new rack damper bolt 79 300 SD

My old rack damper is to weak to stop the shaking at idle. I got the replacement bolt today it is part # 000 074 26 74. It is much shorter than the one on my car now. I have to screw the new one all the way in (without the lock nut) to even touch the throttle control on the injector pump. I have checked all the measurments on the throttle linkage and it seems to be OK. If I remove the linkage and let the throttle control come up to the rack damper bolt the idle is too low. If anybody has any idea what my problem is I would sure appreciate it. The MB engine manual does not cover this. Is there more than one style of rack damper replacement bolt?

Bill Ricker
------------------
79 300 SD