Posted by Al on October 24, 19100 at 10:11:42:
In Reply to: Re: FRONT DIFF. ON '95 BURB posted by Traveler on October 24, 19100 at 08:12:57:
I don't believe the front shaft is turning when the GM trucks (IFS) are in 2H. Yes there is a front axle disconnect, on the right side of diff. Therefore I believe, when in 2HI, the left wheel is turning somthing inside the front diff, but the otherside of diff, inbetween the diff and axle disconnect is also turning, in the opposite direction, similar to rear end when vehicle is in park and rear end is lifted. You turn one wheel by hand, and the otherside is turning in opposite direction in an open diff.
It is correct when vehicle is put into 4H/4L, transfer case engages front drive axle, at same time a switch in transfer case lever turns on a switch to energize the thermal actuator. Thermal actuator heats up an inert gas, gas exapnds and engages the front axle disconnect. When front axle discoonect is engaged, this closes another microswitch lighting up transfer case lever picture (transfer case to front axle on pictograph). Now you are in 4WD.
You can test theory if front drive shaft turns in 2HI by marking it and some point near it for referance marks, drive one block or so, and see if marks are still line up.
If you don't like the fact that it take 30 seconds to 2 minutes depending on outside temp to wait for front axle to engage, on #1 son's topic page, someone posted a TSB for a electronic replacement, that engages alot faster. #1 Son mentions his page and has a link about 12-15 posts down from here. Hope this helps all who were curious how there front axle works. R/ Al
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: The disconnect is in the front diff. Stock is the Thermal Actuator that didn't last too well. It is typically upgraded to the electromechanical model used '98 and later.
: The transfer case is still driving the drive shaft to the front but the diff disconnect allows the axles to free wheel relative to the ring gear.
: If I recall correctly, moving the lever from 2HI to 4 HI does the following: Sends power to the thermal actuator, feedback switch closure illuminates the 4WD pictoral, ABS system flagged for 4WD.
: 4LO works the same and in addition mechanically introduces a 2.72:1 gear reduction and flags the PCM and ABS that 4LO is selected.
: This is why you never get any gear grinding between 2HI and 4HI.