deangermouse · Mar 14, 2017

Just a thought but instead of removing the vcu and prop shafts when the vcu fails, can you not just drill a hole in the case and drain out the liquid? At least it would look OK even if it wouldn't drive the back wheels. Like I said "just a thought "

GrumpyGel · Mar 14, 2017

If you want to lay your car up for 2 weeks while it drains - or splatter silicon fluid all around your neighbourhood to speed things up. Then it won't all drain. But it would free it up probably, but then there's not enough fluid in there, the thing would probably overheat.

Easiest and more reliable to remove props or remove the pinion gear in the IRD.

deangermouse · Mar 14, 2017

Like I said "just a thought " just not a good one lol

Hippo · Mar 15, 2017

If the fluid comes out having drilled a hole in it then the vcu will stop working. Hence no resistance across it, and therefore no drive. It's ok to do if you really want to and the easy option for some. But not good for the environment by leaking fluid on the road. Personally I'd remove the props/vcu instead.

andyfreelandy · Mar 15, 2017

Having flushed one clean inside I can say that the plates all rub together when empty, only thing keeping them apart is the silicon. The plates would wear, heat up, distort and potentially lock up the VCU entirely.

rob_bell · Mar 15, 2017

Without any fluid, I wonder whether the driven discs inside the VCU would rattle against each other to make an all mighty racket???

Nodge68 · Mar 15, 2017

rob_bell said:
Without any fluid, I wonder whether the driven discs inside the VCU would rattle against each other to make an all mighty racket???

In normal driving. The plates on the front and rear turn almost the same speed. So I doubt the plates will rattle or generate any heat from friction.

GrumpyGel · Mar 15, 2017

Nodge68 said:
In normal driving. The plates on the front and rear turn almost the same speed. So I doubt the plates will rattle or generate any heat from friction.

(big) Possibly.... but only in a straight line on the flat. No going round corners or up hills. Definitely no twisty hilly roads.

Nodge68 · Mar 15, 2017

The rear will over drive the front by a small amount (0.8% iirc) with 4 new tyres, driving in a straight line. As the front tyres wear, the difference between front and rear reduces.
As the vehicle negotiates a gentle corner, the rotational difference reduces.
This rotational difference continues to reduce as the corner sharpens. At some point the front and rear will rotate at the same speed. Tuning sharper still will start the front shaft spinning faster than the rear. So there's a rotation speed reversal, once the equilibrium is exceeded.
The greatest difference in speed is when reversing at full lock, VCU issues show up first. Hills are irrelevant unless the front wheels are spinning on a low friction surface.
At no point in the operating cycle would the VCU spin fast enough to cause friction damage. Unless spinning the front wheels. I can't imagine the plates are loose enough to rattle either. But that would need to be tried.

GrumpyGel · Mar 15, 2017

I say that cos dfossil put counters on his props and found they spun at different rates going up a hill.

Taking Hippo's calculations...

Hippo said:
edit: just seen the /h - sorry

At 60mph the rear wheels are turning at 96.56km
That's 96,560 meters per hour
Divide by the typical circumference of a tyre at approx 2.15meter = 44,912 approx
44,912 is the revs of the rear drive shaft per hour at 60mph (assume driving in a straight line)
44,912 x rear diff ratio of (45 / 14) = 144,360
144,360 is the revs of the rear prop per hour at 60mph
Divide by 60 give revs per minute = 2406
Divide again by 60 gives revs per second = 40.1

The props are turning at 2,400 RPM. If there is a 0.8% difference, they are slipping at 20 RPM. I'd have thought that's more than enough to create noise, heat and damage.

In reality I don't think they slip that much, dfossil found it negligible, but if it is negligible in a straight line, then that increases it when turning.

So what ever happens, I can't see "nothing" happening, surely there would be trouble.

Nodge68 · Mar 15, 2017

GrumpyGel said:
I say that cos dfossil put counters on his props and found they spun at different rates going up a hill.

Taking Hippo's calculations...

The props are turning at 2,400 RPM. If there is a 0.8% difference, they are slipping at 20 RPM. I'd have thought that's more than enough to create noise, heat and damage.

In reality I don't think they slip that much, dfossil found it negligible, but if it is negligible in a straight line, then that increases it when turning.

So what ever happens, I can't see "nothing" happening, surely there would be trouble.

I suspect something detrimental would happen if used without fluid for any length of time. I wouldn't want to try it myself. I think in the sort term, it would get the owner out of a tight spot. Removing the props would be a far safer way to protect the the IRD.

dfossil · Mar 16, 2017

I only measured a very small prop speed difference in normal hills and bends - like one or two rpm - see pics - but if leaving the drained prop on why not flush and refill with oil?

Rose TD4 · Mar 16, 2017

dfossil said:
I only measured a very small prop speed difference in normal hills and bends - like one or two rpm - see pics - but if leaving the drained prop on why not flush and refill with oil?

Just as a matter of interest, when I brought my FL to Spain, I had removed the drive shaft. When I went to the IVA (MOT) they would not pass it, as it was not to Manu. Spec. I ordered a s/hand shaft from UK and job done no problem, very strict. Malcolm.

GrumpyGel · Mar 16, 2017

Rose TD4 said:
Just as a matter of interest, when I brought my FL to Spain, I had removed the drive shaft. When I went to the IVA (MOT) they would not pass it, as it was not to Manu. Spec. I ordered a s/hand shaft from UK and job done no problem, very strict. Malcolm.

Its the same here, a change as substantial as removing prop shafts and converting from 4WD to 2WD needs to be "certified". I removed the pinion gear from the IRD (which was like me in the tooth dept. - a bit 'gappy') and continued running with props.

Alibro · Mar 16, 2017

GrumpyGel said:
Its the same here, a change as substantial as removing prop shafts and converting from 4WD to 2WD needs to be "certified". I removed the pinion gear from the IRD (which was like me in the tooth dept. - a bit 'gappy') and continued running with props.

Last time I MOT'd my car the MOT guy asked me if it had the propshaft. I asked him why and he said it wouldn't be a problem if it didn't have the propshaft but the brake test was different.
Apparently when they test the brakes on a complete 4WD car the machine rotates the wheels in opposite directions to avoid problems with the 4WD system.

Nodge68 · Mar 17, 2017

Alibro said:
Last time I MOT'd my car the MOT guy asked me if it had the propshaft. I asked him why and he said it wouldn't be a problem if it didn't have the propshaft but the brake test was different.
Apparently when they test the brakes on a complete 4WD car the machine rotates the wheels in opposite directions to avoid problems with the 4WD system.

That would work with disc brakes, but not drums. Drums are handed and so only work at optimum performance when rotating in the correct direction. Unless they only measure one wheel at a time, letting the other side freewheel?

My MOT tester uses a Tapley Gauge if I present my FL1 with the props in place. Or just puts it on the normal rollers if they are removed.

Alibro · Mar 17, 2017

Nodge68 said:
That would work with disc brakes, but not drums. Drums are handed and so only work at optimum performance when rotating in the correct direction. Unless they only measure one wheel at a time, letting the other side freewheel?

My MOT tester uses a Tapley Gauge if I present my FL1 with the props in place. Or just puts it on the normal rollers if they are removed.

Well spotted Nodge, I think he said they test one wheel at a time.

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