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1988 F350 Dump Truck Transmission and Starting questions

I have a 1988 F350 with 7.3 diesel (no turbo) with an automatic transmission. This is an old state salt truck with a dump bed and only 69,000 miles. The transmission started seeming like it was straining to engage, so I changed the fluid and filter and added Lucas transmission additive. The transmission is still acting up. With any type of load, I have to floor the thing to get it to move at all and you can smell transmission fluid. Once you get up to about 45, it rolls along although I am hitting 3800 rpm at 55 mph. The transmission selector looks like it has the D with an O around it meaning overdrive, but it has never hit a fourth gear since I have owned it (which is not long). It also takes a long time to go into reverse no matter if I have a load or not. I am not familiar with diesels or transmissions, so any thoughts on this would be much appreciated. I bought this as a farm vehicle and it might move once a month but when I need it I need it.

Also, it will not start unless it has been plugged in. It can be 90 degrees outside and when you turn the key to warm the glow plugs, all I hear is a loud click out of a box to the back side of the engine (under the breather) that has a bunch of wires going to it. It will not start. As long as it has been plugged in, even on hot days, it fires right up.

Also, if it needs a rebuild, can the repair man know if the torque converter is bad or not. Is the torque converter part of a rebuild ?

A new TC is generally part of a full rebuild, and it sounds like you need one.

A diesel motor will start without functioning glow plugs. The glow plugs are needed for “cold” starts.

Since you can start the truck if the block heater has warmed the engine, I deduce that the glow plugs are not functioning. That clicking could be a relay in the circuit that isn’t working.

This transmission must be a C6. The E40D didn’t appear until mid 1989, Thec6 has no 4th gear and no lockup T/C. As such the top speed of this truck should be about 70mph with 411:1 axles… If therre is an “O” over the “D” on the indicator then it is simply the wrong indicator. Whatever you do with the trans.(rebuild or exchange) make sure you have a new modulator and MOST IIMORTANTLY and new vauum modulator regulator valve on the injection pump. This new valve must also be adjusted properly when installed. When not functioning prioperly this valve can cause eaither very early or late shifts or no 1st gear at at all (starts off in 2nd).