Good technical Question

[jebiga41]

When my rear diff lock didn't work last year, got stuck in a drift one rear wheel just span and nothing transmitted to the front (that i noticed) with a new vc which had been warmed up. Still maintain that if the lock had worked would have got out of there without a tow

[beelzibus]

If you gun mine pretty hard off the line on loose, the back wheels will spin pretty easily, but then the fronts seem to pull. I think I'll get it in the brake rollers next time I have it at work, bit more scientific I guess.

[syncropaddy]

If you gun mine pretty hard off the line on loose, the back wheels will spin pretty easily, but then the fronts seem to pull. I think I'll get it in the brake rollers next time I have it at work, bit more scientific I guess.

Perfectly normal ..... If you have a de coupler and a solid shaft instead of a VC then that wont happen

[lloydy]

I've now got a new one in a box.
Got both rear wheels spinning on ice and still no pull from the front. Jeds on the same patch spun both front and back

[beelzibus]

If you gun mine pretty hard off the line on loose, the back wheels will spin pretty easily, but then the fronts seem to pull. I think I'll get it in the brake rollers next time I have it at work, bit more scientific I guess.

Perfectly normal ..... If you have a de coupler and a solid shaft instead of a VC then that wont happen

Yes, I'm hoping it's a positive sign that the VC is in good nick. What is the expected lifespan of these things? Assuming of course they've not been abused, and what constitutes abuse?

[peasant]

if vehicle is stationary and you only raise one rear wheel it will spin out and because the vehicle isn't moving there is no relative difference between axles thus no action by the front as the vc isn't dumping any power the spinning wheel is dumping it all, these are rwd vehicles with a vc that only transmits power when there is a relative speed difference between axles...

Just a quick question on this.

The VC sits at the front differential. It gets the power transmitted from the rear gearbox via the propshaft. Up to now I was always under the impression that the propshaft transmits power to the front at all times the gearbox is outputting any ...ie. even with one or two spinning rear wheels the propshaft is still under power.

Are you trying to tell me that there is another differential between gearbox and prop ? Or do the prop and rear axle all work off the same (three-way) differential ?

Because the outputs for the rear drive shafts and the prop are quite a bit away from each other, (see below),

I always assumed that the prop was sort of "direct drive" straight from the gearbox

Serious question, as I really don't know.

[silverbullet]

I always assumed that the prop was sort of "direct drive" straight from the gearbox

It is direct drive. Because all VW transaxles have 1st and 2nd sychro hubs on the lower shaft and 3rd/4th on the upper shaft, the drive for the prop comes out on the lower shaft axis which is that of the differential. It's not like a "traditional" rwd gearbox, with all the synchro hubs on the mainshaft, where the drive to the prop and diff is all on a common axis with the engine crankshaft.

[peasant]

It is direct drive.

So if you have a Syncro just sitting there with one or two rear wheels spinning, your VC is definitely fubar'd

Because the gearbox has 1st and 2nd sychro hubs on the lower shaft and 3rd/4th on the upper shaft, the drive for the prop comes out on the lower shaft axis which is that of the differential. It's not like a "traditional" rwd gearbox, with all the synchro hubs on the mainshaft, where the drive to the prop and diff is all on a common axis with the engine crankshaft.

That explanation really calls for a drawing


all crystal clear now, thanks

[lloydy]

So if you have a Syncro just sitting there with one or two rear wheels spinning, your VC is definitely fubar'd

Mine was, failed under load. Front wheel was stiff to turn as if the VC was working, But as soon as you got the rear wheels spinning [one or two] no power sent to the front wheels

[ghost123uk]

Sorry if seems like a dumb question, but what does VC stand for ?

[lloydy]

Viscous Coupling

[ghost123uk]

Thanks

[syncropaddy]

What is the expected lifespan of these things? Assuming of course they've not been abused, and what constitutes abuse?

How long is a piece of string? I think 100,000 miles is an acceptable figure but mine has lasted almost twice that at 300,000 KMS and is still going strong. Im told that the VC in my white van with 250,000 miles up still works but I aint tested it yet.

[syncropaddy]

This is porn ....

[silverbullet]

Or to put it another way:

syncro gearbox cross-section.jpg

This is porn ....

If you've got 3k burning a hole in your pocket...busschmiede.de for a brand new syncro gearbox - outright!