My father-in-law has a 2005 silverado 3500 srw with the allison trans. When he tried to shift from drive to neutral to coast to a stop while moving at under 10 mph (like you can with a 4L80E) the truck lurched and there was a loud noise from the trans like a grinding or growling as if it stayed partly engaged or trying to shift to another gear. Needless to say he has not tried it again but I was wondering if anyone has had this same thing happen. There was nothing in the owners manual that said you could not do it. Also another question, why can't you shift from 2wd to 4wd high on the fly like a 4L80E? I have a 1994 6.5L TD and can go back and forth on the fly while moving but he has to stop his truck to shift to 4 high (it even says so in his manual). He tried it once (before reading the manual) and the truck lurched and acted like it was going into 4 low (it didn't, once he stopped it went to 4 high), any ideas as to why this limitation is on the allison?

Thanks, Steve

Ok, I have to ask... Why in the hell would he feel the need to shift into neutral while moving??

As for the 2wd to 4wd issue, My 07 classic will shift into 4x4 while moving. I have only tried it at less than 10mph, but it will do it.

He likes to coast to a stop instead of braking to save fuel and brake wear. Also if he is towing he will use the trailer brakes to stop. (He hauls new trailers from the manufacturer to the dealer).

As to the 2wd 4wd issue. His allison wont do it at at all. If he tries, the transfer case or trans. (can't really tell which for sure) makes a grinding noise before thumping (verrrrrry hard) into 4wd. He tried at less than 10mph. My 4x4 can shift into 4wd high at highway speeds if I want.

My allison will shift into 4wd while moving. I always do it while going under 5 mph though.

I was wondering why you have to shift going so slow, why can't you shift at any speed?

I do the shift to N sometimes myself with no problems. Shifting to 4 hi is no problems at any speed with my truck. Mine is a 06 but, that should not make a difference. Sorry I have no answer though.

If you keep the truck moving at a steady RPM, whether doing 30MPH or 60MPH, it should shift between 4wd and 2wd and visa versa. When pulling a hill, you try to shift into 4wd, it going to sound bad because the rear wheels are under a torque condition and the front wheels are just free wheeling . The same goes for when you let up on the throttle , there is torque in the rear wheels trying to slow you down and your trying to get the front wheels to the same torque, thus it bangs going in 4wd. If you just try it at a steady speed ,it should work properly. just my thoughts Charlie

i can shift mine back and forth all day if i wanted usually under 35 never grinds or bad noises just lose the dash light.

Mine does the same thing while trying to go into neutral because as said before the Allison is in a torque stage to slow the vehicle down. But it only does that at higher speeds under 30 on flat ground it will not do it. I can also shift mine into 2WD or 4WD on the fly.

when i'm coasting around 5mph, if i put it in neutral, the truck will slam into neutral, and basically stop the truck dead. why? i don't know. i did it once, said "what the hell?!!?!?" tried it again, said "FU@$%!#@$* this!" and i haven't tried it since. 4WD i can engage/disengage at any speed. a couple times last winter when i was driving in the snow, i thought i could make it up some hills, but quickly to find out halfway up i had to switch 4wd on in fear of sliding back into the car behind me, and it slammed into 4wd. she didn't like it, but thats b/c it was under torque.

Well my truck would grind bad if I tried shifting from 2-4 not 4-2 at any speed but 0 so whille doing the pump rub and once inside the case sh% was bad my shift forks shot, missing bushings cloged oil pickup. So long story short I have a new transfer case now but I still had to put in the pump rub fix. The new one I bought had the same junk clip as the old ones it was no different so it would have broke and had a hole in it also.