m915 air shift probs

[reb87]

Im having trouble with the m915 cat air shifted semi automatic tranny. It dosent shift reliably unless I keep the air pressure up around 110 psi or higher, it is supposed to work with +80 psi. Ive been hauling corn with it and if I use the brakes and shift down to 11 or 12th gear it brings the air pressure down between 100-110 psi and then dosent want to upshift reliably. If I come to a complete stop and the pressure is down there, I really have to work to find a gear that will work. It seems like 4th and 10th or 11th will go in when the others wont work. Im thinking about trying to put in a bigger or extra air tank. Does anybody have any experience with the transmission or have any advice on how to make it work better? Thanks, Ross

 

[jwaller]

yup. common problem with that trans. get more air or raise the pressure on the gov.

 

[co59]

The early M915´s had 2 air tanks.
Then they invented an upgrade kit to have finally 4 air tanks.
If You already have 4 air tanks on Your truck let me know.
Franz

 

[reb87]

pretty sure there are 4 tanks on mine, Ill check

 

[cundupa]

How is the fluid? Does it only shift bad pulling a trailer? I'm wondering if it's in the clutches, there is a screen in the bottom that you get to through a PTO cover, may be plugged. My 919 did not shift good a first, we had to pull it on the trailer, but the more I ran it the better it got. Run some air tool oil through the air lines going to the trans.
PTO gasket is CAT 9N-1507
Did you see my PM?
Chris

 

[BKubu]

Paul Baillargeon in RI has one and he knows them inside and out. PM me if you are interested. I'll give you his contact info.

 

[reb87]

How is the fluid? Does it only shift bad pulling a trailer? I'm wondering if it's in the clutches, there is a screen in the bottom that you get to through a PTO cover, may be plugged. My 919 did not shift good a first, we had to pull it on the trailer, but the more I ran it the better it got. Run some air tool oil through the air lines going to the trans.
PTO gasket is CAT 9N-1507
Did you see my PM?
Chris

fluid is clean and full, I will check the screen.
I finally got some pics taken of the 919 stuff

 

[reb87]

ive decided to shun modern vehicles and going to pull the mixer with horses. I want to be more or less green

 

[Monkeyboyarmy]

It's been a while but I was talking to Paul B. also about these trannys.I recall him saying to pull the cover off of the air manifold and clean all parts and install new o-rings.Also add air tool oil to lubricate all of the valves as cundupa said.The shifter itself could be leaking air pressure.Hear any leaks?

 

[co59]

If You already have 4 air tanks than it is the Ratio Selector.
I had the same problem on my truck.
When You shift You are turning a cam plate.
The cams are activating the small valves.
But the material of the cam plate is not hard enough.
Over the years the cams are grinded down.
Then the valves don´t open as much as they should.
And that is the reasen why You can shift only when
You have full pressure in Your air system.
Removing the Ratio Selector is not much work.
I can see a second truck on the picture.
Change the ratio selectors and try out if there is
any difference befor You take it apart.
Franz

 

[cundupa]

ive decided to shun modern vehicles and going to pull the mixer with horses. I want to be more or less green

It does add an odd look to it!! Thanks for the pics. Did your 915 shift good when you first got it? Cat dealer told me to run a straight 30w oil in mine, the modern 15w40 oils have so many new additives. I used Shell Donax T SAE 30 TO-4 Transmission fluid

 

[cundupa]

Reb, how is the 915 shifting, find anything wrong?

 

[reb87]

I havent had time to work on it, Ive been tweaking on the m944a1.