Gearshift question?

When you can, get in that truck, get the air pressure up to normal, set the brakes, put it in neutral, then turn off the engine. (Need a quiet environment)
- Listen for air leaks
- Operate the gear splitter up and down
Do You hear leaking air?
You should hear a consistent "clunk" as you move the button into high range and the same as you move it into the low range. As long as you are hearing this, then it would appear doubtful there is an issue with the range shifter mechanism and/or an air leak causing issues. (However, I suppose it would be possible for an air leak to be intermittent with truck vibration and movement)
If you hear air leaking at various stages that seem to have something to do with the operation the shifter button, there may be an issue with that as someone mentioned.

 

The main thing is do you hear the "clunking" each time the shifter is moved up and down? If you do, then your transmission is shifting properly, air leak or not. But the only way this would affect how it "down shifts" is if going from the lower upper gear, to the upper lower gear. Some trucks/trannies are more particular about precise rpm's then others, don't look for excuses that may not be in play.

If the range selector is always trying to be in the upper or lower range, then shifting will be virtually impossible, up or down from a stop to highway speed and vice versa. If shifting is only "problematic", then it's probably something other then an air leak in the button lines and a range selector that won't operate properly.

 

If I remember correctly, an air leak of greater than 3psi/min should put the truck out of service. Otherwise the only time air should be an issue is during range selection.

Also you can have an identical truck, engine, and trans w/ 15yrs experiance and still have issues finding a gear. <--> I'm not saying I did... but heard of it happening

 

Yeah, sometimes those dang holes just move on ya...

 

the only time a air leak could cause a issue with shifting is going from high range to low range or low range to high range, other than that air has nothing to do with shifting, although that being said some trucks are easier to shift than others. every truck drives a little different

 

That truck is leagally void from testing students any air leak which would affect your range selector would be a truck that should be out of service and any results ie failure with this truck is void