good tranny to change to?

[Gus63]

I have a 63 chevy k10 pickup right now with the factory sm420 tranny in it with a divorced transfer case. i would like to change to a different transmission, either a 4 speed without the granny, or a 5 speed. i basically want to be able to cruise on the interstate without running 4500-5000 rpm's. what are some good transmissions for a truck that could be put into my truck without much modifying? i still need to be able to tow when i need to, but not much. i was thinking about a nv4500, but they are a little too expensive for my budget.

[martindc1]

Most 4 speeds will all have the same 1:1 high gear, so they won't do you any better than the sm420. I say most because there is only one 4 speed I know of with no granny and where 4th is overdrive, but its from a Ford. You do however have a bit more flexibility since you have the divorced transfer case, so good luck in your search. Seems like I read somewhere about somebody putting an overdrive unit between the transmission and transfer case on one of those.

But what you really need to consider first is your axle gearing and tire size.

A simple solution would be to go to a 700r4 auto. I personally prefer manuals though.

On my 67 K20 with 4.57s, the best thing I did for highway cruising was a muffler.

[Mike C]

Lift it and put TALL tires on. Otherwise, swap in a set of later model axles with less gear. Another option, but not any cheaper than the NV4500 in the end is to swap in an SM465/205 combo with a gear vendors overdrive on the back. You could always go to a TH700, but IMO, a swap to an auto is more than one step backwards...

[Gus63]

So as far as rear end gears go, what do you think would be good ones to go to? I don't really know anything about them. Will lower, or higher gears get me where I want? I have 31 inch tires on, and don't really want to go any bigger. Thanks for the help.

[martindc1]

Depends on your engine, I know that my K20 with it's 250, 31-32" tires and 4.57 gears is just right.

Do you know what gear ratio you have now? What engine do you have?

I agree with Mike, keeping your current transmission and switching to some later axles with the gear ratio you want is probably your least expensive and least complicated option. You will also get the benefits of disk brakes, tighter turning radius and better parts availability.

The gear ratio you would want really depends on your situation and how much towing you'd be doing etc., but if I were to guess, 3.73 or maybe 3.42 would be in the right range. Plus if you need the extra grunt, you always have creeper gear.

[snj8198]

find a 2wd nv4500. i think i see one listed by a motivated seller in the 73-87 classifieds. -steve

[USSkoval]

Someone on here just swapped in a factory GM 4speed overdrive (from mid 80's) into their truck. I think it's really rare though, never saw one before that thread.

[Gus63]

Right now I have a 400 small block in it, but I will be switching to a 454 as soon as I get it rebuilt. I really have no clue what gears I have now. Is there a way to find out? Thanks again! Also, what year of axles would you guys reccomend if I were to switch? Are there any with disc brakes that would bolt almost directly up? If I were to find an nv4500, would that fix my problem, or would the rear end gears still be holding me back? Again guys, thanks, I don't know anything about this stuff, and appreciate all of the help I can get

[Yukon Jack]

Gus, an easy way to check your gear ratio is to put a chalk mark on your driveshaft and one on a tire. Have someone move the truck forward slowly and count the number of driveshaft rotations to one tire rotation. Just over 3 rotations = 3.07 gear, 3 3/4 rotations equals 3.73 gear, just over 4 rotations equals 4.10 gear, just over 4 1/2 rotations equals 4.56.

[1985-GMC]

Originally Posted by USSkoval

Someone on here just swapped in a factory GM 4speed overdrive (from mid 80's) into their truck. I think it's really rare though, never saw one before that thread.

Is this the one you were thinking of? http://67-72chevytrucks.com/vboard/s...=1#post3962721 Ive only heard of these transmissions a few times.

[USSkoval]

Originally Posted by 1985-GMC

Is this the one you were thinking of? http://67-72chevytrucks.com/vboard/s...=1#post3962721 Ive only heard of these transmissions a few times.

Yes, that's the one, thanks. Too bad they are so uncommon.

[Davetopay]

Originally Posted by USSkoval

Yes, that's the one, thanks. Too bad they are so uncommon.

It's a Mopar trans from the late 70's.

[LILRED66]

Pull the pumpkin covers and count the teeth on the ring gear (big one) and count the teeth on the pinion gear (small one), divide the big number by the small number and the result is your gear ratio, exact, with no interpretation or rounding.