Ok Guys, I have a 2002 4.6 FX4. Looking to strengthen tranny a bit. i pull a 6x12 lightweight trailer approximately 75% of the time. Which mod would help? Thanks, I've heard these tranny's are a bit touchy and can be prone to a few issues. Thanks in advance for any help. P.S. already threw a P0713 code for flashing overdrive light. Don't know why, but, it has magically stopped. Thanks again. Newbie to this truck.

 

Neither, just get right gears for your towing needs, tune the ecu and drive it till the trans dies, then build it stronger.

 

Would the front and rear diff sets be the same. I have 8.8 rear with 3.55 gearing. I assume they are, but, you know what they say about assuming.

 

Ratio will be the same. When you buy front gears make sure they are reverse cut. Otherwise, IIRC, everything else is the same. I'm glad I didn't have to worry about my front differential..oh wait I don't have one..

And to answer your question about j mod or shift kit, they may prolong the life of your clutch packs slightly by making the shifts quicker, but it does nothing really to strengthen the transmission. Like mentioned above, re-gearing will take some of stress off the transmission and will prolong the life of the transmission that way.

That and it's more fun around town with a taller gear ratio. I went from 3.55 to 4.10 and it pulls a lot harder now.

 

But what happened to your gas mileage?

 

Who cares? If you tow a lot you shouldn't be to worried about gas mileage, plus 4.10's are badass. Gotta pay to play.

 

If you are getting a P0713, the transmission MIGHT already be slipping. Very first thing I would do is add an extra cooler and route in series with the factory cooler.

second thing is do the Jmod, updated the shift valves with replacement valves from Sonnax and replace the factory separator plate with a thicker "Tuff" plate from Superior transmission parts.

 

Went up 1-2mpg in town when I'm not romping on the throttle(but who gets 4.10 gears and doesn't romp on the throttle). City I average 11-13mpg. Highway stayed the same at 16mpg at 75mph. Little noisier though having a straight piped truck.

The 4.10 and limited slip I installed have been the best thing I've done to the truck so far.

 

For the Jmod... do this:

Assemble the valve body with the stock regulator valve pressure spring, new valves from Sonnax and a new "Tuff" plate (separator plate) from Superior.
Drill the new separator plate like this:
hole 1 = .161"
hole 2 = .1015"
hole 3 = .180"
hole 4&5 = .113"
hole 6 = .161"
hole 7 = .089
hole 8 = not used in this application
hole 9&11 = .125"
hole 10 = .089"

assemble with new gaskets and torque the seperator plate bolts to 100 in lbs, torque the transmission pan bolts to 130 in lbs