M35A3 Transmission overfill?

[DownRange762]

I just changed the internal and external transmission filters on my A3, including blowing out the trans cooling lines per the TM. The manual says drain and refill capacity is 16 quarts. I did not measure the quantity of fluid drained.

During the refill at 8 quarts, still no reading on the dipstick, nor was I expecting one since I thought I was only halfway to FULL. I was just starting to pour in my 3rd gallon I noted the fill tube overflowed. My initial thought was a lot of air got introduced into the system and needs to be worked out. At this point I had put 9 or 10 quarts back into the transmission.

Started the truck as the TM requires the fluid level to be checked hot while in neutral. After several minutes of running, the fill tube overflowed but also bubbled quite a bit indicating at least some air was getting worked out of the system. Checking the dipstick indicated about one quart low so that was added brining the total I put in to 10 or 11 quarts. Trans was still not up to operating temp with the engine running about two minutes later a second large overflow occured out of the fill tube and again some air bubbles. Reading the dipstick this time it shows WAAAYY overfilled with the truck running in neutral.

I have not noted any procedure in the TMs for an air purge following a trans refill.

With the truck off, (yes I know the TM says to read with it running) the dipstick reads about three inches above the HOT full mark.

My questions then are:

1. Is there a credible purge procedure for getting air out of the system.
2. What is anyone else's trans dipstick reading with the engine off. I ask this just to get into the ballpark rather than drain some, put some back over and over.
3. Just how twitchy is the Allison transmission regarding filling. I find it hard to believe I went from just under full to way beyond full with one or two quarts.

Thanks,

 

[martinwcox]

I don't have an A3 (plenty of other types with auto's) and dropping the pan and changing the internal filter does NOT drain the torque converter which can hold 1/3 to 1/2 of the total fluid capacity.

I suspect as you filled her up, filter and lines will purge and very quickly it's FULL.

My Hummer H1 is very similar, I always measure what I drain out and measure the fluid charge to put back in. Cycle the gears and check the level as per the TM.

YMMV

 

[Jbrowning22]

Your Trans vent tube on the back of the cab is probably clogged. Blow it out with some compressed air, and it should be fine. Normally it's just those little spider webs that look like Cotten balls that clog them.

 

[glcaines]

Your Trans vent tube on the back of the cab is probably clogged. Blow it out with some compressed air, and it should be fine. Normally it's just those little spider webs that look like Cotten balls that clog them.

Ditto!!!

The reading on the dipstick without the engine running is meaningless. Also, simply running the engine and checking the level when hot is not sufficient. You need to drive the truck and exercise the transmission in all gears, including reverse. Also, as previously mentioned, the torque converter was still full of old fluid. I prefer to use the drain and re-fill method repeated several times to replace all of the fluid.

 

[DownRange762]

Jbrowning22, you are the lucky winner and thanks for the response. I took at look at the vent lines on the back of the cab and all three were in fact clogged. Cleared those with a piece of wire since I wasn't wanting to pull the entire floorboard out to access the vent fitting on the transmission. Started the truck again and it took an addition 4 quarts without bubbling, spitting or puking. Had that not cleared I would have pulled the trans tunnel out.

GLCains - the reason I asked for the non-running dipstick indication wasn't meaningless as clearly the trans had much less than required for safe operation. I was asking for a "cold/off" indication to get an idea of whether it was in the ballpart of being in a condition to drive. Prior attempts at checking while running in neutral has produced a wide range of results and also lots of oil on the floor.

As you noted, actually running the truck through all gears is the proper way, but I wasn't keen on driving the truck with what turned out to be a gallon less than what was required. Once I got the truck to a safe level to drive it was "exercised" and as you would expect, it took a little more (less than a quart) to bring it up to the Full Hot mark. A torque converter flush would be great. Anyone know why there isn't an inspection plate access that would allow for that on these vehicle? And waterproofing can't be the reason.

 

[Jbrowning22]

Glad it all worked out!

The first time I changed my Trans fluid I ran into this. I was using a really large funnle that I had jammed down in the tube pretty good. Long story short, when it stopped filling I turned the truck on, and a good sized air bubble blasted about a gallon of ATF all the way to the ceiling. Not fun.

FYI, you can get to the vent fitting from underneath, you don't have to take the tunnel out.

 

[DownRange762]

For those that were wondering and might ought to check theirs, here are the vent tubes at the back of the cab, (exterior) complete with dirt dauber nests to ensure you will blast trans fluid all over the cabin when refilling.

 

[Deuce007]

I am hoping to change my transmission oil as well but do I have to blow out the cooling lines or can I just drain whatever comes out of the pan, refill, drive it around in all gears, and repeat?

 

[Maxster]

When you say blow out the vent tube do you mean blow air into the vent hose or suck air out?

 

[Jeepsinker]

Ideally you would remove the line at the transmission and blow air from there out. That is what is intended.

 

[DownRange762]

When you say blow out the vent tube do you mean blow air into the vent hose or suck air out?

Neither. In my particular case with the insect nest obstruction to clear the vent tubes you need to blow air OUT through the vent tubes by disconnecting them further "upstream" of the obstruction. In other words disconnect the lines between the transmission and the obstruction and then direct the air so it blows towards the obstruction and outwards and not toward the trans. Do NOT blow air into the vent tube at its endpoint as that will only shove the obstruction/trash into the transmission.

Hope that helps.

 

[Jeepsinker]

That's what I said... Maybe I need to be more clear... Lol

 

[tashaak]

I had transmission fluid coming out of my fill tube,I mean at least a gallon. If it is the vent tube I cannot find it. I have a 1986 925a1. I got it up to temperature and went to check the level and it just blew out at least a gallon maybe more. Cold it showed very high but it would drop when warm but when I got it under a load that is when it blew out. Could someone help me or could I talk to someone on the phone who knows about this situation. Thanks I was planning on taking it to Alaska this winter but now I don't know. Help

 

[glcaines]

This should be in the 5-ton forum. However, overfilling an automatic transmission can be very bad and can damage the transmission. You need to read the TMs and search for the vent and make sure it is not plugged. Drain any excess fluid from the transmission. Fluid levels are checked for most automatics while the engine is idling in neutral and at operating temperature. Fluid levels measured with the engine stopped are worthless.

 

[Cheswood]

He's asking about an m35a3

 

[tashaak]

I am asking about a 1986 925A1. I read most of the forums but I could not find where the vent is located and where it goes to. Does it go the the intake stack or up somewhere else. Can I reroute the vent to somewhere else up high if it in fact does go to the intake stack? Or is the vacuum caused from the stack necessary. Thanks for responding I am in kind of a bind with the truck not being able to be moved until I get this fixed.

 

[Monkeyboyarmy]

It relates back to the vent tube. Especially in cold weather, the moisture will freeze blocking the vent tube. I had a 923A2 puke about 3 gallons of fluid when it built enough pressure to pop the fill tube. It was about 10 degrees out.

 

[tashaak]

Ah,probably what happened it has been 0 here for a bit. Thanks I will still try and clear the vent. Do you know where the governor filter is located? I want to change all the fluid and filters.

 

[Monkeyboyarmy]

Governor filter? Just one external filter and one internal filter as far as I know.

 

[rustystud]

What I think you did is you put too much oil in to fast. You created an air bubble which finally burped. This is really common filing Allison transmissions. You first start with filling the transmission with 10qts of oil, then you start the truck for just a few seconds. Then you add 10 more quarts then start up the engine again and then add fluid to the lowest line on the dip stick. After getting the unit up to operating temperature you can add the rest of the fluid.