fork clunk

Information on forks/springers/shocks
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jiggs
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Joined: Tue Apr 03, 2012 7:35 pm
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fork clunk

#1

Post by jiggs » Wed Apr 25, 2012 11:52 pm

hey, guys new to this site and think it is outstanding. i checked the knowledge base and found alot about fork clunk.but nothing about my situation: 49 oem front end with 6" over tubes . sliders have brand new bushings everthing redone using nos. rake and trail are correct, bike sits level. using 30# fork oil. have bad clunk -bumps, railroad tracks etc. no steeringhead issues.do i need to add more fluid for extended tubes? any suggestions?



1950Panhead
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Re: fork clunk

#2

Post by 1950Panhead » Thu Apr 26, 2012 12:39 am

Is the clunk on the compression stroke or the decompression stroke?
Do the sliders move rapidly in either direction when you hit a bump?
If you have the correct amount of fork oil there are two possibilities,
the hydraulic valves are not working correctly or even with a stock panhead in certain road conditions the sliders will go to the bottom and clunk.
Jerry

jiggs
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Re: fork clunk

#3

Post by jiggs » Thu Apr 26, 2012 12:55 am

clunk is on decompression...so use amount of oil as spec in manual?

Hog54
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1980 Lowrider

Re: fork clunk

#4

Post by Hog54 » Thu Apr 26, 2012 1:19 am

They all clunk when extended.Thats why the newer fronts ends have an extra little rebound spring on them to stop it.But the newer springs dont fit in the old front ends.



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awander
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'64 FLH

Re: fork clunk

#5

Post by awander » Thu Apr 26, 2012 4:31 am

I wouldn't think the bike could sit level with +6" fork tubes....

jiggs
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Re: fork clunk

#6

Post by jiggs » Thu Apr 26, 2012 4:58 am

the neck is raked at the proper angle for 6"tubes, in fact in the old days this was considered a mild extention. look in a pauhco cataloge they make springers up 12"over. i have several stock bikes, but ilike my choppers too. :roll:

jiggs
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Re: fork clunk

#7

Post by jiggs » Thu Apr 26, 2012 5:30 am

jerry and hog54 thanks for the info.

tomfiii
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Re: fork clunk

#8

Post by tomfiii » Sun Apr 29, 2012 12:55 am

If you are using a 6" spacer it will be too long sometimes you have to trim it down to 5-5 1/2 as you kick out front end it needs less spring pressure then stock rake.

jiggs
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Re: fork clunk

#9

Post by jiggs » Sun Apr 29, 2012 5:28 am

i never thought of that,makes since, thanks

jiggs
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Re: fork clunk

#10

Post by jiggs » Sun Apr 29, 2012 6:00 am

awander: thanks for the reply but it has nothing to do with my question.

panfreak
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Re: fork clunk

#11

Post by panfreak » Tue May 01, 2012 9:31 pm

I had an issue with mine clunking on rebound and added more fork oil; no more problem. Part of me wants to say 11oz, but I honestly can't remember.

panhead george
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Re: fork clunk

#12

Post by panhead george » Thu Nov 15, 2012 1:29 am

Just one thing in regards to the spacer. If the spacer is under tension when you screw the cap on then that is considered preloading the spring. The more preload you have the stiffer the initial part of the travel will be and the harsher the ride will be over small ripples and bumps. If you cut the preload spacer say 1/2" or a 1" then the fork will drop an additional 1/2" or a 1" when you let the bike off the stand. This will lower the bike however much you cut off the preload spacer but it can also top out violently if you were to get the front wheel off the ground due to the spring having no tension on it. What you have is a topping out condition when the fork is on the rebound (up) stroke. A heavier oil would slow the rebound but it would also increase the compression (down) stroke also making the fork stiffer thru the entire stroke. If you extended the fork by 6" that allowed for more air space at the top of the fork so you are correct in needing to add oil to compensate for that extra air space. There is a good chance that the fork may have cavitation due to not having enough oil.If you went to a heavier oil to slow the rebound (up) damping then you would have to possibly weld up your damping rod holes, the ones at the bottom of the damping rod, these control the speed of the compression (down) stroke so the fork would not be too stiff. If you have small holes at the top of your damping rods then these are the rebound damping holes and if you made them smaller that would slow the rebound stroke and stop the clunking. Forks are a lot like a carb, sometimes you have to jet them (change hole size) to get the ride you want.
Good Luck,
Panhead George

Panacea
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Re: fork clunk

#13

Post by Panacea » Thu Nov 15, 2012 4:05 pm

panhead george wrote:Just one thing in regards to the spacer. If the spacer is under tension when you screw the cap on then that is considered preloading the spring. The more preload you have the stiffer the initial part of the travel will be and the harsher the ride will be over small ripples and bumps. If you cut the preload spacer say 1/2" or a 1" then the fork will drop an additional 1/2" or a 1" when you let the bike off the stand. This will lower the bike however much you cut off the preload spacer but it can also top out violently if you were to get the front wheel off the ground due to the spring having no tension on it. What you have is a topping out condition when the fork is on the rebound (up) stroke. A heavier oil would slow the rebound but it would also increase the compression (down) stroke also making the fork stiffer thru the entire stroke. If you extended the fork by 6" that allowed for more air space at the top of the fork so you are correct in needing to add oil to compensate for that extra air space. There is a good chance that the fork may have cavitation due to not having enough oil.If you went to a heavier oil to slow the rebound (up) damping then you would have to possibly weld up your damping rod holes, the ones at the bottom of the damping rod, these control the speed of the compression (down) stroke so the fork would not be too stiff. If you have small holes at the top of your damping rods then these are the rebound damping holes and if you made them smaller that would slow the rebound stroke and stop the clunking. Forks are a lot like a carb, sometimes you have to jet them (change hole size) to get the ride you want.
Good Luck,
Panhead George
George, I think you are confusing hydra-glide dampeners with Showa. The early dampeners only have the bottom holes just above the bushing.The top of the dampener where it slides in and out of the tube has a mystical valve assembly, not really tuneable..Mike

UPSROD
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Re: fork clunk

#14

Post by UPSROD » Thu Nov 15, 2012 6:46 pm

I had a clunk in my 62 FL years ago. I added more oil and changed up to 30 wt. oil. It turned out to be the lower slider tube
retaining ring was coming out after riding it for a wile. I don't know if it was the wrong thickness or what, got two new ones
and that was it. Only noticed it on railroad tracks etc.

Cotten
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Location: Central Illinois

Re: fork clunk

#15

Post by Cotten » Thu Nov 15, 2012 7:08 pm

Railroad crossings come out of no where, Folks.

Beware when riding with a pack, as a 'forced' rough crossing can put your passenger on your shoulders.


...Cotten

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