MYSTERY ISSUE. Doing my head in. Please Help!

[Evo]

Ok,

Driving me absolutely mental, to the point where I'm ready to sell it (MOF has said I'm not allowed to sell this one) but I don't want to be spending money replacing things one by one until this issue is sorted. Haven't been able to sleep, just keep trying to think what it could be and pinpoint where this issue is.

It is a 98 GU 4.5 Petrol, manual.

Nothing has been changed prior to this starting.

So it started almost 2 weeks ago, and has only gotten slightly worse.
When driving, Troll is fine until over 50kph. If feathering the throttle, very lightly on and off, there's a grinding noise/slight vibration (best description would be more of a growling) that can be heard/felt through the vehicle. Under acceleration I can't detect it, and off throttle (engine braking) I can't detect it either.
Also, once over 60kph or so, if the clutch pedal is held in, or if gear lever is put in neutral with clutch pedal out, noise is constant.
It is more prominent at higher speeds.
I can't pinpoint the origin, other than I am pretty sure it is in driveline.

Have been to 3 different places, all have test driven and inspected. Here's their provided info.

1. One says that the front shaft can't cope with lift, needs a second uni joint on one end (double cardan???)

2. One said clutch bearing on its way (they also said uni joints and all wheel bearings are fine)

3. One said rear diff needs rebuild

Don't know which one, if any, to go with.

I have a bit of mechanical knowledge, don't know all, nor have very in depth knowledge, but have thought about a few things. Pretty straight forward I think (in my mind it all makes sense).

Please correct me if I'm wrong anywhere.

With 1. Troll has been driving fine with lift, etc, nothing had changed just before the noise started, plus transfer in 2H with hubs on Auto, would mean front shaft isn't moving.

With 2. 'growl' is worse at higher speed, where as the clutch bearing would only turn as fast as motor rpm (which is lower in a higher gear at speed) plus the 'growl' doesn't change with engine speed.

With 3. I am leaning more to this as the explanation for this 'growl', mainly due to the speed factor, being that rear tailshaft, rear diff, rear wheels (bearings) are all increasing rpm with more speed.

The thoughts I have on 3. also made me wonder if it might be front wheels (bearings) as these also increase rpm with speed increase.
HOWEVER
With front wheel bearings, would the feathering of the throttle on and off (on and off load) cause front wheel bearing issues to become apparent as there is no drive on these wheels?

Any info, suggestions, help in general would be appreciated, preferably before I go looking for a box of matches.

If I have missed anything, or any additional info is needed, please tell me, and I'll do my best.

Thanks in advance.

Cheers,

Evo

[BigRAWesty]

Are all your fluids up??
Diffs, transfer and gear box? And driveline greased??

[threedogs]

Where is the vibration? through the steering wheel or through the pedals

[kevin07]

if its in the tail shaft you should be able to feel it chock the wheels get under there in neutral and have a good push pull session any movement up and down and sideways and that should answer all.

[threedogs]

Not the tensioner pulley bearing ??

[nissannewby]

By what you describe it sounds like the rear tail shaft uni's could be on their way out. I would take it out and inspect that way, it may feel fine in place but once removed you can move it around etc and might find it's seized or knotchy. It's an easy place to start.

Also check to see if there is excessive movement in your slip joint.

[Robo]

So the noise is when vehicle is coasting along right! (engine neither loaded or unloaded).

You mention at 60 kph driving, clutch pedal in or out problem arises, so I'm leaning towards.
manual gear box input bearing, it's another that can make this noise.

tail shafts unbolt fairly easy and in ya hand the uni's can be felt for movement easily.
just mark their alignment and put em back on in the same position they were removed,
otherwise you can get a vibration if shafts are out of alignment.

belts easy to remove from engine and check for noisey bearings.
tensioner, alternator, power steer.


My son's mav had badly worn oil pump chain and gear which made this sorta noise you describe.
this noise transferred through the cooling system also and radiated in the cab through the interior heater core, which at first had me wondering where the devil it was coming from. but it was very loud. so sounds like your's is else where.

[Evo]

Ok, before I answer your posts, there has been some kind of development.

Now it can be heard/felt on acceleration from 30ish up.
Went to a diff specialist today, they dropped tailshaft and said diff is fine, tailshaft is fine, uni joints are fine, said it might be wheel bearings, but sent me down the road to another place.
Transmission specialist. Thought possible engine mount, or a mount, then after drive said its not a mount. Said it appears to be on the output side of transmission, so could be gears or bearing...
So 2 more different answers.

Westy's
All fluids have been drained to check for contamination/particles, all fine, all filled and levels checked again also.

theedogs
Can be felt through steering, pedals, seat (not sure if seat is more in my head) and floor.

Kevin07, nissannewby, Robo
Tailshaft has been removed, slip joint, uni joints, balance, all checked and came up good.

threedogs, Robo
Motor has had a lot of preventative maintenance. All belts were removed, pulleys checked, oil pump is fine, but motor revs/engine speed don't change the frequency or make it worse. So I would say motor is eliminated?

Only gets worse as road speed increases...

Still not really any closer...

Evo

[threedogs]

So you cant replicate it standing still??
brake pads worn right down ??

[Evo]

I will also add, due to my back issues, I'm relying on these 'professionals' as I am unable to check or do things myself.

Evo