First year for Posi/Limited Slip in a Buick?

Does anyone know what was the first year Buick introduced a limited slip rearend into a production vehicle?

 

Based on an examination of the factory parts books, including Group 5.510, the first model year that I see any reference to posi traction is 1959. I am not saying this is the first year. I am just pointing out something that perhaps pushes the date back at least this far.

 

Yes, 1959 was the first year for the factory installed posi, option code Y. 1959 is also the first year a posi section shows up in the chassis service manual. The '59-'62 units will bolt into '56-'58 rear ends. Also see group number 5.504. Here is a picture of a '55 experimental unit:

http://forums.aaca.org/f115/nailhead-prototype-experimental-292065.html#post813354

 

Wow!
I would have never guessed that long ago.

 

I can't be for certain, but I'm almost sure I remember having it on our '58 Century. Even though I was only about 8 at the time, I remember mom missing the driveway and having the right rear wheel hanging off the culvert. Dad just got in the car and drove it on in the driveway and telling everyone he could do it b/c of the posi rear end. It was a big thing at the time.

 

Same discussion with same results so far.


http://forums.aaca.org/f115/first-year-positraction-buicks-184266.html


COME FORTH HE WHO OWNS A 58 BUICK WITH FACTORY POSI SO WE CAN END THIS GREAT MYSTERY!!!!!

Inquiring minds want to know.

 

http://forums.aaca.org/f115/nailhead-prototype-experimental-292065.html#post813354

guy there has a prototype from 56

 

Thanks a lot, I was wondering. Ive got 3 1960 Lesabres. Besides burning the tires, how can I tell if they have that option? I've heard jacking it up and see if both wheels spin same direction. Is that correct.

 

Cars with a posi rear end may have a stainless steel or aluminum tag around or near (depending on the year) the rear end oil fill hole plug indicating "USE LIMITED SLIP DIFF LUBE ONLY". Also, the letter X in a 0.5 inch diameter circle is stamped on the bottom of the carrier housing flange, but this is usually difficult to see. This figure shows the oil fill hole plug tag and the carrier flange stamp.



This figure shows the actual carrier housing flange stamp (very hard to see, so I've highlighted it with chalk).




For 1963-1965, another way to tell a posi from a non-posi is the oil fill hole plug, which is a square fill plug that fits a 3/4" open ended wrench on a posi instead of the 3/8" square plug that fits a 3/8" hexagon ratchet on a non-posi. However, all cars from 1939-1962 used the same square fill hole plug as the 1963-1965 posi rear ends for either non-posi or posi rear ends, so this is not a reliable indicator of a posi rear for 1962 and earlier cars, see Master Chassis Parts Book group 5.400.

To determing posi/non-posi and gear ratio I think you can do this:

1. Set parking brake with engine off while car is parked on a level surface.
2. Chock the right tire, front and rear.
3. Put the car in neutral.
4. Jack up the left rear tire and put a jack stand under the axle.
5. Take a piece of chalk or grease pencil and mark a line on the rear of your driveshaft and on the inner sidewall of the left rear tire.
6. Release the parking brake and use your hand to rotate the left rear tire. If the tire will not spin and the brakes are not frozen, then rear end is a posi and you will need to jack up right rear tire as well.
7. For a non-posi rear end, count how many times the driveshaft rotates for two rotations of the tire. For a posi rear end, count how many times the driveshaft rotates for one rotation of the tire.