Bike feels a little squirrelly - diff. fork oil levels?

[bryan]

I replaced forks and springs on my bike after a minor collision bent the tubes slightly. The forks I bought were supposedly zero-mile rebuilds, but it was clear they weren't when they arrived. I drained thoroughly and put in the same volume of fluid in each (about 10 ml below spec since not everything drained).

I when for a ride last night and noticed it didn't feel quite as stable over parallel ridges or groves in the road. At one point, I hit something (too dark to see) getting into an exit lane that felt like it jerked my bars to the left a bit. I don't know whether it was a severe imperfection in the road or my bike.

Could this be mismatched fork oil heights? The forks feel fine otherwise. Is there something else that could cause this?

My bike had a fork brace previously. I haven't installed the new one I ordered. Would lack of a fork brace make the bike feel so weird if I was used to the additional rigidity/stability it provides? Keep in mind the feeling of the bike over ridges is actually pretty subtle, but it's a noticeable difference to its behavior prior to the work.

Thanks in advance for any words of wisdom. Needless to say the bike is garaged until I figure this out.

[Nessism]

I don't think it's the fork oil unless there is a drastic difference in height. My guess is that you got used to the feel of the forks with the brace and now you don't have it.

[tkent02]

My bike had a fork brace previously. I haven't installed the new one I ordered. Would lack of a fork brace make the bike feel so weird if I was used to the additional rigidity/stability it provides? Keep in mind the feeling of the bike over ridges is actually pretty subtle, but it's a noticeable difference to its behavior prior to the work.

Thanks in advance for any words of wisdom. Needless to say the bike is garaged until I figure this out.

The missing brace would be my guess, if you are used to one and it's not there you will feel the difference. If you bring the fork oil up to the correct level on both sides, you will know that is not the problem.
Volume means nothing, it's the volume of air above the oil that must be the same. Search, there are directions for adjusting fork oil level.

[bryan]

Thanks, guys. I'll try the brace tonight.

It almost has to be the problem. I don't think the fork oil levels could possibly be off enough to make it feel differently. I followed advice from threads here. We'll see what happens.

[Guest]

If it's the 1100, I would have to disagree that just the absence of the brace would affect the handling so significantly. Even stock, the bike should never feel unstable or 'squirrely' unless you are really pushing it to it's limits. Go over the oil levels, along with ensuring that preload and dampening adjusters are set the same on both legs. Check too, the steering for bearing play, and the front tire pressure as well.
As you know, the stock 1100 has a metal brace of sorts, that runs under the front fender....in my own case, adding an aftermarket brace did improver the rigidity of the front end, but not to a huge degree..... most noticeable is the difference when the front end is loaded, like taking downward-spiral ramps at speed etc....the bike tracks more precisely. But even without it, the bike never felt 'squirrely'.
Tony.

[almarconi]

I drained thoroughly and put in the same volume of fluid in each (about 10 ml below spec since not everything drained).

Putting in equal volumes of oil is not enough that is why an oil height is specified. Measure the height of the oil.

You said you were involved in a "minor collision". Did you verify that the rest of the bike is straight. Maybe your wheel was tweaked as well.

[KEITH KRAUSE]

Hard to say if it was involved in a collision.
The bike shouldn't feel funny just because of no brace. Double check your assembly. Make sure the forks are in line with each other by loosening the axle holders and front fender and pumping the forks a few times. Then re-tighten things uniformly. Check the steering bearing play with the bike on the centerstand. Should be just a bit of drag when you turn the bars side to side. Tire pressure correct? Maybe you just missed a basic procedure.
Using a brace is fine but the lack of a brace shouldn't result in your problem.

[trippivot]

1 did you align the fork tubes on the axle ? ( this is a step not many people know)
2 twist the tubes in the trees to verify the lower tree did not get tweaked?
3 did you tighten the front end from
a top down
b bottom up
c just did a random tightening technique?

4 mis aligned rear wheel will make your bike "feel" weird too.
5 is the wheel still "true" and without any "hop"
6 you might need to string the wheels/chassis to check the frame neck did not get twisted a bit

[bonanzadave]

Check the steering bearing play with the bike on the centerstand.

Check too, the steering for bearing play

Is it possible when he loosened the fork pinch bolts that it unloaded the steering stem bearing torque ? Id check that, as suggested, first.

[bryan]

The bike definitely feels better with the brace. Squirrelly was probably not the best adjective - just not as "confidence inspiring." I went back in daylight and checked the spot in the road near the exit ramp where I felt the scary feedback and there was a long, deep groove I hit about the width of a tire. Hitting it would have been startling regardless of whether or not the bike was performing perfectly.

HOWEVER, I definitely have other issues. I've replaced the wheel, forks, triple tree (head bearings while I was at it). I tightened from the top down. Dampening is the same on both forks. I checked oil level with a doll rod, with obviously isn't an exact method, but I don't think it could be too far off.

I rode no handed. The bike seemed to track straight. But a couple of times, with no hands on the bars, they started to wobble from side to side (like a bent wheel). With hands on the bars, everything seems normal. But when off and starting to slow down, it gets wobbly.

I fear the worst: bent frame. I'll retrace all steps. Eyeballing the alignment of the front and rear with a board it looks okay, but that's not very scientific.

I can't believe it could be the frame. It was at such a low speed, and the bike didn't even tip all the way over. But I know it's possible. Ugh.

[bonanzadave]

Tire pressure correct?

Or is the front tire getting worn ? When you torqued the head bearings were the fork pinch bolts loose. You cant draw the top and bottom trees together if they are tight on the forks.

Those hands off wobbly bars scream head bearings.

Im voting Tire (even if its brand new) or head bearings. BTDT.

[bryan]

Man, I'm hoping you're right that it's something that simple. The tire is virtually brand new and aired to spec. Head bearings are also new. However, I need to retrace my steps on installation.

Could something as simple as an unbalanced wheel do this? Or would I feel that all of the time?

Thanks for the help and listening. I wrecked the bike in the most enormously idiotic way, and I don't want to do something even dumber with a dangerous repair. Once my bruised pride heals I'll share the wreck story. Too soon

[79 sh850]

Putting in equal volumes of oil is not enough that is why an oil height is specified. Measure the height of the oil.

This has never made any sense to me so long as the forks aren't connected and are mechanically identical. How can putting the same volume of oil in not result in the same oil height in a bike like mine (a 79 850) where the forks are identical and are independent of one another? If someone could please explain I would be grateful since I have sincerely always wondered.

[Steve]

This has never made any sense to me so long as the forks aren't connected and are mechanically identical. How can putting the same volume of oil in not result in the same oil height in a bike like mine (a 79 850) where the forks are identical and are independent of one another? If someone could please explain I would be grateful since I have sincerely always wondered.

It does not happen so much in the GS bikes, but in other bikes, they may have an anti-dive mechanism in one fork only. That mechanism will take up some space, so it takes less fluid to bring the oil to the same level.

The reason the level needs to be the same was hinted at by tkent. It's the volume of air over the oil that really needs to be the same. As the forks compress, the air becomes a stiffer spring. With different oil levels, the two fork tubes will have different spring rates, which can make for some interesting situations. The manuals call for no more than 1 mm difference. Personally, I don't think most of us would notice as much as 5 or even 10 mm difference, but you have to draw the line somewhere.

.
.

[atb1998]

sounds like either a slightly tweaked wheel or possibly a bad tire. Had the same problem on a couple of other bikes. Both times turned out to be a tire. Figured it out after replacing or checking EVERYTHING else on the front end. What sucks is one of the tires was only 6 months old. Had it replaced under warranty