I have an 86 Chevy w/350 engine, 350 aut trans. I floor it and only one tire spins. I would like to add a posi rear. My buddy has a 92 stock chevy with a 350 also, His truck seems to have posi or limited slip. When he floors it both tires spin, sometimes it feels like one tire catches traction then the other seems to grab traction. Would an axle out of a a 90-93 chevy fit my 86 shortbed??

If they are both 1/2-ton trucks you are looking at basically the same axle in both, the "corporate" 8.5 inch axle.

Just measure the spring perches to make 100 percent sure it is a direct bolt-in swap.

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What should've said was does his truck have posi from factory? How do I check to see? How would I know??

And yes, They are both 1/2 ton trucks.

The only way to positively know if his truck came from the factory is to look inside the axle housing. If it did and somewhere along the line someone serviced the axle the limited slip tag could have been left off, so looking for the tag would not help. Another way is to look for the RPO tag which is most likely located in the glove compartment, it should indicate everything that the truck came from the factory with.

If it only contains the RPO codes a little research with the service department at the local Chevy dealership will identify the parts.

If it contains the RPO's with descriptions, you should be able to tell what it had just by reading through the list.

If his truck's axle contains the Gov-Lock differential, simply jacking up one side and turning the wheel to check will not work.
The Gov-Lock is designed to engage with the centrifugal force of the axle spinning at a certain speed to allow the governing clutch mechanism to engage and effectively lock the differential action.

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You could also put it up on a lift and rotate one tire and if the other one rotates in the opposite direction its not possi.

I found this info and it helped me enormously...

CHEVY GEAR CODES

EASY WAY - Look at codes in glove box which will tell you the ratio and status of open or posi.

GU2 2:73 ratio

GU4 3:08 ratio

GU5 3:23 ratio

GU6 3:42 ratio

GT4 3:73 ratio (GQ1)

GT5 4:10 ratio

GQ1 Open Differential Rear Axle

G80 Positraction/Locking Rear Axle


HARD WAY - If codes are gone or if not stock rear end.

Count the # of teeth on the ring
Count the # of teeth on the pinion

Divide the 2 numbers and that’s what your gear is.


Example: If your ring # is 41 and your pinion # is 12, divide the two #'s would be 3.4166666666... Round it off and you would be 3.42 rear.

Hope this helps you as much as it helped me... ;-)

The axle spline count is different ('88-down has 28, '89-up has 30), but an entire rear end should bolt up fine.

Think the 87 and down are 28 spline...? The never body style came out in 88 with the newer corperate 10 bolt (30 spline)...

I may be wrong but built the rearend on an 88 just two weeks ago...

GM corporate 8.5 inch axles had a rolling model year change of 1988 when the internals were swapped from the 28 spline axles and spider gears to the 30 spline parts. Some 1988's were equipped with the 28 spline parts to use up parts in the assembly plants as many 1988 vhicles were actually assembled in mid to late 1987.

As far as I have been told these WILL interchange.

In looking up the parts, the ring gears are the same, the gear carriers are the same, and the axleshaft bearings, and pinion and axleshaft seals are the same.

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The rear end will fit but both spring perches and the shock mounts need moved. I put a 1990 6-lug 9.5" 14-bolt under mine and had to modify it to work. The gov-loks are known to explode also if abused hard. It would be easier to find a factory posi out of a earlier Trans-Am or Camaro and put it in.

Would it be better ot swap out the axels or can you make the axel you have posi??????