I've a pain in my head now... [Vacuum Hubs]

Howyas Folks!

Bit of a lurker here from next door in Ireland.

Anyways. My vacuum hubs are giving me a lot of trouble. I gave up trying to fix them this evening. Previous to this they were working great. No bothers.

Started during the weekend. Parked up a big grassy verge (bit of articulation of the axles) and I split one of the hoses on the radius arm at the steel/rubber joint. Didn't notice until I drove on some sand later on and popped it into 4wd for some traction. No light initially and then the flashy 4wd drive light after about 15 seconds. That put an end to that evenings fun.

Dropped underneath it and spotted the fractured line. No bothers, I can fix that. Well, I thought I could.

Turns out the rest of the pipes on the front dif were fairly rotten too and probably not airtight in a few places. Grand. Replaced the whole lot (back up to the far end of the radius arm) with copper piping and some 10mm/4mm pneumatic tubing. Popped it into 4wd and the light comes on. Great! But no "clunk" of the hubs. Not so great. Spun the wheels and confirmed there was no 4wd after all. Oh bother. :pinch:

Now for the questions!

• There is suction on both sides of the circuit when the lever is in 2wd. This increases on one side when I plonk it into 4wd but not hugely, I can hear the air hiss and feel it clamp down on my finger lightly.

Should their be suction all the time on both sides of the circuit? I'm guessing no. I think the solenoids have been messed with in the past. One was draped in insulation tape.

• My other guess is that the diff has suck into the unlocked position. Does that happen often?

Apologies for the long winded initial post. :laugh:

Save yourself the bother and get manual hubs. One of the best mods you can do

If I cant fix it tomorrow, I've contacted a seller of an 94 escudo, hopefully there's a set of manual hubs on it.

There should not be suction on either pipe at any time, except for a few seconds after you move the lever.

There have been a few posts on here, but how it works is like this:

There is a pipe connected to the inlet manifold that produces a vacuum.
Inside the drivers side wing there is a vacuum tank.

There are two solenoid valves one to engage, and one to disengage the hubs.

There are 3 spouts on each valve.

one connects to a small air filter and is an atmospheric vent
two connects to the hub (engage/disengage pipe)
three connects to the vacuum tank.

There is a vacuum switch connected to the engage pipe

When the solenoid is off, one & two connect together and three is sealed, so a vacuum builds up in the tank and there is atmospheric pressure in both lines.

When you move the lever into 4wd a timer starts.

First the engage solenoid is activated, connecting the engage tube to vacuum.
Air from the atmosphere passes through the other solenoid valve down the disengage tube( through the filter then from two to one) and pushes the hub across with a nice "click"

The engage tube has a vacuum in it still.
After about 10 seconds, if the vacuum switch did not activate, the 4wd light goes into flash mode (as likely the hubs didn't move). If it did activate it lights up green, and the solenoid valve turns off.

The hubs stay locked in place with a magnet I think, or an overcentre spring

When you go from 4wd to 2 wd, the disengage solenoid is activated for a few seconds, and air pushes the hubs back, and the light goes out. ( there is no switch on the disengage line, it doesn't matter if the hubs don't unlock)


If yours was working perfectly, before you messed, my guess is you have the pipes reversed to one or both hubs.

Just went out there. I've both sides disconnected from the T piece at the end of the radius arm.

Car in 2wd, suction on both sides of the circuit as soon as I crank the engine. It's odd.

the solenoid valves live underneath the battery tray.
If you remove the assembly (note where the pipes go) by breaking the electrical plug (if you can disconnect it without breaking it you are one up on me :whistle: )

You can check the valves out, possibly one has inhaled water and stuck.
Happened to mine, and I squirted GT85 into the ports and connected a battery to the terminals a couple of hundred times and freed them off.

When free and no current, you can suck one of the ports (the one connected to the vacuum tank) and stick your tongue on the spigot.
The other 2 ports you can suck & blow though

With current the vacuum tank port connects to the line port and the vent port should be blocked.

If you have done most of the work, a bit more messing about to get them working properly is worth it, otherwise fit the manual hubs, you need spacer rings, short out the vacuum switch, and blank off the vacuum pipe from the manifold.