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glenns towing #1464956 Fri Sep 02 2022 06:55 PM
Joined: Mar 2019
Posts: 1,438
G
'Bolter
Yea i counted it many times. If it was 4.03 it would've been real close to straight up and down. But it was definitely ¼ turn past that. Thats where I came up with 4.25. Unless you ment 4.30 which would be real close to what i figured at 4.25. Regardless, like you said, dont much matter. Thanks for responding tho.

glenns towing #1464963 Fri Sep 02 2022 08:42 PM
Joined: Sep 2011
Posts: 2,676
L
'Bolter
So you counted 40 turns plus another 1/4 turn when you turned the output shaft 10 full turns? Then 40.25 divided by 10 is 4.025. You have a 4.03 unless I’m missing something.

Lugnutz #1465023 Sat Sep 03 2022 01:40 PM
Joined: Mar 2019
Posts: 1,438
G
'Bolter
Originally Posted by Lugnutz
So you counted 40 turns plus another 1/4 turn when you turned the output shaft 10 full turns? Then 40.25 divided by 10 is 4.025. You have a 4.03 unless I’m missing something.
Well crap. I didnt devide... I stand corrected if thats the way its needed to be done. Thanks for enlightening me and your patience. Im always in a big rush lately. Glad it was a minor detail. But obviously makes a difference.
Therefore apon further discussion on the gear ratio. 1st gear = 4.03 and 5th gear = .86
So if anyone is interested, once again, let me know.

glenns towing #1465143 Sun Sep 04 2022 06:41 PM
Joined: Mar 2014
Posts: 3,138
J
'Bolter
I'm going to try to help Glenn and also help anyone wanting a more fuel efficient truck. If first is 4.03, that's almost a perfect ratio chain if you have a 3.07 or 3.08 rear end, a 235 and you want to use your pickup as a real genuine truck. And by that I mean if you want to load 1000 pounds of stuff in the bed (which I've done many times) and drive without burning up a clutch.

Please let me show you why...
Your truck originally came with a first gear of 2.94 and a rear end ratio of 4.11. That gives you an overall ratio of 12.08. Your OEM 2nd gear was 1.68 and that will give you an overall of 6.90 and 3rd obviously will be 4.11. Please keep these in mind. GM engineers chose those ratios for valid reasons.

With a 3.07 rear end and a 4.03 first, you have an overall ratio of 12.37. Wonderful!!! Your first gear ratio is within hairs of OEM. Your second gear ratio in that transmission is 2.37 and that times 3.07 is 7.27 (remarkably close to OEM). Third gear is 1.49...times 3.07 is 4.57 and then when you hit 4th gear, you're at 3.07 (a 25% reduction from 4.11 (or similar to having old-fashioned overdrive). So the first 3 speeds will not feel different from stock. Fourth (as I said will feel just like an overdrive transmission) and then in fifth the .86 drops things only .14 or 14% which on a flat to mildly hilly road without head wind problems you can lope along all day. 60 to 63 mph will be at about 2100 rpm. If you go faster than that, you're flirting with some notable aerodynamic challenges not to mention the challenges of the front end and braking. With a 3.07 rear end, .86 fifth gear gives you an overall 2.64 drive gear. If you're overloaded, stay in 4th. If not use 5th. If you are using the 1959 or newer camshaft, your maximum torque happens at 2000 rpm, by the way. All 235s from 1959 until the end of production used that camshaft (which is discussed on the GM Heritage pages). It provides higher torque at lower rpms. GM was hoping to help reduce emissions with it.

What happens if you move to a 3.42 rear end? Well, your first gear overall ratio gets taller than I like (almost to 14) and what that means is you'll be needing to shift from first to second before you even get through a city intersection. Which to me is an unnecessary pain. Good luck!


Jon

1952 1/2 ton with 1959 235
T5 with 3.07 rear end
glenns towing #1465155 Sun Sep 04 2022 08:25 PM
Joined: Sep 2011
Posts: 2,676
L
'Bolter
Adding to the last post . . . .
Here is a short VIDEO [youtu.be] of me driving my 1963 C10 with an inline 230. My T5 has a 4.03 first gear and a 3.73 rear axle. You can see that I don’t spend much time in 1st gear. With the 3.07 rear axle and 4.03 first gear you would likely shift at 18 mph when your tach hits 2600 RPMs.
***(Tire diameter does make a difference, but I made the calculations with a common size tire of 235/75R15 with a 28.8” diameter.)

Make note that the shift I make at 2600 RPMs is at 14.8 MPH.
So the 3.07 rear axle makes SOME difference, and a 3.42 would end up between the two.

IMHO, the 3.42 rear axle gear would be a better match for any driving that has occasional hills but the 3.07 would also work well.

glenns towing #1465180 Sun Sep 04 2022 11:22 PM
Joined: Mar 2019
Posts: 1,438
G
'Bolter
Good information. Thanks. Hopefully useful for the future owner also.
Thats if it dont get put to good use before hand...

glenns towing #1465231 Mon Sep 05 2022 01:44 PM
Joined: Mar 2014
Posts: 3,138
J
'Bolter
Good luck, Glenn. I'd be interested if I was closer to Iron City. One other point I'd add...the overdrive in 1959 was a .7 ratio (meaning a 30% reduction) and it was matched with a 4.11 rear end. So, 4.11 x .7 = 2.877. The tires I use make for a 4% addition to the end value, so my final drive ratio is 4% less than the OEM final drive ratio with overdrive. That's as close as I could get. A 3.08 rear (probably more common than 3.07) would have probably brought it to within 3% of OEM final drive ratio, but as Jay said above it does work well. Usually I shift out of first as I approach 20 mph, so Jay's number is right where it should be.


Jon

1952 1/2 ton with 1959 235
T5 with 3.07 rear end
glenns towing #1465298 Mon Sep 05 2022 11:19 PM
Joined: Mar 2019
Posts: 1,438
G
'Bolter
Hey thanks to you both, Lugnuts and JonG. Huge help and understanding of the advantages and disadvantages. Just another example of the knowledge on this site. Hats off....

glenns towing #1467486 Tue Sep 20 2022 10:23 PM
Joined: Mar 2019
Posts: 1,438
G
'Bolter
Still available. Haven't posted on CL yet. Im rather surprised no one here is actually interested. Ha.
If the electronic speedo is the deal breaker, there are modern ways to overcome and get a speed reading. If thats an option. Thanks once again for looking.

Last edited by glenns towing; Tue Sep 20 2022 10:27 PM. Reason: added something
glenns towing #1470495 Mon Oct 10 2022 03:02 PM
Joined: Mar 2019
Posts: 1,438
G
'Bolter
Still here...

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