M920 trans issue

[Karl kostman]

OK I know it sounds worse than it is (I hope)? I have recently got my 1980 920 on the road and everything seems to be working exactly as it should be on the roads out of town anyway, with that said I drove the truck into town the other day for an injector issue and when I was leaving town I had to stop at a red light, I was in like 10 gear when I stopped then I pulled up on the shift lever and pulled it down to 6th gear to start when the light changed, as soon as the light changed I gave it some gas to get moving and it just kind of seemed to wallow there doing almost nothing at all. I ended up dropping down to like 3rd gear to get it moving and then all seemed normal. I do not think this is normal and I can make it do it every time I stop the truck in and hold it there with the brakes for any more than a few seconds. Is there something I am doing wrong? The operators manual is pretty darned weak when it comes to anything to do with driving that transmission. Any suggestions would most certainly be appreciated!
Karl

 

[NDT]

Any time a 7155 is unresponsive in a gear, that is an indication that the dozens of plungers in the control body are sticking. Start by adding air tool oil to the line feeding the transmission over by the muffler, and hope that fixes it. An airline lubricator is next, there are several posts here on how to do it.

 

[Karl kostman]

NDT thanks for the tips on this! How much air tool oil should I add to the trans.? and will I need to change the oil in the trans when things start working as they should?
Thanks again NDT.
Karl

 

[NDT]

I used about a shot glass full of Marvel oil in mine. If the main oil looks clean I would not change it. Search "Cat 7155" on here for others experiences with this issue.

 

[MidnightDuramax]

From your second post it seems like you are questioning about adding it direct to the trans. If i read that wrong I appologize and don't mean any offense by it. What NDT is saying is there are air pressure lines going to the trans for the proper operation. the air tool oil needs to be added into the air line for the trans not direct into the trans. Just wanted put that out there to help save you any future problems.