I have had 30 Year Old Posi-Trac (Positive Traction)Units that worked
just fine with well over 100,000 miles on them. My GM/EaToN 7&1/2 Locker
(which some F-bodys have) has 400,000 on it. It NEVER fails to lock when
it is supposed to.
I think you might be on to something. I just spun the rear wheels
(while off the ground). They spin in opposite directions ! That's not
supposed to happen with a posi rear, right ? Do you think that means
the "clutch cone " has to be replaced ?
No, they should turn the same way even with a bad clutch. Sounds like
you have an open diff. With the trans in neutral put one tire on the
ground and try to turn the other one. It should take at least 30lbs of
force to turn it (break-away torque). I rarely see OEM limited slip
units with more than 70-80K on them that still work well. Maybe if they
are driven mostly in straight lines. :-)
How do you know you have a posi unit? If you're going to change the gear
oil, you'll be pulling the differential cover and you'll know when you see
it. Just have the additive ready and if it's not a posi unit, just don't
add it. I guess even if it's an open differential, putting in the additive
won't hurt anything, would it?
Check the RPO sticker in the center console for "G80" That will tell you
if it has posi in the first place.
On my '84 T/A the tires turn in opposite directions but it has
posi-traction and has always spun both tires. Maybe its a characteristic
of the "cone style" posi-traction units?
On my '71 and '73 T/A which use the "clutch style" posi-traction the
wheels turn in the same direction.
Some Third Gens have a EaToN Locking Diff. Same Diff S-10's use. It's
known as a Gov-Lock. You can have one on a lift and play with the tires
till you force it to lock. Unless your force it to Lock you might think
The only TRUE way to see whats in a "pig" is to take the cover off and
Any Parts Store should have Friction Modifer for Locking/Limited Slip
Deferentials. As of Late I have been using Lucas 80w90 Gear oil in all
my GM rear ends.
(Ok, Ok I have been Priating Lucas from a Company I do service work for.
Free is Free)
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