Hello everyone! I recently bought a 1987 IROC-Z camaro. It has the 9-bolt rear end, and I read that those rear ends were made with posi, and open end. My situation is that I have the car but have only driven it once, and cannot drive it for another 4 months. The center counsel says it has the G80 package but someone could have easily changed it.

Now, people say the best way to check is burn some rubber and see. I would do this but sadly I can't drive the car for another 4 months . The one time I did drive it, I had to drive it across a lawn to the road and took off quickly leaving 2 small ruts in the lawn maybe 2.5 feet long. Or would a open end leave 2 marks in the lawn too? thanks!

 

An open diff could leave 2 marks across the lawn.

Jack up the car with both wheels off the ground. Spin one wheel forward. The The other wheel should turn the same direction. If the opposite wheel turns backwards, it's either an open diff or a gov lock.

The only way to know what's exactly in the diff is to pull the cover and have a look. That would be a good time to change the oil in the diff since you don't know if it or anything else has ever been changed. I doubt anything inside the 9 bolt has been changed since there's very few replacement parts for it.

 

Alright thanks alot... I don't think we have a jack but I'll see if my neighbours do. I also read about how posi's can wear out...if I did have the posi rear end how expensive/hard is it to repair it at home?

 

ive been wondering the same thing. i have a 10 bolt and ive always thought it was posi from the RPO but recently i had to do some work on the rear and jacked it up. i turned the wheel just for kicks and giggles and come to find out, the other one spun the opposite way! my freind told me that in order for it to have "true posi", you have to have some type of locker in it or something like that.

havent had a chance to burn out yet, but as soon as i get it back on its feet ill do that and check it out. its also supposed to have 3.73 gears in the rear so im going to open it up and check it out.

 

The burnout test is not definitive. The only way to be sure is to crack open the rear. The RPO only tells you what the car came with from the factory. The 10 bolt rears broke a lot, and people swapped them for whatever they could find, so a car that had a posi from the factory might have an open diff now. Or an open diff car could have recieved a posi under a previous owner. Or the factory posi could be worn out.

Also, it is not impossible for an open rear to leave two equal length black marks doing a burnout. An open rear simply sends power to the wheel with the least traction. If both tires have an equally low amount of traction both wheels will spin. Years ago just, operating on a budget of zero dollars, we took a car that had slapper bars on leaf springs adn an open diff in the 12-bolt. By grinding down the snubbers on the ends of the slapper bars, and testing after we ground each little bit; we were able to get the car to lay two equal length marks.

9 bolt parts are like hen's teeth. It's a shame because it is a great rear, but short of bearings, races, and seals nothing is available new. There are guys that sell good used ring and pinions, and there's an article on this site about cutting down the cones in the posi units to get them to work again, but that's about it.