Possible diff wind up problem... need some help

[mellows40]

G`day guys,

After recently workin on my Fj 40 changing the c/v`s. a curious sound is coming from the front end. Basicly I put her into 4wd high range without the hubs locked in. Which shouldn`t be a problem.. But at aproximatly 75 kph a harmonic hum started coming from the front end .

I took it out of 4wd high. and then locked in the hubs, back at 75kph... no hum..

the next test went like this 4wd high, hubs locked, and a short drive up the road ( 50 meters a tight u turn and back 50 meters) the car felt heavier than normal, and in the corner it felt like the brakes were on...

Am i experiencing diff wind or somthing else?

I have new cooper atr`tyers on the front and olympic overlanders on the back that are due to be changed.

any help would be greatly apreciated
Cheers Mellows40

[toaddog]

Was the road tar or dirt?

Have you adjusted the brakes and wheel bearings correctly.

Was the noise only at 75 or did it continue after that?

Have you had the front drive shaft off at all?

[mellows40]

Toaddog.


the road was tar.. Brakes are disc`s brand new... noise at 75kph then dissapeared over that.. and came back as i slowed down through 80kph to 75kph... front drive shaft off .. yes but that was a long time ago.. and have been out 4wding without any dramas .. so if i understand where your headed the uni joints .. seem fine. also was a little difficult to get out of 4wd. ie put her in reverse punched the accelerator, stopped then shifted out of 4wd easy

Cheers mellows40

[toaddog]

Never drive your 40 on sealed road in 4x4. Straight line is ok but the tight u turn is what will break things. When you had the drive shaft off did you mark on the flanges where they were assembled and refit in the same position?

Last time I had something like that it was the universal in the tails shaft.

The windup shows up just like it did when you tried to take it out of 4x4.

[mellows40]

Toaddog,

I cannot remember if i marked or not.. That was a long time ago... the tight turn therory is somthing i had forgotten.. i will get the uni`s checked though.. I will look into them.. I am trying to rule everthing out cause I`m trying to build up a vehicle that will take me EVERYWHERE i want.. and most importantly back again.. the straight line harmonic hum at 75kph in 4wd high range is somthing that still bothers me though so till i figure it out... no 4x4 ing...

more ideas would be realy helpful .. thanks for your fast responce Toaddog

[Harb]

on tar even the slightest difference in tyre size, tyre wear etc will cause wind up type problems and things to either wear rapidly or break.

[mellows40]

Thanks Harb,
I understand that but can the harmonic hum at 75kph 4wd engaged hubs unlocked cause damage?... oh yeah great looking rig you`ve got there

[Struth]

Is it possibly simply the transfer gears humming at what is a pretty fast pace for a transfer case to handle?

Or the diff is simply worn, in 4wd no hubs locked the drive shaft is driving the diff using one face of the crown wheel teeth, with hubs locked and no 4WD the axles are driving the diff using the other face of the crown wheel teeth. Likewise on the pinion gear.

I would be looking to the diff gears myself.

Cheers

[Jacked]

i wouldnt worry about it. how often do you drive in 4wd without the hubs locked? and why are you even driving in 4wd without hubs locked? (much easier to leave hubs locked and drive in 2wd )

its like saying my boat overheats whilst its running on the trailer out of water.

as a guess i would say its because you are driving the front diff and axle assembly without any load on it and the hum is coming from tiny little movement in the bearing tolerences. when i used to run cars on the hoist you would get all sorts of harmonic hums and whistles.

[mike_nofx]

Why would you want to ever do 75km/h in 4hi?

One time i was on a track near my place which crosses a tar road (only have to travel 5-6m on tar, when i hit the tar i still had it in 4hi, and on a slight turn of the wheel i could feel major wind-up, it just didnt want to turn! Cant see why anyone would even think 75 on a tar road in 4hi is a good idea!!

Mike

[mellows40]

Thanks for the replies, it has helped put my mind at rest... 75kph that was without the hubs locked in I was told that this was ok to help lube everything up in the front diff... from now on.... I`ll lock the hubs to lube up the diff... but not lock in 4wd hi on tar... ever again..

Cheers to all

[simkell]

the noise could also be the the side gears in the diff center spinning at a rapid rate, as the load across the axles aren't equal. In otherwords there is constant differential action taking place.