Another 'my 4WD doesn't work' question - 95 Jimmy

I have a few simple but odd questions about the 4WD vac system on this vehicle.
1) If the rear end engages in low when I select 4W low but the front diff
doesn't lock, this means my encoder motor is working right? I would then look to the vac hoses, diaphragm under the batt tray, and tcase 3 port switch??
2) Regarding the vac actuator under the battery tray, I have 2 questions:
I) can this be checked without pulling the battery and tray??
II) I have heard that a bad actuator/diaphragm under the tray can cause fluid to backflow through the hoses causing premature wear/deterioration/etc? Does this mean that if I saw trans/diff fluid at the vac reservior ball, it was likely from a bad vac switch under the battery tray??
I am going to replace every single hose and go from there with the cheapest parts first (dash switch is suspect although I've tried 2 from the boneyards with the same results so I'm not convinced that's the right place to look).
My pushbutton dash switch will either lock itself out completely or attempt 4WH but then bounce back to 2WHI. 4LOW appears to 'register' on the dash switch and the rear end certainly gears down although it appears the front end isn't locking.
Thanks, Andrew.
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AWN wrote:

Yes.
Sure, Apply vacuum to it and see if the axle engages. If your wondering how to tell if it engages, Jack up the right front tire so it is off the ground, then make sure that you have the transfer case in 4wd and the trans in park. With the wheel off the ground and the front axle unlocked you will be able to turn the tire by hand. If you apply vacuum to the actuator and then you can't turn the tire the actuator is working and the problem is somewhere in the lines going to it.

Nope, No fluid in that part of the system at all. The vacuum diaphragm pulls on a cable that goes down to the front axle and moves a locking collar to lock/unlock the right axle.
However a bad three port switch could allow some fluid past if it failed internally. Not real likely it fails that way though.

First look at the lines, then check the actuator.
To check the ported switch you can attach a vacuum gauge to the line going to the actuator. Then try to engage 4WD. If the gauge registers full vacuum then it is probably OK.
To make sure the T-Case is working select 4wd and then try to turn the front drive shaft. with it engaged the shaft shouldn't turn (unless you have one wheel off the ground then that wheel will turn with the shaft.)
--
Steve W.
Near Cooperstown, New York
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Thanks Steve! As always, a fountain of knowledge. I will let you know and likely hit you with some more uncertainties as I go.
Thanks again, Andrew.
On 12/3/07 10:52 PM, in article C37A3943.EFEF% snipped-for-privacy@spamnomore.stopit,

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Steve,
I ran all new vac lines and when I pulled the 3rd line from the 3 way switch on the diff, it had a split in it. After I buttoned everything back up, the 4WD works as good as new.
Thanks for your help. Andrew.
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Yep, any leak causes problems. Glad you got it fixed.
Steve W. Near Cooperstown, New York
AWN wrote:

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I have a problem with a 96 blazer 4wd.
I replaced the vacuum actuator last year, and found the diaphragm town (and 4WD not working) again. I replaced it and an old problem came back.
At any random time while driving in 2 wheel I get a clicking sound as the truck rolls down the highway. The pitch changes with the speed. If I engage the 4 wheel high it goes away.
I wonder if the vacuum switch on the Tcase is leaking a vacuum to the vacuum actuator and causing it to partly pull in. The last actuator (1 year old) had the metal disk under the rubber bent and tore the rubber, maybe like it was being pulled at the same rate as the clicking sound I heard.
Any ideals
Thanks
Chuck

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Charles Yung wrote:

If the switch (really just a mechanical valve) is leaking by it can cause that. To check you could connect a vacuum gauge to the line on the actuator and see if you have any vacuum when in 2wd. If you do then the valve is leaking. Another thing to check is the vent line from the valve. It may be plugged allowing a small leak to cause problems.
--
Steve W.
Near Cooperstown, New York
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I'LL check that too. Thanks Chuck

(and
the
engage
vacuum
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it
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Ok, problem solved. I had two problems
First the vacuum line to the vacuum actuator was plugged. When I disconnect the three hose from the transfer case switch the actuator did not release. I used a low-pressure compressor to blow out the line with the three hose connector disconnected. I was getting oil from the line so I put some awesome soap in and blew it through a few times. The vent line was clear. Ran the compressor through it also to remove the oil.
Put it all back together and started it up, and the actuator pulled in. (nuts)
Disconnect the line and the actuator released, ok must be bad switch. Removed the switch and the ball was stuck in allowing vacuum to the actuator all the time. Replaced it and it works like a charm.
Thanks Steve for your help.
Chuck

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I have looked at that same switch a dozen times and I still think it looks impossible to remove. Did you pick up any tips along the way regarding removal?
Thanks and glad you got it fixed. I think my issue might be with the TCCM... Ohh gawd,,
Andrew.
On 1/5/08 3:16 PM, in article KARfj.13638$TO.4623@trnddc01, "Charles Yung"

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It was easy too remove,I unplugged the three hose connector (all at once) and used a 7/8th open end. After you remove it look at the ball on the bottom. it should move in and out freely. Mine was stuck in. Good luck.
wrote:

disconnect
release. I

clear.
actuator
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Charles,
Perhaps my setup is a little different I don't know. It's very tight on top of the tcase on my 95 and it's nearly impossible to actually **see** the switch itself. I'm sure I can do it by feel but it certainly looks like it will take a few ales and some foul language.
Thanks again, Andrew.
On 1/6/08 9:20 PM, in article 90ggj.1057$hS.72@trnddc08, "Charles Yung"

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Charles Yung wrote:

No problem. Glad you found the problem.
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Steve W.
Near Cooperstown, New York
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