Tractor Mechanical Fuel Pump Issue Resolved - New Holland TN75DA

Over the past two years, my TN75DA tractor had become increasingly hard to start and sometimes required "Quick Start" (ether) to get it going. I changed the fuel filter but this did not resolve the issue. I then drained the fuel tank and found that the contained diesel looked more like dirty dishpan water. I added 1/2 tank fresh diesel and the engine appeared to start easier. However, the hard starting condition reappeared. The tractor would start fine one day and then wouldn't the next. Also, the tractor would be running fine, but, then would not restart after being turned off for an hour. It was obvious that the engine was starving for fuel so I turned my attention to the fuel pump. The pump runs solely by mechanical action via a fuel pump cam shaft which is (internal) in the engine. The fuel pump was easy to remove: 2 nuts at the flange location and 2 banjo bolts (one on the suction side and one on the discharge side of the pump). Note that the banjo bolts themselves need to be inspected for entrainment of solids (which needs to be removed before reinstallation) as well as the cavities on the metal hose ends that the banjo bolts pass though when bolted back to the pump. When I disassembled the fuel pump, I determined that the hard starting issue was indeed due to it malfunctioning. The pump contains two small rubber check valves, one on the suction side and the other on the discharge side, I found that both of them had broken off from the ports that they were designed to be attached to. How does the pump function? Here is how I see it (hopefully I am correct): the check valves cycle open and close probably hundreds of time per minute when the tractor is running. When the pump drive cam lobe connects with the fuel pump lift arm, a spring in the fuel pump that is attached to the pump diaphragms is compressed and the pump's diaphragm actuates downwards - creating a suction - the fuel is thus sucked from the tank into the fuel pump. As the cam lobe rotates away from the fuel pump lift arm, the fuel pump spring, which is attached to the diaphragm takes over, forces the diaphragm upwards, and ejects the (now pressurized) fuel from the pump. The fuel now travels to the fuel filter. With the check valves detached from their locations in the fuel pump, the pump cannot adequately create the suction & pressure cycles needed to pump the fuel from the tank and onwards to the filter - the pump in essence is likely just causing the fuel to quiver back and forth. The fact that my tractor did start normally on occassion was probably due to the check valves being close to their design locations by fluke (than anything else) and still being able to fulfill their design roles. Although the check valve stems broke off and rendered the pump useless, the pump likely was in service for 10 years and did serve its function well. The total cost to replace the pump was an hour of my time and $80 for a new pump, one gasket, and 4 banjo bolt washers. I searched the internet for a video that explained/detailed this but came up empty handed so I thought I would contribute and create one. I hope it is of use to you!

[@eoinoshea2806]

Just what I needed to fix my holland
Thanks Dr

[@bradsnyder8802]

Very useful. We have four TN series. I am having a similar issue on a TN55. Can't seem to get it started. Initial thought was the fuel shut off solenoid. May tear the lift pump apart to see if the check valves are floating. Great advice on the lobe position. Thanks!

[@t.d.harris1311]

I'm having a similar issue with a TN65, hard starting, Iv'e loosened the purge nut on the top of the filter and get some air bubbles, then a good flow. Tractor starts better, then after shutting it off, back to hard starting. I have noticed that fuel seems to be draining back into the tank, or what seems to be the sound of it. My question is if the mechanical pump maintains pressure after the tractor is shut off, to keep fuel in the line going to the filter and from the tank. Anyone got any input on this, spent a whole day trying to solve this issue. My next step will be your suggestion, replacing the pump. Thanks for posting this, best regards!

[@carlpatterson8684]

Any special tricks to line the arm up inside the engine or does the new one just go right in?

[@dr.fusion3558]

Hi Carl, nothing special as far as I could determine. I just positioned the pump onto the studs and when tightening the nuts the lift arm will position itself with respect to the cam. So, just take the old one off and install the new one. My tractor now starts like it was new!

[@farmerlovers1145]

Hi sir your tractor rotary pump number