T-400 to 700r4 - Hot Rod Forum : Hotrodders Bulletin Board
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Old 10-23-2019, 06:04 PM
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T-400 to 700r4

My 69 c10 has a th400 behind my 350.
I have 3.42 rear gear with 30in tall tires.
My peak tourqe is at 3600 rpm with my new build.
I drive a lot at 70-75mph. So my rpm on the interstate are 2800 at 75 and 3000 at 80.
I like the sound of a overdrive tranny like the 700r4 but I'm wondering if I have enough rear gear for that. .70 over drive ratio will put my way below my cam.
What do you all think?
My cam is [email protected] .470-.470 lift

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Old 10-23-2019, 06:45 PM
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The TH700R4 .70 overdrive with 3.42 gears and 30" tires will drop your RPM to point where it won't accelerate very well if you want to pass a car.

If it was my truck and I was switching to a TH700R4 I would look at using 4.10 gears with your 30" tires.

Bruce
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Old 10-23-2019, 08:39 PM
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You have more then enough gear to keep direct.
I have a 350 with a 700r4 and 3.42 gearing running 235/75r15 tires in a 87 squarebody that came stock like that.

Overdrive is useless.

The truck before this was a 96 c1500 with a 5 speed. That overdrive was useless also. Found myself going 90+ way to much in that truck.

Keep it direct or get gearing in the 4's.
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Old 10-24-2019, 07:39 AM
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Have you looked into a Gear Vendor overdrive?
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Old 10-24-2019, 10:47 AM
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Huge step backwards on strength too, going from a Th-400 to a weaker 700R4.
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