Of gears and towing...

[Quikshft]

Hey guys, my truck is currently an L31 350 with an SM465 and 3:07 axles with 33” tires. It cruises the freeway quite nicely, but I tow an 18 foot RV that weighs about 4500 pounds, at 55 mph the engine is 1700 rpm. I have been thinking about upping the axle ratio to 4:10 which would result in a 55 mph cruise of about 2300 rpm which I believe is closer to optimum.

I have considered the Ranger Torque Splitter, when engaged it reduces engine rpm by 22%. Interestingly in 3rd gear with a Ranger engaged, my engine rpm at 55 mph would be nearly identical to what a 4:10 axle gets me – 2300 rpm.

If I actually went through with this, I’d be putting a lot of miles on the transmission in 3rd gear. Does anybody see a problem running/towing with the SM465 in third gear?

[Mike C]

The SM465 is an exceptionally durable transmission, but anytime you run power through the countershaft there will be more wear and tear than through direct drive.

I would consider 3.73 gears which would be a 25% increase and should cruise fairly well still.

I have 4.10 in my Jimmy with 35's and the SM465. Turns 2500 or so at 65 mph. If I was going to improve my trucks towing I would build a 383 for it.

[Quikshft]

Thanks Mike C, I kind of figured that was the answer I'd hear. I could go with 4:10 gears and add the Torque Splitter to get the cruise back.

[Mike C]

To me the torque splitter seems to be an answer to a question that doesn’t exist any more. With more powerful engines and transmissions with more gears they just don’t seem to be needed.

For me, cost is important so I would want to know what the financial impact would be.

Also, I just assumed your truck was 4x4 since you were running 33” tires in a 1/2 ton but I could be wrong. That makes transmission length changes more $$$ because front and rear driveshafts have to be modified.

3.73 and 500#/ft torque are the answer to your problem!

[Quikshft]

Oh yeah cost is a critical factor. If money was no object I'd probably start on a NV4500 swap. A Ranger is $1600 these days, that unit isn't going to pay pack in gas savings for a long time. Yes my truck is 4x4 long bed as you suspected.

Realistically, I own this truck to pull my trailer. From the central valley of Calif the beach or mountains are only a couple hours away, the desert is a little more. Probably just need to optimize the gearing in my axles for handling the trailer and live with what the result is on the freeway when not towing - that won't be too often.

[Ironangel]

I've been towing 6000 lbs with a C/10 350/350t and 3:73 gears for six years now. At 75 mph the tach's pushing 3500 rpm on 33" meats. Im thinking 4:11's would be a bit overkill...Just my .02