3.42 Gears

[surfkurf]

Hi All,

I'd like to change my stock 2.56 gears in my 72 Skylark Convert to 3.42 gears. Does anyone know the part numbers and a good place to order them? I also need the Speedo Gears to match.

Thanks

Joe

[NTX5467]

At the production level, that change would require a new differential case (what the ring gear bolts to) as the flange thickness is specific to a particular range of gear ratios. In the aftermarket, they use a spacer that goes behind the ring gear before you bolt it up to do the same thing, but only if you use the aftermarket gear set (which is usually in the 3.91 or 4.10+ range).

Unless you find a stock replacement aftermarket set to do what you want, most of the aftermarket sets might be "deeper" than 3.91 instead of 3.42. If you don't already have a limited slip rear axle, this might be an opportune time to make that upgrade too. If you get an OEM replacement gear set, 3.08 might be a deep as you can go and not change the differential case, but we'd need to look in the parts book to verify that.

There are several full line rear axle parts vendors that advertise in the enthusiast magazines. Buying a new limited slip unit for the 3.42 ratio you desire and then a OEM style 3.42 gear set might be the best way out. Have you also got someone that is proficient in setting up rear axles lined up to do the changeover? Getting the right pattern on the gear set is a key thing that can sometimes test an installer's patience to make sure it's right where it needs to be.

The other side of the deal might be to find someone with a GS that's going to put some deeper gears in the back and is selling their used gear set and diffential case (as a matched set) that is a 3.42. Provided everything's in good condition, that might be the least expensive way out, but it depends on what you can find too. Of course, salvage yard shopping might be an option too.

All things considered, it might be better to chase a 3.08 instead of a 3.42. Might not be that much difference in race ETS but also give you more throttle response without hurting the fuel economy too much at cruise. A little bit looser torque converter with a 3.08 might give similar results as just putting the 3.42 in there, performance wise, without the extra cruise rpms--or even retrofitting a switch pitch converter setup into the vehicle too (presuming you have a THM 400).

Of course, it's your car and you know what your expectations are too . . .

Just some thoughts,

NTX5467

[surfkurf]

Wow, that was a great response. Thank You!!!

Yes I do have someone who actually replaced the stock 2.56 gears last year. Unfortunatly, he has a 72 Olds 442 which makes him very busy in our town since his knows A bodies very well. He said just get the parts and he'll take care of it. He thinks the 3.08 won't be enough for this car. I settled on 3.42 only because I thought anything higher would kill the old engine on the way to the beach. I'm not looking for a racer, but instead a solid driver that doesn't feel like its starting in 2nd gear.

I can talk to him about these ideas. What do you think is the best option? I live close CARS, Inc. (OldBuickParts.com) and they may have something useful. I would think that a 3.91 with a 350 would be screaming on the highway without an O/D.

Thanks again for the help!

Joe