M35A3 Transmision question.

[motomacguyver]

Well, I went ahead and changed out my transmission oil 15w-40w for dexron III. I changed the external filter 1x after changing the oil 3x. I haven't changed the internal filter yet, it should be here today. The problem is that the transmission worked before I did this, now it won't go backwards or into 4th gear. The first 3 gears seem to work just like they used to. Reverse only work if I rev it up and when it tries to shift to fourth it just revs and never really locks in.


I am desperatly hoping this is something very simple like a bubble in the valve body or foaming. Anybody have any ideas what I can do to fix this.

Thanks.

 

[Floridianson]

Ouch wonder if it's time to get the internal filter done. Cloged from the (rap the Dex cleaned out?

 

[mktopside]

Well, I went ahead and changed out my transmission oil 15w-40w for dexron III. I changed the external filter 1x after changing the oil 3x. I haven't changed the internal filter yet, it should be here today. The problem is that the transmission worked before I did this, now it won't go backwards or into 4th gear. The first 3 gears seem to work just like they used to. Reverse only work if I rev it up and when it tries to shift to fourth it just revs and never really locks in.


I am desperatly hoping this is something very simple like a bubble in the valve body or foaming. Anybody have any ideas what I can do to fix this.

Thanks.

I'll talk out my backside here:

Check the obvious things, fluid level? air in the lines? (There is a little port on the passenger side of the radiator. I have never seen a trans cooler line that needed to be bled, but it's worth a shot)

I have heard other A3 guys talk about the shifter linkage on these transmissions coming out of adjustment, and causing some serious trans issues. Maybe yours is partially in reverse, and partially stuck between D and 3? I don't know the TM off the top of my head, but look for the instructions on how to properly adjust the linkage.

If that doesn't work........ Call your local Allison dealer.

Worst case scenario is you have to replace it, used and rebuilt AT545's can be had for betweek $1k and $1500........ or, UPGRADE TIME!!!


Check the linkage first though.

 

[glcaines]

When you drained the oil was it clean and clear? Did any visible trash come out? Based on your symptoms it sounds to me like low fluid pressure. I would definitely change the internal filter before proceeding. Also, when I changed out from motor oil to Dextron III, I also did the drain and fill routine a total of seven times, driving several miles between drain/refills. I did not change the internal filter, only the external filter, but I plan to change the internal filter. When I talked to Allison, they told me I most likely did not need to change the internal filter since my transmission had so few miles and the motor oil was clean. However, I plan to change it anyway.

I remember reading another post a while back where someone was changing out to Dexron III and their transmission quit working after the change. I would recommend searching for that post and find out what the final result was.

 

[motomacguyver]

Thanks a lot guy's, I will check out the trans cooler purge port and will be changing the internal filter.

 

[ryker725]

Sounds like some air in the system to me. You're probably compressing a pocket of air as opposed to building hydraulic pressure. Check the TM and see if there is a procedure for bleeding. That and the filter is probably all you need to get squared away.

 

[Rustygears]

Sounds like trapped air in the valve body. Is it really cold where you are? To properly get things refilled after a change, the fluid needs to flow like water. You may need to let it sit and idle for a good long while to bring the temp up if the ambient temps are really low to get the fluid thinned out. Then retry, etc.

Did you do just a drain & fill, or did you try some of the more creative flushes that have been described on this site? Did you look at the old fluid - color & smell? DexIII will loosen up a lot of crud that the 10w40 leaves behind. Have a look at the dipstick.

Also, pay close attention to oil level. The 'full' mark on the dipstick is only accurate when the fluid is at normal operating temp, per the dash gauge, and engine running at idle, per the TM. You may have underfilled the tranny if you measured dipstick level when cold and engine off. This is a common mistake and leads to lots of problems (and later abnormal wear).

 

[renovate7]

I've done 2 drain and refills and have one more to go as I convert from 15/40 to Dex III. How many miles on the truck? Did the 15/40 oil coming out look/smell new and clean? Did you only add back as much as came out? My TM is wrong when it says these hold 22 qts. My truck came with the shallow trans pan and only holds 15 qts total. My drain and refills are only 8 qts. First guess is overfill/underfill. Second is plugged internal filter. If it worked fine before this it's something simple...I'd also do what Rustygears said and let it sit and warm up, then check fluid level.

 

[Rustygears]

As I recall, TM says refill is 9qts. Most of the fluid is still in the torque converter and cooler/lines/ext filter.

My migration from 10w40 to DexIII was around 8-9 qt drain and then when refilling, once I started it up, it took a lot of fluid to top up to 'full' from the 'full' indicated when the engine was off.

Wow, the hotel in Tokyo is really swaying this morning. a 7.1 quake yesterday at lunch and two 6+ quakes at sunrise to wake me up. I want to go home to Cali. I live just west of the San Andreas fault and never felt this kind of motion! One more day...

 

[mktopside]

Did fill the trans filter with fluid before reinstalling it?

Try opening that purge valve, it's the highest point in the system so if there is air stuck there it should come out.

 

[glcaines]

Wow, the hotel in Tokyo is really swaying this morning. a 7.1 quake yesterday at lunch and two 6+ quakes at sunrise to wake me up. I want to go home to Cali. I live just west of the San Andreas fault and never felt this kind of motion! One more day...

I know what you are going through I was in an earthquake in Tianjin, China a few years ago and the building was swaying like crazy, everything falling down and machinery weighing several tons was sliding around. All I could think about was the cheap and shoddy construction of the building.

Back to business. I also have the shallow pan and thought seriously about replacing it with the deeper pan. I decided not to because it cuts down on the clearance. I was getting about 8 - 9 quarts per drain, similar to your results. I mentioned this earlier, but I found that my external filter was very loose, but not leaking. I would recommend everyone check their filter. Could be that someone simply didn't tighten mine sufficiently. I like that it's easy to get to though.

 

[Rustygears]

If your filter wasn't tight, you'd be bleeding red stuff, not sucking air. The system is positive pressure and the mess would point to a major leak that would be responsible for the system pressure loss and misoperation. On top of that, you'd bleed out and even more fun as the tranny goes full china syndrome and becomes an ingot of metal alloy.

I think the problem is really underfill - hope I'm right for your sake. Easy fix, too: Start engine, warm up to tranny op temp, check level and pour like mad!

 

[motomacguyver]

OK, I changed the external filter, and purged the tranny cooler valve, no air came out, it was straight atf from the get go. The original oil does have a burnt smell to it but the color was about motor oil color. I have a call in to a local alli$$on dealer. We will see where this goes....

 

[mktopside]

OK, I changed the external filter, and purged the tranny cooler valve, no air came out, it was straight atf from the get go. The original oil does have a burnt smell to it but the color was about motor oil color. I have a call in to a local alli$$on dealer. We will see where this goes....

I'd make sure the linkage was adjusted correctly before taking to Allison; and you might as well drop the pan and replace the internal filter as well. Eliminate all of the stupid possibilities first.

 

[glcaines]

 

[Rustygears]

Ibid

 

[Floridianson]

My guess is the ATF knocked something lose and now it's where it should not be. Good luck hope it's not what I guess.

 

[motomacguyver]

Well. I'm ****ed. pulled the tranny pan, changed the internal filter, and still no love. The Ali$$on dealer say's almost definitely the fourth gear clutch is shot. The reason reverse doesn't work is that the transmission uses first and fourth gear clutches to engage reverse. The guy at GL say's this is the second one he has heard of doing this.

MY FRUSTRATION LEVEL IS PRETTY HIGH RIGHT NOW.

sorry to yell.

 

[renovate7]

Just curious how many miles were on the truck? Was it basically in "good" condition?

 

[glcaines]

I believe you got your A3 at the same sale I did and many of the A3s at Sparta during that sale had low mileage like mine. I find it too much of a coincidence that the clutches went out on your Allison at the very instant you changed out your fluid. I'm wondering if there is not an air pocket someplace inside the transmission causing your problem. If it was me, I would make certain the fluid level was correct after it is hot. If the transmission is not slipping in the working gears, I would drive the truck, slowing down and speeding up, making it shift up and down for maybe 10 miles or so, and see what happens. There also might be some Allison forums that you could post on asking for help with the problem. Another thought is to visit a transmission shop that rebuilds Allisons and try to talk to the mechanic about what might cause the problem. You could also try e-mailing Allison directly and ask for assistance. Good luck solving your problem.