What Rear-end

Im wanting to get gears for my car but i also want to know what type of rear-end i have. i have a 91 rs 305 TBI with Auto and 2.73 gears in the rear with drum brakes...what i need to know is if it is posi or an open differential...if its a open differential i will be looking into buying a new differential...any suggestions there.

You have an open rear end. If it were a posi there would be a metal tab hangine off the diff cover (unless removed). You can also jack up the rear end and spin one of the tires. If they both spin the same direction, it's a posi. It won't though, unless it's not origional, the RS only came with a posi in the 305 or 350 TPI B4C "Special Service" police package.

ya thats exactly what i was told...but just had to make sure...what type of rearend differential do yall recomend since im going to buy a new one.

You have an open rear end. If it were a posi there would be a metal tab hangine off the diff cover (unless removed). You can also jack up the rear end and spin one of the tires. If they both spin the same direction, it's a posi. It won't though, unless it's not origional, the RS only came with a posi in the 305 or 350 TPI B4C "Special Service" police package.

What he said. If you dont feel like jacking your car up and spinning the tire, the you could always try doing a burnout :evillol: . Floor it then quickly slam on the brake... you'll see smoke coming from only your right rear tire. Friend has a car that looks identical to yours and has the same engine. I don't understand why they didn't at least throw posi on the 305's. I can understand why not on the sixers. But c'mon, the 305? GM must have got cheap around that area I guess. I'd go with one off a Z28, SS, or Trans Am. One of those should suite your needs just fine, and you'll also get rear-disc brakes along with it. But unless of course you're planning on shooting out 400hp, then I'd go with a Strange 12 bolt. I hear good things about those. And that's what my friend's goin with on his T/A.

Yeah tcfco, you have the same rear i have. Open w/2.73. Some 305 did come with posi and a better set of gears. Supposely(sp) the rear i bought off this kid has 3.42 gears, it does have posi, the tag is there, and it's a drum setup. The kid i got it from has an 87 iroc, just like me, except he had the T-5, when i have the auto. He went with a fourth gen rear. I gonna go along the roots of getting a fourth gen rear with disc brake. Or you could get 3rd gen 9-bolt really strong from what i hear on here. As for the posi unit, either eaton or auburn would do, check out jegs.cm or summitracing.com.

There was a good article in chevyhiperformance.com from a 2000 issue. It explains rearends some and is a budget builder. They say the 8.5" 10 bolt can be almost as strong as the 12 bolt. It explains what vehicles the 8.5" came in which you can get the housing for about 200 bucks? then get a posi unit and gears for another few hundred. Just do a search for it on their site...The title is "Budget 10-Bolt Upgrade: How To Build A Bulletproof, Posi 10-Bolt For $400 Or Less! February 2000" If you're not running big numbers it will work great for you

Edit:
Here is the link: http://www.chevyhiperformance.com/techarticles/48518/index.html
http://chevyhiperformance.com/techarticles/p113382_image_small.jpg These are what vehicles came with the 8.5" they are all the same except for mounting brackets.http://chevyhiperformance.com/techarticles/p113381_image_small.jpg And these are all the Richmond gear sets that will fit into the 8.5" GM housing

Good luck man!