• May 22nd 2018

Trials and tribulations of the 68RFE. Part Two: QT100 and the Big Stack
BD's approach to this challenging transmission, continued....

There are two fundamental ways to increase a transmissions clutch holding capacity; increase the hydraulic apply pressure or increase the clutch capacity. Part one of this series showed the improvements done to the valve body which allow us to run high hydraulic line pressure.

Here we will discuss some of trials and tribulations on the physical parts when adding more clutches and the effects on those parts due to increased line pressure.

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  • March 12th 2018

Trials and tribulations of the 68RFE. Part One: The Valve Body
BD's approach to this challenging transmission.

Although cited as the weak link in the 2007 to present 6.7 Ram trucks, the 68RFE transmission can be a decent unit if you can correct some of its shortcomings. One of those is cross leaks in the valve body.

It is tribal knowledge among transmission builders that valve bores need to be inspected or vacuum checked and repaired and that flat surfaces need flat sanding to reduce cross leaks, but this "old wisdom" does not always result in a "fix" for newer transmissions. The most common cross leak observed with 68RFE transmissions is leakage into the overdrive (OD) hydraulic circuit; this is in fact the only chronic cross leak area we see on 68RFEs. We, like most others, increase line pressure in our 68RFE transmissions to increase clutch holding capability. The caveat of increased line pressure is increased cross leaks, so it is important for us to correct these leaks when making a performance transmission.

Leaks into the OD circuit will cause the annoying P0871 code (set in 2nd or 3rd gear) but are also partially responsible for the burnt OD clutches we see on a daily basis. This code is triggered when the pressure switch in the solenoid pack detects pressure in the circuit when it shouldn't be. Our experimentation shows this switch triggers at 16PSI, this just so happens to be right around the pressure required to apply the OD clutches (air check this if you don't believe us). This means by the time you're setting P0871s, you've already been dragging the OD clutches.

Certainly there could be minor leaks from many areas, but our exhaustive testing shows there are only two areas we need to concentrate on to correct this leak. 1-The Solenoid Shift Valve (SSV) and 2-The Valve Body Separator Plate.

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