Medium and Heavy Trucks
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Could you please post entire trans model number?
Model # ***** be on drivers door tag or on right side of transmission.
The most common cause of this is the low/high range piston is not fully going in one direction,,this is usually caused by dirt buildup or bad o-rings on low/high range piston.Before doing this make sure you have system air pressure (120 psi)to air filter regulator on back of trans,should be 60-75 going to trans.On back of trans there is a 4 bolt cover that is where high low range piston is passenger side.The cover with air lines going to it.replace o-rings.Low high range piston seal kit.They sell a kit for about $30 and has all needed parts.The piston gets slugged up or o-ring goes bad and will not shift.That is the most common issue.After you remove cover there will be one nut, remove that nut,then take one air line off back side of piston housing and apply air pressure to blow out piston, just be careful it does not hit you.Also mark the outside of piston so you know which way it goes back in, if put in backwards it won't shift.It is a fairly easy job and can be done where you are at.There can be a couple other problems but not as common,,broken shift fork,synchronizer,or aux drive gear.Please take a moment to rate or accept my service so that I can get credit for my time from the web site ,without a rating the web site does not pay me. The question will still remain open for follow up questions if needed.Thanksspanky