Axle wind up?

[stevealex]

Thought I would post my possible experiences of this phenomenon. I have been running uneven tyre tread depths since I got my doka on the road last september, was pobably 6-7mm difference between the fronts and backs.

For the last few weeks before I changed to new tyres, the pickup had started to develop the typical syncro vibration between 30-50 mph which I thought would be due to worn engine or gearbox mounts. The front wheels were also starting to get very tight on full lock.

With new matching tyres all round the vibration has gone, so I can only presume this was related to axle wind up in some form. On full lock, it now only very slightly scrubs the front wheels . Also I don't know if this is just due to different tyres, but on the old set the pickup had pretty bad understeer, with the new tyres this is a million times better.

I have waited a couple of weeks to post this to see how the vc would do now. All appears ok, it engages well off road but is not too tight as it passes Aiden's test in g on full lock.

It just goes to show the importance of sticking to the 2mm difference rule on tread depths.

Does anyone else have any ideas what could have caused the vibration?

[max and caddy]

prop u/js are good ? or maybe wheel balance?

[stevealex]

Propshaft is fine no play, the wheels were recently balenced and no weights had shifted or come off.

[syncropaddy]

the typical syncro vibration between 30-50 mph

What is this you speak of? Owned a Syncro for 7 years and never came across it.

The front wheels were also starting to get very tight on full lock.

Nothing unusual about that at all. It just shows that the VC is on the tight side of things which does not mean it worn. My first Syncro did that all the time

With new matching tyres all round the vibration has gone, so I can only presume this was related to axle wind up in some form. On full lock, it now only very slightly scrubs the front wheels .

That, to me, says that the tyres/wheels were the cause of the vibration

It just goes to show the importance of sticking to the 2mm difference rule on tread depths.

Does anyone else have any ideas what could have caused the vibration?

The "2mm rule" seems to be a rule only in Scandinavia. It says nothing about 2mm in either of the owners manuals I have. Other causes for vibration could be a sticking caliper

[HarryMann]

The "2mm rule" seems to be a rule only in Scandinavia.

Andrew we have discssued this before, fairly recently?

I mentioned it and it took ages to find the origin, cab signs etc but it is definitely in VW VC 4WD research papers and applies universally IMHO

That common syncro vibration is not uncommon, you seriously must get out in a few old Syncro wrecks more often

[lhd]

The paper work that came with my VC fom Tristar connections states the 2mm rule for the warantee.
The original prop I had caused the same vibration at them speeds, I bought a new one from Syncro services and the vibe has gone, although the old UJ's had no play they didn't move smoothly so could be due to the joints losing lubrication/drying up over time?
Rob.

[stevealex]

What was interesting to me was that the vibration disappeared instantly with the new tyres, nothing else was changed or worked on. I do think the 2mm rule smacks of avoiding warranty claims; but there is definitely something in this, I know there is also a percentage figure knocking about.

The old set of tyres were in decent condition, reasonable quality and similar in tread pattern. The only issue was 6-8mm difference in tread depth.I cannot think of anything else that could have been causing the transmission vibration. Unless you believe in miracles like taking wheels on and off fixing things (each wheel even went back on the same hub)

Steve

[stevealex]

Harrymann, Fancy saying my pride and joy is an old wreck

Steve

[silverbullet]

Wrecks or not - Andrew only drives the best - my gut feeling would be that 6-7mm of wear differential across the axles is not insignificant.
Nominal tyre dia is ~650mm (allowing for different tread patterns etc.) so would 6.5mm or 1% cause enough rotational speed differential to push the VC into the start of hump mode?
A torsionally loaded prop with worn U/Js might well start to drub, I tend to find that my early petrol one only really rattles if the engine is "out of the green" but that could well be transmitted from the engine and maybe made worse through drivetrain backlash i.e I'm finding all the harmonics.

[max and caddy]

both my td syncros have had the props fitted the wrong way round when i bought them...that most likely doesnt help either.. worth checking yours.

rubber at front on a diesel, back on a petrol is correct.

[HarryMann]

Yes, that's it M+C and I bet VW discovered that one by trial and error

I do think the 2mm rule smacks of avoiding warranty claims; but there is definitely something in this, I know there is also a percentage figure knocking about.

Definitely !

[syncropaddy]

The "2mm rule" seems to be a rule only in Scandinavia.

Andrew we have discssued this before, fairly recently?

I mentioned it and it took ages to find the origin, cab signs etc but it is definitely in VW VC 4WD research papers and applies universally IMHO

- my gut feeling would be that 6-7mm of wear differential across the axles is not insignificant.
Nominal tyre dia is ~650mm (allowing for different tread patterns etc.) so would 6.5mm or 1% cause enough rotational speed differential to push the VC into the start of hump mode?

I think this discussion fizzled out but it is also said that there is a 2% designed slip factor in a VC so if Ian's calculations are correct a 6.5mm (1%) will make no difference.

I still stand by my opinion that the 2mm thing is utter nonsense.

[stevealex]

Proof of the pudding is in the driving. The van went from very uncomfortable to drive to no problems, in the change of a tyre.

I think what this may highlight is the real world, the vc may well of all ready given it's best and the drive train may have a little wear and tear; at 24 years old this is probably likely.

I think the 2mm rule is overkill but in light of this I would see it as best practice.

I haven't checked the position of the prop doughnut, but will do tomorrow. My gut feeling is that although there is nothing major wrong, there is something awry in the drivetrain, which the tyre difference was highlighting

Steve

[HarryMann]

With a big difference there will be a prop torque loading that must to some extent lead to the trans mounts winding up, changing relative alignments if nothing else.

The fact to be remembered is that when off-roading with large loads going through the prop and trans mountings, we ar going relatively slowly and in a low gear. For significant AWD loads to build up when cruising on tarmac at raod speeds, is an entirely different thing, and we know that the critical speeds for prop vibes is ~35~45 mph depending on wheels and gearing.

*The ringing prop vibe at low speeds is something like 1400 Hz IMO

[HarryMann]

Andrew, I will look for that discussion because I think we did come to some conclusions on this. I've driven at a lot more tread differnce for some time, but 'within 2mm of any other tyre' is not a ridiculously narrow spec. (for a road vehicle) ?

What we are saying and theyw ere too, is recommended, optimum, etc. No-one would recommend or go for optimums lower spec than necessary, unless it prevented the vehicle becoming well adopted or indeed a practial on-road proposition.