The Stovebolt Site Forums The Shop Area Driveline Differential ratio

My project has 54 sheet metal and a 53 or older frame. Other components are an on-going surprise. The 54 shop manual says the diff number is on the right side of the carrier flange. I can find no number anywhere on mine. With the torque tube I can't jack up the rear and count revolutions to determine the gear ratio. Is there an alternative to removing the rear cover and counting teeth?

I think (but am not sure) that Chevy and GMC used the same rear ends in '53 and '54. This info is from the 1939-54 GMC Master Parts Book.

You are showing 6 lug wheels, so it should be a 1/2 ton.

1953 used a 4.11:1 rear gear.
1954 used a 3.90:1 rear gear.

A few bolts and a gasket, plus a lube change- - - -that seems to be the simplest, most accurate way to address the problem. There's probably no need to count teeth- - - -a stamped number on the ring gear will probably give the ring/pinion tooth count- - - - -9-37, for instance, is a 4.11-1 ratio.
Jerry

treegrower - Below is a pic from the 1948-51 (info same through 1954) Chevrolet Truck Shop manual to show where the stamped rear axle ID number is. You may need to do something like the suggested guidance in this Legacy Tech Tip Reading Indented Numbers to help you read what's on the axle pumpkin.

Bill Hanlon is correct on the standard rear gear ratios for the 1/2 ton for 1953 (and earlier) and 1954 axles. The decider on what yours is will be from decoding the stamped ID number.

If it has a prefix of "M" it's a 1954 1/2 ton model year. "L" is for 1953 1/2 ton model year. "K" is for 1/2 ton model year 1952. "J" is for 1951 1/2 ton model year.

The unit number will consist of two letters, the first being the model year and the second being the plant it was built at. That is followed by one or two numbers indicating the month built and then followed by one or two numbers to indicate the day of the month built.

If you want to save yourself opening up the axle, try to bring the original stamped info to view so you can know for sure what you have.

Here it is 2 months later, and it just gets better. I found the stamps on the diff, and they are J E 614. That tells me it is a 1951. Three questions--what is the gear ratio inside? Two--we know the frame is 53 or older. Are 53 and 51 frames the same? Third-- in pursuit of an open drive line, what later pumpkins are a direct bolt in? I would rather replace just the pumpkin instead of the entire axle if possible. I think the main issues are the bolt pattern of the carrier to the axle housing, and the compatibility of the axle shafts.

Well, I've found the JE prefix to be 3.42 ratios in the past but that isn't a promise. Not at all a common ratio for a pickup in the 1950s so I'm immediately suspect. My guess is 614 is a production date. It doesn't match any of the data I have here.

Sorry...I failed to answer your other questions...there are no direct bolt-in rear ends I'm aware of however if you can find a rear end from a late 1960s/early 1970s Chevy or GMC pickup the width should be okay and the 12 bolt rear ends came with a large number of ratios. The one I'm using is 3.07.

Post on the VCCA says J E 614 is a 3.55 ratio, made January 6 in Buffalo, NY. 1951 date. The letter K would be for 1952. Another hint for you. To me it suggests a passenger car gear set.

treegrower - Your “JE614” decodes as a 1951 Detroit built 3100 unit with standard 4.11 gears. “614” is the “unit number” from the assembly line and indicates it was built June 14th.

According to the GM Heritage files, the ‘51 and ‘53 frames seem identical.

On bolt in pumpkins to upgrade your existing axle, a Chevy 1955.1-62 open drive 1/2 ton pumpkin is a basically bolt in swap to change out your torque tube.

IIRC, it’s a relatively easy process, using the existing axle shafts. There is one key thing that must be changed though.

The existing axle housing mounts have to be modified (welded up) or replaced with welded on spring perches to prevent the axle from rotating and destroying your driveshaft and other stuff.

Lots of previous conversations on the topic if you search the subject- converting to open driveline.

Welding those pivoting housing mounts with the big rubber bushings in them successfully is about as likely as finding an honest politician. Save yourself a lot of grief and weld some new, rigid spring mounts onto the housing. They're available from racing supply places like JEGS or Racer's Wholesale.
Jerry

Continuing the discussion--is a car carrier/ pumpkin the same as a half ton pickup unit? Will definitely weld on spring mounts--there is a Youtube video about this.

Car carrier/pumpkin and 1/2 ton truck pickup units are not the same. The shapes of the pumpkin are significantly different and do not interchange between main axle housings.

That's not to say you can't mount a complete car rear axle in the same spot as the original truck axle, but that's going to leave you with 5-lug axles/wheels in the rear, not to mention a weaker rear axle overall.

Critical information. Thanks for saving me from a bad mistake.

Any chance of emailing the link to the u-tube vid?

I just confirmed this one How to Install a Modern Rear Axle // 1954 Chevy 3100 Project. There are others if you search.

Thanks for the edit. I don't know how to prevent that from happening