I am almost finished with the water pump on the 150 HPDI but I can not get the nylon bushing and the steel collar to compress onto the shaft. I have tried putting them together above on the narrowed area of the shaft but can not push it down onto the larger diameter part. I have tried to assemble them in place down against the pump housing and can not get the steel collar to go over the nylon. Has anybody done this lately and how did you complete this? My manual does not show this step. Thanks