Effects of vacuum on 4wd.
- Thread starter scrubber3
- Start date
Monterorider
Adventurer
vacuum disengages front axle disconnect. So if you don't have vacuum you will have permanent 4WD. Smartly done by Mitsubishi since if you loose a tube in a bush you will have your 4WD system functioning. With center diff won't matter much on pavement.
Monterorider
Adventurer
Many moons ago I made a post about it in other forum How active track disconnect works
scrubber3
Not really here
So theoretically if I have manual front locking hubs, I can disengage this system without any ill effects?
What could be a cause of a sudden disengagement of the drive train when in any 4wd mode when applied a load to. It is not the transfer case, though this has caused the destruction of one transfer case already. 2wd is fine. When it disengages, it produces a horrible grinding noise. If I had an exploded view of the transfer case innards and where it ties into the transmission, I'd be fine to figure it out.
Any help is welcome and let me point out that my montero, even without 4wd is a beast off road. Granted the rear locker helped.
Monterorider
Adventurer
If you are careful about it. If you have your front wheels disconnected but engage 4Hi in transfer. All of the engine torque will travel vi viscous coupling to rear wheels. It wheel burn it out in no time which effectively will lock up your center differential and make your truck part-time 4wd only. How do you tell "disengagement of the drive train when in any 4wd mode" what do you mean by that
scrubber3
Not really here
Upon shifting into any position other than 2wd and applying a "load" upon the drivetrain, there is a noticeable disconnection of the entire drivetrain and a grinding noise. The vehicle doesn't move and grinds until placed in neutral of course. Upon letting everything stop spinning, place into 2wd. Once that engages fully, I can apply all the load I desire without any ill effects. It shifts into 4wd and will act fine until I start up a hill or over rocks or give the accelerator a good push from stop. This is when it "comes out" and proceeds to grind and doesn't progress anymore.
I am under the impression that the vacuum/vacuum actuator may be responsible for this pending the vulnerable position of the actuator and the fact that when it happen the first time with the old transfer case I had just got through some major rocks and tree limbs. One limb which was responsible for tearing my new cv axle boot.
I'm interested to see what you guys conclude.
Monterorider
Adventurer
Are you shifting past 4Hi into 4Hl or 4Llc. Hubs engaged? If former sounds like your chain is broken, stretched or slips or some other t-case innards damaged. Gen 1s were know for chain issues but Gen 2 are pretty stout. People wheel it with 37's and low gearing. There is always a possibility of some hidden defect of course. Ask somebody to look under your truck when grinding happens. If front drive shaft spins then - it's front axle if not - t-case. If it's axle it could be broken diff. There is really not much to break in actuator.
Monterorider
Adventurer
it has got to move forward in 4Hlc or 4Llc because it's part time mode. So it tells me you are only engaging 4H. Put front on jack stands. spin wheels, listen for bad sounds from diff. Everything rotates as appropriate? Put in in 4H lower one side (or ask somebody to hold opposite wheel) . Transmission in N check when you spin driver's side wheel that drive shaft rotates. If it does listen for sounds in t-case.
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Wait.... didn't your tcase give up the ghost recently? Are these part of the symptoms for that... or?
Monterorider
Adventurer
Sounds like it.
scrubber3
Not really here
I have just replaced the transfer case. Reluctantly as I know how stout they are. It just made sense that it was the culprit and indeed there seemed to be some damage to it. I know that there is a slide bar on the front differential that is vacuum activated. This is why I asked the question of what effects disconnecting the vacuum would be. Since this happens When applying a load, I may be putting a vacuum on the system disengaging the front axle just enough to cause the grinding. Which would be the actuator or can. Though I do wonder why it seems the whole drivetrain disconnects.
Another question would be how certain are you that the system is fail safe 4wd? Lack of vacuum = 4wd engagement. If so it would somewhat solidify a possibility of the culprit being vacuum related since it happens when accelerator is pressed against a load. Therefore creating more vacuum. Given the fact that of the actuator was allow the vacuum to go past it(possible diaphragm issue) the negative pressure would in turn disengage the front axle just enough to cause the grinding.
Another question would be how certain are you that the system is fail safe 4wd? Lack of vacuum = 4wd engagement. If so it would somewhat solidify a possibility of the culprit being vacuum related since it happens when accelerator is pressed against a load. Therefore creating more vacuum. Given the fact that of the actuator was allow the vacuum to go past it(possible diaphragm issue) the negative pressure would in turn disengage the front axle just enough to cause the grinding.
Monterorider
Adventurer
I'm very certain. When you say 4WD what position of transfer case you mean. 4H 4Hlc or 4Llc? As a side note: never wheel in 4H even more (purely IMHO) there is very little reason to not be in 4L unless going high speed desert racing. Not too many of those in Virginia I suppose.
If everything works on jack stands sound like stretched/loose chain. Why did you replace t-case?
If everything works on jack stands sound like stretched/loose chain. Why did you replace t-case?