Quote:
Originally Posted by unruhjonny
Thanks for the link to that TSB, I did some more digging and created jpgs of the FULL TSB and saved them to my computer.
That TSB prompted me to decide to get the LMC electric (replacement for a thermostatic) actuator & corresponding actuator harness upgrade.
Between the front diff, and the rear, what is the logic for these actuators?
Is it because of the theoretical(?) increase in mileage from a more conventional posi - based on the merits of both wheels receiving power full time equating to lower mileage??
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It's for lazy people, that don't want to exit the vehicle to turn in manual hubs. Also, all the driveline stops turning when the differential side gear disengages, helping fuel mileage as well as slowing wear in the front propeller shaft, transfer case bearings, and U joints. Both axle shafts and CV joints continue to turn, even in 2 wheel drive.
Manual hubs would stop the CVs, and axles from turning, further decreasing wear, and raising the MPG. Evidently GM thought the buyers would be resistant to having to manually engage/disengage hubs, so they chose to just disengage the side gear from the spider gears in the front differential.
Warn used to make hubs called selectamatic that would engage when the transfer case was shifted into 4 wheel drive, letting the occupants stay in the vehicle. I haven't seen any of these hubs for decades though.
Back in the 70s when all the manufacturers made full time 4 wheel drive in all the SUVs, and light duty trucks. It only took a few years for the aftermarket to make a kit to change over the full time, to part time. This helped fuel mileage, as well as save a lot of wear and tear on the double cardan U joints on the front shaft, and the exposed U joints in the axle shafts. Gas shortages also played a big role in trying to attain better fuel mileage by converting the full time 4 wheel drive to part time.
Detroit stayed away from full time 4 wheel drive after people that had owned a full time rig didn't want to buy a new replacement with full time 4 wheel drive.
At the time i owned a Jeep with full time Quadra trac, and when the chain broke in it I opted for an early transfer case, and manual hub setup to get rid of the problematic Quadrea trac. Jeep was the only full time system that the aftermarket didn't make a part time kit to eliminate it.