We have recently been seeing an increase in catastrophic vacuum pump failures on the older diesel engines. This includes premature diaphragm tearing, piston failure or drive mechanisms breaking apart. If you have recently experienced such a failure in your pump, you need to inspect your engine BEFORE installing a replacement. If you don't, the replacement pump, or replacement diaphragms could fail in a few weeks!!! Scroll down to read more.........
Problem & Solution
Common among these chassis:
The problem seems to occur when the pump drive (in and out motion) is overstressed. This can be caused by excessive side to side load or excessive pumping action from the engine that "overdrives" to pump. When you remove your pump you will see the round cam plate that rotates and drives the pump in and out. The cam plate is attached to a shaft that goes through the timing device and also drives the injection pump. This shaft rides in a big bronze bushing and when that bushing wear out the shaft can move side to side as well as in and out. You may also notice a noise in the engine that is difficult to diagnose.
Inspect the cam plate surface for wear or other signs of damage. This plate can be replaced with a good used one and it is simple to remove and install by removing the two bolts that hold it to the timing device.
Inspect the shaft bushing for excessive wear. Grab a hold of the end nut with a vise grip and move side to side and pull in and out. You should only feel the slightest play in both directions. If it moves more than 1/16 of an inch the bushing should be replaced. We currently do not have instructions for replacing this bushing. You will need to refer to the factory engine manual. It does require removing the injection pump from the engine.
This is what the bushing looks like: