The Stovebolt Site Forums The Parking Lot Big Bolts what rear axle do i have? w/ pics

Hey fellow bolters,

I have a 1949 chevy 6400.Im wondering what type of axle this is so i can have better luck with the gears when i change them out.Also, if anyone has any helpful tips or links on restoring the 2 speed vacuum changer, it would be greatly appreciated.
Thanks, Dan
http://i612.photobucket.com/albums/tt202/dantheman176/IMG_0723.jpg
http://i612.photobucket.com/albums/tt202/dantheman176/IMG_0724.jpg
http://i612.photobucket.com/albums/tt202/dantheman176/IMG_0728.jpg
http://i612.photobucket.com/albums/tt202/dantheman176/IMG_0729.jpg

I just went out to find my gear ratio of the rear end and found it to be 3.11:1 Im guessing the axle is in high gear. Any suggestions for changing out the gears on this axle to get some extra mph's?

Thanks again,
Dan

Hy dantheman49-6400, that is a Timken double reduction two speed, it has a high speed ratio of 6.13 to 1, and a low speed ratio of 8.1 to 1. To shift from low to high vacuum and atmosheric pressure are reversed at the diaphragm shifting unit on the differential, so that diaphragm must be in good condition. The capacity of that axle is 13,000 lbs. hope that helps.

Both of those ratios do not match what i found on the truck right now... i jacked up one side of the axle and for every one time the wheel spun around, the driveshaft spun around 3 times. making it a 3:1 ratio, or something close to that, correct?

you have the original axle 3B cites, the reason you don't get the 6.1 ratio is you need to turn the wheel twice, not once, that truck would have a hard time getting rolling with a 3.1 ... if in doubt take off the cover and count the teeth

Bill

You have to double what you get with one wheel jacked up which gives you 6.03. There were no rear ratios in the 3's 2 tons in those days.

so with a ratio of 6.03:1 do you think my axle is in high or low?

by 3B's listing of the specs, 6.1 would be the high ratio

Bill

What type of axle is a popular swap for this big truck.i wont be needing to haul anything heavy like its set up for now. Im looking more for comfort and a little more speed.

Dan

Hy dantheman49-6400, that high speed ratio is actually a little better than most, most of the Eaton two speeds I've seen are 6.50 to one. If you put on the tallest tires you can you'll gain a bit of speed. What do you intend to use the truck for?

i use the truck as a weekend warrior.i wont be needing to haul anything big. just want to make the truck a comfortable driver that i can tow a car at the most with.

That is about as fast a ratio as you will find for the rear. If you want to go faster, the next plan would be an auxiliary transmission or a 5 speed OD transmission. However, if you have the original engine, you don't have enough HP to go much faster than you do now.

I have a 1962 261 in the truck. What is the auxiliary transmission? Where does it go?

Hy dantheman49-6400, an auxiliary transmission is mounted on the frame, in between the transmission and the rear axle. Some of them have three gear choices, underdrive, direct, and overdrive, some have only two, direct and under, or direct and over. The ones appropriate for your truck are getting rarer as I type, and they are expensive, they also require mounting crossmembers, shift linkage, and custom length driveshafts. Personally I think an overdrive transmission would be a better choice, I think a fairly common one is the NV4500 [I may be wrong on the number] hope that helps.

would the nv4500 be a direct bolt in on my stock driveline setup of a 1949 chevy 6400 with a 1962 chevy 261?

Hy dantheman49-6400, I believe the easiest NV4500 for the swap is one designed to be used in a Dodge application there is a spacer/adapter to be used/purchased, but it is still the most straightforward swap of this transmission to our running gear. there may be some information in the Tech Tips section, or start a new post asking how to swap an NV4500 into your truck, hope that helps.

There are rear axles available with faster gears.
The simplest would be a single speed from the same years, they bolt in and can have marginally faster gears.

Here's a tech tip about swapping a later model rear axle with lots of faster gear choices.
http://www.stovebolt.com/techtips/bigbolts/p30swap/
Only big complication is they have disc brakes, and it's normal practice to also have disc on the front if you want them on the rear, and putting them on the front is not nearly as easy as the rear axle swap.

Also don't be fooled into thinking you can travel as fast as you want with the proper gearing. The 261, while it is a good engine, with it's still relatively low HP in combination with the heavy truck will limit how fast you can go. Just guessing from my experience, but I expect you'd be unhappy with anything faster than 4.56 gears.

An overdrive transmission swap like the NV4500 is also a great idea.

Here's a site where you can calculate speeds and RPM with given ratios and tire sizes.
http://www.onlineconversion.com/bigger_tires.htm

Grigg

If you are looking for speed you will most likely need to change out the entire drive train. If you just want a little more speed I would either change out the rear end to a more modern with a higher ratio or add an auxiliary transmission.

While a little more expensive than finding a used older auxiliary you could easily add a gear vendor over drive (http://www.gearvendors.com/agmanual.html). If you change out the rear axle you may have an issue as your wheels won't all be the same. If you change out the transmission....then what is the point in keeping the original engine as well.

If you do change axles make sure you try to sell it....there are a lot of people who would for sure be interested in an old two speed...depending upon location and price of course.