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TH400 Transmission Build - Turbo 400 Revival

Posted in How To: Transmission Drivetrain on December 1, 2006
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Automatic transmissions are steadily gaining popularity in off-road vehicles. There are the few hard-core old guys (including our trusty leader) that won't do it with anything other than a stick shift, but many feel that an auto tranny is far and away the way to go when off road.

Before we started the rebuild we dropped the transmission off with David Dibs of Orange County Transmissions to get gutted and cleaned. Our TH400 received the entire B&M package. A rebuild kit, a deep-sump aluminum pan, a B&M torque converter, a flexplate for a Chevy big-block, and Trick Shift tranny fluid to make this tranny hold up for not only big horsepower, but also endurance.

Auto transmissions absorb more vibration and transmit less shock load onto other drivetrain parts than a manual transmission does. The fluid coupling of the torque converter behind the engine provides quite a cushion against shocks that could break axleshafts, output shafts, or U-joints when things get caught or bound up.

Off road, an automatic transmission frees up a hand that would otherwise be dedicated to a shifter, plus it frees up any thought put into shifting, allowing you to fully concentrate on the obstacle ahead. And when you are climbing a hill, an auto tranny deletes any pedal dance that you'd have to do between a clutch pedal and brake pedal as you ascend.

But auto trannies aren't perfect-in fact, far from it. Many are considered weak by off-road standards and unable to stand up to the rigors. The more popular heavy-duty trannies are old three-speeds, since the four- and five-speed overdrive transmissions of today can have frustrating computer controls. A few of the most bombproof: Ford's C6, Chevy's TH400, and Chrysler's 727 are all considered the all-time end-all auto trannies for swapability and strength.

We recently had Orange County Transmissions buff up a Turbo-Hydramatic 400 transmission with a B&M rebuild kit, and deep-sump pan for our Ultimate Adventure K5 Blazer. Dave Dibs of O.C. Tranny used all the integral B&M components, plus added a couple tricks of his own.

And the rest of the Blazer? Check out the first part of the frantic build that Fabworx accomplished in less than a month and a half starting in this issue.

PhotosView Slideshow
PhotosView Slideshow


Orange County Transmissions
Costa Mesa, CA 92626

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