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.

AWN wrote:
> 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??

Yes.

>
> 2) Regarding the vac actuator under the battery tray, I have 2 questions:
>
> I) can this be checked without pulling the battery and tray??

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.

>
> 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??

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.

>
> 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.
>

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!