Differentials 101
Thread Starter
Melting Slicks
Joined: Nov 2002
Posts: 2,460
Likes: 5
From: Wheaton IL
Differentials 101
Ok some really basic questions here......
I have the car up on jackstands for the first time and am really going through the basics. The previous owner had no history and no knowledge. There are two things I'd like to determine:
1) If the differential is operating correctly
2) My Gear Ratio
1) On other cars I've worked on (non-posi) if I rotated one rear tire, the other rotated in the opposite direction. On my 65 the other doesn't rotate (propeller shaft does). I have the brake pads on still - should the standard dragging be enough to hold the other tire?
2) Do I need to rotate both tires to be able to measure the rotations of the propeller shaft vs. the rotations of a wheel? Are their markings on the differential itself that would identify the ratio (assuming that the gears inside have not been changed)? Where would this marking be?
Thanks :thumbs:
I have the car up on jackstands for the first time and am really going through the basics. The previous owner had no history and no knowledge. There are two things I'd like to determine:
1) If the differential is operating correctly
2) My Gear Ratio
1) On other cars I've worked on (non-posi) if I rotated one rear tire, the other rotated in the opposite direction. On my 65 the other doesn't rotate (propeller shaft does). I have the brake pads on still - should the standard dragging be enough to hold the other tire?
2) Do I need to rotate both tires to be able to measure the rotations of the propeller shaft vs. the rotations of a wheel? Are their markings on the differential itself that would identify the ratio (assuming that the gears inside have not been changed)? Where would this marking be?
Thanks :thumbs:
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,925
From: Washington Michigan
Re: Differentials 101 (Allcoupedup)
If both wheels turn the same direction and the prop shaft rotates, you've got a Posi; the '65 300hp had a 3.36 as the standard axle, with the 3.08 as a "highway" option.
Look at the bottom machined surface of the differential carrier, just forward of the rear spring lower mounting plate, and you'll see a series of numbers and letters stamped into that surface that identify the date the diff was built and the ratio it had originally (you may have to clean it up with a stiff brush to read the codes). Post the numbers and we can decode them for you.
You can determine the ratio easily by marking a tire and the prop shaft and noting the number of prop shaft rotations when you turn the wheels one full turn; 3 rotations is a 3.08, 3-1/3 rotations is a 3.36, etc.
Look at the bottom machined surface of the differential carrier, just forward of the rear spring lower mounting plate, and you'll see a series of numbers and letters stamped into that surface that identify the date the diff was built and the ratio it had originally (you may have to clean it up with a stiff brush to read the codes). Post the numbers and we can decode them for you.
You can determine the ratio easily by marking a tire and the prop shaft and noting the number of prop shaft rotations when you turn the wheels one full turn; 3 rotations is a 3.08, 3-1/3 rotations is a 3.36, etc.
Thread Starter
Melting Slicks
Joined: Nov 2002
Posts: 2,460
Likes: 5
From: Wheaton IL
Re: Differentials 101 (JohnZ)
JohnZ -
Found it.... It was hidden under some sqished out sealant. 63 8 CA. Can I interpret this as a August, 1963 3:36 non-posi differential?
Man..... the only thing i've found on my car that IS 1965 is the carb and the intake. Haven't checked the heads yet.
Anyhow, with positraction if I spin one wheel the other should spin in the same direction right? If the opposite wheel does not spin at all while the propeller shaft is spinning does this verify I have a non-posi differential?
Thanks for helping out a rookie
Brian
Found it.... It was hidden under some sqished out sealant. 63 8 CA. Can I interpret this as a August, 1963 3:36 non-posi differential?
Man..... the only thing i've found on my car that IS 1965 is the carb and the intake. Haven't checked the heads yet.
Anyhow, with positraction if I spin one wheel the other should spin in the same direction right? If the opposite wheel does not spin at all while the propeller shaft is spinning does this verify I have a non-posi differential?
Thanks for helping out a rookie
Brian
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,925
From: Washington Michigan
Re: Differentials 101 (Allcoupedup)
JohnZ -
Found it.... It was hidden under some sqished out sealant. 63 8 CA. Can I interpret this as a August, 1963 3:36 non-posi differential?Brian
Found it.... It was hidden under some sqished out sealant. 63 8 CA. Can I interpret this as a August, 1963 3:36 non-posi differential?Brian
If the opposite wheel doesn't turn or turns in the opposite direction, you either have a non-Posi diff or the Posi unit is worn to the point where it isn't working any more.
Investigating what you have is like detective work, and tells you a little about the car's history - these cars are 37 years old, and there aren't many left with all-original drivetrains; how many other nameplates of cars do you see on the road that are 37 years old? Not many! :cheers:
