How to test a used positraction?
Jim Stoltz
Treier) writes:
>
>Does anyone know how to test a posi rear end (70-81 Firebird)?
>I have heard that when you spin one wheel, the other should also spin,
>but I thought I also heard this wasn't a valid test. The rearend is
>disc brake equipped, so I would like to buy it, but if the posi is no
>good, the price would be way too high. ($300).
>
>Phil Treier
>
If you put it up in the air, both wheels should spin in the same
direction when you spin one. A better test is with a torque wrench on
one side and someone holding the other wheel (or put it on the ground).
You'll be able to turn the wheel with the torque wrench - the ft/lbs
that it takes to turn the wheel is an indication of the condition of
the posi unit. At least thats how it works on a *gasp* Ford
traction-slop. I would imagine that any clutch-type differential would
be tested the same way.
Jim S
Phil Treier
Dan Dotson
should be impossible for someone to hold the other axle in place while
you are turning. You can jack up one side of the car, leaving the
other wheel on the ground, and try to turn the wheel that's up. If it
turns, the unit is either NOT limited-slip or it's shot. Be careful-if
you turn too hard, (with a good posi) the other wheel will drive the
car off the jack! That's the reason for the warnings in the trunk on
GM limited-slip-equipped cars.
BTW, $300 is a fair price for the disc-brake version, IMHO.
Dan
URL http://www.hway.com/dandlyin
e-mail Da...@azstarnet.com
Markus Strobl
>Does anyone know how to test a posi rear end (70-81 Firebird)?
>but I thought I also heard this wasn't a valid test. The rearend is
>disc brake equipped, so I would like to buy it, but if the posi is no
>good, the price would be way too high. ($300).
>
>Phil Treier
>
Jack one side of the car up so the wheel is off the ground. The other wheel
has to still be on the ground. Put the transmission in neutral. Attach a
torque wrench to a lugnut on the wheel that's up. Point the wrench in the
direction of the lugnut, ie if you use the lugnut that's pointing straight
up, point the wrench upwards. Measure how much torque is need before the
wheel starts turning. GM spec is atleast 40 lbs-ft. If it's in the 30 lbs-ft
range, it's probably rebuildable for cheap. I had a 32 lbs-ft posi. I put
in a new clutch preload spring, and shimmed the clutchpacks. Total cost was
$20 and the torque reading jumped to 55 lbs-ft.
$300 sounds reasonable for a disc rear.
---
Markus Strobl 96 Z28 6M Black/grph. Borla, !CAGS, PEG2, QLC
Dallas, Texas 1LE driveshaft, Honker, T-tops, CD, leather
F-member 9/93 14.09 @99.40 - When stock - 27.5mpg @85mph
Brent Moss
|> Does anyone know how to test a posi rear end (70-81 Firebird)?
|> I have heard that when you spin one wheel, the other should also spin,
|> but I thought I also heard this wasn't a valid test. The rearend is
|> disc brake equipped, so I would like to buy it, but if the posi is no
|> good, the price would be way too high. ($300).
|>
|> Phil Treier
|>
Get a floor jack that can roll and jack up on side just a quarter inch off
the ground and drive it a foot or two. If it moves then its working ok.
Put the cradle of the jack on the axle near the wheel being jacked and line
up the rollers to go the direction you will drive, so that the jack does
not swing around; if it falls off, big deal. It only falls 1/4-1/2"
--
bm...@es.com