Gear Ratio ID?

[Dave Koch]

I understand there is a stamping somewhere on the differential that identifies the gear ratio. I tried using a small mirror and flashlight, but couldn't seem to find the stamping. Does anyone know exactly where this number is located. Car is a 66 small block 4 speed.

Thanks,

Dave

[Tom B.]

Re: Gear Ratio ID?

Dave,

The 66 I had, had it stamped on the flat bottom edge of the housing in front of the small plate that bolts and holds the rear leaf spring under the housing. If I remember correctly it was a series of stamped letters and numbers: 2 letters for the ratio/or positraction code, a space or two, and then numbers for the date: month (one or two digits),space, day (one or two digits),space, and year (two digits-I think). The characters were something like 3/8", maybe 5/16" tall. Try looking there.

[Tom B.]

Re: Gear Ratio ID?

Dave,

The 66 I had, had it stamped on the flat bottom edge of the housing in front of the small plate that bolts and holds the rear leaf spring under the housing. If I remember correctly it was a series of stamped letters and numbers: 2 letters for the ratio/or positraction code, a space or two, and then numbers for the date: month (one or two digits),space, day (one or two digits),space, and year (two digits-I think). The characters were something like 3/8", maybe 5/16" tall. Try looking there.

[Joe L.]

Re: Gear Ratio ID?

Dave---

Tom is correct, but the numbers are often very hard to read. Also, that just tells you what gears ORIGINALLY resided in the case, not necessarily what resides in there now. Best and easiest bet is to determine the actual ratio is by observing the exact number of times that the driveshaft turns while someone turns one of the rear wheels(off the ground, of course)through exactly 1 revolution. That information is "for sure" which ratio you have.

[Joe L.]

Re: Gear Ratio ID?

Dave---

Tom is correct, but the numbers are often very hard to read. Also, that just tells you what gears ORIGINALLY resided in the case, not necessarily what resides in there now. Best and easiest bet is to determine the actual ratio is by observing the exact number of times that the driveshaft turns while someone turns one of the rear wheels(off the ground, of course)through exactly 1 revolution. That information is "for sure" which ratio you have.

[Jack H.]

Re: Gear Ratio ID?

Solid advice from Joe! What's on the label isn't necessarily what's packaged inside....

Also, MY Muncies are often found with square paper tag and handwritten broadcast code (FA, Etc.) attached to the upper rail of the pumpkin that can only be observed when the assy is removed.

[Jack H.]

Re: Gear Ratio ID?

Solid advice from Joe! What's on the label isn't necessarily what's packaged inside....

Also, MY Muncies are often found with square paper tag and handwritten broadcast code (FA, Etc.) attached to the upper rail of the pumpkin that can only be observed when the assy is removed.

[John Rohe]

Re: Gear Ratio ID?

Dave,

Tom's posting is a complete and accurate description of what you should find stamped on the bottom of your rear IF it is the original one. If the date code seems right then you're probably looking at the original rear. If it is NOT the original rear here are a few other things to look at.

There is a casting date on the driver's side of the housing. It is visible without dropping the rear with the driver's side rear jacked up looking at the side of the housing from under/in front of the rear tire. The date code should be Month (letter) Day (1 or 2 digit #) Year (1 digit #). There is also a casting # on the passenger's side of the rear, but I believe that to be up too high as to be visible without dropping the rear.

FYI, the date stamp on the bottom of the rear changed from the "MM DD YY" format in model year '71 (I believe) to a julian dating format where, for example, "146" stands for May 26 (the 146th day of the year).

Good luck. John R.

[John Rohe]

Re: Gear Ratio ID?

Dave,

Tom's posting is a complete and accurate description of what you should find stamped on the bottom of your rear IF it is the original one. If the date code seems right then you're probably looking at the original rear. If it is NOT the original rear here are a few other things to look at.

There is a casting date on the driver's side of the housing. It is visible without dropping the rear with the driver's side rear jacked up looking at the side of the housing from under/in front of the rear tire. The date code should be Month (letter) Day (1 or 2 digit #) Year (1 digit #). There is also a casting # on the passenger's side of the rear, but I believe that to be up too high as to be visible without dropping the rear.

FYI, the date stamp on the bottom of the rear changed from the "MM DD YY" format in model year '71 (I believe) to a julian dating format where, for example, "146" stands for May 26 (the 146th day of the year).

Good luck. John R.

[Dave Koch]

Re: Gear Ratio ID?

Thanks everyone. I had to take a wire brush to it, but found the number stamped right in front of the spring. AL 4 15 66 (3.08 Apr 15 1966). Build date of car was May 27, 1966. I'll be checking the drive shaft to half shafts turns next to verify the ratio.

Thanks, Dave

[Dave Koch]

Re: Gear Ratio ID?

Thanks everyone. I had to take a wire brush to it, but found the number stamped right in front of the spring. AL 4 15 66 (3.08 Apr 15 1966). Build date of car was May 27, 1966. I'll be checking the drive shaft to half shafts turns next to verify the ratio.

Thanks, Dave