Time for a new diff.

[Larry.sisk]

I'm looking for another Diff . For my 72 pickup I want just a good daily driver that will stand up to some hot rodding I have a 350 with a TH350 trans is there any particular new or used diff that all the truck builders of trucks my year flock to or what's the best thing to look for at the wrecking yard thanks in advance. By the way the diff I'm running is way too low geared when I'm doing 55-60 it is wound too much another thing is that it has 6 lugs and my front has 5 lugs is that normal ?
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[leftybass209]

The 6 lug rear ends are from 1970 and prior. There's not a particular gearset that people are snatching up, it just depends on what engine/trans/rear combo that suits a given person for their lifestyle. There were several gear ratios that are common. Taking a wild guess, you may have 4.11's or 3.73's. A better gearset for acceleration AND highway cruising would be 3.42's. A gearset that won't win you any holeshot awards, but was the OEM standard gearset when ordered with a TH350, were 3.07's.

[halfstep]

There are many experts hear that can and will correct or add to what I am sharing, but this still should help:
No info on year etc. of your truck, but it appears you have a 1970 or earlier rear, which tend to have the 6 lug pattern. Cheapest, easiest would be to find a c10 rear out of a 71 or 72 that has an milder gear ratio and would/should have a 5 lug (5x5) bolt pattern - both issues solved! Putting in a rear from another vehicle would require a lot more work...welding brackets, plumbing brake lines, fabricating e-brake cables, etc.
Before anything, though, you should confirm the existing gear ratio so you have a baseline. This can be done by cleaning off the axle tube on Pass side (I think) generally on the top or back and closer to the pumpkin and look for an alpha numeric code this can be cross referenced to give you the ratio. You may also find the axle ratio listed on the glove box door build sheet, but if your rear is not original to the truck or has been changed it is not likely to be correct. You can also jack it up and mark you driveshaft and rear pinion and rotate the rear tires to figure your gear ratio. Absolutely accurate is to pull off the cover (then replace gasket and add/change gear oil) and count ring teeth vs pinion teeth 37 ring teeth / 9 pinion = 4.11 ratio). Sometimes this is even stamped on the ring gear. Once you know your gear ratio then you want to look for a lower numeric gear ratio. Taller tires can help offset or reduce wheel rpm's but not that much, better and balanced tires may be quieter.
As far as other rears go, from what I gather here, the 6 cylinder trucks tended to default with 3.73 gears for more low end pull making up for lack of engine size. V8s more often had 3.07 gears. Even lower (higher numerical ex. 4.11) gears were often put in trucks that had to work. You will still have to confirm the gear ratio of any rear you get.
Another even easier, but more expensive option would be to go to a shop and have them install lower (numerical) gears in it and possibly re-drill or change the axles to 5x5 like you have in the front.
A word of caution, though... these trucks do not get good gas mileage regardless of engine size, or gear ratios. A 2 barrel 283 with a 3.07 rear is just as likely to get 10-12 mpg as a built 350 or stroked 383 with 3.73 gears. So if it's just noise at cruise, I'd just insulate the cab and do door seals... Of course there are many here with unicorns dancing in their back yards that will swear to 18-20 mpg and quiet cruising speed but your chances of either are as good as seeing those unicorns.

[Larry.sisk]

Originally Posted by halfstep

There are many experts hear that can and will correct or add to what I am sharing, but this still should help:
No info on year etc. of your truck, but it appears you have a 1970 or earlier rear, which tend to have the 6 lug pattern. Cheapest, easiest would be to find a c10 rear out of a 71 or 72 that has an milder gear ratio and would/should have a 5 lug (5x5) bolt pattern - both issues solved! Putting in a rear from another vehicle would require a lot more work...welding brackets, plumbing brake lines, fabricating e-brake cables, etc.
Before anything, though, you should confirm the existing gear ratio so you have a baseline. This can be done by cleaning off the axle tube on Pass side (I think) generally on the top or back and closer to the pumpkin and look for an alpha numeric code this can be cross referenced to give you the ratio. You may also find the axle ratio listed on the glove box door build sheet, but if your rear is not original to the truck or has been changed it is not likely to be correct. You can also jack it up and mark you driveshaft and rear pinion and rotate the rear tires to figure your gear ratio. Absolutely accurate is to pull off the cover (then replace gasket and add/change gear oil) and count ring teeth vs pinion teeth 37 ring teeth / 9 pinion = 4.11 ratio). Sometimes this is even stamped on the ring gear. Once you know your gear ratio then you want to look for a lower numeric gear ratio. Taller tires can help offset or reduce wheel rpm's but not that much, better and balanced tires may be quieter.
As far as other rears go, from what I gather here, the 6 cylinder trucks tended to default with 3.73 gears for more low end pull making up for lack of engine size. V8s more often had 3.07 gears. Even lower (higher numerical ex. 4.11) gears were often put in trucks that had to work. You will still have to confirm the gear ratio of any rear you get.
Another even easier, but more expensive option would be to go to a shop and have them install lower (numerical) gears in it and possibly re-drill or change the axles to 5x5 like you have in the front.
A word of caution, though... these trucks do not get good gas mileage regardless of engine size, or gear ratios. A 2 barrel 283 with a 3.07 rear is just as likely to get 10-12 mpg as a built 350 or stroked 383 with 3.73 gears. So if it's just noise at cruise, I'd just insulate the cab and do door seals... Of course there are many here with unicorns dancing in their back yards that will swear to 18-20 mpg and quiet cruising speed but your chances of either are as good as seeing those unicorns.

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[Larry.sisk]

Originally Posted by Larry.sisk

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Thanks very much now I need to get out there and inspect this rear end so I'll know , the local wrecking yard has a 94 chevy Silverado 4x4 that I was thinking about looking into how much trouble it would be to swap out but you raise a great point what's my current gear ratio I'll need to know . Thanks everyone for your help I am able to drive this truck today because of the help I've got from all the knowledge on this forum
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