Faulty solenoids. Bad wiring harnesses. Defective valve bodies. Malfunctioning mode selectors. Blown transmissions.
If your shop has seen these FMTV issues lately, they may be misdiagnosed problems caused by the same thing: improper installation of the MD3700SP Allison Transmission Gen 4 control valve module.
Various figures in two TMs show diagrams for installing the transmission plug, pipe and helical compressed spring, but
they show the installation in reverse order
Also, the TMs don’t provide any installation instructions.
Without instructions, most mechanics will simply follow the incorrect order shown in the diagrams, which will always create this problem.
If your shop is diagnosing FMTV solenoids, wiring harness, valve body, mode selector or transmission problems, look first to see if the transmission plug and spring have been installed according to the TMs. If so, reverse them before you replace any of those other costly transmission parts.
Aside from the cost of parts, improper installation due to the TM misprints costs an estimated 2.5 man-hours to correct.
There’s really nothing to tip off this mistake. The plug and spring will seem to fit properly no matter which way they’re installed. So you have to be aware of the TM misprint and follow the instructions in reverse order! Until the TM corrections are published, the following figures should be installed in reverse order from what is currently shown in the TMs:
||21 & 22
||21 & 22
||22 & 50
Removal and replacement of the valve body for FMTV Gen IV and Gen V Allison transmissions is moving from field level to sustainment. All down parts, except the filter, will also be moved to sustainment level. This will happen during the next revision of the IETM. Until then, follow the reverse installation procedures discussed here.
Just to clarify, transmission repair at the field level is now prohibited. Units can only remove and replace the transmission. internal transmission issues such as valve body replacement can ONLY be done at the sustainment level.