M916 transmission air leak


New member
Black Hawk, CO
I have a m916 that has a transmission air leak. It has a Cat 7155 transmission. Air comes out of one of the vent cap when I engage the shifter. Air leaks equally in all forward and reverse gears. Other than that, the transmission seems to work fine until I run out of air pressure. I'm wondering if anyone else has run into this problem and has a fix.

R Racing

Active member
St. Leonard, MD
Yes , Do a search on cat 7155 Transmission and or manifold. You have 1 of 2 problems . 1 a stuck poppet valve , 2 a few bad O rings in the manifold.Bleed the air system first. Try going to the passanger outter air tank. Remove the airline from the rear of the air tank and fill it with as much air tool oil as it will take and reattach the air line and let it build air and try it. If that doesnt work. Bleed the air down first. On the passanger side of the shifter there are 3 bolts that hold the umbilical cord to the shifter. Remove the bolts and pour air tool oil in the 13 ports in the umbilical until it wont take anymore. then bolt it back on the shifter and build air and try. If this doesnt work you will need your manifold rebuilt ( its not for the faint of heart) I have rebuilt 4 myself .
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