Cornering Wobble...why?

Easterntide · May 12, 2014, 07:37:40 AM

Had a fantastic albiet tiring 300km back-country solo tour yesterday. As i'm upgrading bits and pieces, other bits and pieces show their weakness. Its my 2nd week on my 91 fj12 and i'm getting more and more comfortable with each ride. Yesterday on the twisties i was really noticing the wobble in the corners.
What is the cause of that? is it shock linkage or the yamaha oem shock itself? my tire pressure is spot on. Tires are new (battleaxe's). not even riding aggressively compared to a more experienced rider.

is the wobble actually dangerous or is just an annoyance?

Had a bmw shock on route but apparently it got lost in transit, the company came good immediate and reimbursed me (well done!!!). While i would prefer an RPM plug and play shock i'm too cheap at the moment...so i'm hunting another bmw shock down now.

Don

magge52 · May 12, 2014, 09:00:26 AM

Don, congrats on the new FJ. I just bought a 92 myself. Great bike so far after about 250 miles. Your wobble could be coming from the front or rear suspensions. The front could be loose/worn steering head bearings, clapped out fork oil or just the soft front suspension. The stock legs have a lot of initial dive on braking and can cause a weave or wobble mid-corner especially over any bumps. I found there are preload adjustments for the forks but stiffening up mine hasn't done much to help. The rear shock can cause the same symptoms if rebound damping is weak. Haven't done any mods to mine yet but a suspension upgrades from RPM are right at the top of the list along with brake upgrades. hth

George

Easterntide · May 12, 2014, 03:13:19 PM

But is it dangerous or is it used as an indicator of 'don't go any faster'?

I
My first and cheapest option will be to drain the existing Fork oil and possibly get new springs...or valves. Not sure which is better bang for buck.
Then the BMW shock/new doglegs.

FJ_Hooligan · May 12, 2014, 04:06:28 PM

As I was dialing in my rear shock I expereinced a rear waggle when accelerating out of corners until I got the rebound damping cranked up enough. A few more clicks of rebound damping tamed everything down.

red · May 12, 2014, 04:21:13 PM

Quote from: Easterntide on May 12, 2014, 07:37:40 AMYesterday on the twisties i was really noticing the wobble in the corners.
What is the cause of that? is it shock linkage or the yamaha oem shock itself? my tire pressure is spot on. Tires are new (battleaxe's). not even riding aggressively compared to a more experienced rider. is the wobble actually dangerous or is just an annoyance?
Don

Don,

Are the tires balanced? Put the bike up on the centerstand.
Rotate the rear tire slowly and watch where the tire meets the rim. There is a line on the tire, very close to the rim. If this line wanders away from the rim someplace, the tire could be mounted slightly off-center in one spot, giving a "bulge" there.
Put a screwdriver on something solid (concrete block, brick, et c.) very close to the rim, and rotate the tire rapidly. With the screwdriver tip very close to the rim, you will see if the rim is bent.
Grab the top and bottom of the rear wheel and apply some side forces, to see if the swingarm has any play or looseness.
Raise the front wheel. Check the front tire for a mounting "bulge" as you did on the rear tire.
Check the front rim for any bends, with the screwdriver trick.
Turn the handlebars from side to side. Check for any excess looseness, and for any "notchiness" or "detents" in the steering.
Put the wheels on the ground. Sit on the bike, hold the front brake firmly, and see if the bike frame can be moved forward and back, causing the steering head bearings to wobble up and down.

Beyond these checks, then maybe it is time for fork maintenance, or a new rear shock, but check the other stuff first.

While you are making improvements, consider adding a front fork brace. This is not a fix for any problems found, but it is usually an improvement, even on a good stock set-up.
If the steering head bearings are bad, you could replace them with tapered bearings, making a big improvement there for little extra cost.
I would consider a wobble in turns as dangerous, and definitely worth fixing.

Cheers,
Red

Country Joe · May 12, 2014, 05:15:57 PM

Quote from: Easterntide on May 12, 2014, 07:37:40 AM
Had a fantastic albiet tiring 300km back-country solo tour yesterday. As i'm upgrading bits and pieces, other bits and pieces show their weakness. Its my 2nd week on my 91 fj12 and i'm getting more and more comfortable with each ride. Yesterday on the twisties i was really noticing the wobble in the corners.
What is the cause of that? is it shock linkage or the yamaha oem shock itself? my tire pressure is spot on. Tires are new (battleaxe's). not even riding aggressively compared to a more experienced rider.

is the wobble actually dangerous or is just an annoyance?

Had a bmw shock on route but apparently it got lost in transit, the company came good immediate and reimbursed me (well done!!!). While i would prefer an RPM plug and play shock i'm too cheap at the moment...so i'm hunting another bmw shock down now.

Don

Don,
I tried an R1200RS shock on my 1990 FJ. I mounted it up, built new dogbones to get my rear ride height about 1" higher than stock. I found the spring rate marginal for one up riding I was (210 lbs. geared up at the time) and completely unrideable 2 up. It ground the midpipe on a V&H pipe at nearly any lean angle. I will sell you the shock, without the hydraulic preload adjuster, (I am using it on the Honda Goldwing GL 1800 shock that I currently have on the bike). If you are very light, it may work for you, I didn't work for me.

Also, check out the items the other guys have mentioned. Even with the ragged out rear OEM shock, I experienced very little wobbling in corners, just some pogoing.
Joe

Easterntide · May 12, 2014, 07:12:18 PM

Locally a person is selling a BMW f650gs from a 2000 model year. Good value if it would work.

Easterntide · May 15, 2014, 01:14:36 PM

Going to follow Joes advice and hunt now for late model GL1800 rear shock. fingers crossed and all that....

fj johnnie · May 15, 2014, 04:02:56 PM

About ten years ago I had a similar thing with a 90. At highway speed it would gently rock back and forth. It seemed as though the pivot point of the rocking was above my head. Weirdest thing I have ever experienced on a bike. Long sweepers at high speed, 120 - 160 k range. Never got worse. I just thought it was my tires. Check swing arm and suspension linkage bearings as well. Many people ride around with pooched swing arm bearings.

Country Joe · May 15, 2014, 06:14:17 PM

johnnie,
That sounds like the behavior of many of the motorcycles of the 60s and 70s. Bombing through high speed sweepers would bring out a low frequency, high amplitude weave. Felt like there was a hinge in the frame of the bike between the seat and gas tank. I'll never forget the first time I experienced it, I was on my Dad's Suzuki GS 750. His Triumph Bonneville would do it on occasion as well.
My FJ has never hinted at doing the weave, I would be checking out all the things that have already been mentioned.
Joe

Easterntide · May 21, 2014, 01:23:38 PM

So.
Fork seals ordered and new headset bearings. i've pushed and pulled on the rear wheel while on center stand and could not perceive any movement. Tire pressure is correct and tires are mounted straight and true.
Also have a new GL1800 shock on its way.
will push pull on the front wheel elevated tonight just cause.... hoping its as simple as a loose front end.

Taking it to a local mech for the bearings/seals and will get him to give it a look though at that time as well.

Easterntide · May 23, 2014, 06:30:55 AM

Had the bike on the center stand last night to install SS clutch cable. after pushing it off the center stand i felt a significant thud up front. put it back up and checked ..sure enough the front end had fore/aft play that was due to a loose steering adjustment. As I've said I've got the new bits on order (early next week) but in the meantime i may see if i can snug up the existing bearings.
I've downloaded the microfiche showing the parts but are there any specifics i need to know about making adjustments and what tools are needed to tighten up the lock nuts?
tried doing a search for steering and bearings but nothing much came up...

Easterntide · May 23, 2014, 04:23:39 PM

Amazing how much just tightening the steering bearings makes it feel like a completely new ride!!!
F'n hell! It's hard to know what's wrong if it's a new thing and particularly if your doing this all solo. Thankfully lots of cats here are kind enough to step in and add value.
Much happier person tonight :-)

Country Joe · May 23, 2014, 05:44:39 PM

red · May 23, 2014, 07:58:30 PM

Quote from: Easterntide on May 23, 2014, 04:23:39 PMAmazing how much just tightening the steering bearings makes it feel like a completely new ride!!!
F'n hell! It's hard to know what's wrong if it's a new thing and particularly if your doing this all solo. Thankfully lots of cats here are kind enough to step in and add value.
Much happier person tonight :-)

Easterntide,

At least the fix is in sight, and it will get there soon. Now, this next part is really tough . . . I doubt that the steering head just got somewhat unscrewed lately. It is more likely that a few of the bearings got shattered, and the pieces are still close by, looking to make trouble. You have the good parts coming, so the best plan for now is to stay off the bike, until the steering head is cleaned out and the repairs are made. Even a small metal chip in there can lock the steering, and that never ends well. You can bet big on this issue, but the payout will be very small, and to me, it's just not worth the risk. Live to ride another day. All IMHO, of course.

Cheers,
Red

News:

Cornering Wobble...why?