i was recently told by a local dealership that when i flush the trans fluid in my allison to just replace external filter and dont drop the pan and replace the internal one because it will cause problems in the long run but on the other hand the dealer i bought the truck from said to drop the pan and replace both filters. why would one say one thing and the other say something different.

allison recommends changing the internal filter only after a rebuild. some guys do it when they swap the stock pan out for a deep one. some guys change the external spin on every oil change (5-10k miles). the best filter for the external spin on, IMHO is an OEM Allison red filter. they're cheap if you buy them from an allison dealer or big truck shop, you will pay thru the nose if you get them from the stealer (5x more).

good luck!

Yep, dont touch the internal unless your doing tranny mods that warrant dropping the pan, just change the spinon filter regularly and dont lose the magnet!!

the best filter for the external spin on, IMHO is an OEM Allison red filter. they're cheap if you buy them from an allison dealer or big truck shop, you will pay thru the nose if you get them from the stealer (5x more).

$8.49 from Alli Dealer

$34 from Chevy dealer

so you will never need to replace the internal one unless you upgrade and what happens if i do what problems will occur.

Don't see any problems occurring as the internal one is more of a screen than filter. Just a waste of time, money and expensive tranny fluid (if you go with a synthetic like Transynd).

Probably the reason for the one dealership to recommend changing the internal as well is either a lack of knowledge on the Allison tranny or they're trying to make some extra $ off of you.

In addition to the regularly schedule transmission fluid change, just change the spin-on (I change my every other oil change) and you should be fine. Like TimZ said, don't forget to switch the magnet from the old spin on to the new one (keep a spare in your tool box just in case...they're cheap at an Allison dealership).