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Dodge Tech
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Discussion Starter · #1 ·
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.
 

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PAID OFF!!!
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I didn't know 3rd gens. came with 3.21's.
 

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Dodge Tech
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Discussion Starter · #5 ·
I have the 6 speed manual trans so i guess that is why it had the 3.21 it is a slt so it wasn't cause it was a base line truck either.
 

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Devil's Advocate
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ya they were the bottem end gear available only on the 6-speeds. 3.55s were optional.
 

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oh yea, I didn't think about the manual transmission.
 

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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.

Thanks for posting your experience.
 

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All Around Great Guy
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What are the rpms' at highway speed with the 3.21's??? What is your mpg on the highway??
 

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Ramistered User
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I see you did the install yourself. How was that?
 

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Dodge Tech
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Discussion Starter · #12 ·
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.
 

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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.
haha.....you could make some good side money doing gear installs for memebers
 

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I have the 6 speed manual trans so i guess that is why it had the 3.21 it is a slt so it wasn't cause it was a base line truck either.
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!

Thanks..Ed
 

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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.

Johnnyk
 

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Dodge Tech
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Discussion Starter · #16 ·
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!

Thanks..Ed
Well i put the 3.92s because i heard that the stock carrier was made differently for the 4.10s. I didn't want to run into a problem since i was using all chrysler parts. The other reason on why i used 3.92s was because one of my co-workers had a good used set of gears. The same co-worker had a trac-loc carrier that had a broken clip in. I bought a new clip package and installed it myself for $10 (employee price). Total for parts including the carrier, gears, new bearings etc. was about $250.
 

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Discussion Starter · #17 · (Edited)
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.

Johnnyk
The engineers probably chose the 3.21s because of epa regulations and trying the get the mpgs higher for highway IMO.
 

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Once and future owner
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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.
 

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i sure hope you knew what you are doing in there.
 

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how is it driving now? seeat of the pants test i bet went awesome:D
 
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