Allison 5 speed auto slipping????

tnwalkinghorse · January 7, 2004

ALL,

I have a 2002 3500 Diesel with the Allison auto. The truck has 51,000 miles on it. I haven't pulled anything worth mentioning with it since it was new. I am starting to notice a strange behavior now. Several weeks ago when I went to pass a 18-wheeler on a hill, I noticed my engine RPM's were up, but I was going to fast, until I took my foot off the gas and the trans went into a higher gear. Well today, I was at a light at the bottom of a moutain. When it turned green, I stepped on it to beat the ford next to me (haha). Anyway, it shifted fine from 1st to 2nd but then when it was going into 3rd gear, again the motor RPM's climbed and the truck went no where until I took my foot off the gas, and then it smoothly shifted into 3rd gear. Does this sound normal? When I drive the truck like granny, everything shifts fine, but when I give it the gas, that's when it seems to slip or sitting in between gears (almosts like in neutral)

ANY IDEAS what can be causing this???

Thanks,

Matt

QUIKSOCALHD · January 8, 2004

I'm not a tech or anything but I have had similar problems with me 2000 Z71 and it simply turned out that I was a little low on Tranny fluid. I mean, it took barely a half quart and it ran normal after i did that. I would check the fluid if you haven't already. I have a 2500HD CC with the Dmax/Ali combo and haven't encountered a problem like that yet and I'm running two different chips and exhaust, etc, but I am also only at 17k miles though. Good luck!

tnwalkinghorse · January 8, 2004

I will check the fluid. But as I was just checking around the forum. Somebody else said that the computer might have a strange behavior memory recorded. They say to disconnect the battery and let the computer reset for at least 10 minutes. Do you think this will help if the fluid is OK?

QUIKSOCALHD · January 9, 2004

It definitely might help. I know the Allison is heavily computer controlled so this may reset some code that is set off, but not displaying a warning light. I have not heard of any slippage problems under gear 4-5 shifts. The fluid thing is the only thing I can think of since I encountered a similar problem on my old Z71. Very similar also because my slippage came when i had my foot in it and not at slower acceleration. Good Luck!