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3.55 to 3.92 gear swap

62K views 96 replies 42 participants last post by  tbone1957 
#1 ·
I purchased my truck off the lot and didnt really think much about the gearing. Now that I have owned the truck for little over a month im wishing it had the 3.92 gears. Has 3.55's in it. Has anybody done a gear swap? Can I just swap the ring and pinion or do I need to do something with the front transfer case also? Or do I need to get a complete differential?
 
#2 ·
Changing the gears is basically changing the ring and pinion gears. In a 4wd, you have to do both differentials. Now the hard part; after replacing the ring and pinion, you have to 'setup' the differential. Failure to do this 'WILL' cause premature failure. Setup requires a few specialty measuring tools and generally a decent set of shims and a few years of training and experience.

If you decide to take on this project yourself, I will do my best to find the exact differential setup manual for you....but in all honesty, gaining your first time experience is best left for a junker....not a 2011 DD. :smileup:
 
#4 ·
Yes... if you decide to do this, please post the time and costs.

I have the 3.92s and love them. It was a prerequisite for my purchase.

--deepblue
 
#5 ·
I feel like an idiot on mine. I took a build sheet into my dealer and told them to find it. They found my exact truck but with the 3.55 rear end. I never thought to ask if one was limited slip and the other wasn't. So I took and 3.55s and have regretted it ever since. This is on my list of to dos but there are other things above it at the moment. Get the looks right, then I'll worry about the gears. I'm interested in end cost though...
 
#6 ·
I had a buddy "help" me change the gears in my Wrangler first from 4.10 to 4.56 and then again from the 4.56 to 4.88.....

and when I wanted to change the gears in my Ram from 3.55 to 4.10 I still didn't feel comfortable doing it myself. you are taking measurements with tolarances in vary small windows (a couple of thousandths of an inch).

if you try it take your time and let us know how it goes.
 
#10 ·
You'll have to get 2 donor vehicles....one that was hit in the front, and the other in the back so you can get the remaining good part from each one. :LOL:

Doing a complete assembly swap is likely to '....easier.....' (hesitation) as a DIY project, but I'm not sure how that would affect your drivetrain warranty. At least you wouldn't have to deal with setting up the diffs....and like Pull-Ya said, you would get LSD to boot. :4-dontknow:
 
#9 ·
That might be the best way to go because I think that you will get the limited slip along with the 3:91's. I think if you just change the ring and pinion you will have to invest in the limited slip also to be happy.
Jay
 
#11 ·
when you get the parts that you want, have a ASE Certified shop do the changes, don't do it yourself, your drivetrain warranty will go out the window
keep your receipts, all of them

both differentials have to have the same gear ratio, the rear differential should have LST or a Locker
 
#22 · (Edited)
OK what Ive got listed so far.

Front 3.92 Gears Part # 5015895AC from wholesalemopar.com -- $373.89
Tru trac differential Part#EAT913A368 from 4wheelparts.com 535.99
Dana 3.92 Ring and Pinion Part# YUK-YG D44-392 from 4ws.com 261.95
So $1171 in parts. Gonna check around see what I can get them installed for.
 
#26 ·
I canceled my order at the last minute because I felt I was making a mistake by taking the 3:55's over the 3:92's, so I got the exact same truck with the 3:92's.
3:55's aren't junk. It's a good rear. It narrows down to personal preference and what you are going to use it for.
 
#27 ·
Guys what it really comes down to is a minimal difference in fuel mileage for a moderate difference in performance.

The following isnt for a Dodge but I would expect similar differences.

According to Roger Clark at GM the difference in their gas engines between a 3.42/3.55 and 4.10 was about 0.4-0.6 mpg in EPA Combined Ratings so that likely amounted to about 1.0 mpg worse on the highway.

Source:
http://www.trucktestdigest.com/axle ratios.htm

PS This doesnt apply to modern diesels that have a very narrow sweet spot for optimum fuel mileage.
 
#32 ·
Anyone done this? Can anyboby tell me how involved this job would be? meaning is this a diy install or only for qualified techs? This seems like the way to go for me as I'm really not unhapppy with my ratio just the fact I have an open diff.
 
#33 ·
if you are asking the question then qualified techs. setting up the ring and pinnion requires some special tools. if you get the pinion depth/backlash wrong it'll be back to square one and your gears will whine. you'll also need a hyd press to install the new bearings.
 
#34 ·
Oh I thought from reading this link if the ring and pinion are already set up and you're just changing the carrier this would be something I might be able to tackle. I do in fact have a 10k hyd press. but if I do have to mess with backlash then I guess it would be over my head. Thanks
 
#39 ·
The Trac-Lok is what they call a lunch box locker, it just replaces the spiders, and not the carrier. It doesn't affect tolerances on the Ring and Pinion at all. A locker, like a Detroit, replaces the carrier, and therfore due to minute manufacturing differences in tolerance will need to be completely re-setup. I know lots of guys who have done the Trac-Lok themselves. I even know a few who have set up their gears or installed a Detroit Locker themselves with no problems.

The only concern I have with the Trac Lok, is the durability. How well will it hold up to a 400 hp engine? I have seen them fail with a 200 hp Jeep motor, but it was with deeper gears and bigger tires in off-road situations, not street driving.
 
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