M923A1 Allison Hard downshift into 1st

[Jayco36REQS]

I've noticed that my M923A1 allison trans has a very hard downshift into 1st as I'm approaching a stop... is this normal?

 

[markmontana]

Yes -it is very common.

 

[Hoefler]

Mines does this-it cant be good. Even throwing it into neutral while still get the harsh down shift.
I have spoke to an Allison shop in my area (Mpls-St Paul)-they have a guy experienced with the transmissions in these trucks. Told me that it may be the modulator or possible a spring in the valve body. I have yet to bring it in to get this corrected. Am not driving my truck to its corrected. Its hard on the drive train.
Google Allison shops in your area-it will list shops that specialize in various transmission-look for one that list the trans in your truck if you have concern about it.
Pete

 

[wsucougarx]

Mine shifts hard as well.

 

[91W350]

I think the 6.44 gear has a lot to do with it. If hard downshifts are a sign of trouble, I have a yard full of it.

 

[Karl kostman]

Mine does the same thing Like Glen said it seems to be all of them

 

[monkster]

Mine too.

 

[wheelspinner]

Same

My truck is the same. I drove these 923s in Belgium for ayear when they were brand spankin new and they always had the hard downshift. I didn't even notice it in my new 923 cuz it just seemed normal.

 

[crasheej]

I noticed this in the new fire trucks that I delivered. So Idon't think it is just tese trucks. I got so it was just that way.

 

[rrrr]

Mine to. It got a fair amount better when I switched over to Dextron 3 tranny fluid.

 

[FASTNOVA]

I would like to see what anyone has done to correct this on their truck.

 

[wsucougarx]

Everytime I slow down I just cringe in ancipation of the hard shift. When it does, I get that uneasy feeling like you get when you grind a gear. For me, it's hard getting use to it.

 

[Bolkbich]

Some of mine do it some dont. The trucks that downshift hard dont shift as nice on the upshifts . They kinda flare up when shifting into certain gears...like a tiny free rev going into the next gear.....if i shift it manually and let the engine rev all the way to the governor it will shift perfectly. Im sure a trip to the RIGHT allison dealer would tell us its an adjustment... but im skeered to see the bill when i find out i picked the wrong allison dealer.

 

[hemichallenger]

I adjust the linquage on the fuel pump on my 8.3 and at a idle rolling to a stop I am almost stopped before it shifts into 1st so it is not as hard but didnt fix it.

 

[rrrr]

In addition to switching over to Dextron 3 I also adjusted my tranny linkage at the IP this also helped. When cold my tranny shifts a little hard when warm its great.

 

[KaiserM109]

rrrr,
Thanks for your advice on tranny fluid and to others about shifting the Allison. I'm going in a week to pick up an M923 at Ft. Benning, GA.

Also, thanks for your avatar, I have been wondering what an M923 looks like next to an M35. Not as huge as I was afraid of. I think I will paint a smiley face on the bumper which should be about back window height on most imports. Maybe a fake license plate with "TI 3VOM" would do (look in a mirror).


Arlyn

 

[Beerslayer]

About half of the 939 trucks I have driven downshift hard, but what I noticed is that the harder you decelerate the harder they downshift. I came into a stop sign off the freeway a little too hot once and it downshifted so hard it killed the engine. Scared the crap out of me.

Try a more gradual deceleration and braking and see if it makes a difference.

That said, a couple of the trucks shifted beautifully, not what I was expecting at all.

 

[Jayco36REQS]

Thanks for all the replies.... I'm new to the MV's and just learning their quirks..

Thanks for the fluid advice rrrr... good to know!

 

[poorman4x4]

First i just added a quart, stopped doing it a little bit, switched to dexron 3 stopped completly, hasnt done it since, been almost 8 months

 

[jonesal]

It's interesting. My M923 used to downshift firm but not harsh. I noticed that it does have a new modulator installed. I swapped out the 10 weight motor oil for Dex III and it's downshifts pretty nice now.