72' Catalina & Bonneville

[Gary H]

I'm working on two cars for a customer, and I can't seem to find out whether rear gears and a Posi unit are available for them. The cars are a 72' Catalina and a 72' Bonneville. If it makes a difference, the Catalina had a 350 engine, and the Bonneville had a 455.

[Ben M.]

They are not available new and are unique to this era of car. You can still sometimes find kits for them but beware as most of the "fits all cars of this era" ones you readily run into advertised by various dubious internet sites and parts stores are not correct.

If you want a posi or different gear ratios the best bet is finding one of the people who parts these cars and has a stock.

[Stuart]

The factory brochure for 1972 lists the available gear ratios: 3.23, 3.08, 2.73 and 2.56. See pages 20-21. Posi was an option, see pages 54-55. https://oldcarbrochures.org/United%20States/Pontiac/1972%20Pontiac/1972-Pontiac-Full-Line-Prestige-Brochure/slides/1972_Pontiac_Full_Line_Prestige-20-21.html

['ol Pinion head]

The Catalina will have the 8.5 c-clip axle '71-76 B series 2door/4door rear.

The Bonneville will have the '71-76 8 7/8 MP series rear/12 bolts attaching the ring gear.Most likely the '72 Bonne was built as a 3.08 or 3.23 single track. Used posi carriers are avail for the 8 7/8 MP series rear, have had several of the mid ratio versions & a few of the low ratio versions, they are rebuildable, just have to be careful not to buy a high ratio version. Several times, I've pulled the 30 spline side gears/spiders & clutches out of the early MP series high ratio carriers & shimmed them up in later low ratio MP series posi carriers that originally came with 28 spline side gears.

[Gary H]

Thanks, guys, for the replies!! I actually spoke with the folks at JDRace.com and he said there's such a poor choice for parts that he recommends just getting a later 8.5" corporate rear end out of a 73-76' B body car and use it instead. He said it would be a direct bolt in. We'll probably go that route.