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I have a 1940 1/2 ton I want to change the running gears to modern..What rear end fits.to give me an original look with the running gear able to handle a 350 motor I want to install

When you say look original, do you mean torque tube drive line? If so, I've beleive the 49-54 car rearend will interchange and the automatics come with 3.55 ratio. Check the tech tips for more information on this topic.

thanks ,by original I mean a rear end wher my tires wont be outside the finders or to far under the finders..

is there a modern equivalent that has about the same deminsions but with disk brakes i have a 39 and same type of queston applies to me far as the 49 to 54 stuff would rather have reference to something alittle more common at most salvages

used a 79-80 malibu under my 37 and it works like a charm. I had to move it about 1 1/2 inches to get the wheels centered in the wheel well but thats easy with a piece of metal with offset holes drilled in it.

There is a tech tip here on the bolt that list the width of rear ends of a lot of donor cars that will work. You'd be surprised how many!!
On most all of them you will have to add a set of perchs/saddles and weld them to the new housing. Just don't weld them till you set the pinion angle.

I believe its the firebird that some guys use that have the rear disk brakes but I'm sure there is others.

I have a 1940 gmc, and I used an IMCA modified f@rd 9 inch rear. I was able to spec out width, number of axle splines, lug pattern, and size of disc brakes. I ended up with a 61 inch wide rear... 2 inches wider than stock with the stock 6 lug on 5.5 inch bolt circle. I am using 16 X 7 rims with 4 inches of backspacing. Don't know for certain that the tires will clear as I don't have it all together yet. I did the math several times before I ordered.

It may be possible to get a pumpkin from a 54-59 chevy 1/2 ton and use your stock axle. You will have to modify the axle mounts, and you would still be stuck with the huck brakes.

John

Late 80's Camaros/Firebirds are 62" wide from mount surface to mount surface. The IROC-z's came with posi/disc in 3.08, 3.42 and 3.73 with the 3.08 the most common. Not familiar with the mounting width of your year truck but they are a 5 on 4-3/4 lug pattern and front disc conversions are available in that size from most vendors.

The diffs are from behind the 2.8 V6 with automatic transmissions. They're a great conversion into AD's and hopefully the earlier trucks....plentiful, relatively lower mileage and cheap. If 62" will work, it's another option.

Dave

i have seen trucks like mine and all the way up into the 50s with the camero rears they always look too wide was looking for something alittle narrower but i have heard S-10 rears arn't a good choice for some reason

The S-10 rear ends will look too narrow with the wheels inboard too far on an AD truck. If you plan to use wide tires and rims you can fool around with the backset of the wheels to pull them out closer to the fender. Also because the S-10 is narrow ,you will have to tub the pick up bed sides because the tires will rub.

I'll post this again and guys .... it's worth reading & keeping in a file

Rear Ends ::
http://www.chevytrucks.org/tech/rear_ends.htm
Suspension Measurements ::
http://www.teufert.net/other/rear%20end%20dimensions.htm
https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=403959

78 & up Monte Carlo, Regal, etc. with 10 bolt axle == 58"