2013 Berg 4CS Problem

I sold my 2013 Husaberg TE250 in March 2015 to a good friend.  I am now trying to help him with a couple of issues.  What would cause the 4CS forks to have a thunk sound when they top out? Also they seem to have lost some pre-load. It's as though there is extra play when the front end is lifted. 

 

Here's another strange thing that happened when the bike was mine and I am now wondering if it's related. I had two rebound caps strip out where the damping rod connects in the center.

 

July 2014 - I had the forks re-valved. The tuner called me when he was reassembling the forks to tell me that the rebound cap somehow stripped out where the damping rod threads into it. My first thought was that he must have cross-threaded it. I had him button everything up and ship the forks back to me and I ordered a new cap. I installed the new cap and all was well.

 

Jan 2015 - I was replacing seals.  As I was removing the rebound cap from the damping rod, it was spinning right off just like normal and suddenly became hard to turn. By the time it was over it was stripped out just like the first one. I ordered yet another $100 cap!  I know for a fact that I installed the first replacement one correctly (all the way down onto the rod and then tightening the jam nut)

 

Is it the damping rod what actually stops the forks when they top out? If so, why would there be a thunk sound? Is it possible that something is causing an abnormal amount of force on the rebound damping rod and causing it to be pulled from it's threads in the cap? 

 

Just from doing lots of seal replacements over the years I am pretty sure that the damping rod stops the forks from extending before they get to the point of where the inner and out tube bushings slam into each other correct?

 

Thank you, very much. 

 The threads on the damper rod are fragile , when you tighten the spring retainer/center nut against the cap it's easy to damage the the rod , I'd check that first as well as the top out spring on the other side of the damper rod next to the piston .

 Wow , I guess the 4cs has had a few revisions from 13 to 2016 . Thanks for the info !

Thank you for the help!  Sounds like a dead ringer for our problem dwb79.  We will tear them down and take a look.

Yep the caps are garbage I keep 4 rebound in stock and 2 compression

Loss of preload is from the spring seat collapse

Pressure ramping is from the inner tube acting like a bike pump

If you haven't yet you will lose the rebound adjuster knob it's caused by the o ring on the rebound valve failing (deep inside) and the for mentioned ramping pushing it out

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