M939 Transmission Swap Options

[engineer233]

Hello guy's. I have a M936A1 . My transmission is now slipping when shifting between first and second gear. Also when it downshifts from second to first it drops in extremely hard. I have done my fair share of reading and can't really find a answer for the question I'm about to ask. Later on I am planning on going with a big cam Cummins 350 or 400 when mine if ever fails and have thought of upgrading my Allison tranny now . My question is what will be the most logical upgraded transmission to use ? A HT740D? I'm just not sure of my options so any and all opinions will be helpful.

 

[Artisan]

If I were you, I would bring the truck to an Allison repair
facility before you think of a swap. The slipping question is a concern,
the hard downshift tells me you are running empty. Put a few tons
of something in the back and drive it again and see how that tranny
feels, AFTER you resolve the slipping issue.

 

[hklvette]

If I were you, I would bring the truck to an Allison repair
facility before you think of a swap. The slipping question is a concern,
the hard downshift tells me you are running empty. Put a few tons
of something in the back and drive it again and see how that tranny
feels, AFTER you resolve the slipping issue.

Seeing as the OP is using a 936, running empty is not the problem IMO.

Slipping and hard down-shifts may actually be caused by the modulator cable sticking (hard down-shift) and being out of adjustment (slipping up-shifts). You can in fact have both at the same time, I know that I did. I re-adjusted the cable per the TM and lubricated the cable with light oil (think PB, WD40, etc) until it would retract freely. You need to get the lubricant underneath the rubber "collar" that is on the end of the cable for it to work.

 

[Artisan]

snip
I re-adjusted the cable per the TM and lubricated the cable with light oil (think PB, WD40, etc) until it would retract freely. You need to get the lubricant underneath the rubber "collar" that is on the end of the cable for it to work.

Might you remember where in what TM you found that info ?
I need to learn that trick.

 

[mikey]

This may be a good place to start:

http://www.steelsoldiers.com/showthread.php?134829-M939-A2-Series-M927-A2-Driving-Question

Mikey

 

[engineer233]

I spoke today with the closest Allison repair shop and the first thing he said was modulator cable or a possible valve body issue. None the less I plan to start with filter changes and double checking the modulator valve cable. Hopefully will do it this weekend or early next week.

 

[hklvette]

Might you remember where in what TM you found that info ?
I need to learn that trick.

Lubing the cable I came up with myself, or at least didn't reference the TM for. Page is 365-6 in the -23-3 TM

 

[engineer233]

Update. I had a couple minutes to work on my truck today. On inspection of my modulator cable I found it was hanging up on a return spring on my injector pump. Replaced the large diameter spring with a smaller one so the cable could clear and tested the truck back and forth in my driveway. The slip and hard shift was way better. Hopefully now I can adjust it the rest of the way out. I will let you know how it turns out . I did price a new modulator cable from cccables.com , $158.25 total with shipping. If it won't adjust out for me I will try a new cable.