Never heard of Shell Spirax MD3 if it is not TES295 approved fluid get it out as fast as you can, also no flushing allowed on this trans no matter what anybodys shop says, just the double drain method is good..
When determining whether or not a fluid is TES 295 approved, look and/or ask for one of two things: The Allison TES 295 approval number and have the Allison Logo. Or you can use what you want but dont expect the trans to live long life
Sounds like the NSBU switch (Neutral Start Back Up) switch. symptoms could be PRNDL display may not show up or only a partial display, no engagement even though your shifter is in D or R (like you were in neutral), codes, or shift range inhibited on the DIC display, easy fix and part cost about 75.00 at a local allison dealer , do not get one at the GM dealer because they charge like 250.00. BTW 06-up 6 speed transmissions no longer use an external NSBU switch
Originally Posted by avolnek
While the pan is off they should be replacing the filter as well as adjusting the bands.
their are no bands to adjust on the allison transmission, the clutch packs are set at install..Internally, the transmissions have three planetary gear sets controlled by 5 sets of clutches, labeled C1-C5. 2 clutch packs (C1-C2) are rotating, and transfer input torque to certain elements in the planetary sets, while the remaining 3 sets (c3-C5) are stationary and lock each of the ring gears and their coupled components to the case when engaged. These transmissions contain no bands, sprags, or roller clutches - all gear changes are accomplished by direct clutch-to-clutch changes.