Allison 5sp: Transmission oil change

[gilbertc9]

Hi guys, I'm thinking of changing out the transmission fluid on my duramax and going synthetic. Can someone tell me the proper way to make sure all the old TF is removed so I am not mixing syn with conventional or does it not matter if they mix. Also how much will I need?. Just turned 50,000 miles should I replace internal filter at the same time?.
2005 GMC 3500 Dually LLY
Thanks

 

[DieselD]

I just put a Trans Go Jr in my truck yesterday, put in a new internal and external filter as well. I bought 3 gallons of Mobil 1 Full sythetic ATF and it used up every bit, only problem was its $8 a quart! I know there is still fluid in the cooler, radiator, lines and converter but i am planning on doin a full build soon and figured it would be good to run the 3 gallons through at first to get it throughout the trans. Mine is running real nice, you can mix regular ATF with sythetic, its not a problem.:thumb:

 

[Heath]

Many people just do a pan drain(about 8qt) and refill. Put on a new spin on. The fluids should mix fine. This is the easy way to gradually change out the fluid. The other is to flush. I tried it myself once and probably won't again. Not a one person job. I went to AAMCO with my fluid and had them do it. Then you can change both filters and be good to go.