M920 Cat 7155

[GAR16]

Hi, I just got my M920 home and am having some trouble with the CAT 7155 tranny. She will not shift into gear until at least 110lbs pressure and sometimes she just will not shift into gear no matter how much pressure. Geting into reverse seems the most difficult. Any advice? I'm hoping ya'll can help.

 

[R Racing]

Look under the drivers door. There you will find a air tank.At the back of that tank is a red hose. bleed your air down and remove that hose. put about 2 tables spoons of air tool oil in that line and reinstall it on the tank. then start up your truck and let it build AIR TO 120 psi and pust the button in to activate the trans . now shift the beee geeebees out of the trans. you may have to add oil a few times and cycle the shifter . this works most of the time to get it going again.

 

[wreckerman893]

Wait until you are going down a steep hill with a load on and the air drops below 80 PSI......she will kick into neutral and you will be freewheeling with no engine braking ability.

This design flaw was addressed with a Modification Work Order (MWO) that added another air tank to help prevent that from happening.

The "Ktty Cat" tranny can be tempremental, and if it breaks it can be hard to find a CAT dealer that has a mechanic that can work on them....they were not a lot of them used in civy vehicles.

I like them unless I have to foot the bill to get them repaired.

Once you get the feel for "Slap Shifting" them they are a hoot to drive.

 

[R Racing]

Hey WM at some point the Gov changed that valve out to 1 that trips at 60 PSI I have 2 shifters here both with a 60 PSI release.

 

[GAR16]

Hi R Racing, thanks for the reply. My truck has been painted and everything is green. Is it the line that comes out of the back of the tank directly under the driver's side door?

 

[R Racing]

Yes thats the 1 . the 1 towards the rear of the truck. its about 5/8 " in dia.

 

[GAR16]

Hi R, well I did as you advised. The first time I put in 2 oz and then the remaining 2 oz. The forward gears are much better but the reverse gears are still a problem. It absolutely not go into reverse until at the air pressure exceeds 110 psi. Other time it just will not go into reverse no matter what pressure, especially after I've driven more than 10 miles. I don't know if has anything to do with anything but the reverse alarm will not go off even after you are driving forward. Any other ideas?
GAR

 

[R Racing]

Sounds like ur reverse servo is sticking.could be in the shifter bur my gut feeling is in the trans.we r still out of power so im sending this from my phone.maybe floridianson (James ) he has the manual can chime in with which servo.I do have a spare trans.

 

[GAR16]

Hi R, glad to hear you are ok but sorry to hear you are without power. Did you receive any damage from the storm? Any help would be greatly appreciated. This M920 was rebuilt in 2008 and only has 186 miles on it. It make all the usual noise like all shift changes but will not go into reverse. Thanks again for your help!

 

[R Racing]

Try from neutral lifting up on the handle about 3/8" and pull to R2 and see how that works and if it does then shift to R1. And see if it stays in reverse.then if it does shift to 1 and see if the reverse alarm goes off. For some reason if u skip R1 it seems to go in reverse consistently. See if it works for u ? Got 2 trees on the shop roof .but not threw it thank God ..im very lucky many here not so lucky.had a tornado touch down and took down about a acre of trees besides the shop and in front of the house.got other houses down the road.

 

[NDT]

Try the oil again but use much more. I filled the entire air line with marvel oil after disconnecting it and holding it up next to the cab. Put it in reverse right away so hopefully the oil will get into the reverse piston and allow it to loosen up. Sounds like it is stuck in place.