Ha ha, just had to make a 60's joke out of that. I AM confused though. I just bought my '68 400 and am trying to make heads or tails of what I've got here. I asked the guy who had it if it had a POSI rear and he said "No, it's a limited slip differential." Isn't that the same thing??? Or not always? It's supposed to be somewhere between 3.16 and 3.26 (he wasn't POSItive but just said he knows it tachs 3000 at 70mph which is true).

Thanks for answering a dumb chick question, ha ha!

Maybe he was trying to be cute. Posi is a trademark of Eaton, but it is a limited slip, so yeah- same thing.
Or maybe he has limited slip and open rearends confused.

It may be a 3.23. They were pretty common, and with a ~26" tall tire (~235/60/15 or ~215/70/14), would put you around 3k@70mph.

An easy test to see if it is a LSD or open, is to get one tire on a slippery surface, and one on dry pavement, and floor it. If they both peel out, it is probably a LSD. If only the one on the slick stuff spins, it is likely an open, or a worn out LSD.

Or jack it up and turn one rear wheel.

- Jake

JBeaudry,

That's a gorgeous car - congrats on a great purchase.

John

Thanks. I signed over every dollar I had in the bank, except the $40 in gas it took to get home, but I'm very happy. It's funny, I keep going out to the garage and just looking at it... Yes! It's Real!

It's so nice that this website has a great group of people who know so much. When I had my Chevelle (before internet) it was just like Chilton's or Haynes, or ya dig through old issues of Chevy High Performance, ha ha.

You should have a 3.23 gear.My 69 Bird runs the same,3000 RPM @70 MPH,with 3.23s,I have 235/60/15 on the rear with a 4 speed Saginaw,not sure on the tranny gear ratios though.The best way to tell if you have a LSD,is to take off the cover.My car will spin both wheels if they get equal power,but I DO NOT have a LSD,just an old fashion open diff.

Nice color! Welcome aboard. BTW, I also have a 3.23 rear in mine. Not sure about tach at 70, but the new tranny should help that I'm putting in a 200-4R soon.

Yeah, open rears can squawk both tires. One way to tell posi/lsd is to lift both rear wheels off the ground. Spin either wheel in either direction. If the other wheel spins in the opposite direction, it's on an acid trip.

Most LSD rears will spin both tires the same direction if you jack it up and turn them by hand. Also if it is in gear, they'll probably just be locked.
An open or 'one legger' will let you just spin one wheel while jacked up, and the opposite may spin in the opposite direction. But yes, the only real test is to take the cover off and look at what is in there.
The grass test is a decent one if you dont want to go thru all that work. It's not foolproof though; one tire on wet grass, one on dry pavement... Grass and LSD seem to go together just fine.

LOL

While driving my car onto the ramps in the garage this weekend I managed to leave 2 black marks on the floor of my garage from the rear tires spinning.

While on dry pavement if I puch it the car will leave 1 solid black mark. I've had the rear cover off and have verified it is an open rear....

I should be able to tell a different story in a couple weeks. Changing from a 2.56 open to a 3.23 posi.

You can burn both wheels with an open, its just a matter of touch and feel. I do it all the time, you just have to work the clutch a wee bit longer than normal.

No wonder your looking for a second tranny Nash

I raced my 69 Bird at a local track a while back and everytime I took off,I spun both tires,and when I`m out "playing around"it will usually spin 2 tires,then after awhile it will change to 1 and sometimes back to both.

I'm surprised nobody has mentioned it is not "Posi" or "LSD" but rather "Safe-T-Track".

I think 'limited slip differential' describes the Safe-T-Track too, as well as the Sure-Track, Torsen, etc... trademarks.

68 BLKBRD, the tranny handles it just fine my friend! Its the clutch assembly and associated parts that are really taking the torture......rather well for the moment!