Hoping for some advice here. I've done a search and read a lot of the old threads and am getting ready to pull the trigger on re-gearing the rear end in my '93 D350 (4.10 posi currently). Not the most friendly set-up for a highway road trip cruiser.

I do zero towing. 95% of my driving is unloaded save for the aux tank and minor tools. Furniture moving and the occasional Home Depot run. I'd thought about swapping to a 3.07 (I'm running a Getrag 5sp and stock size tires).

The shop I'm working with has a lot of experience setting up custom rear end gears and tells me we can most likely put whatever I want in there with a little customizing.

So do I go with something like a 2.8x or even the 2.5x range? I'd like to get some excellent mileage cruising the 75mph interstates (read torque peak at 75 mph to be at 1500-2000 rpms at 70-80 in 5th). Any opinions?

Pipe dream or bad idea for reasons I hadn't considered?

 

Check out Gearvenders or Gear venders they sell spcecial transmissions that will do exactly that

 

The way I understand it is that the 3.07 rear is a dana 70u and it has a larger housing to fit everything in there. I didn't think any taller gear ratios could be jambed in there but I would like to be wrong.

Try to get it with a limited slip or locker then let me know if it works good so I can do it too

The gear vendors are nice but are about $3,000. The new ones have electric shift and can be shifted under full load.

 

I've read on the gear vendors and unless I comes across a smokin' deal on a used one, the price is a bit prohibitive.

The 3.07 with housing swap was what I initially thought was going to be my best bet but I'm hearing from my shop that they believe a lot more is possible with some custom set-up work within the existing Dana 70 housing.

 

The trucks that had 3.07 gears had a Dana 71 not a Dana 70. And from what I understand the housing was machine bigger inside so there was clearance for that big ring gear.

 

I have a gear vendor and for anybody with a 5speed truck and 4:10's it is quite nice upgrade and a different truck to drive after the fact (you can keep up with traffic). Just my 0.02$

 

What did it do to your MPG ?

 

Whoops, thats right. I don't know what I was thinking.

 

I personally think it would be easier and cheaper it you just swapped in a 71.
I have a 71 in my truck with the 727 auto. I figured out if I were to swap in a A518 it would get me about 3-4 mpg. Which is enough savings in fuel for a year to pay for that swap.

Now since your truck is a 5spd I would think you could get another 2-3mpg over the auto 4 spd.

 

I picked up 12 MPH going with 3:54s.
From 4:10s and i think 2 MPG

 

The ring gear is the same diameter on all the ratios. the pinion gets larger as the numeric drops. So large at 3.07 they had to move it over a bit.
cheers,
Douglas

 

Changed d350 5spd from 4.10 to 3.54 gears and went to 385 tires for a gain of 20%. did some work on the pump and turbo and it got me about 2mpg when towing and 4.5mpg empty. Most of all "woke it up" so it now performs like it never did stock.

 

If I could get 4 mpg more out of one of these, @ $4 a gallon for fuel thats 60,000 miles to payoff. Not too bad.

 

Sounds like very little experience on the Dana 70's.

A 3:07 gear will not work in your current axle housing. Like Douglas stated. The pinion is offset to allow the larger pinion gear to fit in the axle housing. Here is a pic of a 3:07 and a 3:54 pinion side by side. Note the size difference.





Now the good news. A 3:07 uses the same carrier as a 3:54/4:10 ratio. So adding a L/S to a 71 axle is easy. Match the spline count up for your axle, reset the back lash and your done.

With 3:07's. 235/85/16's with my .79 OD on my G56. I see right at 1650 RPM at 60 MPH. 80 MPH comes in at 1900 RPM.

 

To make it an all-purpose rig, a 6 speed and 3.07s would be about an ideal set-up.
It's what's going into my next ride.

5 speeds and a lot of weight with the 3.07s aren't a great combo with that wide 2nd to 3rd ratio gap.

Mark.