For an upgrade to a stock transmission with engine power up to 300 HP, we like to start with a low stall triple disc converter that will keep the engine in its torque range of 1700-2200 RPM. The upgraded converter will have the engine working at about 500-800 RPM lower than a stock converter. The stock converter usually lets the engine rev to 2300-2800 RPM, which is past its peak power RPM. On a 24 valve Cummins Turbo Diesel with the "Common Rail" system this torque range will be slightly higher.
Along with an upgraded converter, we also recommend installing a stronger 1-2 band apply lever while the transmission is out. If the factory's apply lever breaks, the transmission must come out to replace it. In addition, there is a stronger apply strap and anchor for the band - we recommend upgrading this as well. The front clutch seals should also be upgraded with one of our new, updated seals. The final component recommended for replacement is the front band apply piston cover. This cover often gets worn and can leak oil pressure while in 3rd gear.
Why does this cover wear out? The cover has a hole in the center for the second band apply pin. The apply pin pushes on the lever that applies the band, in turn the lever acts just like a rocker arm on the engine and the apply piston cover acts like the valve guide in the cylinder head while keeping the apply pin centered. When the apply pin strokes, it will "scrub" on the lever at the contact point just like a valve stem will scrub on a rocker arm. This happens because the valve stem and the apply pin move straight up and down, while the lever or rocker arm will travel in a circular arc at the contact point. The circular action wears out the hole in the cover much like a valve guide wears. If we were to use a "roller tip" rocker arm, the valve guide would last much longer. A new billet cover, with an internal seal, eliminates the leakage caused by this type of wear.
Often, with a good working low mileage transmission, upgrading the front drum seals, adding a stronger band lever, a new strap and anchor and the band apply piston cover is all that is needed. If the transmission has a lot of miles and you decide to replace the converter, valve body, front drum seals and band apply lever we would then also recommend replacing the input shaft and hub with a new Dodge shaft. The pair is pre-assembled and run in a lathe to check for straightness. While the transmission is out it is easy to check the front gear train and the front drum. We have instructional videos on our site which walk you through this process.
If a truck is towing heavy loads or the engine makes over 400 horsepower, we also recommend "Billet" input shafts and hubs. These components are made from much stronger steel then the factory components.
The lube circuit of the valve body is modified such that there is always line pressure feeding the lube circuit. With the factory valve body, when the transmission gets hot, oil to the lube circuit may be lost while decelerating downhill if the engine is at low RPM or idle. With our upgraded valve body this will not happen. Our valve body has increased pressures starting at 60-75 PSI at idle and up to 150-175 PSI at wide open throttle. A factory valve body has pressures of 50-60 PSI at idle and 85-95 PSI at wide open throttle. This valve body is capable of lockup in 2nd - 4th or optionally, all forward gears. If 1st - 4th lockup is desired, a toggle switch can be added. A manual lockup switch is used with an exhaust brake or to keep transmission temperatures down while towing uphill. We do not recommend letting the transmission shift from one gear to the next while the converter is locked. The valve body comes complete with all solenoids. The governor solenoid is a new Borg Warner solenoid; or the customer can upgrade to the GM solenoid. When using a new valve body a stronger 1-2 shift lever is also recommended. The higher pressures may break the stock lever.