Front end wobble
 

I have '95 3AJ and it is having a bit of problem with a wagging front end at times. Any suggestions of things to try would be very welcome.

When driving on the freeway, mostly above 60mph/100kph it will start to wobble when switching lanes or entering a turn, usually more of a problem when accelerating/on the gas. Wobble is rather slow, 2 to 3 cycles per second. I have done a few things to the bike but the problem has been there since I got it.

Bike has 6600 miles. I have put in Progressive (brand) springs, the sag is ok. springs are stiffer than stock.
Fresh fork oil, Bel-Ray 10wt. Flushed forks well when changing oil but did not take them apart. oil level set per manual.
Telefix fork brace, (follows road grooves less, still wobbles).
Stock rear shock, spring rate is ok, damping is barely there at all.
New Avon Gripsters on both ends. 30 and 33psi (2bar and 2.2bar)
Cleaned and adjusted head bearings per manual. Bearings look good, no notchy feel.

What might be causing the wobble? Any and all suggestions and ideas will be welcome.

Forschmiedt, try to check and retight wheel spokes.
AnteK

yes, check also the rims and the front wheel bearings

mika

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Its not the windsock effect from the high mud guard is it?

Thanks for the suggestions, these all seem like simple things to check. Keep 'em coming!

I'm a big guy at about 275lbs (125kg). Could a worn out rear shock make the front end feel loose like that?

AnteK, The wheel spins straight and true. Could the spokes be evenly loose all around? I will see if I can find how to check for proper tension.

Mika, I checked rims and bearings before, but will double check.

simmo, I have recently replaced the stock fender with a smaller Acerbis supermoto fender. I will try a bit of street riding with no front fender and see if it acts differently. If that makes a big difference, maybe a low fender is in order for street duty.

It's the oil. SAE10 is good for new forks. Try SAE15 or better still 15W20.

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Fred, XTZ660, Holland.

Hello
I had the same problem as you on my 3AJ.
One mechanic and only one, made miracles to my bike, the one I recomended on repair shops around the world, though I guess its unusefull for you cause you're not from France, anyway, here's the possibilitys:

-frame bend in an accident(low probability on a 3AJ, this mechanic had never seen one during all his 30 year long career, and he had serviced quite some machines..)
Though he had seen bend steering axles/fork holders, they will deform if accident and save frame! Control it by placing the lower holder on a perfectly flat surface, there should be no play.
Look under low bearing for play on any side meaning axle is not straight.
Start by checking your steering ends for signs of any smash, if no sign, forgett the rest.

-Spokes unequally tightened making rim wobble left/right(high probability!)
You can't visually see it and only a pro will know where to screw, 0,5 mm makes wonders.

-Steering head bearing play adjustement(high probability), the bolt should only be tightened 0,7 kg.
/or worn bearings!!

-Fork alignement, make sure both are exactly
on the same level in holders, or untight screws a little, with wheel axle tightened, pump up/down, align and tight screws starting on low holder.

-Your tyres(All cross shaped tyres wobble a little on road, example T63)

-Rim equilibration, gyro effect, do you have a gripster?

-Oil level, 10W is a bit thin on road, 15W is recomended.

-Wheel bearings.

Good luck,

Matt



[This message has been edited by Matt595 (edited 20 September 2005).]

On other bikes this kind of thing is mostly caused by weaker farmes in combination with too much tyre pressure and high windscreens fi.
Now, owning a 3AJ and never had this kind of thing, and driving with hgher tha standard pressures I would start checking the bolts between engine and frame. They tend too loosen making the whole structure weaker. There's 3 on top, 4 low in front, 1 main axle rear suspension, 1 below that behind the engine.

easy check, quick to do. Retorque to factory setting.

Auke

[QUOTE]Originally posted by Forschmiedt:
[B]I have '95 3AJ and it is having a bit of problem with a wagging front end at times. Any suggestions of things to try would be very welcome. <snip>

New Avon Gripsters on both ends. 30 and 33psi (2bar and 2.2bar) <snip>

That sounds way to high.Try 20psi and 22psi
Thats what they're ment to be.
hope that helps

bnai




[This message has been edited by bnai (edited 22 September 2005).]

Lots of good excuses to spend time in the garage. Much more enjoyable way to spend evenings than the couch and TV.

I will try the tires at different pressures and see how it feels. I asked Avon what they suggested for the tires on my bike but I didn't really like his answer. He said street bike tires should run at 33 and 36psi. Generic answer for a not-very-generic "street" bike.

2,0 bar front and 2,2 bar rear is definitely good. Don't lower.
1995 3AJ? I thought they stopped in 1991?


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Fred, XTZ660, Holland.

You're probably right, Fred. That number caught my eye on the left side bottom of the barrel and stuck in my brain. 3UY perhaps?

I know I have seen information on how to identify what model it is but don't recall now where.

Follow-up;

I've checked most of the things suggested.

Lowering tire pressure made handling worse. I'll leave it at 2 and 2.2bar for street duty.

The rim was a bit more out of true than I had thought, about 1.5 to 2mm wobble at worst, and has a shallow dent, maybe 1mm deep over 100mm. A few spoke were a bit on the loose side also. Fortunately the bike has seen little dirt and was stored inside so there is no rust and the nipples all turn.

I spent a bit of time tensioning the spokes and getting the rim a bit closer to true. I now have it down to about 0.5mm at the worst spot. It's not really much harder than trueing a bicycle wheel, just bigger.

Not perfect but a noticeable improvement. I think I'll spend a bit more time tweeking spokes for now and probably have the wheel rebuilt with a nice alloy rim for next summer.

its a long while since I had a yamaha, but I don't suppose its any different to the tunes I've played with Honda set ups. it sounds like you have a bad ratio of front to rear spring rate and damping.

you've pointed to all the right bits:
- lets face it, you're a big bloke on a pretty pedestrian bike
- you've changed the front spring (generally, I wouldn't do that) and you've got thin oil at the front. I'd go with the 15W
- you've got no damping at the back (regardless of the sag) so the wobble from an oversprung(?) front doesn't dissipate at the back

for your weight, I wouldn't stiffen the front, but I would increase the damping front and rear and increase the rear spring rate 25% by fitting a new spring to a new (better damped) shock. you essentially need to raise the rear and lower the front to allow for 125kg

in my view, tyres, rims etc only add fractions to a rear-end-heavy, underdamped crock. over tightened steering bearings and loose other bearings/spokes etc won't help, but I reckon you've got a bigger problem rather than a whole heap of minor things

Yes, start with the basic settingts of the springs and dampings. See www.ohlins.com for this.

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Fred, XTZ660, Holland.

I changed the spring because of the horrible brake dive with the stocker. I haven't tried heavier oil yet as I've over-spent my toy budget for a bit, bike expenses may have to wait until after x-mas, I'm afraid. I was hoping to try anything free or cheap first.

You mention lowering the front. Is lowering the front (raising the fork tubes) worth anything in your opinion?

A new shock is absolutely in the plan for the bike. I figured the lack of damping was not helping. I have found three brands available here in the states; Ohlins ($700.00), Works ($550.00), and Hagon ($375.00 and $50.00 for heavier spring). I have had Ohlins and Works on other bikes and would own either again except for the cost. Since I recently bought my home I am heading towards the Hagon unless I hear their quality is not up to snuff.

I remember myself having the same wobbling problem and trying to solve it all through front end, but at the end it showed itself as a misalignment of chain and sprockets at the rear. Check if your chain stretch is changing in one turn, and if so, check the alignment and rear wheel bearings.

a. can ozcan
i o n i a

My 3AJ(s) both wobble a little at speed - especially loaded up. Check your steering head bearings.

Having said that, my 2 cents is to look to the rear end - problems at the rear tend to manifest themselves as front end handling issues. Your lack of damping in the rear shock may be the cause...

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Barry
3AJ Tenere

Yes, the next thing I buy for the bike will be a new shock. Unfortunately, this will have to wait until the new year.

Just Harden A Lot The Rear Spring And Put About 0,5cm Up The Forks

I cant comment on the Hagon for the XT600, but when the rear OEM shock on my last R100GS headed south I bought one. I was financially challenged at the time, which I would say is the only reason for buying one.

Re wobble, whenever its happened to me its been (in order of frequency):
- tyre pressure
- knackered tyre
- tired forks (oil and springs)

Again not XT specific, but I dont think it needs to be, Im also a robust 100kg plus fellow. Encouraged to hear of similar people on XTs.

bob

it is rear weak problem

Tip - if the front wobbles, it's the back end - if the back wobbles, it's the front
 

your initial post said it all - no damping in the rear shock. And you're a big bloke.

Tip - if the front wobbles, it's the back end - if the back wobbles, it's the front end. usually...

My suggestion -
time for a decent rear shock. AND the heavier springs in front considering your size are a good idea. Slightly heavier oil in the front, same amount.

Well the posts seem to all be going in the direction of replacing the rear shock, and I agree. I hope you find the funds to do it soon. I have 2 personal experiences with behavior similar to what was described in the original post. First was caused by Givi cases mounted too far back on the bike, and the absurdly soft and underdamped stock suspension on the Suzuki Bandit 600. Second was on a racetrack on a YZF600R at 140mph. This was repeatable lap after lap in the same place on the track. 2 clicks harder on the rear rebound damping adjustment was the difference between some wiggle and no wiggle. These may be different circumstances and different bikes, but I think the causes of wobble are the same with any motorcycle - baring any mechanical problem, it seems to go back to the rear shock being the primary culprit, with a spring that is too soft and/or rebound damping that is too weak. I guess the theory is that with the rear end bouncing around the castor angle is always changing, and that castor angle is one of the fundamental things that makes a bike balance itself.

What's interesting about bikes is even though they can be so unstable with the wrong setup, they are amazingly stable with a decent setup. I can't count the number of times I've experience some road hazard that destabilized the bike and then felt the bike recover from a big wobble in less than a second or two, even at really high speeds like those on a race track - as long as one keeps their arms relaxed and lets the bike's geometry do its thing. Well that's my slightly philosophical thought for the day.

Good luck fixing your problem.