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Discussion Starter · #1 ·
I have a 72 chevy, Im putting a 383 stroker in it with a 700r4 tranny, I just found the rear axle code on my truck and it says that its a 3.07, does anyone have any experience with installing an overdrive in an older truck, I think that the 307 might be a little too small for the overdrive, I was thinking a 3.42 or 3.73. I haven't actually been into the rear pumpkin yet to see if it was changed out. What do you guys think?
 

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Robbo just my opinion 3.07 would be to tall, a 700r4 with a 29 inch tire and 3.73 gears at 65 mph will put your RPM`s at 1900, just into the sweet spot for a small block torque band, with 3.07 you`ll be below the torque band with a small block, overdrive would not even be practical until you got above 80 MPH..
 

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I had 3.07 in my 78 with the 700,and at 60 to 65 I wound up driving in D3.Rpm was to low causing a constant bucking type of thing going on when in D4.29 inch tire and went to 3.73,but now thinking about going back to 3.42.Most common ratio in stock trucks with the 700 was 3.42.Towing package came with steeper gears
 

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Discussion Starter · #5 ·
Thanks for the input guys, I'll have to dig into it more and find out, what would you recommend if I decided to do a posi, I was thinking if I need to rebuild the rear end to add a posi unit to it.
 

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Gm used the 3.73 rear axle ratio with posi quite extensively in the 4x4 and towing packages, you should be able to find a donor axle from an auto wrecker or Craiglist easily enough, years you will be looking for `68 to 78, truck, blazer, or suburban. I`m assuming you have coil springs in the rear, that will be what rear axle you`ll need to pull from, just grab the entire unit.
 

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Like Rich said those were used widely in the 4x4 trucks ,but if your building a 2wd the 73 on will be leaf sprung.I believe also will use 6 lug axles.Those units came with a gov-lock posi which were very dependable but not up to a lot of abuse.If that's the case then I would go with an Eaton or Auburn.Also the 3.73 uses a 4 series case so if you don't like those gears the 3.42 wont work,but if you go with the 3 series case(3.42 down) and want to change to 3.73 then gear sets are offered in a 3.73 thick.Now as my memory seems to be slipping a little some others might want to chime in and add better info
 

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Gm used the 3.73 rear axle ratio with posi quite extensively in the 4x4 and towing packages......
:confused:

I think you will find that the 3.73's are one of the most average available gears used in the 60-66's in the 2 wheel drive trucks. With the factory I-6 and manual shift trans. the 3.73 this was the standard gear set in a 2 wheel drive truck.

With an overdrive trans I would go steeper than a 3.73. Get into the 4's... you're stop light to stop light performance will be awesome, and your highway performance will be good too.
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John anim_25
 
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