Rear End Gears Swap

Q: Rear End Gears Swap

1) I want to be able to change to “highway” gears when I plan a long road trip, and then put the others back in when we get home. Is this possable?

2) If the rear ends from those other Pontiac models are a direct bolt-in, will the gears out of them swap into my rear as well?

A: Have you done this before? Gear swaps require some considerable skill to perform. Getting the lash and tooth engagement correct are probably the toughest part. A dial indicator would be among some of the specialized tools you would need. So, figure on $250 for gears, another $100 for tools, or $250 to get a shop to do the install. Going from 3:23 to 3:08 or even 2:73 shouldn’t require a different carrier. Figure a weekend to do it yourself, for the 1st time, and then half a day once you get the process down.

Excessive gear noise, and overheated fluid are common signs that a mistake was made.

As you want to hang onto you lower gearset, my suggestion would be to either get a second rear end (replacing the rear ends would probably consume less time than changing gears), or consider some type of overdrive. You didn’t mention whether you had a stick shift or an automatic. You could replace the automatic with a 200R, or the stick trans with a T5 or Tremec. Either will get you an overdrive, reducing your highway RPMs. Of course, this would be more costly at first, but consider the cost of 3 or 4 gear changes.

My buddy, who has 3:73 gears in his 65 El Camino, uses a taller tire (235/70s) mounted on a spare set of wheels for the roadtrips. He carries his cruising wheels and tires (225/55) in the bed, and we swap them when we get to our destination. This gets him what amounts to a taller gear that makes the RPMs at highway speed (2700-3000) a bit more liveable.

2)The 1st generation Firebirds use an 8.20″ 10 bolt unit that was unique to the Pontiac and Buick cars. There is a corporate 8.20 whose gears will not interchange, used in Chevys. In 1970, GM went to one 8.50 10 bolt carrier across the board. This unit can be found in Novas, Apolos, Omegas, and Venturas, 1970 thru 74, and 2nd generation Firebirds and Camaros. The second generation F body rears will fit under your car, but you will need to relocate and replace the spring perches, and use a unique rear u-joint.

Luckily, tall gears are plentiful in these cars.

There are 2 other 10 bolts, a 7.50″ used in late 70s and 80s cars, and a 8.875″ unit used in trucks. So when presented by someone selling you a 10 bolt gearset, be very careful about what you’re buying.

Don’t forget to correct your speedo gear, whatever choice you make.

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