ahhhh
the old missing ball bearing torquing the drive unit scenario
dont ya hate it when that happens?
those are the ones that always seem to bite ya till ya figure it out
good job!

Well a little info for everyone we finally found the problem the steer pivot bearing that the drive pedistal mounts through had one missing ball when you turned left the motor armature would torque into the field windings.Replaced the steer pivot bearing customer says unit has never run this well guess they had problem for a while so if you get this problem cheq that bearing even if unit steers ok

remove the steering gearbox
jack truck up
try to turn drive unit left to right as if steering
should need hand strength to turn if shimmmed correctly
if you can turn with finger tips it is shimmed too loose
if you need to put your shoulders into it, it is too tight
from memory it should be 15 lbs using a fish weight scale to pull around
I will try to find the exact tension later

how about checking the power cables to the motor
check the crimp on the terminals
maybe your loosing connection on one cable while in a turn

only turning left would make me think that possibly the battery is rolling

Yes it does, even when the brake is completely removed the same problem is occurring.
when we dropped the drive unit only the top end was rebuilt. Has anyone heard of maybe the helical gear at the bottom binding under load? or in one direction of travel only?

just to reiterate, this is currently only happening when turning left (puf) and plugging the machine.

thank again for any help on this one, all ideas are welcome

this truck have an electric brake on that motor?

i'm just thinking outloud, dont mind me ;o)

this truck will be the end of me!
now the truck will do the same problem as before when making a left turn and plugging. WTF
any one?
i want to just say dont plug left

the lower support bearing for the drive motor is on the pinion shaft. removing it will replicate the problem, the fan will contact the motor housing. any other ideas?

How about taking the gear off the motor shaft and installing the motor back on the gearbox. Spin it up a little and plug it. If everything works ok than you have proved the problem is in the gearbox.

Ok so I'm back in the same spot.
This truck is still giving the same symptom as last time. When I plug the motor makes a horrible noise (metal on metal) and stops the truck instantly.
the drive motor upper bearing, drive motor lower bearing on the pinion shaft and the upper drive unit bearing at the base of the pinion shaft have all been replaced, new shims and all, including the base plate.
When I swap out motors from one truck to another the problem stays with this truck,
The plugging diodes have all been changed out and aside from changing out the oscillator card I'm at a loss any ideas?

The upper drive unit support bearing is probably bad. It causes the drive unit to deflect and the motor fan to hit the side of the drive motor and lock up the motor. Recommended replacement on the bearing is 5000 hours, and less if you have rough floors or rail guidance.. If you see aluminum flakes around the bottom of the drive motor, that's the problem.

the 'poles' on the drive motor may need to be re-insulated and tightened down, if the field windings move at all, they can get a spot in the corner where they wrap around the pole shoe that can move and short to the frame of the truck.