The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - no 4x4 -2004 chev

68C15 · 03-29-2011, 10:05 PM

to accurately diagnose these a guy needs to know how the system operates

the shift module tells the shift motor to engage X case based on inputs from dash switch, vacuum switch on top sends vacuum to diaphram under battery, that pulls cable to engage a dog clutch on front diff

half of the time I find a bad shift motor, half the time I find a bad actuator diaphram.

most of the problems with the motor is the encoder (position feedback sensor) while sometimes it is the motor being stuck due to lack of useage.

if the vacuum actuator has a broken diaphram you should replace the vacuum switch on top of the X case due to ATF being sucked into lines. follow it up with a good hose flushing with brake cleaner and blow gun.

03-29-2011, 10:05 PM	#4
68C15 blood type; Retumbo Join Date: Jan 2004 Location: next to my reloading bench Posts: 10,269	Re: no 4x4 -2004 chev to accurately diagnose these a guy needs to know how the system operates the shift module tells the shift motor to engage X case based on inputs from dash switch, vacuum switch on top sends vacuum to diaphram under battery, that pulls cable to engage a dog clutch on front diff half of the time I find a bad shift motor, half the time I find a bad actuator diaphram. most of the problems with the motor is the encoder (position feedback sensor) while sometimes it is the motor being stuck due to lack of useage. if the vacuum actuator has a broken diaphram you should replace the vacuum switch on top of the X case due to ATF being sucked into lines. follow it up with a good hose flushing with brake cleaner and blow gun.