M923 trans shifting early

[diverman555]

When I put the trans in high gear it will run up to 2050 RPM and shift into 2nd, the it runs up to about 1950 and shifts into 3rd, then it runs up to about 1600 RPM and shifts to 4th the same with 5th, so in those 2 gears it really lug and is slow until the RPM get up to about 2000. any one know why it would be shifting early in 4th and 5th gear. In order to get the RPM's up I downshift to a lower gear and manually shift.
This is on a remanufactured 1985 M923.
Thanks

 

[tie6044]

I think they all do that, it gets worse if you have 14.00's on them too. I like to shift them manually through the gears when taking off from a dead stop.

 

[diverman555]

The one I have with 1400 shifts at 2000-2100 every time but the one with 1100 shifts different.

 

[BKubu]

Take the truck to an Allison dealer and have them check the shift points. They will set it optimally. Once I get an Allison, my first move is to bite the bullet and take the truck to an Allison dealer (or a shop that is a licensed Allison repair location) to let them service the transmission the first time. It costs a few bucks...a few hundred...but it is well worth it in my opinion.

 

[porkysplace]

J.B. DLCO www.JBDLCO.com is your local authorized Allison dealer in Detroit .

 

[nf6x]

I'm wondering out loud here... would an Allison repair shop be likely to have equipment that would let them do a better job of flushing out the 10 weight oil and replacing it with ATF than the way I'd do it myself with the repeated drain/fill/drive method? I haven't flushed my M923 transmission yet, but it's on my to-do list.

 

[319]

I'm wondering out loud here... would an Allison repair shop be likely to have equipment that would let them do a better job of flushing out the 10 weight oil and replacing it with ATF than the way I'd do it myself with the repeated drain/fill/drive method? I haven't flushed my M923 transmission yet, but it's on my to-do list.

I'd have an Allison dealer or authorized shop do it.

 

[Beerslayer]

Take the truck to an Allison dealer and have them check the shift points. They will set it optimally.

That's the first thing I did. It shifts better now but they still didn't get it quite right. I will end up having to figure it out myself.

One thing they did find is that at one time the military had replaced the transmission with a slightly different type and did not have or use the correct bracket to attach the shift linkage to the transmission, so they had to refabricate it.

I'm wondering out loud here... would an Allison repair shop be likely to have equipment that would let them do a better job of flushing out the 10 weight oil and replacing it with ATF than the way I'd do it myself with the repeated drain/fill/drive method? I haven't flushed my M923 transmission yet, but it's on my to-do list.

As I recall when I had mine done, they just did a drain and flush twice like you or I would have to do.

Out of the four 939 series trucks that I have bought so far, two of them have had something goofed up in the transmission shift linkage.

 

[quickfarms]

Linkage is the first item to check. The second is the shift points. They are adjustable but you have to drop the pan. My FT900 shifts all gears at 2500, this does not lug the engine and it moves.

The Allison spec is for the 2-3 shift at 200 below governor and the rest at 600 below governor. The 1-2 is manual.

 

[BKubu]

I'm wondering out loud here... would an Allison repair shop be likely to have equipment that would let them do a better job of flushing out the 10 weight oil and replacing it with ATF than the way I'd do it myself with the repeated drain/fill/drive method? I haven't flushed my M923 transmission yet, but it's on my to-do list.

I am not sure, Mark. Maybe, you could do it. However, they know how the transmission SHOULD shift and they set it accordingly. Perhaps, you have the manuals on that. We are talking about a few hundred bucks (I think it cost me like $350-400 the last time they swapped the shift modulator, flushed the old 10W oil, and replaced the fluid). I don't think that is crazy.

I'll give you an example of something that I don't think you'd know that they did. My truck was hard downshifting from 2nd to 1st...I mean it felt like your fillings were coming loose and you had to make sure your jaws were closed so your teeth did not clash. I took the truck to them and they knew immediately without opening the transmission that it was a little spring in the transmission. It was a fairly easy and inexpensive fix that they could do when they were servicing the transmission. Depending upon the set up of the transmission, a different spring is used that controls how hard the transmission shifts. They knew that immediately. You might have figured that out or maybe you wouldn't. In this particular case, I posted about it here so you might have been able to find that easily.

 

[Karl kostman]

Diverman my 925 shifts somewhat like yours, what I ended up figuring out was to start out in 1-4 then manually shift to 1-5 I usually do this around 1600 rpm, min was shifting into 5th around 1400 rpm which seemed way to low! I got a bid from the Allison dealer and he gave me a quote of 400.00 to drain and flush the tranny and torque converter of the 10 wt oil and this included the tranny filter inside also, the DexIII to refill was not included for that price. Please keep us posted on your course of action and the results please.
KK

 

[rrrr]

Check the TM's. There is a shift linkage on the IP that is adjustable. I had to do this on mine. There is also a couple of posts on this so use the search.

 

[diverman555]

your right RRRRRR I found out there is a adjustment on the IP and I worked on it and it did help but not quite where I want it. I got it to shift at 2050 in 1-3 but forth drops and shifts at 1600 and the same for 5th it just lugs to much shifting at 1600. I can't get it to shift any higher in 4th and 5th. I will let you know if I find anything else out.
If I was telling you what my truck sounds like would I say rrrrr rrrrr, Just joking.

 

[diverman555]

shifting

your right RRRRRR I found out there is a adjustment on the IP and I worked on it and it did help but not quite where I want it. I got it to shift at 2050 in 1-3 but forth drops and shifts at 1600 and the same for 5th it just lugs to much shifting at 1600. I can't get it to shift any higher in 4th and 5th. I will let you know if I find anything else out.
If I was telling you what my truck sounds like would I say rrrrr rrrrr, Just joking.

 

[rrrr]

I ran out of adjustment on mine but managed to get mine to shift around 1800 in 4th instead of 1600rpm. There is a cable adjustment as well and mine checked ok.

I could pull and put the IP adjuster lever a little further forward to gain some more adjustment but I'm happy with it know. Do you have Dex III in it ?

MY TRUCK MAKES THE SAME SOUND...... RRRRRRRRRRRRRRRR