Possible Cause Of The Front End "Cunk"

[pliskin]

There have been a few members, including myself, that have reported a "clunk" coming somewhere from the front end during slow speed travel. I have pretty much torn my whole front end apart looking for the problem. I did not remove the forks.

Do a search on "fork stiction"
Basically it's an improperly aligned front end causing excessive friction between the rubber seals and shock tubes. I'm almost positive this is the annoying sound/problem I have. Extreme cases can cause the tubes not to slide at all. I've had this happen on a rear shock before (not on the GS).
Here is a write-up explaining alignment tuning. Some of it does not pertain to a GS.
http://vmaxoutlaw.com/tech/fork_stiction_tuning.htm

[ohgood]

There have been a few members, including myself, that have reported a "clunk" coming somewhere from the front end during slow speed travel. I have pretty much torn my whole front end apart looking for the problem. I did not remove the forks.

Do a search on "fork stiction"
Basically it's an improperly aligned front end causing excessive friction between the rubber seals and shock tubes. I'm almost positive this is the annoying sound/problem I have. Extreme cases can cause the tubes not to slide at all. I've had this happen on a rear shock before (not on the GS).
Here is a write-up explaining alignment tuning. Some of it does not pertain to a GS.
http://vmaxoutlaw.com/tech/fork_stiction_tuning.htm

id bet on loose stem bearings and or wheel bearings. jack the bike and start pulling on things, like fork tubes, bars, etc with the forks at full lock left/right.

stiction is something I've seen on mtnbikes, but never motorcycles, unless someone really messed up a tire change. looseing all the triples and the axle, then bouncing the front end may do it for you.

[pliskin]

I've been over every moving part. I've removed every piece from the front including brake caliper, gauges, faring, fender. I even put net springs in. Everything is tight. Bearings are all good and tight. It's been doing is since I got the bike with 4k miles on it. Stiction on motorcycles is quite well documented. One study found 1 in 5 new bikes came from the factory with front end out of spec(machined and cast parts not in spec either). Just not as noticeable on motorcycle as it is on a mt bike. I've experienced it on my mt bike before and it's easy to feel because it's so light.

I am going to be loosening up the tripples and axle and do what you said. I read that helps in some cases.

[Janx101]

i dunno even what stiction is...  and im too lazy to read the link...

and im NOT saying it ISNT that...

but.. is there a bearing in the frame to yoke join?.... that could be wearing... not a radial wear point... but a perpendicular? movement/wearpoint? ..

probably just me trying to imagine impossible stuff again,... and then try to describe it... 

[ohgood]

I've been over every moving part. I've removed every piece from the front including brake caliper, gauges, faring, fender. I even put net springs in. Everything is tight. Bearings are all good and tight. It's been doing is since I got the bike with 4k miles on it. Stiction on motorcycles is quite well documented. One study found 1 in 5 new bikes came from the factory with front end out of spec(machined and cast parts not in spec either). Just not as noticeable on motorcycle as it is on a mt bike. I've experienced it on my mt bike before and it's easy to feel because it's so light.

I am going to be loosening up the tripples and axle and do what you said. I read that helps in some cases.

if the axle is over tightened, or bent, it will stress the stanchions and put the sliders in a bind. more pressure will be needed to overcome it, but once moving, it moves fairly freely. just like you said.


having one weak spring, or one fork higher in the triples will cause stiction.

a broken spring... ewww


could even have a cracked frame or broken bolt at the lower joint. lots of things to check.

how's the swingarm pivots ?

[adidasguy]

Does the clunk happen when going over a bump? I used to get that all the time going into parking lots that had a small bump. Forks bottoming out. New springs and never had it happen ever again.

[BockinBboy]

I've posted about this before too... I noted awhile back that I thought it was sticktion, but I don't think I added my fix.  But it was indeed fork seal stiction!  I pushed the rubber dust caps upward (not the actual seal) and wiped down the fork lightly with fork oil... kept it very clean while doing this... then slid the dust cap back down in place and wiped the top area same way, lightly with fork oil.  Sound has been gone since.  But my seal caps aren't looking too good, and I'll probably have to replace them and the seals soon.  The dust caps are slightly cracking around the edges from dryness; however, the oil did help them along in that regard as well since they aren't working so hard against dry metal anymore.

- Bboy

[bombsquad83]

I think I had the same noise for a while after a fork seal replacement.  It make a lot of sense.  It's gone now after I replaced one fork that was causing seals to leak soon after replacement.

I think this procedure is really interesting.  If I ever seem like I'm having these issues again I'm going to do this.

STEP THREE: ALIGNMENT TUNING

Assemble the fork, leaving out the oil and springs and the wheel and fender. Very lightly snug the triple clamps. Bolt in the axle, tightening it in its clamps without the wheel. Pay close attention to the axle clamps (those arrows go forward - tighten the front nuts first), using normal torque. Now raise this axle /slider assembly all the way to the top of its travel and let it go.



Does it drop to the bottom of its travel unaided? If it doesn't budge, you've got some serious binding somewhere. If it's just a little slow, remove the axle, loosen one of the damper rod's allen bolts (either one), turn the slider 90 degrees, retighten the bolt, replace the axle and try the drop test again. Repeat as necessary, tuning one or both damper rods, until you achieve maximum "drop speed." Take your time. Next, tap the top of one of the fork tubes with a soft mallet to move the tube downward in its clamps a smidge (0.010"-0.020") and try the drop test again. If there's no change, tap some more. If still no change, raise the slider/axle assembly all the way to the top of its travel and tap on the bottom of the leg upward, which will move the tube upward in its clamp, and check with the drop test again. Try with the other leg also. Do you see what we're doing? We're hunting for the best alignment. Because of manufacturing tolerances, the best internal alignment may very well occur when one of the fork tubes is incrementally higher than the other. Say 0.050"-0.080". That's okay. It's far more import- ant to align the fork's parts internally, than it is to worry about what they look like on the outside. Just remember to fully tighten the triple clamp bolts when finished. At this point, try the front fender. Install it and do the drop test. Don't let the fender influence fork movement. Reshape its inner bracket, shim between the fender and the sliders--what- ever it takes to get the same drop speed with and without it. Stiction tuning makes a world of difference. Be sure to do all of the steps in order.

"Whoa...this is a lot of work!" you say. Doesn't the proverbial 'Loosen the parts and pump the fork until it squares up' routine work as good?" Actually, compared to this procedure, that's whistling in the dark!