Hello all,

Have a 89' IROC with (yipes) drum brakes, 15" wheels, etc. Got it not too long ago as a go to market car. Car would hook up rather well, posi was warming up the tires nicely. I drive like a sedated nun (I'm 36 not 16) so I was not incessantly abusing the car or the rear end. In any case, drove it to "the store" last night and decided to remark the street centerline (in a turn) and got only a left wheel. Left the store and only the right spoke up (in both cases the lightly loaded wheel on the inside of the turn). No posi! I noticed a small oil drip area under the car when I first got it and realize that it is gear oil. I've put maybe 75 miles on the car since.

Question is... if a posi gets dry (and I assume the dog leg is evidence of that), is it possible to get it functional again? I'm going to pull the cover, clean the crap out of the inside of the diff, add some lucas oil and put a new gasket on the cover. Can that bring back a posi. It did on my 67 chevelle SS 12 bolt so I'm hoping some of you may have had the same experience. It should be said that I may have had a fluke event where the posi did not hook, but I would begin to question that if it happened twice.

Thanks for your input!

 

No, adding fluid cannot "bring back" a posi. A posi is a system of clutches operated by springs; lack of fluid won't cause them to slip, and adding fluid won't cause them to grip. This of course is assuming you even have one. There's a very strong possibility your car didn't have it in the first place. A drum brake IROC in that year probably has a 10-bolt with 2.73 gears and no posi.

Take off the cover and look. It's the only way to know for sure. Use synthetic gear lube such as Mobil 1 or Red Line, and in case it turns out to be a posi, a bottle of friction modifier additive.

In this post is a good picture of a stock posi unit for a 10-bolt. If you don't see this, then it isn't a posi. https://www.thirdgen.org/techbb2/sho...hreadid=193915

 

Good point on the response! This car was RPO coded as G80, and did readily light off both sneakers when I first picked it up. The diff has some oil on the outside of it, and the typical, nasty smell of gear oil is evident. The leak has been going on for some time and is not a "fresh" thing. I'm confident it is a posi, just not sure why the changes in its behavior without any obvious signs. I was told by a fellow F owner that rebuilding (like the Eaton units) would be one way to go, or looking at an aftermarket vendor for a factory pull out of a 4th gen (which would require a change in axles). The 4th gen diff's are $99 bucks (but require a new pair of getaway sticks).