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Discussion Starter · #1 ·
For my build I have a 4L65e and my stock rearend appears to have 3:08 gears. This doesn't seem to be ideal but can some one tell me what I can expect to see with this combination as far as rpm, drive ability. I have two of these rear ends from origins and parts car, would liked to have had 3:73 but both I have are from a 64.
 

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Hey Mike, how do ou plan on driving the car? a lot of highway, mainly street driven etc. 3.08's are nice highway gears. Its would be a dog off the line. 3.73's would give it nice drivability
 

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I did exactly that. :yes: I went from 3:08's to 3:73's and it changed the whole car's street behavior for the better! :thumbsup: With an overdrive transmission, it's the best thing you can do to make your car more enjoyable. I have a 700R4 transmission which is similar to yours (except mine is not electronic).
Good luck,
Claude.;)
 

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Where I live you need to run 70-75 mph on the freeway to be comfortable. Let's assume your car has a 350 small block with a 3.48" stroke whose torque band is from 2,000-6,000 RPM, weighs 3,500#, has 26" tall tires.

You would want about a 10.75:1 SLR (starting line ratio) or torque multiplication ratio for optimum acceleration. (Note: a 3.73 is not required with the 3.06 first gear in a 4L65) If you had, for example, a turbo 350/400 you'd take 10.75 divided by 2.5 equals 4.30 rear axle ratio; for your 4L65 with a 3.06 first gear you'd only need about a 3.50 rear gear which is not exactly available. Your closest choice would be 3.55. A 3.55:1 rear ratio with your transmission would put your OD gear cruising speed in this range:
RPM MPH
2000 62
2500 78
 
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Discussion Starter · #6 ·
Where I live you need to run 70-75 mph on the freeway to be comfortable. Let's assume your car has a 350 small block with a 3.48" stroke whose torque band is from 2,000-6,000 RPM, weighs 3,500#, has 26" tall tires.

You would want about a 10.75:1 SLR (starting line ratio) or torque multiplication ratio for optimum acceleration. (Note: a 3.73 is not required with the 3.06 first gear in a 4L65) If you had, for example, a turbo 350/400 you'd take 10.75 divided by 2.5 equals 4.30 rear axle ratio; for your 4L65 with a 3.06 first gear you'd only need about a 3.50 rear gear which is not exactly available. Your closest choice would be 3.55. A 3.55:1 rear ratio with your transmission would put your OD gear cruising speed in this range:
RPM MPH
2000 62
2500 78
Should I try to find a complete rearend with those gears or can mine be swapped out? As mentioned above I'm rather ignorant on this subject.
 

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Yes you can change the gears out. If you decide to go that route, make sure you know what axle, gear ratio and gear set carrier you have first. i.e. Is it a Chevrolet axle? Is it a 10 or 12 bolt? What axle ratio (divide no. of teeth on ring gear by no of teeth on pinion gear)? Is it posi or open carrier?
 
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Thanks Steve, Claude, I'm pretty ignorant on gearing but I thought the 3:73's would be better, I'll have to look at my options.
Yes Mike, that's what I'm saying…that 3:73's are best with an overdrive transmission… :yes:

Claude.;)
 

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You can use the 64 Chevelle rear differential housing.

When you order your Eaton Posi, it will be for a 65 - 72 Chevelle. Then order a set of 28 Spline Moser Axles for a 65 Chevelle.
 

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Discussion Starter · #11 ·
You can use the 64 Chevelle rear differential housing.

When you order your Eaton Posi, it will be for a 65 - 72 Chevelle. Then order a set of 28 Spline Moser Axles for a 65 Chevelle.
This is what I wanted to hear, I thought I had read somewhere that I could use my 64 housing and swap to 65 axels with the posi. This will give me the option to continue with my build and do the swap a little later.
 

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I'd leave the 3:08 and swap trannys to either a TH-400 or Th-350... Your driveshaft speed will be lower, less parasitic drag..

I prefer a 1:1 final, with a good coupling converter, you can hit the stators torque multiplication for more speed at will....

My 69 Elco has 2.73s, TH-400, 454 and it's perfect for street duty..
 
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