Vacuum Switch and Filters

Doesn't sound anything like mine.

The way mine works is:

There are 2 solenoid valves "engage" & "disengage"

Both have 3 spigots.

1 goes to the vacuum tank (both valves connect together)

2 goes to the hub line (the vacuum switch is connected to the line on the engage side)

3 goes to fresh air via the filter.

With the solenoid disengaged, spigot 1 is blocked off spigots 2 &3 join, so there is always a route for fresh air to the hub, through the filter.

When you engage 4wd, the engage solenoid is energised, and spigots 1&2 join together, exhausting the air from the line and one side of the hub.

Fresh air goes through ports 2&3 of the disengage valve to the other side of the hub and pushes the hub over.

If the vacuum switch doesn't register a vacuum within about 4 seconds the system flashes the 4wd light, as there is a possibility the hub didn't move.

The valve is de-energised after about 5 seconds and the hub stays where it is.


To engage 2wd, the process is similar for the other valve, except the system doesn't care if there was a vacuum and de-energises after 5 seconds or so.

There is a non return valve in the line from manifold to vacuum tank.

The vacuum switch with some sponge in the eaten away filter. Sorry for the lack of focus with this camera.

A view of an intact fiter with the Suzuki sponge on the solenoid valve.

The mouses work on one of the solenoid filters

Another view of the solenoid valve block.

facade wrote: Doesn't sound anything like mine.

The way mine works is:

There are 2 solenoid valves "engage" & "disengage"

Both have 3 spigots.

1 goes to the vacuum tank (both valves connect together)

2 goes to the hub line (the vacuum switch is connected to the line on the engage side)

3 goes to fresh air via the filter.

With the solenoid disengaged, spigot 1 is blocked off spigots 2 &3 join, so there is always a route for fresh air to the hub, through the filter.

When you engage 4wd, the engage solenoid is energised, and spigots 1&2 join together, exhausting the air from the line and one side of the hub.

Fresh air goes through ports 2&3 of the disengage valve to the other side of the hub and pushes the hub over.

If the vacuum switch doesn't register a vacuum within about 4 seconds the system flashes the 4wd light, as there is a possibility the hub didn't move.

The valve is de-energised after about 5 seconds and the hub stays where it is.


To engage 2wd, the process is similar for the other valve, except the system doesn't care if there was a vacuum and de-energises after 5 seconds or so.

There is a non return valve in the line from manifold to vacuum tank.

Sorry your description does not tie in with either the single cam engine workshop manual section 3d or the twin cam engine workshop manual section 3d or my tests both blowing though and using a vacuum pump and 12 volt supply.

My testing show then when no 12 volts supply applied the line 2 is blocked to the hub and the vacum tank and filter are connected 1 and 3.

When 12 volts applied the filter is blocked (3) and 1 and 2 connect with each other.

Check the workshop manual testing section of the solenoid valve.

auchenblae wrote:
My testing show then when no 12 volts supply applied the line 2 is blocked to the hub and the vacum tank and filter are connected 1 and 3.

Then it would be impossible for the engine to produce a vacuum in the tank as air would be constantly drawn in via the filter. The vacuum tank goes to the one you call line 2 so there can be a vacuum with the valves de-energised.
The valve when energised joins the vacuum tank to the hub.

(As diagram on page 3D6 )

The filter may well block off when energised, as fresh air is not needed, I didn't bother testing that on mine.


Your vacuum switch is different to mine, mine has no filter attached, maybe it fell off but I didn't inspect the switch, as that wasn't my problem, a stuck valve was I freed them off with some magic fluid* and about 50 actuations on the bench.

* most likely GT-85 or JL-69


EDIT: I looked at page 3D12, and the spigots are labelled A B &C

It tests as I described, except the manual does not say that spigot A should be blocked off when de-energised.

C or 3 is the one at the end with the filter on
B or 2 is the one at 90 degrees that goes to the hubs (as diagram 3d6)
A or 1 is the vertical one next to B that goes to the tank (as diagram 3D6)

The tests stated in the manual are B&C join when de-energised (and A has to be blocked off, but it doesn't say that)
A&B join when energised.

Which is what I said.

troggy wrote: Would be tempted to buy them off you j999pre?

Let me know if you want to

Checked again and I am wrong.

No voltgae to solenoid valve, hub to filter route open. From manifold vacuum blocked.

12v to solenoid valve route from hub to manifold vacuum open. route to filter blocked.

OK. I have given up after three days as one of the solenoids the release one is faulty not all the time but some times and then all three spigots are connected.

Set the hubs to 4wd by taking them off and back on with them manual in 4WD.

Shorted the Vacuum switch wiring.

Removed and pluged the vacuum feed from the manifold.

Kirkynet has won.

Tested the car out on the ice and it is working well going in and out of real 4WD.