Ford E40D Transmission Upgrade - Dieseltech

Jose Martinez of STC Performance Truck and RV removes fittings from our '95 Power Stroke's tired E4OD unit prior to installing TCI's new MaXimizer E40D towing transmission and high-torque converter. Jose did the job on his back without the convenience of a twin-post hoist and had our rig back on the road the same day.

A quick fact check:
It makes no difference which Ford engine is under the hood of your truck. The bottom line is the truck's driveline is nothing without a dependable transmission. Our '95 F-350 dualie is powered by the venerable 7.3L Power Stroke diesel powerplant, and thanks to a great maintenance regimen that includes regular oil changes and other truck-care services every 5,000 miles, the engine is as strong as ever with 90,000 miles showing on the odometer. While 90K is considered low mileage by many diesel fans, the same cannot be said about other parts of the drivetrain, especially the E4OD four-speed automatic transmission.

Our second-generation (mid-1990s) version of the E40D really isn't the heavy-duty transmission you'd think a vehicle like a 1-ton needs. This four-speed, overdrive first came on the scene back in 1989 as the successor to the truck-minded C6 three-speed automatic. Despite having overdrive (an answer to the cry for better fuel economy), the E4OD left a lot on the table in terms of shift quality, overall performance, and durability, which are the three main criteria that have raised our concerns about the transmission.

Our truck's transmission is basically the same unit found in Ford's lighter-duty pickups and vans, and it does work well in those vehicles. However, in a workhorse like the F-350, which spends the majority of its road time hauling heavy payloads or towing a (usually) loaded, enclosed race car hauler, the factory E4OD doesn't have nearly the same performance lifespan as transmissions found in comparable vehicles from other manufacturers.

The last time we were at STC, the guys had concerns about the line pressure in the rig's original transmission. Prior to getting started with the swap, Dave Rangel connected a gauge to measure line pressure and took the truck for a road test to see exactly how the unit was doing. The results were not good:

These pressures are well below the 100-plus-psi required minimum. We also noticed during the road test that the soft-throttle shift points were lower, but not too far from normal.