Wont go into lower gears Eaton fuller 10 speed

Do you hear any air leaks on top of the trans?

Does it only do it in freezing weather?

 

I replaced my shifter knob last week due to a similar issue. It was leaking in the shifter knob. Something was worn enough that it wouldn’t split. The part was in stock at Peterbilt and was a quick repair.

 

This is about what I paid for it at Pete. Probably any truck shop would have them.

 

Be careful if you take it apart as there is a small ball bearing in there also. Vaseline can be used to hold it in place to put it back together. If you buy a new knob you won’t have to have that part open as you can install it sealed. The price wasn’t worth the hassle for me so I just replaced the entire knob.

 

The shift knob is probably a fairly good guess. If you can find the air leak I believe you found the problem.

 

Is the air leak coming from the the top...so shifter? If so there is a small allen bolt on the side, remove it and slide the plastic shift cover down and see whats leaking....possible all it is, is the airline is loose in the fitting. Worse case its the shift knob assembly in need of replacement and your half way apart at this point anyways.