Jump to content
  •  
Advertise here

How the Pajero Part-Time 4x4 System Works


Recommended Posts

For many among us, switching between 2WD and 4WD happens with a lever or a flick of a switch, and as soon as your green lights on your dashboard are illuminated to confirm you are in 4x4, you are happy and good to go.

That is, until the system fails on you all of a sudden, and you are left frustrated, not knowing what to do.🥵

I recently found a nice diagram that shows the functionality of a Part-Time 4x4 system, that uses vacuum (created by your engine) to operate the 4x4 system and engage or disengage your front axle and turn your car from a 2WD into a 4WD.

I am not a specialist in this matter, but merely collected what i could find and what i have encountered on my own Pajeros. 

A few items we will be discussing which are vital components to the 4x4 system and also the first ones to check in case of any issue:

Vacuum solenoids. (VSV1 and VSV2 on the diagram)

These are basically just relays or valves which open or close based on a 12V signal and will block the vacuum or let it pass through. They are located in the engine bay next to your air filter box. Due to engine heat, wear and tear, they eventually break down but can be replaced in a matter of minutes. 

www.pajero3.info | Pajero: Vacuum solenoids replace with ...

 

Vacuum Actuator

This actuator works like a cylinder. When applying vacuum to it, the piston will start to move. This actuator is mounted on the front axle and will engage or disengage the axle from the front differential. The actuator is being controlled by the solenoids VSV1 and VSV2.

Actuator cuplare 4X4 fata Pajero IV (poz.32044)Mitsubishi Montero 4-Wheel-Drive Not Engaging: One ...

image.png.eda086b74faac923bccfc9a816e455bb.png

Now lets look at above diagram and chronologically explain what happens when we engage the 4WD system. 

Don't forget to put your vehicle in N first and keep your foot on the brake whenever switching to 4WD or back to 2WD.

Engage 4WD:

1) In the old pajeros (up to 2000) when selecting 4H, you are mechanically coupling the transfer case to activate the front prop shaft. On the newer Pajero models, this happens with an actuator motor. Upon selecting 4H, the dashboard indicator will start to blink to indicate that the 4x4 engaging process has started.

2) The front axle has a vacuum actuator (like below photo) which will now disengage as well and couple the front wheels to the front differential.

Mitsubishi Montero 4-Wheel-Drive Not Engaging: One ...

3) Once the system has detected through the sensors located on the transfer case and the front axle that the vehicle really is in 4WD, the lights on the dashboard will stop blinking. 4WD is now engaged. If they remain blinking this indicates that either there is something wrong with the vacuum system, or the sensor is not detecting the actual position. 

4) As your car is now in 4WD, the power coming from the engine will be distributed via a 30/70 ratio between front and rear axles in 4H, or 50/50 ratio in 4Hlc. 

Once you are back onto tarmac, you will want to get the car back into 2WD:

Engage 2WD:

1) Move the transfer case lever back to 2H. The lights will start blinking on your dashboard.

2) The transfer case will disengage the front prop shaft, and the front axle vacuum actuator will start to disengage the front axle. 

3) Once the sensors on the front axle, and the one on your transfer case are showing the correct position, the lights will remain (rear wheels only).

 

Question:

If in 2WD your front prop shaft is being disengaged by the transfer case, then why do you need the vacuum actuator to disengage the front axle as well ? 

Well, at this stage you need to start thinking in reverse. What i mean with that, is that when you are in 2WD, the engine is not providing power to the front axle, BUT, because the front wheels are turning they are turning the front prop shaft and the front differential. All this is basically lost energy and would only increase fuel consumption, so by disengaging the front axle with the vacuum actuator, the front axle will actually be "freewheeling" and avoid your prop shaft and front diff from rotating. And this is the main reason why 2WD saves a bit on fuel (less rotating mass to carry along). 

Additional point:

The Pajero has a front independent suspension with CV axles, which are basically always rotating (even in 2WD). Many 4x4 vehicles that have a serious lift, suffer from premature wear on these CV axles due to the increased angle. Installing manual locking hubs on the wheels is a good option, as it basically disengages the front wheels from transferring movement towards the front axle, with as a result that your CV axle doesn't have rotate in 2WD (which could be a good recovery option if it breaks down in the desert), but also would mean that you can remove all this vacuum and freewheeling stuff. Many oldskool offroaders go for this option as less electronics and less solenoids in the desert improves reliability.

Troubleshooting:

If at one point your 4x4 indicators keep blinking, have a look at the following

1) Open the engine bay and look where the vacuum solenoids are. (nearby the air filter box). Inspect the electrical connection and the vacuum hoses that are connected to it. A cracked hose will not be able to create vacuum and will be the reason of your failure.

2) Look underneath the car and locate the vacuum actuator at the front axle. There will be 2 vacuum hoses connected to it. Inspect both hoses, and also pull back the rubber booth to see if the piston is not blocked by any debris or sand. You can use a brush to clean the piston that moves back and forth. If your car is in 2WD and you pull off one of the vacuum hoses on this actuator, you should actually see it slowly closing.

3) Be aware that sometimes the system only engages or disengages after driving a bit forward or backward. Many times i have seen the blinking lights disappear only after 10-15 seconds of driving.  It is good to engage the 4WD system every week. Not using it often gets the system to seize up.

Note: Mitsusbishi has thought about this system quite well, and did not want to leave anyone stranded in case the solenoids fail. By Default, if there is no vacuum, the front vacuum actuator should close by itself and keep the car in 4WD. This basically means if you pull of one of the vacuum hoses, your front axle should be engaged and it should work in 4WD. Of course you will have blinking lights because the sensor will be confused, but at least you could continue to drive in 4x4. 

 

  • Like (+1) 2
  • Thanks (+1) 3
  • Well Done (+2) 3

"Go as far as you can see; once you get there, you'll be able to see further."

Link to comment
Share on other sites

Thanks for this @Frederic, from a fellow Pajero owner. I had issues with my system last year, but after trial and error, and changing the "family" of solenoids, all is like new again, and find the system quite reliable. A nice summary how it actually works. Am actually a big fan of the Pajero system including tiptronic, as opposed to using only the automatic option.  Keep this quiet though - don't tell @Wrangeld, as I can hear him say "Always drive in D, the car knows better than you" 🤣😂

  • Haha (+1) 2
Link to comment
Share on other sites

28 minutes ago, Gregory said:

Thanks for this @Frederic, from a fellow Pajero owner. I had issues with my system last year, but after trial and error, and changing the "family" of solenoids, all is like new again, and find the system quite reliable. A nice summary how it actually works. Am actually a big fan of the Pajero system including tiptronic, as opposed to using only the automatic option.  Keep this quiet though - don't tell @Wrangeld, as I can hear him say "Always drive in D, the car knows better than you" 🤣😂

I am but a humble servant of the Pajero. I will let you know the moment that I use the tiptronic. 

 

  • Haha (+1) 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...

Important Information

Terms of use