Hello Gents. I just purchased a 1980 John Deere 750 crawler with a bad motor (rod out through the side of the block). The motor is pretty easy to diagnose but the owner that i purchased from stated that when the dozer get hot after half an hour of pushing or so it starts to slip on one track and get weak on the other. This is a full hydro static machine with the engine-to the splitter- to the hydraulic pump and two separate (transmissions). From my understanding each transmission has its own pump and drive motor. My question to you all is where should i start and what are some good troubleshooting steps to rule out the big items? My initial plan is to get the motor changed out and start running the machine for some testing.
I attached a lack of transmission power flow chart. Your biggest issue however will be acquiring parts for those transmissions.
Thank you! That is a fantastic flow chart and place to start. I have purchased a technical manual for the 750 and hope to have it within the week. It mentioned on the flow chart to watch charge pressure on the gauge. Is there a good diagram of where this charge pressure reading port is located ? I was under the impression there were two hydro charge pumps on this unit/one for each track. Understood on the issue with finding parts. I run into that problem a lot as i run alot of "old iron"
It should have a transmission oil pressure gauge on the instrument panel. There is a check valve in the system that shifted from the higher pressure of the two charge pumps, then sending the lower pressure to the gauge. So which ever transmission charge pressure is lower is what you see on the gauge.