12 bolt didferential gear ratio identification

[Jaycarter]

My 1973 Chevy P10 has a 12 bolt, axle code stamping is : TBT W132 2

CAN ANYONE PLEASE DECODE THE GEAR RATIO FOR ME

 

[Grit dog]

Look like it has a 132:2 ratio. Decoding to 64:1. Lol
Kidding.
Presuming you don’t have a tach in it, or you could figure it out while driving with your phone gps and tire diameter. a 6 banger 1/2 ton van was not built to tow much of anything or haul a lot of weight, so original wouldn’t be too deep.
But it’s a 6er so may have a bit deeper than the tallest gears offered.
No tach, it’s easiest to count driveshaft revolutions.
Takes like 10 min including jacking it up. And no guessing needed.

 

[SquareRoot]

AND STOP YELLING!

 

[Ricko1966]

Look like it has a 132:2 ratio. Decoding to 64:1. Lol
Kidding.
Presuming you don’t have a tach in it, or you could figure it out while driving with your phone gps and tire diameter. a 6 banger 1/2 ton van was not built to tow much of anything or haul a lot of weight, so original wouldn’t be too deep.
But it’s a 6er so may have a bit deeper than the tallest gears offered.
No tach, it’s easiest to count driveshaft revolutions.
Takes like 10 min including jacking it up. And no guessing needed.

You don't even have to jack it up put a chalk mark at 6 o'clock on the tire and a chalk mark at nine o'clock on the driveshaft push the truck slowly forward. Look at the drive shaft every 1/4 turn of the tire. If you don't trust watching the drive shaft tape a piece of string to the driveshaft,and count the wraps of string after 1 wheel rotation,use a little common sense for difference,noting where your tape is for anything less than a complete turn of the driveshaft. 2 chalk marks 1 slow push less than 2 minutes. And this eliminates any confusion about rotation counting with a posi.

 

[RetroC10Sport]

If it hasn't been changed, it's a 4:11 non locking.

 

[hey mister]

My 12 bolt is a 381.
I needed to change the fluid and pulled the cover.
While in there, I took a photo of the numbers stamped on the ring gear.
Never heard of a 381.
The 350/350 won't light em up but at 2500rpm, it does 65. And 11mpg with original Qjet.

 

[Ricko1966]

My 12 bolt is a 381.
I needed to change the fluid and pulled the cover.
While in there, I took a photo of the numbers stamped on the ring gear.
Never heard of a 381.
The 350/350 won't light em up but at 2500rpm, it does 65. And 11mpg with original Qjet.

Its not a 381 that's part of the part number. Look back in this thread I think it was this one,I covered part numbers and gear ratio identification. I'll look back too and through some of my other posts,but I have put all this up. Now if the cover is off all you need to do is count teeth and divide and actually your teeth count is what you are looking for, as far markings and you still have to divide. Nope it wasn't this thread but anyway 381 is part of the ring gear part number not the axle ratio.

 

[Ricko1966]

Okay it wasn't this one I'll look through my old stuff.

 

[legopnuematic]

My 12 bolt is a 381.
I needed to change the fluid and pulled the cover.
While in there, I took a photo of the numbers stamped on the ring gear.
Never heard of a 381.
The 350/350 won't light em up but at 2500rpm, it does 65. And 11mpg with original Qjet.

How tall are your tires?

3.08 with 28" tall tires and th350 is 2500rpm @65.

 

[Ricko1966]

April 25 2025

 

[Ricko1966]

My 12 bolt is a 381.
I needed to change the fluid and pulled the cover.
While in there, I took a photo of the numbers stamped on the ring gear.
Never heard of a 381.
The 350/350 won't light em up but at 2500rpm, it does 65. And 11mpg with original Qjet.

You have 3.07 gears we covered this Jan 8 2025

 

[Ricko1966]

My 1973 Chevy P10 has a 12 bolt, axle code stamping is : TBT W132 2

CAN ANYONE PLEASE DECODE THE GEAR RATIO FOR ME

Look at the pics in post 10 it has marking location and codes.

 

[hey mister]

How tall are your tires?

3.08 with 28" tall tires and th350 is 2500rpm @65.

235/75/15

 

[hey mister]

You are so right...It had slipped my mind that we gad discussed this and I was mistaken.
It is a 308 rear end...
And here's the puctures of the ring gear.
Thank you for keeping me straightened out.

 

[xm20k]

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The code is stamped on the top passenger side axle. You must be registered for see images attach You must be registered for see images attach You must be registered for see images attach You must be registered for see images attach