Overdrive Trans or Ring and Pinion swap?

[Just Mark]

Hi Folks, Mark here. Took my 47 GMC to SETN last month and had a blast. Trailered most of the way, drove about a hundred miles each way. Wanting to drive my squarebody from central Michigan to Lebanon Tennessee next year for the event. The challenge is that my Squarebody is an 81 1 ton Dually and has a pretty steep gear. Not sure exactly what it is, but at 70 MPH I'm turning 3500rpm. Can't drive all the way like that. I'm looking into swapping the trans or the ring and pinion. The truck will never be a "hauling" truck again so I'm thinking a 700R4 would be plenty strong enough.

I really don't know the pros and cons of each. I could swap the trans myself, but would use the Ring and Pinion shop near Detroit for the rear end if I went that route.

Suggestions?

You must be registered for see images attach

 

[Shorty81]

Welcome Mark. That's a great looking dually. I would put a 3:73 in her and let it be.

 

[82sbshortbed]

How tall are your tires? What ring and pinion gears are in there now. I'm thinking of something similar on mine.

I just put a 3.73 posi rear end in my c10 with a th350 and 28" tires and run 2700rpm at 55mph. Which is a little more rpms than I like. So I was thinking of putting in a 700r4 with od or switching out gears to a 3.08 to drop rpms. So I could do more highway driving.

Here's a calculator to maybe help you decide what to do.

https://spicerparts.com/calculators/engine-rpm-calculator

 

[cstew47]

Hi Folks, Mark here. Took my 47 GMC to SETN last month and had a blast. Trailered most of the way, drove about a hundred miles each way. Wanting to drive my squarebody from central Michigan to Lebanon Tennessee next year for the event. The challenge is that my Squarebody is an 81 1 ton Dually and has a pretty steep gear. Not sure exactly what it is, but at 70 MPH I'm turning 3500rpm. Can't drive all the way like that. I'm looking into swapping the trans or the ring and pinion. The truck will never be a "hauling" truck again so I'm thinking a 700R4 would be plenty strong enough.

I really don't know the pros and cons of each. I could swap the trans myself, but would use the Ring and Pinion shop near Detroit for the rear end if I went that route.

Suggestions?

You must be registered for see images attach

I would put in a 700R4/4l60. The gears would depend on your tire size, for example, I am running 4.56 gears with my 4l60 on 35" tires. I am barely above 2500 rpm at 55mph. An added bonus is that this tranny has a very deep 1st gear, so you can take advantage of the low end torque.

 

[cstew47]

I would put in a 700R4/4l60. The gears would depend on your tire size, for example, I am running 4.56 gears with my 4l60 on 35" tires. I am barely above 2500 rpm at 55mph. An added bonus is that this tranny has a very deep 1st gear, so you can take advantage of the low end torque.

 

[cstew47]

I would put in a 700R4/4l60. The gears would depend on your tire size, for example, I am running 4.56 gears with my 4l60 on 35" tires. I am barely above 2500 rpm at 55mph. An added bonus is that this tranny has a very deep 1st gear, so you can take advantage of the low end torque.

 

[cstew47]

Sorry for the multiple posts. I haven't figured this system out yet

 

[Vbb199]

Well, for some scale, i swapped my suburban's 3.42 to a 4.10 with its 31" tires, 700r4.

At 75 or 80 mph, its taching like, 2000-2300



Works out well for towing also. I can load up 7-8k pounds behind it and with the deep 1st in the 700r4, i can get the load moving quickly.



Assuming your 1 ton has a big block, you may wanna consider more like 3.73 + 700r4 so that big block aint yelling the entire time.

I have a sbc, i have no fear of running it hard continuously.

 

[Vbb199]

^ matter of fact i just drove 4 hours saturday to the SC coast....
Mainly highway time...

You must be registered for see images attach

 

[Matt69olds]

I wouldn’t hesitate to run a well built 700 with a small block, or a mild big block. You gain the best of both world, much lower 1st gear to get the truck moving at low speeds, the overdrive will tame the rear end gear, the lockup converter will take a lot of heat out of the cooling system.

Find a reputable shop, have a trans built with a wide band, upgraded servo, upgraded 3-4 clutch, drive shell, input sprag, and some valve body upgrades. Install a big trans cooler, if it’s built a d installed correctly it will last.

 

[Bextreme04]

Since you're 2wd and your profile shows a 350... I agree your cheapest and easiest route would be a swap to a 700R4. You will maybe need to have your driveshaft shortened and you will want to have the 700R4 built well by a reputable local shop and put the biggest trans cooler you can find on it(Tru-Cool 40k is the usual go-to).

A C30 dually would most likely have 4.10's, but that depends on options and power team.

 

[Just Mark]

Thanks Guys, I appreciate the feedback! Yep I've got a bone stock 350 4bbl. I believe the rear end is a 4.10, but not positive. I'm gonna start looking for a 700r4. I'm also gonna make a call to Ring and Pinion shop to get some pricing on putting something a bit shorter in it.

Also, that chart is pretty handy. Thanks for that 82sbshortbed!

 

[Bextreme04]

Thanks Guys, I appreciate the feedback! Yep I've got a bone stock 350 4bbl. I believe the rear end is a 4.10, but not positive. I'm gonna start looking for a 700r4. I'm also gonna make a call to Ring and Pinion shop to get some pricing on putting something a bit shorter in it.

Also, that chart is pretty handy. Thanks for that 82sbshortbed!

Aren't the dually's a Dana 70 rear? The cab and chassis ones are a narrow 14BFF though right?

You might want to check and see what ratio you have now. The Dana 70 has a carrier break just like the 14BFF, so if you have a 4.10 now, you can go lower ratio with no issues. If you have 4.56's you will need special gears or a new carrier to go lower, since the carrier break is at 4.10. Rockauto has ring and pinion kits for around $200 and looks like 3.54 or 3.73 are standard options.
https://www.rockauto.com/en/catalog...drivetrain,differential+ring+and+pinion,10438

 

[C10MixMaster]

Gear vendors overdrive may not be the cheapest option, but you would keep the strength and towing capacity while lowering you highway cruise RPM.

 

[Just Mark]

Any idea if the transmission crossmember from the th400 will work with the 700r4?