Kokeln control arm failure
03-13-2009, 02:25 PM
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Kokeln control arm failure
I was on track last weekend and whilst just starting to brake from around 100mph into a hairpin the front of the car collapsed on one side. The control arm had given way, wheel up in the arch causing damage, and ended up in the gravel trap (rather fortunately).
For those of you that know these arms, they have a threaded collar that sits in the end of the arm complete with a lock nut. A rod end then screws into this threaded collar again with lock nut. The rod end has a bar/rod that fits into the hub spindle.
It appears that the threaded collar has given way - sheared - with the rod end in it leaving the other half of the threaded collar in end of the control arm.
Obviously i am not very happy, i have damage to my front fender, brake line, wheelarch liner, steering arm etc. I spoke briefly to visionmotorsports (receptionist?) after i sent a mail to Kokeln and received no response. The contact number on the then Kokeln site directed me straight through to visionmotorsports. I have resent my mail to them earlier this week and await their response.
A couple of questions - does anyone know what association visionmotorsports has/had with Kokeln, and am i likely to have any fallback/meaningful resolution or response?
Has this occurred to anyone else whom have this control arm, or indeed, this type of control arm.
The threaded collars and locknuts allow for adjustment at the bottom of the arms (camber), i have reservations with the design in the extended mode. If the collar is fully threaded into the control arm, and the rod end fully into the threaded collar they appear quite robust. Once you start to adjust the collar/rod end outwards, there is less of each component in the preceding component, i.e. collar and control arm.
You can determine from the photos (the rod ends are fairly dirty/greasy) the associated dimensions. Rod ends at this size have 43mm of thread. The picture shows how they were set up on the car, the problem being there is only 10mm of combined rod end and collar in the control arm. Which i now know why the other side sheared - I think the assembly has worked loose resulting in little or no combined rod end and collar in the control arm overstressing the collar resulting in shear!
Is the maximum of 18mm of combined collar and rod end in the control arm sufficient, if all is screwed as far in as the collar/rod end will go?
Iif i can obtain replacement collars threaded upto the underside of the nut part, i will screw all the way in (and possibly tack-weld) allowing c28mm of combined collar and rod end in the control arm. This does remove the adjustment function though.
If you have control arms similar in design to these check them out - make sure you have sufficient metal in metal!
JP
For those of you that know these arms, they have a threaded collar that sits in the end of the arm complete with a lock nut. A rod end then screws into this threaded collar again with lock nut. The rod end has a bar/rod that fits into the hub spindle.
It appears that the threaded collar has given way - sheared - with the rod end in it leaving the other half of the threaded collar in end of the control arm.
Obviously i am not very happy, i have damage to my front fender, brake line, wheelarch liner, steering arm etc. I spoke briefly to visionmotorsports (receptionist?) after i sent a mail to Kokeln and received no response. The contact number on the then Kokeln site directed me straight through to visionmotorsports. I have resent my mail to them earlier this week and await their response.
A couple of questions - does anyone know what association visionmotorsports has/had with Kokeln, and am i likely to have any fallback/meaningful resolution or response?
Has this occurred to anyone else whom have this control arm, or indeed, this type of control arm.
The threaded collars and locknuts allow for adjustment at the bottom of the arms (camber), i have reservations with the design in the extended mode. If the collar is fully threaded into the control arm, and the rod end fully into the threaded collar they appear quite robust. Once you start to adjust the collar/rod end outwards, there is less of each component in the preceding component, i.e. collar and control arm.
You can determine from the photos (the rod ends are fairly dirty/greasy) the associated dimensions. Rod ends at this size have 43mm of thread. The picture shows how they were set up on the car, the problem being there is only 10mm of combined rod end and collar in the control arm. Which i now know why the other side sheared - I think the assembly has worked loose resulting in little or no combined rod end and collar in the control arm overstressing the collar resulting in shear!
Is the maximum of 18mm of combined collar and rod end in the control arm sufficient, if all is screwed as far in as the collar/rod end will go?
Iif i can obtain replacement collars threaded upto the underside of the nut part, i will screw all the way in (and possibly tack-weld) allowing c28mm of combined collar and rod end in the control arm. This does remove the adjustment function though.
If you have control arms similar in design to these check them out - make sure you have sufficient metal in metal!
JP
Last edited by frogisland; 03-13-2009 at 02:29 PM. Reason: spelling
03-13-2009, 02:40 PM
#2
Burning Brakes
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Talk to Pete at RSBarn about them, one of the race cars that he preps had a failure with Kokeln arms, it wiped out the car. There is a thread about it on 968forums, do a search for "A-Arm Pin Failures on track". Some further research apparently found the originals were 17mm pins, but there is now a 19mm version of it.
EDIT: RolexNJ
EDIT: RolexNJ
Last edited by stolarzj; 03-13-2009 at 11:15 PM.
