Truck gearing for towing

[WhiplashTX]

Due to unforeseen circumstances, I have to replace the gears and carrier in the rear end of my truck. It currently has 3.54's and is a 24V diesel that's been hopped up and usually runs 33" to 35" tires. I usually only drive it about 5k miles a year but most of that is towing about 8000# around Texas. I also plan on taking some additional trips into the mountains out west in the next few years. Here are my thoughts and looking for some opinions.

Option 1: Replace the gears with 3.54 again and upgrade the LSD, possibly to a locker. While 3.54's are great for general use and served their purpose for 100K+ miles, it just doesn't seem geared right on steep hills with the 4 speed auto.

Option 2: Replace the gears with 4.10's and upgrade the LSD. I think I would be happier with this setup but will have the added expense of regearing the front.

Option 3. Swap in a used Dana 80. It would be a stronger setup than my current Dana 70 but it would probably have a LSD. I'm still not sure whether it was the gears or the LSD that broke first on my current setup. Most modern diesels are running a Dana 80 equivalent.

[Twist]

If it was me with a truck I planned to keep, I’d probably redo the 70 with 4.10’s to compensate for the larger tires if the truck is used for towing somewhat often. I’d also consider not running an LSD but would consider replacing that with an e-locker for when it’s needed.

If you decide on the used 80, you’d be looking at doing the same thing above in order to be on the safe side. Yes, you can swap in a used rear assembly but that can be risky if you don’t know the history of it. You could well have to pull everything out of that set up and redo it pretty quick if you don’t go through it before making the swap.

Whichever way you go, if you do re-gear and the truck is 4x4, put the same gears in the front that you go with in the back.

[TreyRo]

4.10s and E-Locker.

[Kong]

Single or dual axle? If you’ve pushed the HP up on the motor your simply going to crater it again adding even lower gears to the old housing because it’s going to take even more abuse. It would be a no brainer for me and I’d be swapping the complete assembly for a newer/bigger axle with a lower gear set in it.

As far as gearing itself goes what transmission are you running? That matters on the gear ratios to me but for 100% towing I’d be going with 4: somethings for sure. I’ve got mostly 4:88’s and it’s night and day different than 4:10’s we have but they get better fuel mileage. Decisions decisions lol

[cashcropper]

If you have done engine work which should also increase torque the .354 is fine. You should already know the answer to this from the last set of gears. If you feel like you need to go with lower gearing a .373 should be a good all around ratio. The weak point is now the Tranny. Have you upgraded it?

[WhiplashTX]

Single or dual axle? If you’ve pushed the HP up on the motor your simply going to crater it again adding even lower gears to the old housing because it’s going to take even more abuse. It would be a no brainer for me and I’d be swapping the complete assembly for a newer/bigger axle with a lower gear set in it.

As far as gearing itself goes what transmission are you running? That matters on the gear ratios to me but for 100% towing I’d be going with 4: somethings for sure. I’ve got mostly 4:88’s and it’s night and day different than 4:10’s we have but they get better fuel mileage. Decisions decisions lol

If you have done engine work which should also increase torque the .354 is fine. You should already know the answer to this from the last set of gears. If you feel like you need to go with lower gearing a .373 should be a good all around ratio. The weak point is now the Tranny. Have you upgraded it?

Single axle and 47RE transmission. The only issue I've had is the big jump between 3rd (1:1) and OD(0.69). If I'm doing 70, it turns 1800rpm in OD and 2600rpm in 3rd. The truck really prefers to be around 2000rpm and pulls better at 80mph than it does at 70 in OD. I'm leaning towards the used Dana 80 with 4.10's right now.


Everything is upgraded; chip, injectors, bigger turbo, head studs, and fully built transmission. Torque is close to 1000 at the wheels, I keep it turned down for towing though. I know the new trucks are getting close to where I'm at now with a closer ratio transmission but I don't want a house payment.

[WhiplashTX]

Update:

Well, I went with the Dana 80 and 4.10 gears. Solo the revs kinda suck but towing is a dream. EGT's are down 125 degrees while towing and no lugging on the hills in OD. I had dropped down to 33" tires since I started towing so much but will probably go back to 35's. The new axle is open and even moderate throttle spins a tire, looking for a locker now.

[Kingfisher789]

4.10s and E-Locker.

That right there. Tow to get there

[Texas Grown]

Whip, that is the same thing I'm run-n in my '97 F250 4x4: 4.10s and 33"s. 2200 RPM at 70 mph.