only 1999 with 4 button selection has the soldenoid on firewall
3button dont to my understanding
will check vacuum at diaphram under battery tomorrow
thanks for all the help

note i get the hissing under the dash even when all vacuum lines are disconnected (removed check valve and plugged the manifold line) like the guy above said...unless someone ran a seperate vacuum line then it would hiss still

so i not sure yet
will do vacuum test tomrrow
thanks again to all

 

That is what was wrong with my daughters blazer. Solenoid was stuck shut. No vacuum to diaphragm. What if he tries bypassing the solenoid to try and get full vacuum to diaphragm.

 

Good possibility of the solenoid being stuck half way not allowing full vacuum to the actuator. Check vacuum at the solenoid, if vacuum is 18", connect the 2 vacuum lines together and see if the right axle fully engages. If it engages, faulty switch.

 

when i took the battery out of the blazer (while it was running) i then removed the battery tray and had someone else hit the 2hi and 4hi button and the diaphram looks like it is working correctly (i mean its pulling the cable really well) compared to the videos i have seen on youtube it looks like it is working correctly

why has no one said anything about the drivers side tire rotating freely when i have both tires off the ground and its in 4hi (in park or nuetral)

both tires (drivers side and passenger side) will rotate and make the exact same clicking sound when span in forward motion or reverse motion

to my understanding the drivers side front axle is always supposed to be in 4x4 mode

no one hasnt said anything about that

 

The left front axle is always engaged with the differential. It turns the ring and pinion and the right inner axle. It also turns the front driveshaft and chain inside the transfer case when in 2WD. The differential only has power from the engine/transmission when the right axle and the transfer case output shaft are engaged, (when you select 4WD). If you were to select 2WD, raise both front wheels, and manually engage the axle actuator, (not the transfer case) both front wheels would turn, (in opposite directions). The grinding noise you hear are parts 9, 12, & 23 all trying to engage with each other. Similar sound as with a manual transmission trying to shift into reverse without using the clutch.

Parts 9 through 23 all have to do with the axle clutch:

 

Captian Hook
thanks for that image and your good explanation above.

if i understand correctly what you said above (with both my front tires off the ground and in 2wd mode while in "Park") when i rotate my drivers side front tire the front drive shaft should rotate even if the left axle is not engaged?

i only see the front drive shaft move when i rock the drivers side tire back and fourth.

if i put in 4hi then i can get that same exact movement in the front drive shaft when i rock the passenger side tire back and fourth

i will look again later today to see if it makes the opposite front tire rotate in the opposite direction.

the weird thing to note i guess is the front diff drive shaft
the drivers side tire or the passenger side tire (when rocking them back in fourth) in 4hi will move that drive shaft very little back and fourth

so with the passenger side sleeve engaged (supposibly) it does mimic the same results as the drivers side tire rocking with the front diff drive shaft

cant do anything yet as its 6:33am right now but in a few hours i will try and get some more info

is there any chance to got that same pic you posted above in a lil better quality?

thanks

 

have lots of news to report

checked the vacuum hose under the battery at the diaphram
2HI = 0 PSI
4HI = 18 PSI
engine is running with all tests below

i took the diaphram off the cable and attached vise grips
I plugged that vacuum hose that connects to the diaphram
with the front wheels off the ground and tranny in park and in 2HI
i pulled the cable and rotated the passenger wheel
i could feel the cable pulsing in and out as i rotated the tire but when i pulled harder on that cable the pulsing would go away.
im thinking this is the sleeve you were telling me about but not absolutely sure (just yet)
i marked both front tires (valve stems facing down) so i could see if the drivers tire would rotate when i pulled on the cable (hard enough so i didnt feel the pulses) and when i rotated the passenger tire it did not move the drivers tire

so i put it into 4hi
when spinning passenger front tire no matter how hard i pull i always feel the pulses and the drivers tire did not move again
i can actually see the cable where im pulling on it going in and out as i rotate the passenger tire (that is what i mean when i say i feel pulses)

so in 2hi it pulses when i rotate the passenger front tire but i can get that to go away when i pull pretty hard on the cable

in 4hi no matter how hard i pull on the cable i always feel the pule

is there any way this could be the chain?
and the pulses im feeling are the links?
i doubt it because when im in 2hi the front diff drive shaft is not moving and i can feel those pulses until i pull hard

thanks for any info you can give

Captain Hook

i just re-read what you wrote about this:
when i rotate the drivers front tire it dont turn the front drive shaft when im in 2hi
i can rotate the front drive shaft by hand and it dont move any tires

when i manually engage the actuator under the battery (again when i pull hard enough while in "2HI" it will pulse when rotating tire and then stop as long as i pull hard.
BUT it does not turn the front drive shaft or drivers tire

 

Correct. In 2WD the left wheel "drives", (keeps things turning) the ring and pinion, right inner axle shaft, front driveshaft, transfer case chain and the transfer case front output shaft. It is not powered, just spinning at vehicle speed while the vehicle is in motion. This is what permits shift on the fly. When you select 4WD, the encoder motor moves a shift fork, (part #54) that moves a synchronizer, (parts 28 through 32) which applies power to the front output shaft, (#21). This all happens almost simultaneously with the right front axle being engaged.


Normal.

In regards to post #37:

When you pull on the cable, the "pulse" you feel when rotating the tire is because the axle clutch is not fully engaged. You're feeling the teeth trying to mesh. Everything else you mention with regards to the driveshaft turning is normal. You'll need to take the right front axle clutch mechanism apart and see what's wrong, possibly worn pads on the shift fork.

 

Captain Hook

When the front tires are off the ground and i am in "Park" and 2hi is selected and engine is running and all vacuum lines are hooked up and correct...
if i rotate the drivers front tire should the front diff drive shaft rotate?
because it is not

i can rotate the front diff drive shaft by hand while in 2HI
the drivers tire does not spin
from what i understand you said the right tire should turn with the front diff drive shaft all the time no matter what?

 

This is normal for this type of differential. A "locker" type axle will not allow the shaft to slip. I guarantee you that the driveshaft is turning at vehicle speed when in motion. If it wasn't, you're transfer case would be scattered on the road in pieces when you selected 4WD Big mess, big money.

No, it's the left, (driver side) that drives the differential and drive shaft when 2WD is selected. The right, (passenger side) half shaft & CV joints are not engaged with the differential at all, they are free wheeling, just rolling along for the ride... until you select 4WD. Then the driveshaft and differential are powered and the differential sends power to the ground through the wheel with the least amount of traction. Yup, least traction. That's why locker type axles are so desireable, they divide the power regardless of the amount of traction.