2002 S10 Blazer

Symptom: front driveshaft spinning, but front diff not engaging.

So 4WD is in manual/vice-grip mode, no vacuum is reaching diaphragm, (I'm manually tensioning the actuator wire to the front diff.)

I believe this is NOT an indicator for a stuck vacuum switch, so I should not need to investigate that? I believe it is bad vacuum lines, the vacuum supply to T.C. is corroded from oil. There is zero vacuum at the diaphragm hose. I imagine it should be pretty strong/obvious if there is vacuum strong enough to pull the actuator wire.

These vacuum lines are pretty basic, but I'm hoping someone can please confirm my identification of them as I've got to have this fixed first thing in the morning. I believe I should look for 7/32" hose and fittings, is that correct? >>a previous post "Mainly, two sizes are used for HVAC & 4WD: 5/32" & 7/32". Maybe grease them at fittings to seal if there's a non corrosive sealant grease, e.g.dielectric s.p.boot grease? And is there any cure to the symptom of cold weather decreasing vacuum other than just replacing with fresh lines?

If my understanding is not correct, please advise:
In the pic, engine vacuum goes over to the brake booster and then splits.
One line then goes down to the T.C.,
and one line goes to the brakes.
In the left corner, the breather tube is not important to check for leaks?

I'm going to replace the vacuum supply going to the T.C. I plan to splice it midway because the access to the vacuum switch on the T.C. is pretty tight. Do people remove the front drive shaft to access the vacuum switch when testing/replacing it?

The diaphram under the battery is clean, no oil, another reason to believe the vacuum switch is not broken. I believe a stuck switch results in front diff NOT disengaging out of 4WD.

Thank You!

 

I just redid mine with 5/32" line, it took most of a 25 foot reel. I left the vent/breather line alone, just did the two vac lines. A leaky vent line is only bad if you get it underwater. I removed one line at a time, and rerouted them a bit for easier access.

I would replace the entire line not splice it, removing the shaft does provide easier access. I would still remove the mode switch to check it, a busted switch diaphragm will let the vac line suck fluid through it. Number one cause of fluid in the line if the front TFC seal is not leaking and overfilling the case with trans fluid.

 

4 in your pic needs to be hooked to a vacuum ball in your fender well. the nipple is under the abs module. You can plug the hose, but every thing MAY not work unless your rpms are up. Did you physically look at the actuator? They rip and can be easy to miss

 

Thanks slimsummers! will take a look.

Thanks newguy! yeah, actuator is good, but no vacuum reaching it. The one line is badly shot, should be the fix.

 

Why is there a cap on the vent line? I noticed that on my '99 when I replaced the distributor cap yesterday. I was wondering about that......

 

to keep critters and other things which could clog the line.

 

Yep, you'd be amazed how small a hole a Wasp/Mud Dauber can manage to build a nest in. It also helps keep any water dripping over it out.