I have a late '60s early '70s John Deere 500 backhoe I remove the injector pump to replace the umbrella seals no problems there at all the shaft look good the pumps good reinstalling it I cannot get the pump to mate with the black surface to tighten it down it's all about an eighth of an inch Gap I cannot figure out what I'm doing wrong to get it all the way down anybody got any ideas I have found that there's a dot inside injector pump and a DOT on top of the shaft those line up good everything inside the pump fits well just cannot get it to set all the way down