Rear gears

[Gus350]

Looks like my truck has a set of 307 gears in it going off the numbers on the gear. I have a 400 tranny and a 700r would either one of these work good with that gear or should I look at changing the gear while I have it down (and if so to what). I'm not looking for a drag truck by no means just somthing to tool around in lol

Thanks Kevin

[Tom Vogel]

I had those gears in my 69 SWB witha T400 tranny. I loved them.When I got up to 70 on the freeway, I was just begining to move. I really had to watch it, the truck loved upwards of 75. I could roast the tires in town if I wanted to, and the 400 is a bullet proof unit. The truck had the stock but overhauled 350 it came with.
As for the 700r, Ive driven them and they seem like a powerglide with an extra gear, pretty squishy.
Anyway, thats just me, so its fwiw.

[LONGHAIR]

Depending upon the engine power and tire size, you may be ok with that gear and the TH400 transmission. The 700r4 is never going to get along with the 3.07 though, especially with a carburetor.
While it seems like lower RPM at highway speed would mean better fuel mileage, it is not necessarily the case.....again especially with a carburetor. The engine has a "sweet spot" in the RPM range where it will cruise the best. Fuel mileage and acceleration are both improved at this point.
If the cruise RPM is too low, mileage suffers because the carburetor is running in the idle and/or transition circuits instead of the main jets where it should. An overdrive transmission will shift in and out trying to compensate, this does not help matters.
Then if you need to accelerate, even slightly, you have to get too far into the throttle, maybe even kicking down to the next gear. This is another mileage hit.

Of course the opposite is true too. If your gearing puts the cruise RPM too high, it is just as bad.

[Gus350]

Okay thanks so it sounds like I need to go with the 400