NP233 sticking shifts

[Markb873]

Hello again,

1993 s10 Blazer. My 4wd sticks going from 4hi to 2hi. My light in the switch is burned out so I have to listen to the sound the relay makes in the dash. I then confirm its out by trying to spin the front driveshaft. The transfer case has a newer motor in it of maybe 2 years.

When I go to check with the driveshaft to see if it's unlocked I ocasionally have to try to turn it pretty hard and it will "pop" loose. Unfortunatly because it's running I can't seem to isolate the noise other than it's in the transfer case or in the front differential. If the car is off it doesn't help the shifting issue either. It shifts fine between 4h and 4l so I'm assuming it's not in the planitary assembly.

Any input is appreciated!


Thanks,

-Mark

[MT-2500]

Originally Posted by Markb873

Hello again,

1993 s10 Blazer. My 4wd sticks going from 4hi to 2hi. My light in the switch is burned out so I have to listen to the sound the relay makes in the dash. I then confirm its out by trying to spin the front driveshaft. The transfer case has a newer motor in it of maybe 2 years.

When I go to check with the driveshaft to see if it's unlocked I ocasionally have to try to turn it pretty hard and it will "pop" loose. Unfortunatly because it's running I can't seem to isolate the noise other than it's in the transfer case or in the front differential. If the car is off it doesn't help the shifting issue either. It shifts fine between 4h and 4l so I'm assuming it's not in the planitary assembly.

Any input is appreciated!

Have you tryed backing up and rollng forward and puting transmission in neutral?
Thanks,

-Mark

Have you tryed backing up and rollng forward and puting transmission in neutral?

[old_master]

On the transfer case, driver side, upward and inward of the front drive shaft yoke, there is a vacuum switch that screws into the case. There are 3 vacuum lines connected to it: one comes from manifold vacuum, one tee's in with the transfer case vent line and runs up along the transmission dipstick tube. There is a small filter on the end of the hose that must be clear. The third vacuum line runs to the actuator under the battery tray. When 2WD is selected, the vacuum switch connects the actuator to the vent. If you pull the filter off the line by the dipstick tube and apply vacuum to the hose, the actuator should pull the cable to the front axle. If the plunger in the vacuum switch gets stuck, even partially, it will apply vacuum to the actuator and the axle clutch will grind while driving. Wife's description: sounds like a prop airplane taking off. Selecting 4WD HI will stop the grinding immediately. Most auto parts stores have the switch in stock: http://www.oreillyauto.com/site/c/de...eyword=600-500

You can just see the 3 ports on the vacuum switch behind the shift lever in this image:



If you reach over the top from the rear of the case, you can get at it fairly easily. Takes about 10 minutes to replace it with a 7/8" deep socket and a 3/8" drive flex ratchet. While it's apart, check the lines for transmission fluid, the switches have been known to suck transfer case fluid, (ATF) into the lines. If you see any evidence of fluid, clean it out. Fluid in the lines will make engaging and disengaging sluggish.

[Markb873]

MT, I will shift back and forth from, drive, reverse, neutral and it doesn't seem to change anything. I was assuming it was some type of torque lock since the motor would struggle to shift it however there really isn't any consistent pattern on how to get it to unlock. In other words sometimes it will unlock in drive, sometimes neutral, sometimes, reverse, sometimes with the car off.

Old Master, I actually have one of those vacuum switches in a box in storage. I will switch that out tomorrow and post back the results. I will check for that filter. I did have that problem described in the post about the noise but it went away on it's own a few summers ago.

Thanks again,

-Mark

[Markb873]

I switched out that switch finially and it had gunked itself open with transmission fluid. After putting the new one in it sounded like a straw at the bottom of a milkshake in the front end and it even worked a few times until it got itself full of fluid. I know what I need to clean out now.

Thanks again everyone.

[old_master]

Yup, totally disconnect all three lines and blow them out with compressed air. Then put a few ounces of mineral spirits in each line a blow 'em all out again. The actuator below the battery will need to be removed to dump out the oil and clean it out.

[bdarryl]

Does it matter what way the vacumn lines are attached?

[old_master]

The connector only fits on one way, so you can't mess 'em up.