Another M923A2 Transmission Question...

[brasco]

... so I was out driving around town today with my wife, just trying out the new to me M923A2... after a 10 minute stop to take care of some business, I put the truck into Reverse and heard a "grinding" noise as the transmission shifted into reverse... almost like dragging a manual transmission into gear. I shifted back between R and N a few times and still got the grinding noise. The truck operated fine but this is the first time I really noticed it. Is this "Normal"???

Also... in a totally separate incident, I put the trick into drive without pushing on the brake pedal and it killed the engine. I started the engine and pushed on the brake like I usually do and had no issues. Has anyone else had this happen in a M923A2? Do you know why?

The truck seems to operate fine otherwise and I have had no other issues with it.

Thanks for your input.

Don

 

[Coffey1]

spelling

must not be normal my m923 does not make any noise when shifting to reverse.
and yes never put truck in gear without foot on brake.

 

[Artisan]

What position is the transfer case lever in and is the front axle locked in or out?
Do all warning lights work? Is the tranny shifter locking into slots positively?

No, grinding of gears is not normal.

 

[LiqTenEXp]

I would say the only thing that would cause a grinding sound is the transfer case. Make sure you have it fully down if into High.

 

[brasco]

Everything else appears to be normal. The shifter locks positively, the transfer case is in high, lever is down. Front axle lever is in the out position.

The grinding sound stops once the transmission is in Reverse. The sound is very brief, lasting only about a second or less. After that, no more sound and everything functions normally. No noises are heard when the truck is in motion either forward or backward.

Maybe the noise I heard was not "grinding". I don't think it was a U-joint clunking sound but it was pretty brief. Are there any transmission experts who can suggest where to start looking?

I'm going to take it for a test drive today and try to get a better idea of where the noise is coming from and what it sounds like.

 

[Coffey1]

Have you crawled under truck and inspected the under side and grabbed stuff to see if anything is loose.

 

[brasco]

So I did some checking today and didn't find anything loose in the controls. When I first started the truck and shifted back and forth between N and R, I didn't hear anything abnormal. I checked the transmission level and it looked a just little low so I need to fill it up before getting too alarmed.

My wife and I drove it across town, about 5 miles, and decided to check for the reverse noise again when warm. When she put it in R, the transmission shifted but then we heard the grinding noise again. It sounds like the transmission shifts into gear and then something else is happening. I watched the rear drive shaft as my wife shifted between R-N-D. It appears that the drive shaft is shuddering as the transmission goes into Reverse. Sometimes it is worse than others. I think this is the "grinding" noise we sometimes hear.

I also noticed that the transmission shifted much more smoothly when shifting quickly between D-N-R than when allowed to sit in N for a while before shifting to R.

Also... the engine died again when shifted from N-Drive. The brakes pedal was being held at the time. This does not happen all the time, however.

Has anyone else seen issues like this? Temperatures are normal, etc.

 

[brasco]

Update on Transmission Issue....

Here is an update on my transmission issue in case others have the same problem...

So I checked the transmission fluid level again this afternoon (several times just to be sure) and confirmed that the level was pretty low. I added 2 quarts of fluid and checked again. This moved the level less than 1/2" on the dipstick and it was still way low! I decided that adding 2 more quarts would bring the level up to the "full cold" level. When I did this, the level went all the way up to "hot add"...oops too much.... the level change does not appear to be proportional. Also, the engine was running to whole time so the transmission was heating up while I filled it... (about 120 degrees at his point so it didn't look too bad)

After filling the transmission, I checked for the grinding noise again and it was still there when I shifted into Reverse.

I then checked to see if something else could be causing the issue... Idiscovered that the pushbutton on the transfer case hi/low lever was stuck in.I have read that when the transmission is in Neutral and this button is pushed,the transmission 5th gear lockup solenoid valve is engaged. I"unstuck" the button by pulling it out with at pair of pliers andconfirmed that it was indeed working by listening for the air (I turned the engine off to hear it).

After re-starting the engine, I tried to induce the grinding noise again but could not... I think this 5th gear lockup solenoid being engaged when shifting into Reverse may have been causing the noise I heard somehow... maybe a transmission here expert can explain why.... I will monitor and report so others can learn.

Also... After a short drive, I checked the transmission level again and it was way OVER "hot full" could it be that engaging the 5th gear lockup solenoid was using oil from the sump and creating a false “low" reading? I will check again when cold and pull some fluid out if needed.

 

[Jeepsinker]

Being over full won't hurt it until you get to being in the neighborhood of being a gallon or so overfull. The only thing it may do is push some extra fluid out of the vent if you really get the transmission temp hot pulling a Lon grade or something. It will not hurt anything at all to be a quart or two high, certainly since it appears that you have a leak anyway. but if it really bothers you, just pull the filter below the heater and pour it out, then screw it back on.

 

[whiskey357]

check your vent on top of the axles make it is free and clear.....take it to a truck shop for tranny work..they can tell you up front what is not doing its thing the right way ...no sense getting stuck with a big tow bill..cheaper in the long run........

 

[acme66]

Mine has just started doing this in the last week or so. Not every and time only in two places on our daily run, backing into place to load/unload people and backing it into to the yard at the end of the night. We shift down into low and back four or five times a day, maybe a total of 8-10 low range miles and about a 100-120 high range miles a day. I noticed what you describe, if I shift faster it is less likely to grind. Also I found if I let it start rolling back before shifting into reverse it will grind less or not at all. Still however only in those same two spots and no others, both places are after long down hill grades if that matters. Same noise you talk about as well, like a bark but clearly different than the clunking of drivelines. Until I read this thread I was sure it was bad shift points in the tranny. Did you ever learn anything more about your truck? Did it all go away with the button? I am sure mine is working properly, or I was until I read this. My game plan is to change to the fluid Allison currently recommends as 'best' for this transmission, that expensive syn stuff to soften up the banging shifts and then if I saw no improvements take it to a heavy truck shop for a shift point adjustment. Just wanted to see what you had done and if anything worked for you.

Ken