So tonight i removed my 3.21 gears and open diff and installed 3.92s and trac-loc. It took me about 5 hrs. and i am happy as hell on the performance change. I lost the third gear bog and am sure to lose a few tenths of a second in the 1/4 mile. I am going to go to the track in a week or two and see exactly what it does. I have had a personal best of 16.0 with not many prior passes in my life. I have high hopes for mid 15s i feel it has it in it. I guess time will tell.
I've got the same truck only an 08. I am definitely going
to do a gear swap as the 3:21 is way too tall. I find you
really have to slip the clutch in normal driving and reverse
is about useless. Why didn't you go with 4:10 ratio and where
did you get your parts from? Good post BTW!
I've got an 08 4.7 with the auto and it came with the 3.21 rear end. With the 310 hp engine its not as bad as you might think. However, I've got a set of 3.92s waiting for install, but I've been undecided about maybe going with the 4.10 instead. If 3.92s is a good enough change then I think I'll go with it.
Highway with 3.21s was around 2000 at around 75mph and when i went from Vermont to New Jersey i actually got 20 mpg. With the 3.92 i am guessing about 2400 to 2500 at 75 mph.
For the install i am an auto tech at a dodge dealer and have done those diffs. plenty of times. Being that our special tool room is completely un-organized it took me about five hours from pulling the truck in, to correcting the speedometer in the computer and going for a test drive.
Nice job on the upgrade .......... IMHO 3.21's should never even be an option on a 1/2ton truck. Sometimes I really wonder what goes through those engineers heads,damned if I will ever figure them out.
Nice man. You'll definately gain a few 10-tenths in the 1/4. For comparison; I had 3.92's w/open diff in my previous 4x4 Ram and went to 4.56's w/DTT and I gained about 3/10's in the 1/4.
like previously posted, i work at a dodge dealer and have built these diffs. multiple times and double checked all specs. like backlash and turning torque.
I wondered about fitment issues using the stock carrier.
Do you have any more info on this? Also was the 07 the
310hp engine? As far as mpg mine does quite well in its
current state, high 19's.
no mine is the older style 4.7. In 07.5 they released the 310hp 4.7 if i am not mistaken. I don't have official documentation on what will fit and what won't I just heard from one of the guys in the shop that can hold all of the weird information in his head told me he heard of some fitting issues. I didn't want to chance it and also when i went through the starscan (chrysler's pcm scan tool) the only options that i was given for gear set sizes were 3.21, 3.55, and 3.92. If i went to 4.10 i wouldn't have been able correct the speedometer without an aftermarket scan tool.
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