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3.55 to 3.92 axle swap

5446 Views 5 Replies 4 Participants Last post by  rangoneer
I swapped my 3.55 axles tonight with a lightly rolled Durango with 3.92s. They were undamaged and measured up correctly. The swap went surprisingly smooth.

The front differential was a bit of a challenge with tight bolt placements. 7 bolts total. Three bolts are tricky but you can get them with a 24" extension and a an impact from the driver side wheel well. Half-shafts just tap off and slide/tap right back on. New bolts for the driveshaft would make that easier but not necessary with an impact. This turned out to be pretty cheap compared to a re-gear.

Dealing with the parking brakes cables was the tricky part on the rear. Other than that it was pretty straight forward.

All said and done it was $900 and that included the $150 overnight shipping, it took about 7 hours of work, dozen beers and one large pizza :rck: . If we didn't have to mess with the parking brakes and taking the rotors off of the new axle it would have been no more than a 6 hour switch. Definitley a two person job.

Let me know if you have any questions or if you know anyone that needs 3.55 differentials, Watt stabilizer, rotors, calipers, and brake lines included.
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Glad to hear everything went well for you. As long as those assemblies suffered no ill effects from the crash, I think what you did is the better way to go. Obviously, if you had paid someone to do the labor, the cost would be a bit higher. That is the kind project that one feels really good about when you tighten the last bolt, and button her up.

Great job and thanks for the report

So no reprogramming needed at all for this to work perfectly?

Where/ how did you find the axles? Also, what identifys the axles so that you know for sure that you are getting the correct ones?

Is it noticible, right off the bat?
I did not reprogram, nor have i produced any codes. So all is ok as of now. Checking the speedo with my GPS, the speedometer is slow 1.6 mph at 70 with stock wheels. But performance is great and the gears are much quieter than after market.

I got the diffs from Meyer Auto in Aberdeen, SD. It was off of a lightly rolled 04 of which I measured many times to make sure they were true and luckily they were in great shape. was the site I used to locate the specific part and showed the many different dealers that had these parts.

As far as ensuring you are receiving the correct part you just need to be specific with the dealer; what you have, what you are doing and what you need. They know the vehicles well. The 3.92s had a couple different labels wrapped around the axle from Dodge that specified the details.

It is noticeable right away. The D rolls much easier from a stop at light throttle and really moves under heavy throttle.

MPG took about a day to configure. On a controlled test, after the swap the computer showed that I was producing 15 mpg @ 70 and now I am at 18.8 which is still lower than with 3.55s.
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My D with 3:92's has consistantly averaged 14.8 to 15.0 mpg. Thats a combined number hwy and in town. In town it more like 11 depending on the gas used.

On the hwy it would show 18.9 to 20.0 if I keep it under 68mph. Hand calculated at 16.9 t0 17.

I've heard in the past that there was not much differance in mileage between the 3:55's and 3:92's. My Cummins powered 7100lb Dodge truck with 3:54's get 17 in town and 20 on the hwy.

You would think someone would just come out with a detuning tuner for those of us that don't really need 335hp. The AWD don't help with mileage either.

Axle update. Durango is running strong. there is a vibration that I've noticed when i coast at 65 mph. I'm thinking the driveshaft needs balanced, or I might unbolt the rear driveshaft and spin it 180 and see if it still vibrates. Other than that, 3.92s are very nice with 33" tires and a 6.1 cam.
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