93 Blazer Silverado(full size) 5.7L Auto 4WD(lever on floor) not working.
This is my elderly parents vehicle. Four wheel drive has not worked in a long time. They are away on a trip and left it with me to do brakes exhaust and more. Putting it in Four wheel drive should light the indicator, engage the transfer case and the front wheels. Not sure of the order that all happens. Indicator not lighting, transfer case engages (i think) because the front driveshaft locks (not free) but the front wheels are not driven. I also note the antilock light is and has been on for a long time too-does that interfere in any way?
Suspected the actuator, used a test light and it is getting power. We were able, with effort and tools able to pull and push in the plunger, so we lubed it with some penetrant and worked it a bit. We plugged it in with out installing in the axle, and when put in four wheel drive it slowly pushed out with almost no force. After reading forums I replaced actuator, but still no light(both bulbs are good!) and no 4wd. 4wd fuse is good too.
What do i check next.

 

i think theres a switch in the transfercase or in the front differential that should tell that light to light up which might be bad.

if the front driveshaft is engaging and you are sure that front actuator is working then it must be a problem somewhere internally in that front differential.

its been a while but when i worked at a shop where we used to get a lot of older chevys they actually had a updated actuator for sale that the boss swore by. no idea what it was or where you got them he ordered them and i put them in.

 

I have also removed the actuator and using a 3/8 socket extension was able to push in whatever the actuator pushes on about a half inch. There is spring tension on it that pushes it back out. When pushed in manually i still get no 4WD, and spinning either front wheel with it pushed in does not turn the driveshaft either. I visited a couple of familiar shops and their conclusion is that there is something amiss inside the front differential.
Know my parents, they will not chose to spend the estimated 3-4 hundred to get it fixed. I am putting the original actuator back in and selling the new one...

 

its a relatively simple system but it can be made even simpler. The sliding collar for the long side axle shaft can be manually engaged and locked with the Perma-lok slug. Another option is to weld the collar onto the stud axle so its impossible to dissengage. Posi-lok is a manually actuated cable system that replaces the electronic actuator so you have total control over the axle engagement. I have one in one truck and have just left it engaged. To me disconnecting the long side shaft makes no sense at all so i have all mine engaged 100% of the time.

 

Thanks goatman, but i think you have missed something in my posts about the problem.
Neither the permalok slug nor the posi-lok will do me any good. Both take the place of the oem actuator...there is nothing wrong with my actuator; The problem is inside the differential.

 

if if the actuator is good your still going to have all of the problems originally associated with the thermal actuator, so I recommend it be removed from the system regardless.

The only thing I can come up with that would give your results would be a toothless pinion gear which would be very unlikely. It would require high shock loads on the front drivetrain, like bouncing over rocks at full throttle. Also there would be like 14 teeth worth of metal hanging out in the diff housing, Did you drain the fluid?

 

I have not. It is my parents vehicle, they left it with me while they took a trip. I fixed a variety of other issues, and with the left over time, began investigating this issue of no 4wd. I know my parents never abused this truck and have owned it since new. at 200k miles, i will bet that 4wd probably never had more than a total of 20 miles of use total, only to help pull his boat out of the water on wet slick boat ramps(not in the last 15 years). It is not an issue for them so i wont be able to convince them to spend the money to have it fixed("we dont go anywhere when the weather is bad" and they live where the snow can fly and they are 85 yrs old.). The 350 motor runs strong and the tranny has no issues.

 

I have the same problem with my 93 blazer. I don't see a fuse that is labelled 4wd. Which fuse is it?

 

Which version of 4x4 engagement?
Switch on the dash? Manual on the floor?

The engagement normally goes (either electrical or manual)
1st the transfer case into 4HI.
2nd when the transfer case senses engagement it sends an electrical signal to the vacuum solenoid
3rd which should pull the actuator cable on the front differential.

Not sure on the full size where the switch is and when it would light the 4HI light. (normally the switch is in the transfer case - same as front engagement.)
When in neutral (tranmission) and standstill the switch to 4LO should be possible. I would start looking there if the transfer case goes through all the switchings 2HI - 4HI - 4LO and back. Not unusual to have the transfer case go bad (chain) or engagement fork.
Oil change would be nice and probably give some hints. When front differential is engaged manually it would lock the driveshaft regardless of the transfer case being in 4x4 or not. The procedures to check the correct mechanical engagement on all four wheels would require a lift or all 4 wheels off the ground.