Allison Transmission Issue

xr_guys · Mar 27, 2012

OK Guys need some help sorting out the issue on my new used dump truck.
1987 Ford F8000 with 3 axle Dumptruck
4 speed Automatic transmission (maybe Allison MT643)
78 K miles with Remanufactured Cat 3208T

Now the issue, as I was driving it home last Saturday at freeway speed the truck hit ~ 65 MPH. About 15 miles to my place I decided to get some diesel and stop at Shell station, on to the hi way back road. Did not notice anything weird on the transmission shifting until 3rd, the engine max out RPM 2500 and I知 only going at 46 MPH max. The Tranny would not shift to 4th. I back off on the gas and it down shift to 2nd (I think..?), step on the gas again and it shifted up then max out again on 46 MPH at 2500 RPM. What happen? over heated. I'm thinking check the mechanical Modulator cable and device that push the little rod in to the tranny.

Thanks,
XR

BigE_ · Mar 27, 2012

It sounds like your tranny went into failsafe 2nd gear only mode...

I don't know much about trannies, but those are the exact symptoms I had, and then it was time for a rebuild.

xr_guys · Mar 27, 2012

please please, let not be a total failure.

Any more positive idea? like ohh just flush it with a new fluid and it should be good..!:laughing:

Bob Rooks · Mar 28, 2012

78k? That's good. The Diamond Reo mixers I used to work on would only get 68k on a good day. Curious if the reman Cat was the OEM engine?

xr_guys · Mar 28, 2012

Bob,

I'm not sure either if the remanufactured engine is the OEM, good question. I wonder too if it will have the additional piston rings compared to a single?

Well the problem turn out to be the modulator cable it self. To tight and limiting not to have full throttle when you floor the gas. So i just back off the adjustment cable of the modulator per Allison recomendation and the truck ran fine.

Thanks,
XR