Final ratio with th400 in 3rd gear
Any three speed gm trans the 3rd gear ratio is 1:1. In a power glide which is a two speed is 1:1. In a gm 4 speed over drive unit 3rd gear is 1:1. The only trans that does not have a 1:1 ratio I believe is the 6 speed auto.
Registered User
Joined: Nov 2013
Posts: 1
Likes: 0
Buzzbomb I have a TH400 that was behind a 4.3 V6. I now run a 350 V8 and found the final ratio of the TH400 and found that the V6's used a lower ratio. I have 2:73 gears and it drives like a 4:11. Mileage is about 11 MPG.
Trending Topics
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
On The Tree
Joined: Jun 2007
Posts: 165
Likes: 0
From: haltom city/DFW, Texas
The 3rd gear ratio is still 1-1 , I have never seen a 4.3 with a 400 behind it from the factory . Don't think it ever happened ! What is this combo in ?
Registered User
Joined: Dec 2017
Posts: 1
Likes: 0
From: Mcalester, OK
You sure? th400's never came from the factory bolted to a 4.3. Just a taaad bit of overkill. Though I've certainly been wrong before.
TECH Fanatic
Joined: Jan 2015
Posts: 1,114
Likes: 33
From: Fort Worth, Texas
Not technically a TH400, They were TH375's.....Which are based on the TH400 but with a 27 spline output & fewer frictions. By the mid 80's TH350C production had ceased but GM still offered a 3 speed auto & was probably cheaper than a 700R4.
