Fuso Canter Transfer Case vacuum actuation

[SkiFreak]

Not wishing to be too rude here @OzWanderer, but if you pulled your hoses off and tried a few of the solutions suggested, you would find out exactly what happens.
You would then probably get a better understanding of how these systems work too, which can be very useful if you find yourself stuck in the middle of nowhere with limited or no access to outside assistance.

 

[kerry]

On a Mercedes it only needs to hold the vacuum long enough to halt the fuel supply and stop the engine. If it needs to hold vacuum id just put a small ball valve at the end so I could turn it and seal the line

 

[OzWanderer]

Ski Freak....you are correct. I learned that with my Landcruiser after the first round Australia trip, that I must do all these exercises at home. That's what I am going through now. The more problems I have now, the more I learned.

I just discovered that there is no suction at all even with revving up the engine. More tracing tomorrow. I have already replace all the rubber hosings near the solenoids and the actuator. It could be the check-valve near the engine...let's see.

 

[C p weinberger]

From experience, always confirm/ diagnose the root problem before choosing workarounds, undiagnosed underlining issues will always bite you in the butt down the road. The knowledge gained from understanding your platform is priceless.
I’d throw in an analogy to marriage.....?

 

[kerry]

Do you have a Mity Vac? It's essential to diagnosing vacuum problems. (I've owned a bunch of 80's Mercedes where everything is run with vacuum) You can trace down leaks easily wit a Mity Vac and some golf tees to plug lines.

 

[OzWanderer]

Slowly working to trace the problem, it seems at least the actuator arm is rusty and pitted. There are plenty of sand rubbish inside the rubber sock covering the actuator arm. But could not take it ap
art to really clean it, only now able to use my finger to clean it with a lot of Innox and wipe with cloth bit by bit plus blowing air. Cleaned up both the actuator arm as well as the driver arm that goes into the transfer case. I am now able to move the arms by a pair of pliers and with a little bit of strength, in and out. The 4WD drive light now comes on. So at least I can operate it by manual means.

What I don't know is, if the travel is enough for the front-drive gears to be engaged fully. I certainly do not want to crack any teeth if they are only engaged halfway and I started climbing a sand dune. Please see attached picture, and if possible, would someone have a look at yours, to see if the travel is "full" compare to yours. Thanks in advance.

After this, then start tracing the vacuum system to see what is wrong.

Wonder if anyone knows? if I can apply a bit of pressured air, about 40 psi to the actuator, to check if it is working ok. My logic is, the manual says the vacuum should be -9 psi, the net vacuum differential from atmospheric is actually 24 psi. 40 Psi pressure is just 25 Psi above atmospheric. As I understand it, the actuator works on pressure differential.

Of course, I can always "suck" it and see.

 

[SkiFreak]

Don't confuse pressure and vacuum.
I don't have a FGB71 manual, but -9 PSI (9 PSIA) equates to about 18 in Hg.
FYI a full vacuum is 30 in Hg and 0 in Hg is atmospheric pressure (14.7 PSI), when measured at sea level.

For testing you would need an actual vacuum pump, be that motor or hand powered, and a vacuum gauge.

 

[kerry]

Or a good set of lungs and cheeks.

 

[OzWanderer]

Don't confuse pressure and vacuum.
I don't have a FGB71 manual, but -9 PSI (9 PSIA) equates to about 18 in Hg.
FYI a full vacuum is 30 in Hg and 0 in Hg is atmospheric pressure (14.7 PSI), when measured at sea level.

For testing you would need an actual vacuum pump, be that motor or hand powered, and a vacuum gauge.

My understanding is atmospheric pressure is at 15 psi = 760 mm Hg = 30 in of Hg. Total vacuum is 0.

According to the service manual, the actuator works with 500 mm Hg vacuum, which means about 9 psi. Actually, the pressure difference between that and atmospheric is 6 psi negative pressure. I was wrong to say the differential was 24 psi, it is actually 6.

In absence of a vacuum pump, In order words, if I use pressurised air of roughly 21 psi at one end of the actuator, the other side being 15 psi, I should be able to see movements. If I don't understand it wrongly, the actuator has two tube connections, it is the pressure difference of the two sides that make it move one way of the other. Correct me if I am wrong.

cheers

 

[SkiFreak]

My understanding is atmospheric pressure is at 15 psi

Pressure gauges usually start at 0 PSI, because we normally measure pressure above atmospheric pressure (14.7 PSI, to be exact).
Vacuum is a negative pressure below atmospheric pressure, often measured in inches or millimeters of mercury or in kPa.
A full vacuum, at sea level (on this planet), is considered to be -30 in-Hg or -100kPa.
And yes, to be technically correct, vacuum does not "suck", atmospheric pressure "pushes" the actuator. Even though I have heard rumours that there is no such thing as gravity; the earth just sucks!

Don't confuse pressure seals with vacuum seals.
I have no idea what seals are in that vacuum actuator, but seals designed for vacuum do not necessarily work with pressure.

As a simple example...
We have breathers in differentials because the lip seals are designed to keep the oil inside the diff. Without the breather, if the diff is hot and you drive into a river, the air inside the diff is cooled rapidly causing a slight vacuum, which can result in water being drawn past the seals and into the diff. This happens because these seals are primarily designed to work in one direction only.

Personally, I would not use positive pressure to test a vacuum device.
But hey... it's your truck, so do whatever you want.

 

[SkiFreak]

Or a good set of lungs and cheeks.

I don't know about your lungs Kerry, but at best I can only pull about 17 in-Hg on a vacuum gauge.

 

[OzWanderer]

Pressure gauges usually start at 0 PSI, because we normally measure pressure above atmospheric pressure (14.7 PSI, to be exact).
Vacuum is a negative pressure below atmospheric pressure, often measured in inches or millimeters of mercury or in kPa.
A full vacuum, at sea level (on this planet), is considered to be -30 in-Hg or -100kPa.
And yes, to be technically correct, vacuum does not "suck", atmospheric pressure "pushes" the actuator. Even though I have heard rumours that there is no such thing as gravity; the earth just sucks!

Don't confuse pressure seals with vacuum seals.
I have no idea what seals are in that vacuum actuator, but seals designed for vacuum do not necessarily work with pressure.

As a simple example...
We have breathers in differentials because the lip seals are designed to keep the oil inside the diff. Without the breather, if the diff is hot and you drive into a river, the air inside the diff is cooled rapidly causing a slight vacuum, which can result in water being drawn past the seals and into the diff. This happens because these seals are primarily designed to work in one direction only.

Personally, I would not use positive pressure to test a vacuum device.
But hey... it's your truck, so do whatever you want.

You are correct, that's why I am asking the question of whether I should apply positive pressure differentials.

 

[Aussie Iron]

You are correct, that's why I am asking the question of whether I should apply positive pressure differentials.

No, I wouldn't either (use positive pressure).

Dan.

 

[javajoe79]

I have an FGB71 too, and last year the 4x4 selection wasn't working. I found that a couple of the rubber vacuum lines were perished and leaking, so I replaced all the hoses on the soleinoid 'box' and to the actuator with silicon hose lines. I also pulled the actuator semi-down and re-rusted what I could. All that got it going again.

After reading this thread today, I've just been out to check if it was working. Not working! Arghh! I'm fed up with it, and sick of crawling around under the truck for the same thing. Is there an alternative electric solenoid/actuator kit out there? I've even thought of just making it a manual lever - I have to get out of the cab anyway to turn the hub locks. The actuator and solenoid box are in places that are subject to road spray, and road salt in locations like mine so nothing looks the healthiest.

It's common on some trucks to delete the vacuum or electric transfer case shifter with a lever and a push pull cable. My truck is far from a stock Isuzu but that's what I have done so maybe you could too. On my transfer case when you unbolt the electric actuator motor there is a shaft sticking out of the transfer case. I made a lever to bolt to that shaft and ran a push pull cable into the cab where there is a lever to work the cable. Works great, no buttons, vaccum or electronics to fail.

 

[OzWanderer]

Thanks. That would be my last resort. At this stage, I can use my finger to push and pull the actuator after de-rusting, cleaning and lubricating with Lanotec. At least the 4x4 light has come on now. I shall persevere with cleaning the rest of the vacuum system, just replaced all the hoses.

Shall report back what happens, for others to follow later.