Tire wear on 4x4

[jan_rrc39v8]

My RRC has a ZF automatic and is supposed to be fulltime AWD.
I think it has a visco coupling between front and rear axel
So here is my question: how far off are front tires allowed to be compared to those in the rear?
My front tires have 2 - 3mm thread depth
My rear tires have 7-8mmthread depth
They will not have the same circumference ergo the front axel will turn more revolutions then the rear axel.
Can this difference cause damage to driveline components? If yes what part is the most likely to fail?

[kiwicar]

Hi
provided the center diff hasn't ceased solid (which they can do) then there is nothing to worry about, it represents 1 turn difference is 131 between the two ends, the center diff can handle that easily!
best regards
Mike

[softdash3.9]

Range Rovers with viscous couplings are recommended to have even tyre wear.

I have in the past when running tyres off have measures tread depth and matched them into sets so that the viscous coupling is not being constantly used (in a straight line) as you will have now.

As a short term "fix" you could swap on wheel front to rear and the one off the rear to the front so the rotational speed is sorted by the open front/rear diffs providing an even "load" across the coupling, if you are worried.

Is your coupling OK? have you checked it, worth checking periodically.

If you have a tyre chirping or spinning out on loose surfaces (gravel) your coupling maybe seized, another sign is unusual tyre wear.

The viscous couplings eventually sieze up and will require replacement, I believe the viscous fluid "wears" eventually from the shear during differing speeds, minimising the shear should lengthen coupling life.

[jan_rrc39v8]

Is your coupling OK? have you checked it, worth checking periodically.

If you have a tyre chirping or spinning out on loose surfaces (gravel) your coupling maybe seized, another sign is unusual tyre wear.

tire/tyre wear is normal and i don't recognise any chirping or spinning problems you describe. i suppose that's a good sign?

my worry is when the engine is running high-ish revs (over 4000rpm, f.i. during kickdown acceleration) the driveline is rumbling/vibrating a bit. As soon as i let off and allow the transmission to shift to top gear the vibration is gone. the only cause i can think of is this front/rear uneven tirewear...
steady cruising at 70/75mph is no problem.

i know that Volvo 850/V70 AWD cars are real sensitive about front/rear tirewear and these also use a visco driveline...

i will have new tires installed anyway. They will pass tech inspection but i don't want use them next winter.

[softdash3.9]

Check the propshafts for wear, I have had the rubber donut fail on the rear.(the bolt heads can touch, talking from personal experience)

I have also had the pinion nut work loose on the rear diff (that makes a rumbly racket and was an intermittent vibration that comes and goes at different speeds, to find it just lift the rear pinion/propshaft vertically, I got a real shock!!!!!

Hope the info helps

[jan_rrc39v8]

will check a.s.a.p.!
Thanks for the input!