Does my vette have limited slip?
Instructor
Joined: Sep 2003
Posts: 184
Likes: 0
From: boulder wa
All 78-82 vettes are equipped with a Positraction limited-slip diff
1978
code ratio type
OK 3.08:1 positraction
om 3.36:1 "
oh 3.55:1 "
oj 3.70:1 "
1979
om 3.36:1 "
oh 3.55:1 "
oj 3.70:1 "
1980
of 3.07:1 "
oh " "
1981
oj 2.87:1 posi with auto
ok 2.72:1 posi with 4sp manual
1982
oa 2.72:1 posi with standard wheels
of 2.87:1 posi with aluminium wheels
hope this helps a bit
1978
code ratio type
OK 3.08:1 positraction
om 3.36:1 "
oh 3.55:1 "
oj 3.70:1 "
1979
om 3.36:1 "
oh 3.55:1 "
oj 3.70:1 "
1980
of 3.07:1 "
oh " "
1981
oj 2.87:1 posi with auto
ok 2.72:1 posi with 4sp manual
1982
oa 2.72:1 posi with standard wheels
of 2.87:1 posi with aluminium wheels
hope this helps a bit
1st Gear
Joined: Jul 2020
Posts: 1
Likes: 0
Race Director
Joined: Oct 2000
Posts: 12,684
Likes: 3,137
From: Shamong, NJ
All 81 Corvettes, as well as every other Corvette built from 1970 on came with GM's Posi-Traction. Posi became standard on Corvettes in 1970.
Federal emission 81's came with a 2.72 Posi rear axle ratio with the 4 speed and a 2.87 Posi with the automatic. With California emission equipment, both automatics and 4 speeds came with the 2.72 Posi rear axle ratio. Automatic Corvettes with California emissions could be ordered with the 2.87 ratio as a $20 "Performance Axle Ratio". Though I don't think the OP cares since this post is from 2004.
But welcome to the Forum anyway.!
Federal emission 81's came with a 2.72 Posi rear axle ratio with the 4 speed and a 2.87 Posi with the automatic. With California emission equipment, both automatics and 4 speeds came with the 2.72 Posi rear axle ratio. Automatic Corvettes with California emissions could be ordered with the 2.87 ratio as a $20 "Performance Axle Ratio". Though I don't think the OP cares since this post is from 2004.
But welcome to the Forum anyway.!
Pro
Joined: Mar 2022
Posts: 564
Likes: 185
If you want to see confirmation that your car has limited slip or positraction there are two ways to do this, first jack up one wheel off the ground and try to turn it. If its posi it wont turn with the other wheel on the ground, an open differential will. The other is lift both the rear wheels off the ground and support the car either a hydraulic lift or on jackstands, now with the wheels hanging and the car in neutral, brake off turn one wheel while looking at the other. If its posi it will turn in the same direction, if its not being an open rear the other wheel will spin in the opposite direction.
This is true for early positraction, limitedslip, and suregrip rear differentials. Later model limited slip units from GM in their pickups had what’s called a gov-loc limited slip unit. If you test those like this they will act like an open rear confusing old school guys like me
, they are designed to work like an open rear until one wheel slips about 5mph faster than the other then the diff locks up. They are also not as strong as the older units which earned them the nickname “gov-bomb”.
This is true for early positraction, limitedslip, and suregrip rear differentials. Later model limited slip units from GM in their pickups had what’s called a gov-loc limited slip unit. If you test those like this they will act like an open rear confusing old school guys like me
, they are designed to work like an open rear until one wheel slips about 5mph faster than the other then the diff locks up. They are also not as strong as the older units which earned them the nickname “gov-bomb”.
Tech Contributor
Joined: Aug 1999
Posts: 15,177
Likes: 3,995
From: Connecticut, USA
Some notes.
There is a break away test, outlined in the GM manual for testing a stock posi. Do not try this with the wheels hanging down.
If the posi was Tuned it will act like an open differential but work better than a spring loaded posi- if correctly built. Tuned posi's were never offered by GM or sold by Eaton. They are a custom built posi and usually not a problem.
There is a break away test, outlined in the GM manual for testing a stock posi. Do not try this with the wheels hanging down.
If the posi was Tuned it will act like an open differential but work better than a spring loaded posi- if correctly built. Tuned posi's were never offered by GM or sold by Eaton. They are a custom built posi and usually not a problem.
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