3 speed with a 3:08??

[Slick67]

A friend of mine ,U.S. Marine, and fellow 67 C10 owner needs to know if a 3:08 rearend would be too much of a burden on a 6 cylinder with a 3 speed column shift. The truck currently has a 4:11 in it and he is concerned with bogging on takeoff if he changes the rear. I do not see any issue with this swap, can anybody give me an idea as to how it will react? I know highway milage will be better and the RPMs won't be off the chart if he does the swap.

Thanks for your service Brandon!!!!!

[69GMCLonghorn]

It will pull it, you are correct. The question is how well? If you get the RPM's down too low on the highway, the mileage will tank because he'll have his foot in it all the time (I know thru past experience on this one).

If it was me, I'd look into a happy medium. 3.42 gears would be a much better choice. With average sized tires, he'll be around 2500 @ 70 MPH and still have enough low end to start out on a hill without obliterating the clutch in the process.

[brothers69c-10]

our old 69 had a 307 rated at 200 hp with a three on the tree it ha d308's as well and it did fine going down the road. Getting up to speed kind 've sucked cause swhen the motor got warmed up it would lose compression due to the valves seals being shot, but it ran 65 pretty decent. I know he has a 6 banger ,but i would think it would be a little torquier than a 307.

[69GMCLonghorn]

Yeah, it's definitely not like the 6 won't move it. They do very well. The downside to the 3-speed is that you get into that situation on the freeway where you're doing maybe 45-55 and need to get out and pass a truck. Do you hit 12,000 RPM in 2nd and get it done quickly? Or do you stomp on it in 3rd and take your time about it? That's more of a tranny issue than an engine issue though.

I ran a 69 307 with a 4 speed and 4.10's for years. I'd have to go with the 307 on torque. It was rated at 300 lb-ft. The guy that had it before us was a tree trimmer and regularly towed a loaded triple axle trailer up a big hill to the land fill with no problems. One run, he was well over 15,000 lbs.

['72customdeluxe]

It would be pretty hard on the clutch to get it moving with any kind of load in my opinion. My truck has a 350 and does ok just putting around, but first gear on my automatic is really too tall. It'll run 50 plus in first shifting itself. And what really sucks is the gap between the gears. It falls off between shifts. A junkyard overdrive tranny would probabaly be a better use of time than installing 3.08's. And I still run fairly high rpms on the highway. Maybe it will be better without 31 inch tires, but then my rpm will be even higher on the road

[69GMCLonghorn]

There are a 100 different options. One of the best options I've ever driven was a 6 cylinder, 3.42 gears with a 700R4. The 700 has a lower 1st gear than a TH350 or the stick. And then you have the added bonus of the O/D. Guaranteed better mileage and longevity...

[Slick67]

Well....being that we live in Houston, there are no hills so that will not be an issue. Currently the truck tops out at about 75mph. I have the factory 67 rearend from my truck and it is either a 3.08 or a 3.73, but if it will work better than what he has, it's his.

Final Thoughts Anyone???

[bhoeger70]

I had a 87 1/2 ton with the 4.3 and 3.08 gears but had the four speed, it did just fine.

[Blazer1970]

It will be fine as long as you are running a ~28" tall tire.