I have a Cat D6D that starts losing forward power after running for about two hours. Acts like it is not totally shifting into gear. Does not lose any power in reverse. Sometimes I can wiggle the shifter at first and it will move like it should. I can stop it and come back in a couple of hours and it will run fine for a couple of hours. Anyone ever run into this problem?
I think on front of transmission you will find a block that bolts to transmission case it has a line going to transmission pump and a line to steering booster pull that at transmission case pull the tube that is under it and replace the o rings is where I would start
There are quite a few threads in this forum and elsewhere covering this issue. I had an intermittent problem on mine when the oil was at operating temperature sometime it would not engage reverse properly. I replaced all the O-Rings on the transmission control valves and adjusted the spool valves (they have to be adjusted within 0.025") correctly. HeavyEquipmentForums Other things it could be the forward clutch could be leaking when the oil is hot and thin.