Allison Transmission in M923A1

[BKubu]

today I started with "automatic shift test." (See above post for Pic) mine weren't quite to spec so I the printed out of TM "Transmission Modulator and cable Maintance" I found that mine was a little out of adhustment. So I followed the step and got it set. took her out and reran "automatic shift test." and Everything is to specs now. Thanks Bruce for clueing me in on the Modulator.

No problem. Glad I could help!

 

[Beerslayer]

Here's an Allison Automatic shift story for you;;;

Picked up a new to me m923 at Ft Lewis today. Started and ran great, so after checking things over, headed for home. I was shifting up through the gears manually instead of using 1-5. It seems to like shifting the best around 1800 or so.

So after the first fuel stop I just dropped it into 1-5 and let it shift itself up to freeway speed. After it went through the gears, I got this terrible dry bearing wailing sound, kind of like a dry driveline carrier bearing only worse.

I pulled over at the first safe spot and gave everything a good check over. Suspicious that letting it pick its own shift points for some weird reason caused the problem, I went back to upshifting manually. It shifted perfectly and ran out nice all the way home.

So! Is this just my truck, or have others had a similar experience? Was I driving it wrong? I noticed it didn't shift just how I thought it should at other times too, so I will be checking the shift points and perhaps taking it to an Allison dealer.

What say you all?

Thanks!

BS

Edit: BTW, the truck only has 3000 miles on it since a Red River overhaul.

 

[engineer233]

My truck is making the same noise. It is about to drive me nuts trying to find exactly what it is . I did try the manual shifting just last night while trying to find the problem . Mine still made the noise. The weird thing is it doesn't make the noise consistently or continuously. when this starts happening , you can feel it vibrate the truck. I have checked all the u joints and all are good . The only thing I found so far is one of the carrier bearing bolts is stripped out on the front drive shaft.

 

[engineer233]

This started after I made 430 miles of a 550 mile trip home. I ended up towing mine on home till I could find the cause of this.

 

[jstier]

Not being a Transmission expert, I have no idea why it should make any difference between shifting manually or letting trans do it's job. If it is a bearing it shouldn't matter. a bad bearing is a bad bearing. Please let the rest of know what you guys find.

 

[Hoefler]

In low gear driving (M923) in parking lot I get a slight vibration and noise. Feels like it is under the seat-drive line carrier. Once up to speed-it goes away. Its not loud-it sounds like a dry bearing or one that is shot. Hope thread is not dead-need to understand what is causing this noise.

 

[jstier]

You could try and see if you can get movement up and down in the carrier bearing. Use a pry bar if needed. There were no grease zerks on mine and it is a sealed bearing. Mght be able to use a needle tip and get some lube behind the seal, becareful as to not destroy the seal. Good luck

 

[Hoefler]

Jeff
I will try and lift up on shaft -bearing arrangement with bar. The assembly is so far off set to one side, it looks like it could get a lot of spray from the front tire-or mud. I will also check to see if mine has any grease fittings.
Thank you for the info. I will report findings.
Pete

 

[alignv3d]

Are you guys sure you are not hearing the straight cut gears in the transfer case?

 

[Hoefler]

It stops at about 2 MPH.

 

[engineer233]

The noise in mine also stops when the truck almost comes to a complete stop. It does seem to be coming from the transfer case. I drained the tease quite a bit and refilled with a gallon of Lucas. This made it not do it as much or as loud . When this starts in my truck you have to just about stop to make it quit cause it shutters so bad.

 

[Hoefler]

I used a crow bar on my carrier bearing. It moves up and down easily-about 1/2". It looks like there is a bearing that rides in a rubber bushing. It looks like the whole assembly-rubber bushing and all moves up and down freely. Does not seem correct.
Maybe because of this, at slow speed the front axel is trying to buiold inetia in all the drive shafting. It stops when I get her going because-maybe-the shafts are now in motion with inertia and helping to center the carrier. Hmmm...its puzzling me. Maybe I should simply remove front drive shaft and see if it still growls. Would have to do this to change out bearing anyway.
Does anybody else have lots of up and down free play in their carrier shaft?

 

[engineer233]

I removed my front drive shaft thinking the same thing. This didnt help anything where the noise is concerned. Changing the carrier isn't so bad. After you drop the drive shaft remove the center u joint, take the jam nut off holding the yoke on, then beat the c-bearing off an replace with a new on for around a hundred bucks or so.

 

[Hoefler]

OK-will do. Slop and bearings are never a match. The growl now has me maddened. Perhaps I will strap a human under the truck and drive around to see where the growling tiger is hiding.
Have you narrowed down as to where your growl is coming from?

 

[engineer233]

I strapped my brother under mine and tried that. Drove around a while heard the noise, felt a bump, and came home . I still don't know what the noise is and haven't seen my bro. This weekend I am going to pull the axles and run it up that way and put dad under the truck to listen. I will let you know how it turns out.

 

[Hoefler]

Was thinking that it maybe the front axel. Is it possible to simply remove the front hub covers and try it-sort of like running with lockout unlocked.
If running without axels doesnt find it-hope you have more family members ready to sign on for hazard duty.

 

[engineer233]

I hadn't thought of that. I will try that before I call my other brother as I do like him somewhat better. Thanks for the idea."..

 

[FASTNOVA]

Why not just put the truck on jack stands and run it that way or you can remove the driveshaft coming out of the transfer case then put it in drive to narrow it down.

 

[Hoefler]

That is a good idea.

 

[engineer233]

Well I pulled the front axle covers off today and drove the truck. Ahhh no noises or problems. Put them back on and 1/4 mile later theres the noise again. Now I know where to start next.