Front wheel wobble between 50 -30mph, ideas?

[deefer]

Evening all,

Wondering if anyone can advise on common causes for head shake /shimmy/wobble on the xj900s? I have been trying to diagnose it trying various things:

Replaced headrace bearings with new tapered ones

Replaced both front and back tyres (Michelin pr3)

All tyre pressures fine

Replace oil in forks

Upped the rear shock preload to number 5 or 6

Add extra preload to the front forks

Fitted new front discs (old ones had some runout/warp which I thought might be causing the issue)

Replaced front wheel bearings and checked rear.

Checked and cleaned the rear shock linkage bearings


Nothing seems to have fixed the issue, and it's ruining my ride as half my daily cut mite is around 40mph! The problem only started to occur when I replaced the head bearings, but I suspect that was coincidence as the old bearings were worn & they had a groove that the steering settled in.

Any help would be appreciated as it's currently detracting from my enjoyment of this otherwise nice bike.

[neilmud Lord Protector]

All D900s have a wobble at 40MPH but at its worst a light hand on the bars will stop it CD has put an explanation why on here somewhere, for mine tyre wear & pressure was the main culprit but it did let me know when to check pressure , top boxes & panniers can also make it worse & I think someone here found swing arm bearings solved theirs for what you have done already I would suspect headrace bearings or try different tyre pressures.

Neil

BTW you have spent a lot when all you needed to do was take off the top box but I guess you needed that to bring the bits home

[bobh]

Since it only started after you replaced the head bearings, that's got to be the main suspect. Taper rollers are good, but they create more friction than balls and the preload needs to be set up just right. Also, unless you've re-checked and reset (if necessary) the preload after they've settled down they could now be a tad too loose.

There was a discussion on here some time ago about the "locknut" under the top yoke. Basically, Haynes (if you're working to that) has got it wrong - the upper of the two thin castellated nuts, which he refers to as a locknut, is actually just there to prevent the preload (set by the lower castellated nut) increasing when the top dome nut is tightened down onto the yoke - hence the rubber washer, which allows the upper nut to move axially without affecting the lower one.

Some other bikes (e.g. Suzuki) don't have this feature and getting the preload right involves lots of trial and error, which clever Mr Yamaha has eliminated by using this cunning arrangement. It's actually the dome nut that locks up the whole assembly and prevents the lower nuts loosening off, so it's important that that's torqued up correctly.

[deefer]

Evening chaps,

Thanks for the replies, I should note that I haven't changed all that stuff because of the head shake, but I thought I'd list what I had done to the bike.

I.e. I got a rear puncture and the front was quite low anyway so I changed the tyres, the front disc was warped when I bought the bike so I bought new ones and got the front wheel bearings free from my dad and the previous owner hadn't changed the fork oil in 30k miles so as you can imagine it wasn't doing much when I go the bike!

In terms of setting the right free play on the head bearings, assuming I have the front wheel off the ground, what should I be aiming for in terms of looseness?

[deefer]

Also am I Correct in thinking. 36psi front, 42psi rear? I'm running Michelin pilot road 3

[bobh]

Jan 29, 2014 23:22:13 GMT deefer said:

In terms of setting the right free play on the head bearings, assuming I have the front wheel off the ground, what should I be aiming for in terms of looseness?

(Waits for CD or someone else to shoot me down, but) You need a small amount of preload, so that when the front suspension is fully loaded (i.e. on full bump) the bearings will still be in contact top and bottom. I'd say you need to look for them to feel as though they're just very slightly binding, so that a push with a finger end on the side of the front tyre will turn the steering easily, but it won't then flop all the way over. Particularly if you've just changed the bearings to taper roller and put plenty of grease in there, you would expect the movement to feel fairly well "damped".

Of course, if you still have brake pipes and speedo cable etc. connected this will restrict the movement as well, so it's a bit of a judgement call as to how much effect they're having.

The make and type of tyres do have an effect on steering wobble - different manufacturers use different profiles - but there doesn't seem to be a consensus as to which are best. In terms of pressures, I think most stick to 36/42, though some have experimented with higher pressures in the rear.

The main factor that seems to come through in all discussion (and there has been plenty over the years) on steering wobble is the top box - take it off and it usually disappears, or at least becomes minimal.

Good luck - Bob

[Longway]

I find when I've got new tyres fitted there's no wobble at all, but as the front wears the wobble gradually appears

[CD]

As Bob says, set the steering bearings as loose as possible with no slack, then tighten it a little more without making the steering feel stiff. If the new bearings were fitted too tight they might have become knotched which counter-intuitively will cause steering wobble. Ride the bike and recheck. Sometimes the steering can go slack before everything settles down.

A way to test for knotched bearings is to loosen the head race until it rattles a little and ride the bike. Ignore the clunks of course. If the wobbles stop you have worn/damaged bearings.

All bikes however will do a gentle wiggle. Divvies do it around 40mph. Tractor Hardleys between 20 and 30. Sports bikes up to 60 mph. It should stop purely with the rider's hands on the bars and never get into a wobbling vibration.

[deefer]

Evening gents,

Re-earthing an older thread, the head shake issue remains and I have been trying various things to improve the situation. I have a feeling that the problem is caused by a lack of weight at the front of the bike and the heavy shaft drive etc at the back.

I was wondereing if anyone has dropped the forks through the yokes a bit to bring the front down? I was thinking it would move a bit more weight over the front and may help stead the front wheel?

Thoughts?

[m40man]

Jan 21, 2015 23:02:07 GMT deefer said:

I was wondereing if anyone has dropped the forks through the yokes a bit to bring the front down? I was thinking it would move a bit more weight over the front and may help stead the front wheel?

That would quicken the steering a bit & be likely to actually exacerbate the weave / wobble problem, so I don't think it's your answer, sorry.

With hands on the bars, I presume you're not not feeling much / getting any wobbling?

Do you carry everything including the kitchen sink in a top box? That certainly makes any wobble worse, if so.

When on the centrestand, check that if you try to lift the rear wheel, you can't feel any play in the rear shock linkage. (Re-reading your first post, I see you checked the linkage - so if this included leaning over the saddle, arms each side, trying to 'yoink' up the wheel, feeling for any play, ignore this . )

[davy]

I have never experienced this wobble on my D9 I wonder if this is due to the stiffer forks as it has always had extra fork oil to stop it being too bouncy. It now also has a longer rear shock from a fazer but was smooth and wobble free before this was fitted. Might be worth adding a few cc's of fork oil as an experiment.

[bev]

Jan 22, 2015 7:34:16 GMT davy said:

I have never experienced this wobble on my D9 I wonder if this is due to the stiffer forks as it has always had extra fork oil to stop it being too bouncy. It now also has a longer rear shock from a fazer but was smooth and wobble free before this was fitted. Might be worth adding a few cc's of fork oil as an experiment.

When I got the D9 I put in 15w fork oil and experimented with slightly higher levels of oil. Syringed some in and out to see what the difference would be, I always thought the standard fork was too soft, you can go too far with that though. I also added pre-load by inserting metal Disks, it's not got pre-load adjusters, removed that after a while and left the 15w slightly over filled. Worked for me.