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Ford Bronco E40D Transmission Rebuild

Posted in How To on January 1, 2010
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Photographers: Off Road Images

We've been waiting for this to happen-it was only a matter of time before the overly weak stock E4OD in our Bronco went out under an overly heavy foot. We'd been getting on The Juice pretty hard. A recent engine swap and some performance upgrades had given the Bronco some kick, and it seemed like we were on a mission to kill a transmission.

Ah, sweet salvation for The Juice! The transmission has been thoroughly cleaned and is ready for the rebuild. The Derale Atomic-Cool transmission cooler sits in front of the tranny to the left, and to the right is the PML transmission pan. Time to get crackin'!

Finally, after a full day of high-speed hijinks on some great dirt roads up near Moab, Utah, we felt the tranny starting to go. We weren't about to stop since we were in the middle of nowhere, so we stayed in the throttle until so much white smoke poured out that we couldn't see anymore. The 140,000-mile old E4OD was history.

We were able to get the vehicle back to SoCal, and into one of the best transmission shops we know of, Orange County Transmissions. After some investigation, it was determined that a small fluid leak had eventually left the Bronco's E4OD transmission devoid of ATF, which had doomed it, though we're pretty sure our driving didn't help matters either. We had broken transmission rule number one (which dictates that transmission fluid should be checked before and during long, taxing sessions of driving). The gang at OC Transmission tells us that a great many transmission failures can be avoided by following this simple rule.

Pro Torque produces a dizzying array of converters that can be matched to pretty much any application. We think our Bronco's stock stall speed was somewhere in the 1,800- to 2,000-rpm range prior to the rebuild. This performance converter has a stall speed somewhere near the 2,200-rpm level. Pro Torque also produces custom converters for tricky or super-high performance applications.

A rebuild was in order, and we continued to hang around the shop to learn what this would involve. Being that we willfully admit we like to abuse our vehicles, transmission temperature is always a concern. In fact, the OC Transmissions crew told us that insufficient cooling is another big transmission killer. Derale Cooling Products came to our aid, providing us with their Atomic-Cool external transmission cooler, which included an electric fan to further enhance its abilities.

The torque converter is an essential rebuild component. It acts as a fluid coupler that transfers power from the engine to the internals of the transmission. It also allows the engine to remain running at rest without stalling, like a slipping clutch. When bolted to the engine's flywheel, a converter actually multiplies the torque provided, and transmits movement (rotation) into the transmission itself. It is the torque converter that determines a transmission's stall speed, the point at which (when a foot is held on both the gas and the brake) the vehicle's tires start spinning or the engine's rpm level will no longer increase. Higher stall speeds mean a vehicle can be launched from a braked position at a higher rpm, thereby allowing the engine to quickly reach and stay within its peak horsepower range. With this in mind, Pro Torque provided us with a torque converter with a slightly higher stall speed than stock.

Being that we hammer The Juice pretty hard and heat is a transmission's worst enemy, we wanted to make sure we used an external, remote-mounted transmission cooler. Derale hooked us up with this great Atomic-Cool unit. An electric fan attached to the cooler further enhances cooling capabilities. The unit looks very similar to a small radiator.

Other parts common to transmission rebuilds include bearing kits, new clutches and seals, clutch housings, snap rings, and a reprogramming kit-all of which we needed. TransGo provided the reprogramming kit (sometimes referred to as a "shift kit," although that term is actually the brand name of B&M's reprogrammer line, rather than a generic term), which will provide us with faster, firmer shifts, thereby reducing slippage and keeping the vehicle's power to the wheels. And PML provided us with a really nice finned aluminum transmission pan that allows more fluid capacity and some other perks.

If this sounds like a lot of parts and components to you, you're right, and OC Transmissions tells us that the casual off-road enthusiast probably shouldn't just crack into a transmission without prior experience. For one thing, specialty tools are required during the rebuild process. Also, a tiny mistake in measurement or clearance can cause major damage.

PML provided us with this transmission pan for the rebuild. It features an increased oil capacity, aluminum construction, a magnetic drain plug, a black powdercoated finish, and exterior fins to help alleviate high temperatures. Thick walls and a machined gasket surface combine to make this one tough, leak-free tranny pan.

Still, it's handy to know what's involved in such a rebuild, and with just a little knowledge, it's possible to dictate the specifications you'll want to match a rebuilt transmission to its host vehicle. Plus, if you have a general understanding of how a transmission works, you're less likely to be taken to the cleaners by an unscrupulous tranny shop (this is also why it's good to find a respected, experienced shop like OC Transmissions). We held our camera as the experts at the shop rebuilt The Juice's tranny and explained it all to us. Check out the photos to see the primary steps of a transmission rebuild.

PhotosView Slideshow
PhotosView Slideshow


Derale Cooling Products
Los Angeles, CA 90063
Orange County Transmissions
Costa Mesa, CA 92626
PML, Inc.
Inglewood, CA 90302
Pro Torque
Bohemia, NY 11716
El Monte, CA 91733

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