transmission fluid change

[HAGE.NY]

Drop the pan or do a full fluid flush? The dealer only drops the pan. Is it adviseable to get a full fluid flush of transmission fluid on 2003 Duramax?

[DmaxMaverick]

Depends on how many miles and how you use the truck. Heavy towing, it should be serviced about every 25K. Light/infrequent towing and commuter use, 50K is OK. The spin-on filter should be changed at about 50% of the service interval, as well as at the first 5000 miles.

If you are changing fluid types (going to synthetic/Transynd), you should do a complete flush. If you are just "servicing", a drain/fill is fine. If towing heavy, a flush wouldn't hurt.

No reason to drop the pan. It has a drain plug. Allison recommends that the internal filter only be changed at overhaul. If you do drop the pan, the gasket can be used again, so don't waste money on new unless you damage the old.

Use the search feature for the transmission flush. The subject has been discussed at great length. You will also find detailed instructions on how to do the flush yourself, which is simple.

Cheers