Motorcycle Safety & Driveability: driveability, fork, suspension

Question
Pat,
I changed my '83 shadow 500's fork seals this weekend (still didn't stop the leak but that's a different question).  This mornings commute was fine until I decelerated down a hill at 30mph.  I felt a slight wobble that was quite unsettling. The road was dry but the wobble made it felt like the bike wasn't gripping the road.  I pulled over, everything was tight.  

You mentioned in a previous post about the forks needing alignment.  How can they be out of alignment (not parallel) if the forks are held at three places (the triple tree fork clamp, the fork clamp 8" below it, and the fork brace just above the fender? Your previous post stated using a pane of glass to determine alignment.  I'll do that but, given they do need aligning, how do I adjust it?  I see no means of adjustment for this. Wouldn't a fork have to have a slight bend for the un-parallel effect?  Again, the wobble wasn't there before the oil seal replacement (i.e. took the forks off and on).

Answer
More from my tech: P.S. On the bike issue...if he can bounce up and down on the bike when he is sitting at a stand still it's not the forks binding...have him check to make sure he didn't change the geometry [put the forks back in at a different height] when he put them back on and check all of his bolts to make sure none are loose...a loose axel pinch bolt can cause a hole slue of handling problems.

From my tech: The two might be related...but it is more likley there is another problem.  Did the bike work OK before the work was done?  As to the leaking...what type of seals did he put in, and how much fluid?  If he used decent seals, and didn't grossly overfill them he may have damaged them while installing...a worse cause could be that the fork tubes are pitted badly and no ammount of seal replacement is going to fix them.

Good luck in your repairs!

Pat

Forks go out of alignment when the bike is involved in a crash. Sometimes you can't tell until you ride it. It could be that the triple is tweaked or one of the fork legs is tweaked. The solution is replacement, though sometimes people bend them back with success.

But this is unlikely to be your problem if it wasn't a crash that led you to replace your fork seals!

I'm consulting my fork expert for additional help (I will follow up again if I learn anything.) I think the wobble and the fact that the forks are still leaking are related.

Suspension systems like fork tubes are designed to absorb irregularities in the road, riding inputs like steering and braking, and keep the tire's contact patch in contact with the ground at all times. They do this by using a combination of spring pressure, hydraulics, and valves to regulate the rate at which the suspension moves. If the suspension is not working properly, the tires have to absorb road irregularities, rider inputs, etc. They're only meant to flex a little, to carry the bike's "unsprung" (unsuspended) weight.

So, it sounds like there is something broken, assembled wrong, or you missed a step in your fork seal replacement. It's causing the forks to not work properly, and loading the bejeezus out of your front tire, which is making it skip and hop and wobble.

Imagine if you'd just used two steel tubes, rather than fork legs, to connect your front wheel to your triple--the tire would have to do all the work. (Or think about this from the opposite perspective: if there were no oil in the forks, and no valves or shims, and the springs were allowed to move in complete freedom, you'd have the opposite effect: your front end would pogo up and down like basketball being dribbled.

It is likely something that is keeping your fork spring(s) from moving freely, or something that is causing a hydraulic lock of the oil--maybe a valve or shim or shim stack installed incorrectly? Something's binding up.

Remove the forks, and try to compress them manually--put one end on the ground and try to shove it in and out. One fork will likely be a great deal more difficult to move than the other, or both of them will be stuck.Trace back your steps, see what's causing the forks to still leak, and you'll probably have your answer.

I am not much of a mechanic so I can only give you theory here. I have a friend who is a terrific mechanic and very good with forks and I've asked him to send me his thoughts on the matter. I'll let you know if he has some advice.

Pat