Hi,

My question is will a 69 442 12 bolt rear end fit a 69 Chevelle? The measure is 55 3/4" between the backing plates approximate.

Thanks for your help.

I believe it will fit, although it may not be a "chevy" 12 bolt style. A true Olds "12-bolt " rearend has twelve bolts on the cover but only ten on the ring gear and pressed on bearing axles, no c-clips. These were the early predecessor of the 8.5 corporate 10-bolt. New Ring and Pinions are a little pricey for those olds style 12 bolts. The easiest way I know to quickly tell the chevy 12 bolt from the Olds style, is the cover. The chevy 12 bolt has the full grooved cover, plus 12 bolts holding the ring gear to the carrier. While the olds may only have an oil groove on the right side/corner, and the ten bolts holding the ring gear to carrier. The olds may also have the square ears on the bottom of the center section, when looking at the rear-end cover, similiar the the 8.5 corporate 10-bolts that came after it. Hope this helps.

Forgot to mention the olds 12-bolt style may have a BOP, yoke. (Buick.Olds, Pontiac), and may require a conversion U-joint.

Is it better than my 69 10 bolt?

If the rear end already has a posi and the gear ratio you want, then I'd say it's an upgrade from your current 10 bolt. If it's not a posi and doesn't have the gear ratio you want, I'd hold out for a good price on a chevy 12 bolt.

If you had to buy all the parts, some used, i.e. posi, and a new ring and pinion for the type "O" 12 bolt, you'd end up spending about the same as if you bought a chevy 12 bolt. I have heard that the original axle bearings on the O type axles were inferior and a new design exists to replace them.

It would be nice to have the parts availabilty of more common rear ends like chevy 12 bolts and 10 bolt corporates, for future parts upgrading/replacement. Hope I haven't confused you.

No you have not confused me, I got burned. I just picked up my "12 Bolt" IE "bonified 10 Bolt" Olds rearend. Anyone out there need a boat anchor?? It is a 69 12 bolt type O rear end out of a 69 442.

Does it have a posi and a good set of gears?