Hi,

I locally found an 1988 K5 Blazer posi from a 10 bolt, 28 spline 8.5 3:73 rear end. Is the posi unit interchangeable with my 8.5, 28 spline 10 bolt rear end of my Nova? I am assuming it is, but wanted to make sure. Is the 3;73 gear ratio better than 2:73?

thanks

So-Cal Jack

It will bolt in (fit) but the posi is a ratchet type designed to work in mud and snow and other low traction applications. It will snap the first time you drop the hammer with slicks. For drag racing and street use (pavement) you need an Eaton clutch type that can slip a little before it locks up.

The speed differential (ratcheting pawl) uses a weighted piece of metal that works against a spring to grab a gear as it spins by (kind of like trying to put your transmission in park before you stop moving, you can hear the pin looking for the hole and feel the jolt when it finally drops in). You can just as easily shear that pin off if too much force is applied. This is what happens to the ratcheting pawl, it is a cast piece that will rip off in a heart beat on the road (that is why that K5 Blazer has a decal that covers the back of the drivers side sun visor to warn what happens if you drive on pavement in four wheel drive).

1977 was the only year (all one of them) that GM used Eaton posi differentials in trucks because the four wheel drive was full time so that when you put it in 4WD low it locked up the transfer case and the posi’s went to work giving true 4WD. (I still have my ’77 K20 Suburban TH400 full time 4WD transfer case, Dana 44 front differential, full floater rear Dana 60 and the hardware to put under my current 1987 502 powered Suburban).


Big Dave

The Eaton Governor Lock that was used in these trucks just won't handle the abuse of a performance car. Chances are that the one in this truck is already broke. There is a small gear on the end of the governor that breaks easily if the power is applied to quickly. If you can get it cheap enough you could run it until it breaks. It will fit in your car rear end. The gears will too.