Flushing M977 Transmission

[Karl kostman]

Hello Folks I have a 1985 M977 HEMTT and and it was shifting differently than normal this spring and yesterday I drained the oil in the transmission and changed the filter. Upon draining what came out was Dex, I dont know what type of Dex but it was red. Well I drained 8 gallons out of the trans and replaced it with 8 gallons of Non-detergent 10 wt oil, how long and is there a procedure that I should do before I drain it again and refill it with my straight 10 wt, hopefully eliminating all the Dex that is currently left in the transmission?
Thanks much for sharing your experience with this!
Karl

 

[Karl kostman]

Hey guys did I ask this question incorrectly, was it not understood what I am looking for? just trying to get rid of the Dex in my M977 transmission, thats all? Thoughts or procedures?

 

[BKubu]

There might be someone on this list who knows, but why not contact an Allison dealer? I've been involved in threads about 10w vs 15w40 vs Dex vs the latest synthetic lubricant. The multiple times I have taken trucks with Allison trannies in...they have pushed (initially) Dex, and more recently synthetic. Never 10W or 15W40. Others have defended the other lubricants. My Allison dealer told me to go with either Dex or the synthetic...not 10W or 15W40. I am sure others will chime in. So, you will need to make up your own mind or ask the dealer, which I did. I would ONLY go with Dex or the Allison synthetic. My $.02.

 

[Karl kostman]

There might be someone on this list who knows, but why not contact an Allison dealer? I've been involved in threads about 10w vs 15w40 vs Dex vs the latest synthetic lubricant. The multiple times I have taken trucks with Allison trannies in...they have pushed (initially) Dex, and more recently synthetic. Never 10W or 15W40. Others have defended the other lubricants. My Allison dealer told me to go with either Dex or the synthetic...not 10W or 15W40. I am sure others will chime in. So, you will need to make up your own mind or ask the dealer, which I did. I would ONLY go with Dex or the Allison synthetic. My $.02.

Thanks much BKubo
I have an Allison dealer in town I will give them a call tomorrow!

 

[HDN]

If it were my HEMTT and I wanted to do a flush and fluid replacement, I'd probably consult with the local Allison shop to see what they'd put in it. I hate breaking and replacing transmissions, and from what I've read on here any work like that on a HEMTT tends to be more difficult compared to anything else

I know that M35A3 owners with the Allison AT1545P transmissions switching from 15W-40 to Dex 3 do something like drain the transmission, fill with Dex 3, drive a few miles and run through all gears, drain transmission again, and fill with fresh Dex 3. I'm thinking filters should also be changed when doing the final fill. In your case you'll be doing the opposite, and probably at less expense since you aren't filling up with Dexron stuff twice!

This is covered a few times in the Deuce forum, probably with much better instructions than I have above along with some tips for not wrecking your transmission doing this changeover. I haven't made the switch myself and don't plan to - the truck drives fine with 15W-40 and shifts pretty smoothly with the pedal to the floor I'm not really hard on the truck either so I expect this setup to last awhile.