Engaging 4WD High without locking hubs (FG649)

[Bris31]

Guys, I have front LSD (ATW) and today I changed the LSD oil with premium mineral 85W-140 with Limslip. My intention was to lubricate the front diff so decided to have a short drive around the block. As it is all bitumen here, I didn't lock the hubs and tried to engage 4WD High lever while truck was rolling slowly. There was screeching noise from front diff so I backed off the lever immediately. Then I locked the hubs, rolled the truck and 4WD High lever engaged smoothly. Tried few times dis-engaged, engaged while driving, no issue (btw I tried this on short straight stretch on bitumen though, without any turning).

In last 8 years with this truck, this is the first time I ever tried to engage 4WD High while driving WITHOUT locking the hubs, so bit concerned.

Question is it normal, by design? Or a problem somewhere!!

Thanks in advance.

 

[SkiFreak]

What's the point of engaging 4WD, high or low, without engaging the front hubs?
It just does not make sense, as it would have absolutely no effect.

 

[SkiFreak]

Also... if, as you say, you have a diff center from ATW, it will be a Quaife Auto Torque Biasing (ATB) differential.

This is from the Quaife website:
"the Quaife ATB Differential does not require any special lubricants"

 

[Aussie Iron]

It is pretty normal if you don't have your front hubs engaged and try to put it 4WD to get a lot of noise. Nothing in the front diff is spinning so no synchronization of the two shafts.

Dan.

 

[Peter_n_Margaret]

Engaging 4WD with the hubs unlocked happens in the transfer case and will cause the front tail shaft to rotate which will turn the front diff and cause the front axles to rotate.
So what?
No harm should be caused.
I do not understand how this could cause a noise in a diff that is "normal".
I suggest the noise came from the transfer case instead. While mobile, you have half the transfer case rotating and the other half not rotating with the hubs out. With the hubs in, it is all rotating at the same speed as you engauge.
Cheers,
Peter
OKA196 motorhome
EDIT Beaten by Dan

 

[Ultimark]

I have an Isuzu NPS with the same front differential from ATW, yes it is the excellent Quaife ATB unit (Torsen type).

Last year we crossed from bitumen in pouring rain to a very slippery dirt road on the Eyre Peninsula, I pressed the 4WD button only to be hit with a screeching mechanical noise emanating from the front end, or at least it certainly sounded as though it was coming from the front end. I immediately remembered the front hubs weren't engaged and turned off 4WD; immediate noise cancellation.

I stopped, engaged the hubs and off we went in 4x4 mode; noiselessly.

On another note, when we sometimes have to reverse in somewhere and it is tight and up hill, I engage 4WD low range, but without the front hubs engaged. I then reverse in very slowly and easily without needing to slip the clutch. In case you are wondering, I often need to use a full lock to lock with the steering wheel . Been doing this since we've had the vehicle, which is 3 years and I've never heard anything noise wise emanating from either the hubs or anywhere else. Usually when doing this the windows are open and I'm listening for anything untoward.

The ATB front differential is the best thing since sliced bread when traversing loose surfaces and so far it has been nothing short of brilliant in sand, I'm not in a hurry to find out how good or bad it is in mud, no doubt one day I'll find out.

Mick.

 

[SkiFreak]

I engage 4WD low range, but without the front hubs engaged. I then reverse in very slowly and easily without needing to slip the clutch.

Hmmmmmm... I must admit, I had not considered doing that. ?

 

[Peter_n_Margaret]

On another note, when we sometimes have to reverse in somewhere and it is tight and up hill, I engage 4WD low range, but without the front hubs engaged.

Yep. Useful technique.
Cheers,
Peter
OKA196 motorhome

 

[Tudor Tanase]

Yep. Useful technique.
Cheers,
Peter
OKA196 motorhome

Yes, very useful your clutch will thank you. And no gas pedal required, everything is done in idle. Just be gentle as you have 2x the torque the rear axle would otherwise see.

 

[Tudor Tanase]

with hubs open and vehicle moving, trying to engage 4wd means trying to force something spinning (rear drive - e.g. think rear prop shaft) to connect with something stationary (front drive - think front prop shaft). They're only designed to connect when stationary or when moving/spinning at the same speed - no synchros or the like. Which is why they're protesting...

 

[Ultimark]

Yes, very useful your clutch will thank you. And no gas pedal required, everything is done in idle. Just be gentle as you have 2x the torque the rear axle would otherwise see.

Yes, and easy to do some real damage.

Isuzu with their NPS model restricts the torque output in low range first and reverse gears from 419Nm to 377Nm, but even then, if you give it a handful you could be literally stretching things.

Not at all sure about the Mitsubishi brand of vehicles though.

 

[Ultimark]

with hubs open and vehicle moving, trying to engage 4wd means trying to force something spinning (rear drive - e.g. think rear prop shaft) to connect with something stationary (front drive - think front prop shaft). They're only designed to connect when stationary or when moving/spinning at the same speed - no synchros or the like. Which is why they're protesting...

Bingo!

Took a little bit of thinking for me to realise exactly what you were saying, dead right.

Mick.

 

[Aussie Iron]

Engaging 4WD with the hubs unlocked happens in the transfer case and will cause the front tail shaft to rotate which will turn the front diff and cause the front axles to rotate.
So what?
No harm should be caused.
I do not understand how this could cause a noise in a diff that is "normal".
I suggest the noise came from the transfer case instead. While mobile, you have half the transfer case rotating and the other half not rotating with the hubs out. With the hubs in, it is all rotating at the same speed as you engauge.
Cheers,
Peter
OKA196 motorhome
EDIT Beaten by Dan

Yes, you are right it is in the transfer case. The noise is what happens (normal) when you try to engage 4WD without having the hubs engaged.

Dan.