allison transmission changing fluid

[HAGE.NY]

When changing the fluid on my 2003 Duramax is it best to just change the fluid in the pan or should I seed a dealer that flushes the transmission and changes all the fluid?

[DmaxMaverick]

Although your question would be better served in the "2500HD/3500 HD Trucks & Drivetrain" section, the quick answer is no. You don't need a dealer to do a complete flush. Actually, it is better done without a flushing machine. I suggest you use the search feature of this BB. There are several threads in the "2500HD/3500 HD Trucks & Drivetrain" section that cover the procedure in great detail. Procedures cover complete fluid replacement and routine service.

If you haven't serviced it since new, I'd suggest a complete fluid replacement with Transynd, Amsoil TorqueDrive, or quality synthetic ATF. Be sure to replace the external spin-on filter (don't forget the magnet on the top of the filter). It is not necessary (nor recommended) to remove the pan or replace the internal filter, except at overhaul.

A routine service involves only a drain/fill and external spin-on filter change. This is fine if the truck is used for light duty, or minimal towing. A drain/fill will replace about 1/3 of the fluid.

Welcome to TDP. You'll find a wealth of information at your fingertips.

Cheers