I have a 2004 f150 fx4 with 79,000 miles on it. I bought the truck two years ago with 61,000 miles on it and I am not sure if the previous owner did a transmission fluid change. This truck is not my daily driver, but I do tow a snowmobile trailer often in the winter and I am probably taking it to Myrtle Beach (from PA) at the beginning of August. I have not had any problems with the transmission (knock on wood), but my question is whether I should flush the tranny and replace with new fluids or leave it alone. I have heard so many conflicting reports that I am not sure what I should do. I have heard people say that if you wait too long, you shouldn't do it at all. SO WHATS THE TRUTH? What about the rear end? Is there any routine maintenance I should do on it as well?

Thanks for the opinions

 

I recommend a full tranny fluid exchange at 30k when used for towing and a differential fluid replacement (both axles) at 100k. I would get the tranny done soon.

 

Had similar concerns when I starting having issues w/my one owner 98 F150 4.6 w/4R70W and approx 125K miles. I hadn't had the fluid flushed since the 55k mile mark so it was way overdue for service.
I had heard the same things that flushing a tranny w/high miles would only stir up the debris and clog up the valve body so my plan was to drop the pan and drain torque converter, change out the filter and refill. Unfortunately I must have an odd-ball TC as it didn't have a drain plug. So I didn't drop the pan. I had heard about the power drain procedure but decided to go to the dealer for a clean, flush & fill. Since I had already purchased the MC Mercon V they only charged me for the labor and cleaner fluid.
Long story short, the flush not only corrected the tranny issues I was having, it also improved shifting and MPG. Improvement all around..... It's not an everyday driver now but I've put about 2k trouble free miles on it since (knock on wood)

Did I luck out? I dunno but in my case it was WELL WORTH the flush and I will have it done again when due.

YUMV.

 

I would NOT let them use "cleaner fluid". Just exchange the tranny fluid.

 

thanks for the advice. I am going to start calling around for some prices.

 

I would not hesitate if I were you, get it done soon!

 

made an appt. this morning to get it flushed for $120. They said they drain the TC, drop the pan and change filter and flush the system. Thanks for the advice, I've got my fingers crossed that everything looks good up in there.