Lowering differential gear ratio. Dana 44
 

Looking for some guidance/ confirmation from anyone that has changed out the ring and pinion to get a little more high end out of the old girl. I’ve read through what I could find here and have talked to Jake about his setup. Not trying to get in a debate here about them being old work horses not meant for speed yada yada yada. Please keep it to the mechanics.

Seems doable than I got to reading somewhere about different thickness gears so I called spicer tech support to confirm. The gentlemen from spicer seemed knowledgeable and said to go lower than 3.92 (current setup) I would have to change out the carrier as well which they do not offer.

My goal is to be able to cruise around 60-65mph. My current set up is 1960 V6 305A 4-wheel-drive with an SM420. Dana 44 front and back at 3.92.

I was looking at the 3.54 part# 22856-5x or the 3.31 part# 706017-2x. Obviously my truck is 4x4 so I’d have to do both front and rear. Could get pricey and I don’t want to start pulling things apart to find I didn’t order the right stuff. If someone could confirm they have done so and specific parts it would be greatly appreciated.

I’ve also considered putting a gear vendor overdrive so I gave them a call. Their bolt on over drive is 14” long (and back ordered for several months). Taking 14” out of the drive shaft would put it at a pretty sharp angle. Not sure I am comfortable doing that. (See pics) Thoughts?

Regards, T.J.

Re: Lowering differential gear ratio. Dana 44
 

My '62 Suburban came from the factory with 3.92 gears. Prior to my purchase 25 years ago, someone had changed the rear gears to 3.54, but neglected to do anything with the front end. I found that out after driving it 1300 miles from Phoenix, AZ, and attempting to drive up my steep gravel driveway. After I locked in the hubs and put the T-case in 4 high, the truck refused to move forward more than a few inches. That's when I realized the mis-match in gears. I had a local 4x4 shop change the front to 3.54 to match the rear. With 32" tall tires I have no problem with freeway cruising. It turns 2600 RPM at 70 MPH.

Re: Lowering differential gear ratio. Dana 44
 

A lot of good info here http://www.billavista.com/index.html

To my knowledge the same carrier works with 4:10 and down, so if your going from 3:92 to 3:54 you should be able to use the same carrier.

Re: Lowering differential gear ratio. Dana 44
 

From what I've read looking around at Dana 44 info, there is a split with the carriers. One carrier fits 3.73 / 3.55 / 3.31 / 3.07 / etc gears, the other fits 3.92 & higher numerical gears.

https://6066gmcclub.com/attachment.p...1&d=1698451614

This isn't much in our interest unless running tall 4x4 tires, but you CAN buy special thicker gears to run a 3.92 & up numerically on the 3.73 - 3.07 etc carriers.

The one thing about the older GMC Dana 44s that the carrier bearings are a slightly different size then most newer Dana 44s. I believe ours also use the fine spline, I believe it's a 30 spline axle shaft?

I have a 2wd 1962 GMC 1000 Panel Truck with I believe from my notes 10 years ago is a 3.07 ratio Dana 44. I'd like to keep it a 2wd for fuel MPG purposes although a 4x4 panel truck would be very cool... But I have a Suzuki Samurai LWB TDI swap project for a 4WD rig...

I'd really like to be able to pull dirtbikes on a trailer up steep gravel forest service roads, so it'd be nice to run a Detroit TrueTrac or Nitro Helix limited slip torsen worm gear lockup type limited slip unit. I'll have to look into this to see what it takes to swap to a TrueTrac or Nitro Helix carrier.

The other option is I believe Honda Passport / Isuzu Rodeo Dana 44 rear axles are 6 lug and about the same dimensions wheel mounting surface to wheel mounting surface. Perhaps rear disc even.

But I welded shut my lug holes and drilled my axles to 5 on 5" lug pattern to match a nice set of wheels I got and to match the 76-91 Suburban 5 lug disc brake coil spring front crossmember that I got to swap to disc brakes & have common and affordable front end parts.
So I'd either have to have a special rear axle for 5 lugs, or buy special aftermarket front rotors to run 6 lugs on the disc brakes, but then I could use the same wheels as my Suzuki Samurai with Toyota axles or the 1988 Toyota 4WD pickup. All same 6 on 5.5".

Now that I realized I can ratchet strap the front suspension down on my dirt bike about 3" more than it sits when I'm seated on the bike, and be able to stuff it into the back of the panel truck, I'm a lot more interested in getting this thing set up as a nice highway cruiser with a limited slip rear differential. Dodge Dakota V6 Magnum (& '87-'98-ish Jeeps) 2wd AX-15 transmission with 3.83/2.33/1.44/1.00/0.79 ratios should give me a really great fuel economy at 55 mph on 3.07's or 3.31's, even 3.55's, and will do decent enough at 70mph. The current 3.34 1st gear Saginaw struggles a little off the start on 28" tires & 3.07 diff ratio, but a 3.83 1st gear should do quite well. 3.55 would be ideal off the line but if I run the low miles GMC 351C big block V6 that I've got instead of the stock 305D, I'm going to have tons of off idle torque and will be wanting to do everything to keep the RPM down for fuel economy...
3.07 & 28" tires on an AX-15 0.795:1 overdrive 5th puts 1600RPM right at 55mph, and 1600rpm is where the 305D and 351C make their peak torque (& generally peak torque RPM = peak fuel efficiency RPM), so switching to the 351C makes most sense with 3.07 gears. 70mph = 2050rpm. Fuel miser gearing with the torquey low rpm medium duty commercial truck engine!

3.07 & 3.31 & 3.55 gears are fairly readily available, FYI. 3.42 are not common.
If you have a 3.92 differential, that's probably the lowest you can go numerically without switching carriers.


I thought about swapping a VW 2.0TDI turbodiesel engine, that'd do great with 3.73's, but still wouldn't get any better than 33mpg tops. If I could get 23mpg on the 3.07 diff with the 0.79:1 overdrive 5th gear AX-15 transmission, that would be close enough, diesel costing $1 more per gallon would mean it would cost the same per mile at 25 miles per gallon gasoline versus 33 miles per gallon diesel. So I guess keeping the 900 lb big block V6 is it then! Upgrading to a lower miles 351C from a forward cab stake bed truck over my 277,000 mile 305D... I hope the used engine is as good as it was stated to be!