Posi question
Thread Starter
Melting Slicks
Joined: Jun 2001
Posts: 3,281
Likes: 6
From: NC USA
Posi question
Should a posi always produce two black marks? Aren't both tires grabbing at all times when going in a straight line?
I was out fooling around this past weekend on a service road near me and was doing burnouts and noticed I was only making one black mark. :confused:
I was out fooling around this past weekend on a service road near me and was doing burnouts and noticed I was only making one black mark. :confused:
Tech Contributor
Joined: Aug 1999
Posts: 15,175
Likes: 3,986
From: Connecticut, USA
Re: Posi question (Marks69BB)
maybe you don't have posi? It was still an option in '69. I remember seeing a 69 coupe, base motor,3 spd manual,and open differential for sale about 15 years ago.
Thread Starter
Melting Slicks
Joined: Jun 2001
Posts: 3,281
Likes: 6
From: NC USA
Re: Posi question (gtr1999)
The code on the case is for a 3.08 posi and I've checked RPMs to verify they are 3.08s. I'm almost sure it was producing dual black marks before. :confused:
Drifting
Joined: Mar 2001
Posts: 1,411
Likes: 2
From: St. Louis, Missouri
Re: Posi question (ry)
sounds like limited slip to me
A non limited-slip differential is a non-posi or "open" differential
Here's one way to tell what you have (I haven't tried it though, your mileage may vary):
Jack up the rear of the vehicle and spin a rear wheel. If the other one spins the same way, you have Positraction (or a locker or spool or something).
If it spins the opposite way, you have an open (regular) rear.
If it doesn't spin at all, you have a problem (locked up brake, broken axle, etc.).
Race Director
Joined: Apr 2000
Posts: 11,840
Likes: 0
From: Galloway NJ
Re: Posi question (Neo Fender)
sounds like limited slip to me
I believe "positraction" is just a propietary name that GM used to describe a limited slip differential.
A non limited-slip differential is a non-posi or "open" differential
Here's one way to tell what you have (I haven't tried it though, your mileage may vary):
Jack up the rear of the vehicle and spin a rear wheel. If the other one spins the same way, you have Positraction (or a locker or spool or something).
If it spins the opposite way, you have an open (regular) rear.
If it doesn't spin at all, you have a problem (locked up brake, broken axle, etc.).
I believe "positraction" is just a propietary name that GM used to describe a limited slip differential.
A non limited-slip differential is a non-posi or "open" differential
Here's one way to tell what you have (I haven't tried it though, your mileage may vary):
Jack up the rear of the vehicle and spin a rear wheel. If the other one spins the same way, you have Positraction (or a locker or spool or something).
If it spins the opposite way, you have an open (regular) rear.
If it doesn't spin at all, you have a problem (locked up brake, broken axle, etc.).
might be time for a rebuild...
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Safety Car
Joined: Jun 2001
Posts: 4,004
Likes: 2
From: Severna Park Md
Re: Posi question (Marks69BB)
A good posi with tight clutches should most often but not always leave two even marks. Especially with vette IRS. With a solid axel car like a chevelle or camero the tq of the driveshaft turning in one direction can cause oppisite rotation of the axel housing and place more weight on one tire than the other making one mark blacker than the other. With the vette IRS you dont get this effect since the diff is bolted directly to the frame. If yur getting one mark then you either got an open diff, or a worn posi.