Chasing a front end wobble

[oldrookie]

Old tires--handlebars wobbled at 45 mph.
New tires--balanced properly, still wobbles, but at 50 mph.

Checked the alignment as best I could and the tires appear to be in alignment, so it looks like steer head bearings are next.

At Griffin's suggestion I bought new steering head bearings a while back. To be honest, I had been hoping to avoid putting them in, but that seems to be the next logical step in getting rid of the wobble.

I don't feel any notchiness in moving the bars slowly side to side. The bars don't seem to self-center. If anything, they seem to move almost too easliy. I also don't feel any play when pulling on the wheel.

I'm going to tighten the stem nut a bit, but I suspect it is a forlorn hope and I'm about to learn more about my bike's steering head.

Any other checks I should run before tearing the bike apart?

Thanks.

 

[redstedman]

Get the frt end up in the air & see if you can move the forks side to side or up & down in the str head. Unequal air and or fork oil can mess up the balance too. Forks too high in the triples will cause too light a footprint on the front also. Always check tire air preasures before riding. A wobble demon is a bad thing.

 

[Dogma]

The stem nut should be tight enough to cause some drag when you turn the bars. How much drag is hard to say. Enough to get rid of the wobble, but not enough to make the bike weave.

If you're not familiar with the steering head, you may need to know that the top triple clamp will need to be loosened to do this. Loosen the pinch bolts and the bolt on the end of the stem (9 on parts fiche). Then you can tighten the nut that tightens the bearings (31). Since you probably don't have the special tool, you can use a punch and a hammer in the notches. The top triple clamp will have some space under it now, so tap it back into place and tighten everything back up (torque wrench on the pinch bolts, until you get the feel for them. You need less than you'd think.).

Take it for a ride and adjust as necessary.

 

[oldrookie]

Thanks. I'll follow up on those suggestions before tearing it totally down.

Truth is, at 27 years old, it needs the whole front end serviced anyway. I've just read horror stories about getting the races out.

 

[trippivot]

front end wobbles often are caused from REAR WHEEL ALIGNMENT and worn out SWING ARM BUSHINGS.

and;

directionally backward installed tires

radial tires on a bike designed for bias ply tires.

mix matched size tires

wrong tire pressure

bent frame, bent fork tube, bent triple tree base ...

 

[RHODESIA SMITH]

hello old rookie,

had exactly the same thing- was the headstock bearings- they tend to make a wave like indentations when they wear. you will not feel it while turning thye handle bars standing still and it is extreamly difficult to feel while riding.

change the bearings- it made a huge difference, and it was not too bad to get the old races out- it is a time consuming job , but can be done with not much do.

there is a procedure in the works manual on adjusting the rear swing arm bearings- - the bearings can come out with o ut having to take the arm out. although i dont think they are the problem you have - more to be with the headstock bearings.

let us know how it goes

 

[oldrookie]

front end wobbles often are caused from REAR WHEEL ALIGNMENT and worn out SWING ARM BUSHINGS.

and;

directionally backward installed tires

radial tires on a bike designed for bias ply tires.

mix matched size tires

wrong tire pressure

bent frame, bent fork tube, bent triple tree base ...

Well, tried to check the rear wheel alignment yesterday.

Tire are new Shinko 230's which are used on a lot similar era GS's.

The tires are OEM sizes.

They are rotating the proper direction. Pressure is good.

So, with the options left...I'm hoping for steering head bearings. Could potentially be the swing arm bearing, or the frame. I know the bike was hit on the right side hard enough to bend the rear brake pedal.

Doesn't act funky before I hit 50. In fact, it rides great and corners very well at lower speeds.

 

[Dogma]

Notched steering bearings cause the bike to weave. Even with the front end off the ground, the notch can be easy to miss.

If a wobble is the fault of the bearings, there's something else going on with them.

If tightening them doesn't fix it, go for the replacement. The procedure doesn't look to be much different from that for a GS. Plenty of folks around have done it (including myself a couple times) and there is more than one thread here on it. You can do it. You already have the parts. It just takes a little time.

 

[oldrookie]

The plan is to replace them.

I did find one video saying that the bearings can be tested by letting the handlebar fall a short distance to one side or the other. If the bars bounce, the bearings are loose.

Anyone able to confirm that test is accurate?

I'm still going to replace mine, but I'd like to know if that test is correct.

 

[Dogma]

Necessary but not sufficient. If they bounce, they are definitely too loose. If they don't bounce, they might need to be a little tighter yet. I've not heard of that test, really. Too tight would be the bike feeling like it's weaving a little at something like 30-40 mph. I'd rather be on the tight side, just short of weaving.

 

[oldrookie]

Thanks, Dogma.

I think I'll try tightening the bearings to see if I can confirm that test, then I'll tear it down and replace them.

Might be useful information at some point.

 

[oldrookie]

I tightened the bearings and the bike was definitely better, but still felt a bit nervous. Not as big a wobble, but not quite happy either.

I then tightened them a bit more and I think I have confirmed that the bearings are toast. There are three or four very distinct notches as I turn the bars from side to side. Can just about feel the bearing dropping into them as the bars are turned.

Okay, good to know that it will likely be worth the learning curve to tear the front end off the bike and wrestle the races into submission.

Now to get the time needed to do the job.

I also think the test mentioned above might have some merit as long as you know the bearings are in good shape. Useful info to tuck away.

 

[oldrookie]

Quick update. Have the front end off the bike. Got the top race out easily, but that bottom one is requiring more patience.

Seems the PO had changed the bearings at some time. The bearings are tapered bearing and not ball bearings.

Several things done to the bike that are on the "recommended upgrades" list for the GR model.

Haven't tried to get the bearing off the steering stem just yet.

 

[oldrookie]

Was beginning to think I was imagining that the bearings were bad. The top race and bearing set was fine.

Finally got the bottom race out this afternoon...and it was clear that the race was heavily scored from the bearings. Had to be replaced.

Used wire cutters to cut the cage around the bearings on the bottom of the stem and got that off. Have to get the rest of the race off the stem and then I can begin the assault on installing new bearings.

Progress, slow, but progress.

 

[oldrookie]

Got the race off a couple of days ago. Bwringer came by tonight and put the new bearings on and set up the front end to check the brake drag I mentioned earlier. His help and educational assistance greatly appreciated.

Hooked up enough wiring so it would start up for the first time in a couple of weeks. Sounds good...still.

Next to remount the headlight, hook up the speedo and tach cables. Should be able to ride it sometime tomorrow. Hoping the wobble is gone.

Spending the morning watching my son run cross country..then to the bike work.

 

[BassCliff]

Hi,

That sounds like progress! Yes, that Brian is a heck of a nice guy. A handsome fellow too.

So let's get a picture of you riding that GS step-child tomorrow.


Thank you for your indulgence,

BassCliff

 

[oldrookie]

Well, some joy, but not total joy. Still something causing a shake at about 50. A lot better than it was, so now on the next most likely cause.

Rear alignment?
Swing arm bearings?
Disc brake? (Brian did note that the disc has some issues.)

Who knows? At least I know the headstock bearings are not the cause.

 

[TheCafeKid]

Check the swinger bearings, shock bushings, wheel bearings.
Also, sans a runout gauge, a quick and dirty way of seeing disc warp is to wrap a long, thick zip tie around the fork leg and then trim the excess off so that the tip *just* touches the brake disc. Spin the wheel slowly, if the disc grabs the zip tie, or the gap between the two grows, you know your disc has some warp going.
I've read it both ways, many people say a disc can cause wobble, but with it being a single axle, I just don't see how it can. But, check it anyway.
You said the bike was hit, and if hard enough to bend stuff, I'd seriously consider trying to find out if the frame and or steering neck angle have been tweaked. Rake and trail changes can cause some instability. But even a slightly tweaked frame can make a bike feel really really funky.

If you know the forks are fine, and there is no bind anywhere in them (something else to check,) and your discs are fine, and the bearings are fine, the rear end is the likely cause. Like suspension issues, usually what you feel in the front, is caused by something wrong in the rear.
For example, over or under damping in the rear shocks can translate to a feeling in the bars of wander or wiggle when cornering.

I'm not familiar with the tempter model, but you may ask around to see if this perhaps is also a common trait due to frame geometry. Many bikes of the modern era suffer from headshake due to short wheelbases and steep fork angles. Then again, many of those bikes are fixed with steering dampers from the factory. A by-product of sharp steering angles designed to quicken and lighten steering feel sometimes is higher speed instability.

 

[oldrookie]

Thanks for advice. Brian checked the forks pretty carefully last night and checked the wheel bearings a short time ago. Can see the disc has a slight warp and is dragging a bit at times.

Will start with the alignment. I may have messed up the alignment when I reinstalled the rear wheel after a tire change, but it had a wobble before the tire were changed.

The Tempter has a pretty relaxed steering head geometry.

 

[bwringer]

The brake disc is definitely significantly bent, probably from recent tire extraction efforts. The fork tubes and the triples are straight and in great shape. The steering stops were unmarked, so although the bike was definitely dropped in the past, it wasn't run into a tree or anything. Just by eye, I'd say runout is at least .5mm and close to 1mm -- pretty significant.

The rims have a wee bit of wobble to them, as do all spoked wheels, but I've seen much worse that hasn't caused issues. No broken spokes.

There are still a few things to check, but I'm guessing it's the bent brake disk -- just thinking this through, 50 mph seems to me the point where the wheel would be spinning fast enough where the rotor whacking the pads would cause some odd effects... fortunately, I have some GS850 discs lying around, and they're the same part number. :dancing:

The rear suspension is a monoshock, so we'll double-check all the various bushings, bearings, and linkages as well. Swingarm bearings could also cause issues.