A Positraction Rear that doesnt act Posi
07-21-2005, 11:45 PM
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A Positraction Rear that doesnt act Posi Hey guys,
I am somewhat new to this board, so once again I say hello to all of you. I bought a 1999 Camaro Z/28 with a 4 Speed Auto and the RPO codes say I have a 2.73 Posi Rear in the back. The problem is that I dont have two spinning wheels whenever I hit the gas, I just have the passenger side. Now I already know that the driveshaft pinion seal is leaking (a somewhat common thing in these F-Bodies), and the car has 64,000 on what seems to be a well cared for clock. Any ideas as to why my car is not acting posi? Any help is greatly appreciated.
I am somewhat new to this board, so once again I say hello to all of you. I bought a 1999 Camaro Z/28 with a 4 Speed Auto and the RPO codes say I have a 2.73 Posi Rear in the back. The problem is that I dont have two spinning wheels whenever I hit the gas, I just have the passenger side. Now I already know that the driveshaft pinion seal is leaking (a somewhat common thing in these F-Bodies), and the car has 64,000 on what seems to be a well cared for clock. Any ideas as to why my car is not acting posi? Any help is greatly appreciated.
07-22-2005, 07:13 AM
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There are two posi units available from GM...the standard unit is called the Torsen and it is driven by small "spider" gears that are housed withint the posi case. The second option is the Auburn posi, which GM calls an upgrade. That posi contains clutches and heavy springs and works via friction on the clutch plates.
It is possible for both units to fail. When the Auburn fails, it's usually because the clutches are burned up. When the Torsen fails, it is usually a little more dramatic...like broken spider gears.
The one tire fire you are describing is probably a result of one of those two cases, and would require either a rebuild of the posi or a new posi unit. My suggestion would be to find a used Torsen diff in the FS section (about $50) and have it installed in your car along with a new pinion seal. While you are in there, have the crush sleeve replaced with a solid pinion spacer...that will help the life of the rear-end a little and it only costs about $20.
It is possible for both units to fail. When the Auburn fails, it's usually because the clutches are burned up. When the Torsen fails, it is usually a little more dramatic...like broken spider gears.
The one tire fire you are describing is probably a result of one of those two cases, and would require either a rebuild of the posi or a new posi unit. My suggestion would be to find a used Torsen diff in the FS section (about $50) and have it installed in your car along with a new pinion seal. While you are in there, have the crush sleeve replaced with a solid pinion spacer...that will help the life of the rear-end a little and it only costs about $20.
07-22-2005, 11:57 AM
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The stock F-body Torsen will only split torque to about
a 2:1 ratio. A little bit of right tire lift, and you'll spin
that one leaving only 2X spinning tire back-torque to
drive the other side. If this does not exceed stuck-tire
breakaway torque, the left rear won't spin. This depends
a lot on the tire compounds as well.
With the T-2R I have no problem lighting them both off.
But the OEM piece has an inferior torque split, less meat
in the gear-gizmo and no preload. If you're going to tear
into it, might consider going to sportier gears too as this
will be a minimal labor increment.
Then again, another grand or so and you'd have a 12-bolt
or 9" Ford paid for....
a 2:1 ratio. A little bit of right tire lift, and you'll spin
that one leaving only 2X spinning tire back-torque to
drive the other side. If this does not exceed stuck-tire
breakaway torque, the left rear won't spin. This depends
a lot on the tire compounds as well.
With the T-2R I have no problem lighting them both off.
But the OEM piece has an inferior torque split, less meat
in the gear-gizmo and no preload. If you're going to tear
into it, might consider going to sportier gears too as this
will be a minimal labor increment.
Then again, another grand or so and you'd have a 12-bolt
or 9" Ford paid for....
07-22-2005, 12:58 PM
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How hard is the shimming of the rear and change out of the pinion seal? I'm thinking of changing gears when I change my leaking seal as well. But everything else is fine with rear.
