Looking for 4wD vacuum actuator location

Hey guys
Have a 91 super custom and my 4wD doesn’t seem to be engaging and no dash light when button pressed.
Was told to check if there’s suction on the vacuum actuator hoses but am not sure where to find them or what they look like in order to do that.

Would super appreciate any thoughts or suggestions on this or how to do that. (Checked fuses already) No dude so will take all the help I can get lol!

Happy Hiacing
Carley

Hello Carley

You don’t specify your model, but I’m presuming you have the vacuum-actuated part-time 4WD setup with the dash button that, when everything works, gets a green light on the dash. You likely also have lockable front hubs, too?

The system is vacuum-actuated and the vacuum is the same as the brake booster, so it’s generated by a pump, probably incorporated into the alternator (bizarre I know). I think some models have a vacuum pump driven via an auxiliary belt.

There’s a fine tube that winds its way from the alternator to the vacuum-tank under the vehicle pulling a vacuum. The tube is actually a double pipe with the opening up under the driver’s seat. So the air is pulled from under the seat via the tank under the van back to the alternator. Mad I know, but the double tube is so the reservoir tank pressure is lowered from a place that should be fairly clean and dry. Various solenoids direct ‘vacuum’, (well lowered pressure) or returns atmospheric pressure to the transfer case, so you should also be able to follow the hoses. The system is actually quite elegant and simple.

There’s pressure and electrical diagnostic processes you can follow in the first page of my show us yours, section. The post is a little way down the page and actually about dash switches incorporating lights, but it was the 4WD actuation that triggered the discussion.

Hopefully you just have a simple leak but the system has a number of ways it can fail to work and I’d advise being careful to understand how it works and how it can fail before diving in.

There’s a picture of the reservoir (before painting) on the last post on page 2 of my show us yours page where I’m dealing with removing the gearbox. Other pictures of the gearbox there show the diaphragm arrangement etc.

Finally, do take a look at the longish first post on my show us yours section as there are loads of hopefully helpful resources and links there to assist with finding out everything you might want to know about what’s where and how to work on it.

HTH!!

Thanks so much for all the info here! Greatly appreciate it.
Not sure if I found the exact post/photos you mentioned but seem to be getting a bit more of an understanding of possibilities.
Pulled cluster yesterday and nothing obviously wrong there so you’re most likely right about the vacuum situation!
Thank you

You get to the home screen (https://hiace-super-custom.forumotion.com/) by pressing the home button.
Then scroll down to the ‘Show Us Yours !” page. The most recent post there is from ‘Chris_Alpine’. My posts are described by my username.

HTH!!

Hi Carley,

I had a problem with the 4wd light no longer coming on when I press the 4wd button. For me, the problem was that one of my 4wd solenoids died. If you look under the van, you should see a square airbox with 2 solenoids and some vacuum lines. Whenever I need to turn on 4wd, I have to stop and go underneath the van and swap the vacuum lines going into the 2 solenoids. I can't find a new solenoid, so this is the best next thing unfortunately.

This is for a 92' supercustom. Might work for you.

Hahaha well if it works it works I guess! Thanks for this info!
I just went underneath and I can hear it click when someone else pushes the 4x4 dash button(still no dash light)

I pulled each hose off and held I little piece of cellophane up to each of the
hose ends when the button was pressed. No suction on top hose and only a tiny bit on the bottom one. (I’m not sure how much suction it should have to begin with though?)

Any thoughts?

It could be that one solenoid is clicking but that the other is broken. I'm honestly not sure how the system works, I just tried swapping the tubes based off some advice I read online and it got the light to come on after driving like 20ft. I did end up pulling the solenoid off and testing for a click with a 12v battery and it was definitely dead. Or you can test them via voltmeter. Then you can at least rule out solenoids.

Hello both.

I think the reservoir / box is available (via the EPC for example) but the factory solenoids are not.

That being said it’s ‘just’ a box with a suction pump elsewhere on the vehicle and the solenoids divert the suction to the transfer case. If I had to build another one I’d start with an aluminium tank or cylinder of some sort and rig up replacement 12V solenoids and an air fitting for the suction. The advantage of aluminium would be it’ll have sufficient wall thickness to make it a bit easier to tap in the necessary fittings as a steel box would generally have much thinner walls.

If you want something a bit bespoke then a tig welder could knock up a box with correct attachment brackets and with the necessary threaded ports for off-the-shelf solenoids to be attached. It would not be too expensive, but fine LiamM if you just want to swap hoses. I understand.

You’re missing out on a useful feature of the 2 to 4WD and back though that you can engage and disengage it when driving. The speed and other aspects are on various stickers etc. The vacuum system ensure it’ll only change settings when the vehicle is ‘happy’.

Carley, I pointed you to my show us yours page where there is a diagnostic of the whole thing; electrical and pneumatic. It even has the required pressure values.

Wonder no more!!

You might also need to investigate the general state of the vacuum system on your van as well.

Good luck!!