Tailshaft flange swap advice VT VX 4 bolt to 3 bolt

[losh1971]

This part is concerning as the rubber shouldn't scrub out, it's there for dampening. It can come loose from the housing in spots but shouldn't spin to scrub.
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This ^^^^^^.

 

[krusing]

Just out of interest,

Is the LS1 worked/modified ?

What's the reason for the change in Diff ?

 

[Immortality]

@Immortality Your expertise is required please.
Lowering it changes the angle of the tailshaft.
I think the angle it's supposed to have, is something like 6 degrees?

On a IRS car the diff is solid mounted to the rear K frame which is rubber mounted. Yes the whole K frame can move but it won't change the diff angle the most minute angle. When lowering a IRS car you don't change the drive shaft angles.

Live axle cars are different as the drive shaft moves with the rear suspension and the pinion will rotate up ward under load due to suspension flex. In a ideal world the angle across the uni at the diff should be the same as the transmission and because the rear suspension flexes they allow more angle across the diff uni at rest to allow for that suspension flex. This is why people fit adjustable top arms on live axle car, to adjust the pinion angle. IIRC, for a live axle car with rubber suspension they allow 4-6° for suspension flex and then for more firm suspension they reduce that angle.

Non of this should have any bearing on the centre hanger mount however.

This part is concerning as the rubber shouldn't scrub out, it's there for dampening. It can come loose from the housing in spots but shouldn't spin to scrub.

Can you see where exactly the rubber has come from? Unless the angles are way out forcing it to rub on something.

Agreed. Something doesn't sound right there. Nothing should be touching the rubber hanger mount to be able to wear away at it.

 

[Lex]

On a IRS car the diff is solid mounted to the rear K frame which is rubber mounted. Yes the whole K frame can move but it won't change the diff angle the most minute angle. When lowering a IRS car you don't change the drive shaft angles.

Live axle cars are different as the drive shaft moves with the rear suspension and the pinion will rotate up ward under load due to suspension flex. In a ideal world the angle across the uni at the diff should be the same as the transmission and because the rear suspension flexes they allow more angle across the diff uni at rest to allow for that suspension flex. This is why people fit adjustable top arms on live axle car, to adjust the pinion angle. IIRC, for a live axle car with rubber suspension they allow 4-6° for suspension flex and then for more firm suspension they reduce that angle.

Non of this should have any bearing on the centre hanger mount however.



Agreed. Something doesn't sound right there. Nothing should be touching the rubber hanger mount to be able to wear away at it.

Thanks fot that!
Much appreciated!

 

[JSIN12]

UPDATE;

I'm about 99% sure I've found the problem and kinda embarrassed i didn't think or realize this stuff sooner..

The tailshaft angle was way off. As you can see in photo 1, the bottom half of the bearing rubber was being worn away coming into contact with the shaft dust cap due to the angle being too much. But this was only happening under load. It wasn't fouling anything when turning by hand under the car.

First of all, the gearbox mount is completely gone to the point it's touching the cross member. See photo 2 and 3. Pretty sure there's supposed to be a big gap there in photo 2, haha.
This was angling the tailshaft downward from the box, especially under load.

Secondly, when the tailshaft centre bearing blew the 1st time it also ruined the cup/bracket that holds it in place on the cross member, so i got a second hand bracket from the local wreckers. The V6 and V8 VN to VT all have same size cup holder bracket and cross member for centre bearing, despite the tailshaft being slightly thicker between the two, all the supports and brackets are all the same size. But that's where i also messed up. The bracket i got was from a V6, which is all well and good. But upon reading through the service manual, the V6, although being same size centre bearing, it has washer spacers between the cup and cross member it bolts to (I'm assuming to compensate for the thinner shaft) the V8s do not use these washer spacers. See photo 4 and 5 that show the spacers that are on the V6 but not supposed to be used with the V8. Having those spacers angles the centre up ever so slightly more in the centre for the V6 shaft. (The spacers are not in photo 1 as I've already removed them as soon as I realised)
So, gearbox mount dead, causing the shaft to angle down from box. And centre bracket spacers angling the V8 thickness shaft up further than supposed to be in centre. Having that much angle was causing the dust cap on the tailshaft to foul on the bearing rubber under even the slightest bit of load. It spun without fouling with no load applied when turning by hand underneath, but as soon as any load was going though the drive line there was enough movement to foul on the rubber.

So yeah. I'm pretty sure I've solved all my tailshaft issues.
Hopefully!

So, have ordered new;
Gearbox mount (Mackay A2564)
Engine mounts (Mackay A5302H)
Centre bearing (Mackay CB1026)
Tailshaft CV joint (CV855)

So, I've given up on the idea of swapping back to the VX style double donut coupling tailshaft as I'm pretty sure I've finally solved the repeated centre bearing failures.

Also, photo 6 and 7 is the car in question. Just because, why not? Been with me 14 years now this coming weekend on the 10th of May. Was my first ever car back in the day and still kicking it in the semi retired occasional cruiser life..