seeking vacuum transfer case info (1 Viewer)

[jblueridge]

Last weekend I put the t-case in 4Low.
The green 4WD dash light did not come on though it was in 4Low.
Later, I shifted back to 2High but it took a long time for the front drive to disengage.

I am reading up on these systems but I don't understand a few things.

Why are there 3 Transfer Indicator switches, as listed in parts manual? see pic below

Where is the 4WD indicator switch located, the one that causes the dash light to come on?

Can someone explain the electrical diagram I included below that shows the vacuum switches?

Lastly, Parts List says there are 2 transfer relays but the diagram shows only one. Is there another diagram I need?

Thanks for any wisdom you might share.

 

[Felde]

The 4WD indicator switch is located on top of the T-Case. (Hard to get to). It has about 30cm cable on it that goes into a round connector to the harness then.

Read the diagram right to left. Consider lower part only (ignor the neutral position switch...)
BY (right) is positive. WB (left) is negative. The BW and B in the middle is a bit confusing as it actually is positive, too, just switched.
The TRANSFER CONTROL SWITCH is a toggle switch, I suppose, consisting of upper and lower switch in the diagram.
Also the TRANSFER CONTROL SOLENOID is toggeling: Unlike a relay, which only actively applies magnetic force to engage and falls off by springload, the solenoid applies magnetic force to engage AND disengage (two coils). It actively pushes and pulls.
The TRANSFER L4 POSITION SWITCH is most likely not the same switch that controls the 4WD indicator light, as it is associated to L4 only.
I also think we are rather looking at toggeling 4H 4L here. 2WD is not the topic here, I guess.

Think trough the static condition of L4 engaged, first (so, the oposite conditionof what the diagram shows):
When L4 is engaged, the TRANSFER L4 POSITION SWITCH is closed, which makes the TRANSFER CONTROL RELAY to engage (coil circuit).
The load circuit provides power to the TRANSFER CONTROL SOLENOID lower coil, which *keeps* it in L4, IF (!) the load circuit gets fed some positive from the TRANSFER CONTROL SWITCH *lower switch*, which therefore must be engaged.
Engaged means: Upper switch open, lower switch closed.
Hence, if the switch is disengaged, this solenoid circuit collapses and the tcase goes out of L4.
But the system is not expecting the L4 to jump out by itself:
When disengaging the TRANSFER CONTROL SWITCH, this actually means the upper switch is engaged, activating the upper solenoid coil, which actively moves the Tcase out of L4.
The diagram shows the situation disengaged.

The thing to recognize here: The t-case actuates the TRANSFER L4 POSITION SWITCH mechanically. Only if in L4 the lower circuit remains engaged. If the Tcase is forced out of L4 mechanically, the circuit collapses and makes the solenoid to collapses, too, instead of working against the mechanical force (which would destroy it).

On the other hand, the lower circuit is useless before the Tcase actually gets into L4, because the TRANSFER L4 POSITION SWITCH is open. It requires a different force first, to actually get into L4 and close the position switch....
This is what the vertical BW in the middle does: It engages the TRANSFER CONTROL RELAY coil also in 'not L4' (which rather is 4H, not 2WD).
But this has no effect, as the load circuit of the relay gets no power from the lower TRANSFER CONTROL SWITCH *yet*.
Now (I guess) languishment / sluggishness comes into effect:
If you now press the switch to engage L4, the upper switch disengages and the upper solenoid collapses, letting 4H go, and the lower solenoid engages, pulling into L4. Portions of a second later however, the relay coil circuit gets cut from its supply by the upper switch via the vertical line...
But Vacuum solenoids take a bit to languish , so the movement continues, long enough to engage the TRANSFER L4 POSITION SWITCH, which takes over, revives the relay coil circuit and continues pushing into and holding the L4.

I guess, this is how it works...
If anybody has a smarter idea or better insight, just rectify me.
The above is based on thinking over it, not knowledge.
Good luck Ralf

 

[jblueridge]

It will take me a while to digest all that info.
Thanks.

I checked vacuum lines and the vacuum switches mounted on the firewall.
All that stuff is working properly.
I might disassemble the transfer case diaphragm that does the actual shifting.

 

[Felde]

Hi
System was designed and engineered by Japanese geniuses. Hard for others to digest It took me about 1.5h yesterday to think on this and put it down in writing. But it was fun.
(Others play chess, I think trough diagrams).

But I didn't attend to you actual issue. My bad.

The green 4WD dash light did not come on though it was in 4Low.
Later, I shifted back to 2High but it took a long time for the front drive to disengage.

In essence from my above elaboration:
The two solenoids actually actuate the diaphragm from one side each (push/pull, alike a double sided hydraulic cylinder).
I said,
- the one solenoid is kinda pushing it into L4, the other kinda pulls it out of L4. But it's one diaphragm only.
- the TRANSFER L4 POSITION SWITCH is presumably actuated by languishment / sluggishness of the vakkum system, which includes the diaphragm.

I think, your diaphragm may be leaking / is perforated, so the pressure supposed to move the diaphragm just passes, causing the diaphragm to not move properly and the 'logic' of this system being messed up.

Guess, you are on the right track, buddy
Good Luck Ralf

 

[AirheadNut]

I would agree with @Felde that it sounds like a vacuum problem, either with supply or in the diaphragm itself. The best way to test it would be to get a hand vacuum pump with gauge and perform leak tests on the various components of the system.

The vacuum diaphragm only engages and disengages the front driveshaft, it is separate from the mechanism for shifting in and out of low range. There are three electrical switches on the transfer case: one to detect when the front drive has been engaged, one to detect when low range has been engaged, and one to detect when the transfer is in neutral.

In your case if the vacuum supply is weak or the diaphragm leaks, then the front drive will not engage, the switch (4WD Indicator Light Switch in the electrical diagram above) will not ground the circuit and the 4wd light will not come on. The transfer will still shift in and out of low range manually, but it won't be in 4wd or may take a long time to build enough vacuum to engage or disengage the front drive.

In the second diagram you posted I believe the Transfer Control Relay is a Normally Closed relay, meaning that when the coil is energized it opens the circuit to the 2wd vacuum solenoid, keeping it off. When the Transfer Control Switch (H4 button) is pressed power travels through the relay coil, turning off the 2wd VSV and also activating the 4wd VSV (the upper one in the diagram).

If the transfer case is shifted manually into low range without pressing the H4 button, the L4 Position Switch is closed, sending power past the H4 switch and activating both the Transfer Control Relay coil (disengaging the 2wd VSV) and the 4wd VSV.

Here is a diagram showing the different states of the system, hopefully the colors show up ok.

 

[jblueridge]

Thanks for this explanation!
Great diagrams too!

My vacuum pump works well as do the vacuum solenoid switches. Vacuum lines are good too.
I fear it might be the diaphragm so I will take it apart when I get a chance.

Here's a shot of my vac gauge measuring the vacuum in the front axle engage line.
I disconnected the line where it enters the diaphragm housing.

 

[AirheadNut]

Sounds like the diaphragm. If you have access to a hand vacuum pump I would recommend disconnecting the lines to the diaphragm and attaching the pump to one side. Pull a vacuum and see if it holds. The other option would be to just unhook one line, then actuate the VSV for the other and see if there is suction on the unhooked port.

 

[jblueridge]

Right. I don’t have a hand vac but I was thinking of doing a leak test with one line disconnected as you described. I will put a Tee in the other line to connect my vac gauge.

 

[jblueridge]

I put a vac gauge in the system of lines and with the engine running and full vacuum created, there was no sign that the diaphragm actuator is leaking.
Vacuum gauge needle did not move at all.

I made a schematic of the way I placed the vac gauge. Let me know if this is not a valid way to test.

 

[jblueridge]

I jacked it up and placed it on blocks.
Watched all 4 wheels spin as I repeatedly engaged and disengaged 4Low and 4High.
Seems to work fine except the dash light indicating 4WD does not come on.
I will test that switch when get my voltmeter back from a friend.

 

[jblueridge]

I removed the switch in the t-case that is supposed to light up the 4WD dash indicator light.
The switch is dead: stuck open.
Bypassing the switch with a length of wire made the dash light come on.
So that is one thing that is definitely not working.