide to push the forks down through the yokes so rather than 2mm showing they are now 2mm recessed into the yoke. I thought this might help as the rear was raised with the SDR shock. Also the front end has felt a little like she may wash out mid corner especially since the SDR shock went in. I thought it might help with this. I did fear she wouldn't steer as quickly but after taking her out today for a fast Finchingfield blast with Shade I found the steering was just as good and in fact the front end feels far more stable while cornering, allowing me to push a bit harder without the feeling the front end might wash out. Unfortunately although it has made the front end more stable and did tone down the wobble a tad its still there and kicks in at the slightest imperfection in the road at 115-120. i can hit 130 if the road is perfect and keeping a firm grip with legs and light grip with hands helps a little but it's not perfect. I worry about taking her on track like this. Last thing i want is a buddy getting past me because I have to back off at 120-ish

I have checked suspension setting as they are as she was setup by MCT. The SDR shock wasn't in her then but I got Big Ash's settings off him and they were very close to my own. I will next try setting everything to standard and see if that makes any difference. After that I'm at a loss and will probably have to take it to MCT and get him to rag it down the road and see what he thinks. (he managed to melt my rear when he took it out after setting up suspension came back with big grin saying "she's got some grip on the rear!" I wish I could push her that hard )

Any suggestions guys are most welcome as I'm kinda scratching my head here as to what is causing the problem. I have also changed both wheels to my spares and that makes no difference.

This hapens every time I change her showes ...stops after riding and working the tyres for a while...

Mate you've covered most things. I can only suggest you string line your wheels, other than that front wheel balance or tyre problem .

I have had loads of bikes that wobble at speed but that has usually been because they were crap. The only one I had that was good and then started doing it was a GPZ550. Much head scratching but it turned out the the damping in each fork was different. That bike used a pnumatic element in the damping arrangements and the pressures were different on either side. Once equalised order was restored. I mention this as the symtoms were the same as you describe, is there any chance you have unballanced damping with left and right forks adjusted differently? Just a thought.

I was thinking tyres until the last sentence...just today I had to replace my new Power pure front tyre with another because it wobbled on me at 90mph....and it hops around 30 mph's...Defect tyre..grrrrrr

wow same problem here but mine is around 170kph (australia). on an 06

so to try and fix the problem, i re-checked all the forks, steering bearings and got the tyre and wheel balanced, that was unsuccesful so i got a scotts steering dampner, it is up to its hardest settings but the wobble is still there.

so the solution to my problem is hopefully in the rear tyre, how you ask... im looking for a lower profile rear tyre as that will change the shallow steering angle of my o6 and lengthen the whole bike, i belive its the trail that i am changing.


if that fails im going to stringline the whole bike.

what do you think?

Could I suggest new head bearings (not just re packed), wheel bearings, new swingarm bushes, check all pinch bolts are correctly torqued... Then if it persists, check all welds on frame for cracks. However, you went from a bike with the steepest steering angle, then made it even steeper with the ser shock.

So ofcourse it is going to be less stable again... If u don't have a steering dampener, I suggest that too. If the bike wobbles so much it suggests that there is some play somewhere within the chassis

High speed front wheel silliness usually has more to do with rear suspension settings than anything else. Does the wobble only happen under acceleration ? What about when you back off the throttle ?

Your suspension guy says the bike has a lot of rear wheel grip. You say lengthening the wheel base (pushing the forks down through the triples) gave you more front end feel. Sounds to me like too much suspension bias to the rear. I would try stiffening up the rear to prevent squat under acceleration.

Other than that, is the front tyre showing signs of abnormal wear. If so, check your fork oil weight and level.

I'd be looking at putting the stock rear shock back on the bike (at least as a trial) to see if the problem persists. Simple, quick and effective at either eliminating the problem or eliminating the rear-end from the list.

John

If you're having problems with your front wheel, simply wheelie everywhere. Job done

Problem was there with original shock and SDR shock. I pushed the forks down into yokes as an experiment to see if it helped this and to see if it made the front feel less like it may wash out while cranked right over. Def worked on the second count.

It is there on acceleration and steady throttle after 115-ish mph. Other people have suggested the rear being the issue. I'm going to play with suspension this weekend. Set back to standard and then set it nice and stiff and see if makes a difference.

Will check frame for cracks although I'd be gutted if it was. Part of me is thinking its the head bearings again. Do you think running around with them only tightened to finger tight for possibly a few months could cause serious bad wearing? If nothing else helps I'm going to have to change them again.

A few suggestions once you have checked all the basics:

As you mentioned you have very good rear grip which I guess is under Power? this suggests possibly too much rear weight transfer,

Have you checked your rear loaded sag? your forks could be topping out under power which will certainly cause the problem you are having,

maybe too much rear sag and not enough on the front?

Secondly Chain tension, as you have a longer rear shock the swing arm angle will be steeper, the standard chain tension maybe too tight? the chain could be locking up the rear suspension which again will cause severe instability...

I always decide the chain tension on modified bike by compressing the suspension to get the rear wheel spindle inline with the front sprocket nut and allowing 25mm chain slack at that point, then release the tension and check again, note down the total chain slack for future adjustments,
You only need to do this once and once done you know you are getting the chain tension spot on (I never trust manuals as they are written by failable humans beings!)

Last and what I think it is
Tyres....... There are a few bikes with steep steering head angles that are so close to instability that the wrong tyre choice can push you over the edge (TL1000s, Early R1s, 16inch front wheel Blades and 05,06 SDs)
I have personal experience of pointy Michelin tyres transforming the first 3 into slappy monsters! changing back to a rounder profile tyre, Metzelers/Pirellis etc with no other changes and stability restored, basically a fast steering bike does not need pointy tyres to speed up the steering any further
Another thing; you may find that you need slightly lower pressures in Pointy tyres, try dropping a couple of PSI front and rear, see if there is any improvement

Personally I would only use Michelin tyres for burning GATSOs

Great post Russ

Ok just had a chat with a buddy who is a mechanic. When I repacked the head bearings recently he suggested tightening up and then over tighten to about 35nm. Then have a feel before slackening off again and retighten to correct 25nm torque. At the time I did this it all felt very notchy when over tightened. I thought this was just because it was over tightened. Seems this should not be the case and it should have just felt tight if anything. If the head bearings are shot again this would make sense as my problems all started when I originally changed the top yoke and the bearings were obviously released. Not even sure I properly torqued the head up again on that occasion was my first time changing a yoke and I didn't realise the bearings would be released in this way. My bad and lesson learned. On that occasion the bearing were indeed shot and I had them changed. Repacking them this time did help a bit but didn't get rid of the wobble completely.

I will check everything else of course but this is what I'm leaning towards now. Hopefully its just the lower bearing as he said this is the one that takes all the stick. The speed humps in London are a fooking joke they really are, not only in size but distance apart. In my road they are every 60 odd meters

Thanks for all the input guys. I will check things people have suggested. The only thing that changed when this first started was the top yoke thing though. This wobble is exactly the same as that one was. Fingers crossed it's that.

hi ..had the same thing when i first got my 05.....head shake just as you describe...i cured mine when i set up the static sag.......the rear shock was set up for a heavier rider than myself and i needed to loose quite a lot of pre load to get it right...just thinkin that the extra ride height given by the sdr shock is maybe causing a similar problem in your bike ...that is lessening the trail with the resultant loss of stability at high speeds......just a thought..the good set up is in there somewhere..this is such a great bike with genuine adjustability..the pay off for that is that you can get it wrong..good luck.....peace

I am going to check suspension but the original problem started 4 months before I bought SDR shock. This is exactly the same problem as then and then it was head bearings. I'm only looking at £35 in bearings so not the end of the world. Will check sags again as well as setting everything back to standard.If neither fix the problem though and I'm going to start panicing

I thought the torque rating was 12nm for the steering head bolt

your right it is 12nm

If you over torque the steering head bearings during installation you stand a chance of ruining them by dimpling the race surface. This will creat notchiness and I would presume the possibility of some sort of stability issues due to front not being able to center (id caster back to center) smoothly.