Rear Gears Swap - 3.08s

I'm posting this in case anyone is interested in swapping low ratio gears to higher 3.08s. I know, most guys here want the lower ratio for burnouts and great acceleration. But if you're like me, and just want to enjoy a nice weekend cruise in the car, 3.55's weren't cutting it. On main roads or highways, I'd be at 3000 rpm around 60 mph. Sure, you can get an overdrive tranny, but my TH400 was freshly rebuilt.

So I swapped out the 3.55's in my 65 442 (stock rear) in favor of the 3.08's. Since 3.08's are not available new for BOP, Chevy gears need to be used. Chevy gears of course are not directly compatible with BOP internals, but it can be done.

The BOP rear has three different carriers depending on the gear ratio.

2.56 - 2.78 (2-series)
2.93 - 3.23 (3 series)
3.36 - 5.13 (4 series)

Normally, going from 3.55 to 3.08 would require a change in carrier. The normal carrier for the BOP 3.08's would be Auburn part# 5420114. But using this carrier with the Chevy 3.08's would move the ring gear over too far. But you can use the Auburn 5420113, which is typically for BOP's 4 series ratios. This lines the 3.08 Chevy gears up properly.

Then you need to yoke and sleeve adapter as follows.

- 1310 Chevy yoke (25 spline to fit the Chevy gears pinion shaft is 25 spline )
- Sleeve for the 1310 yoke (this is what makes the seal from the Pontiac rear fit the Chevy yoke)
- U-joint to mate the Pontiac drive shaft to the Chevy yoke ( moog 372)
- U-bolts and nuts for the yoke

Now I did not figure this out myself of course. I spoke to Jim at JDrace.com. This guy knows rears like the back of his hand. Highly recommended.

www.jdrace.com/

The RPM's dropped about 400, which makes a huge difference for the big block. And I still have no problem burning rubber if I want to (stock 400).

Hope this helps someone looking to do something similar.