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.

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

Life is not like a box of chocolates
it's more like a jar of jalapenos-
what you do today could burn your ass tomorrow!

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%spamdoctor (AT) spamnomore (DOT) stopit,
"AWN" <spamdoctor (AT) spamnomore (DOT) stopit> wrote:

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.

Yep, any leak causes problems. Glad you got it fixed.

Steve W.
Near Cooperstown, New York

AWN wrote:
http://www.pronews.com offers corporate packages that have access to 100,000+ newsgroups

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

"Steve W." <csr684NOT (AT) yahoo (DOT) com> wrote

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

Life is not like a box of chocolates
it's more like a jar of jalapenos-
what you do today could burn your ass tomorrow!

I'LL check that too.
Thanks Chuck
"Steve W." <csr684NOT (AT) yahoo (DOT) com> wrote

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
"Chuck Yung" <cbelect (AT) verizon (DOT) net> wrote

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"
<cbelect (AT) verizon (DOT) net> wrote: