Chasing a front end wobble

[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.

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.

[oldrookie]

The brake disc is definitely significantly bent, probably from recent tire extraction efforts. .

That seems entirely likely. What I learned from that process was that I have a LOT to learn about changing tires.

[oldrookie]

Just reset the axle nut this afternoon. I had it below the torque settings in the manual when I put it back together yesterday afternoon. Taking a short run as soon as the rain lets up a bit. (No rain gear yet.)

[oldrookie]

Bwringer came by last night and took the bike for a run. He's pretty sure what I am feeling is the warped disc.

He also pointed out that the rubber bushings under the handlebars are shot and are probably amplifying what I am feeling.

Big thank you out to Bwringer for going the extra mile (or ten) to check the bike out.

[pete]

I can't believe I haven't replied to this yet!

Glad to see you're making progress, and also great to see more forum member awesomeness from BWringer too

[oldrookie]

Hi Pete!

S'alright, haven't had time to check on how your paint job it going either!

He had it up beyond where I've backed off and didn't feel anything he'd consider a problem. I am greatly relieved.

Felt bad that it started raining (some lightning involved) just before he headed home. Great, Universe, help a guy out and get rained on.

Did help him get his bike sold, so did get to offer some small measure of payback for his help.

Front wheel off again tonight with start on replacing the bent disc. (Never let me change a tire again.)

[pete]

Hi Pete!

S'alright, haven't had time to check on how your paint job it going either!

He had it up beyond where I've backed off and doesn't feel anything he'd consider a problem. I am greatly relieved.

Felt bad that it started raining (some lightening involved) just before he headed home. Great, Universe, help a guy out and get rained on.

Did help him get his bike sold, so did get to offer some small measure of payback for his help.

Front wheel off again tonight with start on replacing the bent disc. (Never let me change a tire again.)

That's alright mate, it's progressing very slowly because of incorrect materials used

I wanted to follow this in case I had similar issues once mine finally hits the road...

I need a new front disc too actually, but haven't gotten that far yet.

Hopefully that sorts it for you and you can ride straight and just enjoy it

[oldrookie]

That's alright mate, it's progressing very slowly because of incorrect materials used

I wanted to follow this in case I had similar issues once mine finally hits the road...

I need a new front disc too actually, but haven't gotten that far yet.

Hopefully that sorts it for you and you can ride straight and just enjoy it

Me too!

Have to fix a leaking condensation line in the basement tonight and all I really want to is work on the bike.

[pete]

Me too!

Have to fix a leaking condensation line in the basement tonight and all I really want to is work on the bike.

Isn't that always the way? We'll get there eventually

[old_chopper]

Kind of late to reply but a tip to make removing the races a WHOLE lot is easier; weld a solid bead around the inside of the race where the bearing rides. When the weld cools it contracts and shrinks the race, usually it will fall out. Obviously it's no good to reuse but you wouldn't need to remove it if it was still serviceable.

[oldrookie]

Saw that technique discussed, but I don't have a welder. Had to do it the old fashioned way...ask someone for help.