Positive Traction?

[coreyc]

I have a 9" rearend. Excuse my lack of knowledge, but how can I tell if it has positive traction or limited slip with out taking it apart? When I turn the center section both wheels turn, but either side will stop with very little resistance and the other side keeps turning. Thanks for your help. Also is there a way to find out the ratio?

Thanks,
Corey

[trularin]

Simple, but not necessarily accurate is to jack the rear up and chock one wheel. Try to turn the other. If you can turn it freely, it IS NOT posi.

[blykins]

If you jack it up and turn one wheel, the other wheel will turn the same way if it's posi. If it's just an open rear, you can turn one wheel and the other one will turn the opposite direction.

[vettestr]

corey,
Tough to do this alone but turn pinion yoke exactly ten times and count rotations that causes a tire to turn. Say tire turns 3 1/2 times then you have 3.50 to 1 ratio.
You can determine the rear gear ratio by counting revolutions. With the car up in the air or the rear tires anyway and safe. Place a mark or tape on the pinion yoke and the housing so you can easily and accurately count revolutions. Place tape on tire and fender or a way to count revolutions and have ball. Jeff c

[olddog]

Originally Posted by coreyc

When I turn the center section both wheels turn, but either side will stop with very little resistance and the other side keeps turning.

You have described an open differential.

[2KWIK4U]

Corey,
It's almost impossible to tell if its a posi without tearing it down. The True-Trac carrier for the 9" will act as an open diff, since there are no clutch discs internally, only helical gears. It won't lock up until a sufficient torque is recognized between the axles. The best way to tell is to nail it!!. If you leave two black marks, it's a posi or some type of limited slip.

Brad W.

[olddog]

Originally Posted by 2KWIK4U

The True-Trac carrier for the 9" will act as an open diff, since there are no clutch discs internally, only helical gears. It won't lock up until a sufficient torque is recognized between the axles.

I never heard this before, but I haven't heard it all yet. Maybe I just learned something new.

[2KWIK4U]

The following link lists several posi/ls units and explains the operation. The SureTrac is another "open until needed" carrier.

http://www.eatonperformance.com/diff...-Truetrac.html

Good source for rebuilding and specs too.

Brad W.

[2KWIK4U]

BTW,
The True-trac is the carrier that Currie recommended for my build. They told me it works great for the strip, plus the design allows for better cornering on road courses since almost full power can be applied in the corners without affecting the ability to turn. I've only made half a dozen 1/4 mile passes, and probably 3 hrs at Mid-Ohio, but it sure works well.

[Ron61]

I am not familiar with the True-trac unit, but my 69 Cobra came with the SVO posi unit in it and if I jack up just the right side I can't turn it as the left wheel holds. Blykins gave the simplest and easiest quick check. Just get both back wheels off the ground and turn the right one as that is the drive wheel on all older cars and if the left wheel turns backwards while the right wheel is turning forwards it is an open rear end.

Ron

[MaSnaka]

Is it possible a posi or locker type dif can act as if it's open by say a malfunction?? I jacked up the rear end and spun the passenger side tire clockwise and the driverside tire spun the opposite direction. The tag on the diff indicates it's a locker but I haven't given it the black mark on asphalt test ...yet. I am actually wondering if I have a GM rear end, because it doesn't look to be a Ford 9", 8.8". I will post pics of it sometime to try and get it id'd, but it may be some time before I can get to that. Thanks, John

[Ron61]

John,

A posi should only act as an open rear end if it is broken or the clutches aren't engaging. When doing the tests, use the right side rear wheel as that is the normal driving wheel on an open rear end.

Ron

[2KWIK4U]

This a quote from the service manual for the TrueTrac from the link posted above.

Final Inspection:
"To verify the TrueTrac differential is properly installed, restrict the rotation of the pinion shaft (by placing the gear shiift lever in park for automatic transmissions, or in reverse for manual transmissions) and raise the axle so both wheels are off the ground. When one wheel is turned by hand, the other wheel should rotate freely in the opposite direction. Check in both directions."

I agree that posi's with clutches will not rotate or has resistance if only one wheel is raised, or will rotate in the same direction if both are off the ground, but not all posi/LS units react that way and it can only be determined by dissassembly or peformance characteristics.

Brad W.

[CobraEd]

If the clutches are all worn out, it will act exactly like an open rear.


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