3.08 rear gear with wide ratio 4 speed
Converted my 66 GTO from auto to 4 speed and still have the 3.08 rear axle in place. Anybody else running this combination and what are the pros and cons?
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Pro: MPG (but really need a 2.56 with a M20 to get 2000 rpm at 70).
Con: Frequent clutch replacement Back in the day, there was a Saginaw 4 speed with a 3.31 first gear but kinda marginal on torque. |
Have you driven your car? Why don’t you tell us?
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Taking off will require a lot more than normal clutch slipping to get rolling, especially on a stop at a grade or steep hill. So you can expect premature clutch wear and replacement - and maybe some embarassment when you stall the car on a steep hill. Most wide ratio manual trans cars from the factory will run a 3.23 and up with 26" tires. It is doable, and I have not knowing much about cars in my youth, but I also was replacing clutch discs about every 3 months with the way I drive - and I figured I was just buying NAPA brand discs that were junk. Now I realize it may have been the rear swap from the close ratio M21/3.90's to 3.08's. |
I switched from 3.42 gears to 3.08's in the 12 bolt in my '64 GTO with the original M20. Effective 1st gear is nearly 7.88 - very similar to how it left the factory with the original 3.23 gears which had an effective 1st gear of 8.26. I drove the car with 27" tires for 20 years with 3.23, 3.36, 3.42 and 3.08 gears..
Original factory tires for a '66 GTO were actually a little over 27". https://www.cokertire.com/tires/750-...8-redline.html It works fine and RPM's at 70 MPH is about 2700. |
3.08 rear gear with wide ratio 4 speed
I did the swap years ago and barely drove the car before sticking it in storage so I don’t recall how it drove. I noticed in the Restoration Guide on pages 310 and 311 charts showing all the rear gear/transmission combinations offered in 1966. For cars with standard brakes, a 3.08 ratio was only available with auto trans and A/C. For cars with metallic brakes, a 3.08 ratio was available with a 3 speed, a 4 speed, or an automatic with or without A/C. The chart does not seem to specify whether the 4 speed was a close ratio or a wide ratio. If this combo was so hard on clutches, it seems surprising that it would be offered by the factory. Maybe I’m missing something.
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A friend of mine ran a 3.08/ 4 speed in a 1972 Ventura 2 which should be close in weight to your car with no problem. Give it a try.
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My 66 stock tripower/ 4 speed had high 2's when I got it. Hardly got out of 2 nd gear in town. Had to shift to 1st at corners. Went to 355's. Much better. All depends on driver needs, type of use, terrane. and future uses. Good luck.
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With the wide ratio M20, a 3.08 rear gear is perfectly fine for regular driving. It may not be the preferred rear end for doing burnouts or the drag strip, but I don't think that's your objective. |
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2.73's
I'm running a M20 2.73's with a trutrac stock 455, 235/60/15's in my 66 Goat
From everything I read thought for sure I'd have chatter, Nope.. you can roll the clutch right out I drive the car all the time and everywhere its not a burn out machine but is a great all around driver. |
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You know I never thought about that contributing to the low temps the car runs 180 on a 90° day might see 200° If I drive it hard that’s with stock factory cooling setup and factory exhaust with resonators if you can believe it.
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Rich |
I was going to find a set of 308 gears for it and I had another 10 bolt with 3.55’s I had ran in another Gto this car came with a 8.5 10 bolt and the 2.73 gears where like new so I gave them a try.
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I converted my 77 T/A from auto to a ST10 with a 2.41 rear. That was less than ideal. Realistically I should’ve looked into a Richmond 4+1 but instead I swapped to a 3.08. Way more practical than the 2.41/4 speed setup. Still highway friendly but not a dog either. I also don’t feel like it’s overly hard on the clutch to get rolling. The 2.41 though did feel that way.
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I have run the ST-10 3.42 first gear trans in a few diff cars.Now in a 62 GP with 421HO and 2.68s in the back.Great combo for driving,would not try to beat on it with big sticky tires.Tom
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The beauty of the Pontiac V8 is that it has more than enough low end torque so that gears like 2.56:1 will still burn the tires. Case in point being my old 1964 conv clone with stock never taken apart 389 and 2 speed auto with 2.56 rear and 14" tires. It would smoke these tires with no effort, yet ran cool as a cucumber (just at 180) at 2000 rpm at 60mph. I think the new owner loves it more than I did.
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The answer depends on what you want to do with the car. I just want a cruiser so it works great and keeps highway rpm down. if you want something snappier try a 3.55 or 3.73. I've had other cars with a 1:1 4th gear and 3.55 they are pretty good at highway speed |
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