how to identify the gear ratio on my truck

[mikeoverland]

Hi all! I hope your Christmas was less complicated than mine was (my mom and dad were in a bad car wreck). Since there is no info tag on my truck because some yoyo removed it and there is no id tag on the differential is there a way to see what gears i have without spinning the wheels and looking at the driveshaft or taking the entire pumpkin apart and counting the gear teeth? I've always been told that the gear ratio is stamped somewhere on the differential but I can't find any markings..... any help would be appreciated as always.

Mike in Leon Springs Tx
owner of the 1981 C10 known as "the basket case"

 

[TotalyHucked]

Without your SPID or the tag on the rearend, you’re gonna have to either jack it up and spin the wheels and count or take the rear cover off and count teeth.

 

[Keith Seymore]

It's really the only way to be sure.

After 40 or 50 years there's no telling what's in there, regardless of what's stamped on the tube or in the SPID.

K

 

[Ricko1966]

You can get close and use process of elimination by taping a piece of string to the driveshaft. Put a chalk mark at 6 o'clock on 1 tire. Push the truck 1 turn of the tire. See how many times the string wrapped around the driveshaft.The more turns of the tire you give it,the more accurate your estimation. Example the tire turns 3 times,you count 9 wraps on the drive shaft you are in the 3/1 vicinity 12 wraps 4/1.

 

[mikeoverland]

I appreciate the info. Since I'm off on Monday I'll see if I can figure out what I have.

Mike in Leon Springs Tx
owner of the 1981 Square Body known as "the basket case"

 

[Ricko1966]

Hotrodpc has a lot better method post 32 how to figure gear ratios without removing cover from 2020.

You must be registered for see images attach

 

[75gmck25]

Go to this site and you can find info on what ratios were offered each year with different engine/transmission combos. That should help narrow down the possibilities.

1973 - 1987 Chevy Truck Specs, Engines, transmissions, transfer cases, and rear ends, gear ratios - Chuck's Chevy Truck Pages

Also, have you made a trip to Pick and Pull San Antonio and Roosevelt Auto Parts yet? The last time I visited they had a much smaller selection of squarebody trucks, but still worth a visit.

Also, for engine parts you can usually find other GM vehicles of the same vintage and get useful parts.

 

[mikeoverland]

Also, have you made a trip to Pick and Pull San Antonio and Roosevelt Auto Parts yet? The last time I visited they had a much smaller selection of squarebody trucks, but still worth a visit.

I haven't been to pick and pull for probably 25 years. I used to go there for my 1987 Regal and my 1988 Subaru dl. Apparently Roosevelt Auto Parts has several parts that I need including a new windshield. I just need to get over there and make teh parts happen. I did go to the website that you suggested but all of the information was on the K series and not the C series. I don't know if the information is the same between the two.

Mike Overland Leon Springs Tx.
owner of the 1981 square body known as "the basket case"

 

[Grit dog]

If it has a tach and you know what rpms it runs at a particular speed in Drive or 1:1 gear and your tire size you can figure it out using one of the online gear/rpm/ratio calculators.

 

[Ricko1966]

I've got the formula written down somewhere if any wants it. I'll try to find it. It's something like Pi r round divided by dinner guests = ~ servings.

 

[mikeoverland]

I've got the formula written down somewhere if any wants it. I'll try to find it. It's something like Pi r round divided by dinner guests = ~ servings.

I love this group!!!!!!!! when i read this response to my question i fell out of my chair laughing! THANK YOU for the good laugh because i needed a good laugh.

Mike in leon springs tx

 

[Bextreme04]

If you haven't changed your diff oil in a while, just pop the cover off and look. The gear ratio will be stamped on the side of the ring gear and can be clearly seen. It will be a sequence of numbers. Mine was 41 10, which tell you that the ring gear has 41 teeth and the pinion has 10. Divide the big number by the small for your gear ratio. Mine is 41/10=4.10.

Added bonus that you will also be able to tell if it is a G80 or has had a limited slip or locker installed at some point. Plus you will know you have fresh clean gear oil in it afterwards.

Edit: Fixed my stupid

 

[Big Ray]

If you haven't changed your diff oil in a while, just pop the cover off and look. The gear ratio will be stamped on the side of the ring gear and can be clearly seen. It will be a sequence of numbers. Mine was 41 10, which tell you that the ring gear has 41 teeth and the pinion has 10. Divide the big number by the small for your gear ratio. Mine is 44/10=4.10.

Added bonus that you will also be able to tell if it is a G80 or has had a limited slip or locker installed at some point. Plus you will know you have fresh clean gear oil in it afterwards.

Ahem...4.4....whistle emoji here

 

[Bextreme04]

Ahem...4.4....whistle emoji here

Dang... wrote the right numbers up top and then put the wrong ones in the equation... it's been that kind of week

 

[WebMonkey]

the axle tube stamp will tell you pretty quickly.
just get a wire brush and clean up the passenger side tube to find the stamped code.