Diesel Transmission Tech Pages

Ford, GM, & Dodge Diesel Transmission Specs, Ratios, & Info

 

Note: This transmission guide refers to the diesel applications of each transmission. Many of these transmissions were used in additional applications in 1/2 ton trucks & mated to gasoline engines; the dates and applications below may not reflect such uses.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The transmission behind your diesel will work 2 to 3 times harder than a transmission behind a gasser. Diesels produce much more torque, and they build torque at much lower RPMs. Massive torque at low engine speeds tends to wreck havoc on torque converters and clutches. So what do you look for when choosing a transmission? In terms of automatic transmissions, you want one that was designed specifically for diesel applications. A modified gas transmission just won't hold up to the abusive in the long run. A dedicated diesel transmission will compliment to powerband of the diesel and be fully capable of managing the high torque output, even in severe conditions. It should also have a efficient cooling system (again, not one designed for a gas engine) and some sort of serviceable filtration system (external mounted & redundant filters are a bonus). In terms of manual transmission, it's all about the input torque capability. Manual transmissions are brutally strong, but they also have their limits. Large gearsets are a plus. You can always install a stronger than stock clutch, but you increasing the input torque rating is much more difficult, if not impossible in some manual trans.

 

Manual Transmission Vs. Automatic Transmission:

As automatic transmissions become more & more sophisticated, the advantages of manual transmissions over autos continues to decrease. Due to their high input torque ratings, automatic transmissions are being phased out of the current diesel market. Dodge is the last manufacturer to offer a manual transmission behind their diesel, but it comes at a hefty 150 lb-ft loss (the 800 lb-ft HO 6.7L Cummins is only available with an auto trans, manual trans truck produce 650 lb-ft).

 

Automatic Transmission Benefits:

• Convenience - anyone can drive one. Automatic shifting & downshifting (newer models feature "Tow/Haul" settings). A lot easier to drive in stop & go traffic.

• Higher input torque rating. Diesels are beginning to exceed the torque limits of available manual transmissions (though medium/heavy duty transmissions could be used, they are not an ideal fit for lighter duty trucks).

• No gear grinding - planetary gearsets are in constant mesh.

• Easy to find - manual transmissions are becoming increasingly rare.

 

Manual Transmission Benefits:

• Simplified design leads to less problems in the long run (no internal clutches, cooling system, or planetary gearsets).

• Puts driver in complete control - auto transmissions sometimes have trouble "thinking" as they age.

• Downshifting to control vehicle speed is often more effective.

• Lower first gear comes in handy if you have a dedicated tow rig work truck.

• Lighter transmission weight.

• Cheaper to repair/rebuild. Lower operating costs.

• Less parasitic loss - more power is transmitted to the pavement (but auto trans are being increasingly efficient).