Rear gear change

[JOZW30]

Am planning to change the rear gears in my 72 W30 4 speed this spring and would like some advice from the experienced.

The car originally came with 3.73:1 posi but somewhere in the past was changed to 2.73:1 (it's really pretty sad.....).

I usally go to several shows where I drive 45 minutes to an hour on the freeway. That's really abou the worst of it. The rest is 35 - 50 MPH to the local cruises and shows.

I want to have fun off the line when I feel like shredding some rubber. Should I go all the way to the 3.73's or would I get about the same rush from a change to 3.42?

Also, I have never done this before but am certainly mechanically inclined. Is this a do-it-yourself project or better left to professionals? I'd love to do it myself if it not too risky.

Also, what parts do I need to get? Gears, bearings, clutches, axle seals? Any other tips or advice?

I can't wait for Spring this year!

[beater68427]

I put 3:42's in my olds, It had 4:11's for a while I started to get worried with the oiling system at the higher sustained engine rpm. The 3:42 work fine with the 455 a blast to drive and good all around gear. Your car is a 72 so it should have a corp 10 bolt with 28 spline axles, parts are very available at a decent price, you might just post a wanted ad, but you will need your 5 stars

[GM-26]

My Chevelle has a LS-6 454, M-22 tranny and 3:73's. This is a really good overall gear ratio. I drive all over Long Island to my friend's houses with no problems. With this gear ratio the car is really responsive and isn't screaming on the parkway. I didn't tackle the rearend rebuilt. I brought it to a local race shop.

[markjohnson]

I think it would be wise to assemble a complete new rearend and just swap the entire unit out. 2.73's will turn ANYTHING into a slug! On the other hand, I think 3.73's are always a good choice for a fun street car with great highway manners. A second rear end would also mean very little downtime when it comes time for the swap. You could be done by Noontime if you start on it early on a Saturday morning.

[JOZW30]

Thanks guys,

I found a calculator for RPM with a specific gear ratio and tire size. With my BFG's at 65MPH with the 3.73's, I'll be running around 3100RPM. Again, it's usually less than a couple hours total between 3 or 4 trips.

I don't think I have the space for a second rear to hang around just for highway trips but the idea makes sense.

I sense from the responses so far that having this done proffesionally is the best route.

Thanks again for the input.

Joe

[Salvatore]

373's!

[Jerry@CHP]

Joe,

The 3.73 rear ratio is a good choice. You probably have an M20 which is the better trans to have for your application.

As to setting up rears, I've been doing them now for almost 40 years and I had one yesterday that kicked my as......Had the pinion out four times setting the depth, changed the back lash about six times trying to get a good pattern on the gears. The aftermarket gears are much harder to set up in getting a good pattern. They give you a tolernace on the pinion to check depth but most of the time after you check the pattern when setting the depth, it's not good at the depth that they recommend. You also need a good supply of shims for the pinion, side carrier shims, clutch shims, etc. The aftermarket shim kits are a joke! GM has always been the best for these items but a lot is being discontinued now. As to tools, you'll need a depth gage, inch pound torque wrench, .001" dial indicator, a torque bar attaching to the yoke to help in crushing the crush sleeve and more. After all these years, I still hate doing rears!

Jerry

[JOZW30]

Jerry, good info, I will have it done professionally. The place I usually get my trans work done can do this. They did suggest I get the parts myself as "this stuff is getting harder to find" (I think they aren't very internet savvy).

I found a place that sells GM (OEM) ring and pinions. Is this best option?

I want to use the best parts. What else should I buy?

Oh, and 3.73 it is!

Joe