Tranny for towing

[Stitch]

I have a C20 crewcab shortbed that I'm putting a 6.2 diesel in with a 700R4 for now...the 6.2 diesel is going to stay in the truck and probably get a turbo...We are getting around a 30 ft travel trailer and going to tow it with the C20...I know the 700R4 probably won't last long towing all this, so my question is...

What would be the best transmission and rear end gears to put behind a turbo 6.2 for towing and gas mileage?...I know that I'm not going to get great gas mileage towing the travel trailer, but I'd like to get decent gas mileage and I also don't want it to be a slug...I want to be able to go 70 in a 70 mph zone...it can be a standard or auto transmission...and I can change the gears in the rearend...it has 4.10s now...just need to know what would be the optimum setup for towing the travel trailer...I won't be towing anything heavier than that, and I'll only be towing that a max of probably 5-6 times a year...

thanks guys...

[Matt Man]

Originally Posted by Fat Hoe

I have a C20 crewcab shortbed that I'm putting a 6.2 diesel in with a 700R4 for now...the 6.2 diesel is going to stay in the truck and probably get a turbo...We are getting around a 30 ft travel trailer and going to tow it with the C20...I know the 700R4 probably won't last long towing all this, so my question is...

What would be the best transmission and rear end gears to put behind a turbo 6.2 for towing and gas mileage?...I know that I'm not going to get great gas mileage towing the travel trailer, but I'd like to get decent gas mileage and I also don't want it to be a slug...I want to be able to go 70 in a 70 mph zone...it can be a standard or auto transmission...and I can change the gears in the rearend...it has 4.10s now...just need to know what would be the optimum setup for towing the travel trailer...I won't be towing anything heavier than that, and I'll only be towing that a max of probably 5-6 times a year...

thanks guys...

i was going to say a turbo 400 until i read that its the 6.2. i would say a nv4500 with 3:73 gears with a 31 inch tire. as far as 70 goes you probably could do 70. but even with a turbo 6.2 it might have difficulty keeping that.

[TwoFiftyShifter]

How heavy is the trailer? Pulling it is only 1/2 the equation... will you be able to stop it from 70? My biased vote is for an SM465 4-speed with a 3.42 axle ratio. Very strong setup, has low gears for around town, and would be about 2600 rpm at 70.

[James McClure]

I'm with 250. I have a 7000 pound utility trailer I pull regularly but with 3:08 gears. 350CID & 465 trans. I can get 15 MPG if I'm easy on the gas. jim

[D13]

You 700R4 might suprise you, mine went a long way including towing abuse. Just don't drag race it.

4l80E with a stand-alone controller, out of a 90's diesel. It's a 400 with OD and lockup.

Not sure why the 6.2 turbo, why not pick up a complete 6.5T 4L80E out of a later model and swap it in?

400 is fine behind a 6.2, just need the 1 ton control system and a good converter.

Manual, NV4500 would win for me. You already have a hydraulic clutch cab.

[Pyrotechnic]

The SM465 would be the most cost effective route. Yeah it's not a 5 or 6 speed, but the ratios are wide enough to where you can put rear end gears that will get good gas mileage in 4th gear, and the granny gear will still have plenty of ratio to get it moving.

[Stitch]

I am swapping the 6.2 out of my other truck that I have...so I'm using what I have already...I was think about the 4l80E, but I thought I would need a computer with it...I thought that would be too complicated..maybe i'm wrong...

and about it stopping, I don't see why not...the travel trailer will have trailer brakes, and I'm converting the 14 FF in the rear to discs...it'll have hydraboost brakes, so I don't see why it won't stop...if you see something that says otherwise, please tell me...I want to be able to stop...

so I have a few questions...

what's a 1 ton control system?

what do you mean by hydraulic clutch cab...the cab had an auto in it...

what's the better transmission for towing? SM465 or NV4500? What's the cost difference between the two? and also, I might not have been clear about the gas mileage thing...I don't really care the gas mileage I get towing...I know it's going to drop drastically...that's fine...I am going to be running WVO while towing long distances, won't be running WVO around town probably...I only have a 12 mile commute to work...I would like to keep the gas mileage good around town unloaded though...I get 26 mpg in town now...I know I'm not going to keep that going from a 1/2ton swb to a crewcab 3/4 ton swb...

rear end gears? I have 4.10s now, if I went with either of the standards, what would be a good gear or will the 4.10s be fine?

what is the optimum rpm for the 6.2 diesel to cruise at on the interstate? that'll help determine the gears I'm sure...also, I can cruise at 60 or 65 while towing is fine with me...if that'll help...I've towed cars on car trailers down the highway before, but never towed a travel trailer before...It'll be a new experience for me for sure...I would say the travel trailer probably wieghs as much as a car and car trailer setup, but the wind resistance is going be alot higher with the travel trailer...

thanks for all your help guys...

[Big Port Jimmy 6]

I had a C30 rollback with the granny 4 and a 6.2 and it would pull two cars at 80 + and get decent mileage. Jay

[Stitch]

when you say granny 4, which transmission is that...and what rear gears were in it if you remember and what kind of mileage did it get...I know that's alot of questions, lol, but I'm wanting to do this once...thanks

[munger]

granny low is the sm465 4 speed tranny the mosr common 4 speed in gm trucks

hw said hydralic clutch cab because a 87 would of had a hydralic clutch if it was a manual

[Stitch]

thanks for the clarification...

[MR .T]

Originally Posted by D13

Not sure why the 6.2 turbo, why not pick up a complete 6.5T 4L80E out of a later model and swap it in?

I like the 4l80e idea

[dan76]

http://www.novak-adapt.com/knowledge/sm465.htm

To reduce your initial outlay, I'd suggest the SM 465 trans. It's rugged, has a deep first gear and is economical to obtain. I've bought two in the past year for about 100 each. However the NV 4500 is my choice if towing frequently and/or using as a DD due to the OD feature and toughness. But it's expensive. I've pulled a couple from wrecked trucks at reasonable cost but folks tend to price them high...especially the 4wd models. However since your truck is an auto, you'll have to rig the hydraulic clutch system. If you're handy it's not much of an issue.

[82swampthing]

sm 465 or nv4500.

[D13]

TH400 uses vacuum modulation to control shifts. Diesel's don't make vacuum like gassers. TH400's were used behind normally aspirated diesels and some turbo conversions (like 6.2 with Banks) in some 1 ton and delivery van applications, and in military units. These have a vacuum pump and throttle sensing system to modulate the TH400. I have heard there is also an aftermarket system available for the turbo set ups.

Early diesels with the 4l80E have a stand-alone controller that senses throttle input and controls the trans. 6.5 NA applications, late 6.2, and some early 6.5 turbo packages, again in 1 tons and heavy vans. This is a great rig for a swap if you can find one. The key is to get one before all the electonically controlled functions went together, so it must be a diesel pre-Duramax set up.

[Stitch]

D13, thanks for the information...

what would be the optimum rpm to cruise on the highway at 65 mph be...

and what would be the correct gear ratio for the rear end to put the engine at that rpm using a 4l80E and an SM465?

thanks for all the help so far guys...I'm definitely going to get this truck right with the help here...thanks again...

[jrp267]

Depending on cash a th400 with a gearvendors overdrive would be nice. And then 4.10 in the rear. You can tow in od with a gear vendor unlike the 4l80e

[Stitch]

what does a gear vendors OD cost...and that would work, because I have to get my driveshaft shortened anyways...

[jrp267]

Ohh they are pricey. They go on ebay for about 1500 rebuilt or 26 to 28 new.

[1973GMC_1500]

I would say SM465, but mine doesn't tow like I thought it would. The gears are WAY too far apart. You pretty much have to hit the governor before shifting and then it is almost lugging too hard to pull through.
I'm going to make a 30 mile (each way) trip pulling a '28 gooseneck this weekend, will let y'all know how it goes.
A turbo 6.2 would probly be ok. But my 700R4 6.2 burban seemed like it could accelerate a lot easier than my SM465 C20 (the stick is still way more fun tho)

[jrp267]

But another bright side is the gear vendor will also split every gear in the tranny. http://www.gearvendors.com/

[Stitch]

what about a built 700r4

[munger]

to pull good with power and mileageyou need a 20% overdrive like 0.80 not .70 or 1:1 idk where you can find a tranny like that

my dad has a 06 gmc 1500 ccsb it has a 4l60e and always jumps in and out of third and fourth when towing to low of rpms in od to high in direct and its basically a 700r4 so its not good for towing

[Stitch]

the gears will keep it in the power band where it needs to be...I'm not asking of the ratio is good in the 700r4...

I'm asking if a built 700r4 will tow what I'm asking...that's all...thanks

[jrp267]

I have seen some very well built 700 r tow heavy but they cost as much built as anything else. so its an option.