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Old 10-03-2012, 05:33 PM
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3.70 or 3.90 with a t5 trans x 235 motor

I've got my truck in the shop right now and I'm getting a new transmission and rear end put in. It's a 50's era chevy with a 235 motor. I'm not concerned with highway speed, I'd like to give it a little more get up and go driving in town. I'm replacing the 4.11 gear ratio and the shop is suggesting the 3.90 rear would be the best fit for the new 5 speed transmission. I talked with a friend who thinks the 3.90 is probably going to drive about the same in town as the 4.11. He's suggesting a 3.70 gear to me. I know this has been discussed to death, but most people seem to want greater highway speed, I want faster starts. What do you guys think, 3.90 or 3.70 as the better all around choice for this truck?

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Last edited by getset; 10-03-2012 at 05:36 PM. Reason: spelling
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Old 10-04-2012, 09:04 AM
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If you want pep, keep the 4.11.

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Old 10-04-2012, 09:30 AM
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Keep the 4.11.
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Old 10-04-2012, 10:39 AM
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theres more than one T5 ratio.

What did it come from? Amc, Iszuzu, S10, Camaro? 4, 6 or 8 cyl.

If you have the usual T5 hybrid conversion (V8 camaro guts and an S10 tailhousing), that has a 2.95 1st gear, which is plenty for 3.73s, let alone 4.11s
Find out what your first gear is and then pick your rear gear to match
If the trans is out of your truck, lock it in 1st gear and turn the input 10 times. Count the number of turns on the output. For example, if 10 turns on the input gives you 29 turns of the output, thats a 2.9 1st gear. Which I wouldn't recommend with a rear gear higher than 3.73. If you have a deeper 1st gear than that, you really should drop the axle ratio a little because those transmissions aren't that strong.

If you have an S-10 trans with a 4:1 1st gear and a set of 4.11s; thats 16:1 total reduction (4x4=16); which is like taking a Muncie or a TH350 and putting 7.00:1 gears in the axle. 1st gear will be useless, not peppy.

Last edited by AutoGear; 10-04-2012 at 10:53 AM.
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Old 10-04-2012, 11:04 AM
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what RPM does the 6 rev up to when acellerating under full power? what size are your rear tires? Does the engine make fair power? or is the engine close to stock? a slow revving engine with low horse power uses torque to accelerate and using to much gear wont help as you will be shifting more than you should be.
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Old 10-04-2012, 09:52 PM
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Quote:
Originally Posted by vinniekq2 View Post
what RPM does the 6 rev up to when acellerating under full power? what size are your rear tires? Does the engine make fair power? or is the engine close to stock? a slow revving engine with low horse power uses torque to accelerate and using to much gear wont help as you will be shifting more than you should be.
The engine is mostly stock. I'm not sure about the RPM's under full power, but it maxes out at about 65 mph right now. My friend was warning me about having to shift too much, as well. Thanks for the information. I'm just getting into this, so don't know too much about it all.
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Old 10-04-2012, 10:01 PM
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Quote:
Originally Posted by AutoGear View Post
theres more than one T5 ratio.

What did it come from? Amc, Iszuzu, S10, Camaro? 4, 6 or 8 cyl.

If you have the usual T5 hybrid conversion (V8 camaro guts and an S10 tailhousing), that has a 2.95 1st gear, which is plenty for 3.73s, let alone 4.11s
Find out what your first gear is and then pick your rear gear to match
If the trans is out of your truck, lock it in 1st gear and turn the input 10 times. Count the number of turns on the output. For example, if 10 turns on the input gives you 29 turns of the output, thats a 2.9 1st gear. Which I wouldn't recommend with a rear gear higher than 3.73. If you have a deeper 1st gear than that, you really should drop the axle ratio a little because those transmissions aren't that strong.

If you have an S-10 trans with a 4:1 1st gear and a set of 4.11s; thats 16:1 total reduction (4x4=16); which is like taking a Muncie or a TH350 and putting 7.00:1 gears in the axle. 1st gear will be useless, not peppy.
I don't think the shop has the transmission or rear end actually picked out yet. I'm assuming they're going with a T5 S-10 five speed transmission. There going to be putting a 55-58 era chevy posi rear end on it. I'm going to be running the original 15" wheels. Unfortunately, I'm not aware of what the first gear is.

I did talk again with some friends and decided to trust my mechanic with this one. I needed to get him paid as he's had it several days now and I kind of hate to question his judgement. I told him what I was wanting and he's basically saying this is correct from what he's researched. For me it's super complicated and since I'm making a significant investment, I was hoping there was maybe an easier way of figuring out the right rear end gearing for the job. I'm sure it will be fine. I'll have it back in a couple weeks or so, I'll let you know how it turns out.

Thanks for the information.
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Old 10-04-2012, 10:08 PM
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the 55 era diff is a drop out so changing rear gears is easy. quite often you can find someone to swap centre sections with..Dont be afraid to put a 2bbl carb and headers on that engine some day,,,just dont expect v-8 power.
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Old 10-04-2012, 10:25 PM
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I had a 1950 Chev pickup. Hopped up 1955 inline 235 engine. Dual 1 barrel carbs, head porting, Camshaft from Schneider Cams.

Rear end was a 3.73 from a 1968 Chev truck, Saginaw 4 speed trans. I dont remember the 1st gear ratio in the saginaw.

Truck would smoke the tires easily in 1st and 2nd gears if I wanted
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Old 10-05-2012, 06:42 AM
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Crosley;

That truck sounds like a blast. Any pictures?
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Old 10-05-2012, 03:25 PM
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I agree about putting a 2 barrel carb on the engine, I'm planning on doing that and probably going by my local speed shop when I get it back to see what other upgrades they might suggest to get the full potential out of the engine. I'm also planning on getting the truck re-painted, but am probably going to have to save up some money and do that next year.

Here are a couple pics of the truck...

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Old 10-05-2012, 04:06 PM
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I pulled a 3.70 out of my roadster and installed a 3.25. I have a s-10 T5 and run the Hwy quite a bit. If, like you say, you don't care about hwy driving, I believe you will be very happy with the 3.70. Low gear will be VERY low even then.

John L
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Old 10-05-2012, 04:38 PM
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I would put a turbo 350 in it. But thats just me.
Cool truck BTW.
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Old 10-05-2012, 06:07 PM
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I would think a 3.55 gear may even work well with the 5 speed trans if you get there.

In my 1950 chev truck the saginaw trans bolted up easy. I modified the shifter so it moved forward on the trans several inches.

A T-350 trans may make the truck a little mellow of a driver. All depends on what is wanted.

Quote:
Crosley;

That truck sounds like a blast. Any pictures?
AutoGear... I have no photos of the truck on this computer. I think there are some photos still on Inliners.org ... easy to find my 50 chev truck. Color was pink, with black top of the cab.
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Old 10-05-2012, 08:34 PM
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Quote:
Originally Posted by Crosley View Post
I would think a 3.55 gear may even work well with the 5 speed trans if you get there.
I agree Crosley. If I could snap my fingers and make it happen I would probably go to a 3.50. Probably won't go to the trouble to change it though. For one thing 4th gear and 1st gear are great even if 5th is a little tall.

John L
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