1992 S10 Blazer. The actuator for the front wheel engagement keeps failing. I have replaced it three times ( all new units) and only lasts about 7 or 8 months. The diaphram gets small holes in it, from what, I don't know. This last one that failed I tore apart and found several drops of what looked like old oil coating the inside. How can oil travel that far when it's a vacuum? I beleive the oil is causing the failures and don't know how to stop oil from getting into the actuator.

Other questions. Will worn shift linkage effect the 4WD shift motor? Will it keep the shift motor from working at times? Where can I find schematics for the steering column switch located under the dash, on the column, that is related to the 4lo - 4hi push button?

Thanks in advance.

 

Fluid in the vacuum system can be caused by a combination of problems. A leaking front input seal can cause an over full condition in the transfer case which can cause a leaking vacuum switch to allow fluid into the vacuum system.

I have cleaned one too many vacuum systems on s-series vehicles from the engine to the actuators under the dash for the HVAC system and can attest to the royal pain in the butt that this situation can be.

I would recommend that you pull the fill plug on the back of the transfer case to see if fluid pours out. If it does, you need to remove the transfer case to replace the input seal.

While you are there, replace the vacuum switch and flush the lines out with a 70/30 mixture of water and Dawn dish soap. Do it to the point that the mixture comes out clean. Check all of the lines under the dash for signs of contamination as well.

 

Thanks for the quick responce.

Never thought of the front transfer case seal leaking. Already replaced the vacuum switch. Will have to get busy on the vacuum system flush and the fluid level check.

Do you have any info on the other questions?

 

I know this thread is almost a year old but just experienced the same problem on two new actuators. Replaced one right before we had a snow storm here a day after Christmas. ( Ilive on L.I.) It lasted up until 2 days ago. Upon inspection I noticed the diaphram was torn and fluid was present. I didn't flush any lines but did clean things up a little and replaced it. I plow a little with the truck and replaced it right before going out this last storm. Within 12 hrs I lost 4wd and upon inspection the diaphram was torn again. No fluid so I'm at a loss of what could have caused this. Suggestions I could think of (just brainstorming) too much vaccuum, rubber on diaphram too thin? Could transfer case fluid break down the rubber on the diaphram?

Right now I have it stuck in 4wd high with the cable pulled out and held in place with a pair of vice grips. I would love to be able to shift out of and into 4wd on the fly and not have to pull the battery and tray to do this.

Any help would be appreciated!

Thanks.
Rob

 

I'm in the same boat rc1626. I replaced all the vac lines and checked, replaced, the seals in the transfer case and trany. The new actuator lasted about six weeks. It to developed a hole in the diaphram. I too, had to use the vise grips for a short while.

I said screw it. I've put enough money into this project and still have the same problem. I went and got a platic coated choke cable and rigged a bracket under the battery box to hold it and the front axle shift cable. Ran the cable to mount under the dash. I now shift into 4 wheel manually.

I think the after market actuator is junk, not made to last. You'd think they'd make the rubber to be oil and gas resistant and little stronger. MO

Make sure to plug the vac line to the actuator if you go manual.

 

Gear Grinder,
Manual engagement will be the only way to go. I just purchased a 4x4 posi-lok unit. Basically it is an aftermarket set-up like the one you made w/ a cable run from under the battery tray where the problem actuator sits to under the dash for manual engagement/disengagement. Thanks for your response.
Rob