Tailshaft flange swap advice VT VX 4 bolt to 3 bolt

[JSIN12]

After some VT VX tailshaft advice.

I have a VX Sedan 6 speed manual with LS1
It has a series 1 VT style tail shaft (the 4 bolt flange with centre CV joint) the diff was originally a 3 bolt many years ago but was swapped many years ago and had the little nub on end of pinion cut off when flange/yoke was changed to 4 bolt style that's in it now.
I've read a lot that you can change diff from 3 bolt to 4 bolt, but not the other way around. This is purely because of the little nub for the spigot that you cut off the end of pinion when changing flanges.

Now i want to go back to VX VY style tail shaft with the rubber donut couplings as i keep shredding centre bearing with the VT style one. I just prefer the VX style. Much easier to change bearings, eliminates the centre CV joint that's a huge pain to pull apart, and I've always had much less issues with the 3 bolt style compared to the 4 bolt styles in all my VT VX over the years.

Now, obviously, i cut the extended end off the pinion on the diff to suit the 4 bolt many years ago when changing the flanges, but not sure if it's going to be a huge drama going back. I've heard many say you can't. But I'm after options and ideas to avoid changing diff or pulling it apart to change pinion out.

I've had two ideas, but not sure.
Idea number 1; use one of those billet alloy donut couplings at the diff in replace of the standard rubber type one. I figure that extra length on the pinion that goes into the spigot on tailshaft is there to help keep it centred. But if that coupling is solid it shouldn't really matter then, should it?
Anyone ever used those solid billet ones? How are they?

Other idea I've had is meticulously weld another little nub of steel onto the end of old pinion and shape it to slide comfortably into spigot.

These are just brainstorming ideas and just after someone who might have done anything like it before or has any other smart ideas to avoid having to change the diff or pull it apart to swap out pinion.

It's a very solid super tight 3.73 LSD with strengthened internals. Don't really wanna swap it or have to pull apart what isn't broke.

Any ideas or advice from anyone who's maybe done similar would be appreciated.

 

[krusing]

Well unfortunately it is broke, missing the original pinion spigot,
They are there for a reason to keep it centre
As you said, you don’t want to pull it apart,
But the only way I can see the tail shaft to run true, is to get a spigot welded back on, then re-assemble the diff.

If you try and do it any other way, you can possibly cause a lot of vibration in the tail shaft, because it’s not running/spinning true/dead centre,
Before you start, first I’d find a person with a lathe, with good welding skills,

Do it once, do it properly,

(Where is an action, there is always a recaction)

 

[Immortality]

Without pulling it apart the only option is possibly the alloy coupling.

Welding? Not sure if it's a good idea but it would have to be pulled apart and welded and then machined true otherwise you are just creating more problems.

Strange that the centre support bearing is failing constantly. Maybe a sign of bad mounts? Have you tried different suppliers for those centre mounts? I've heard a few stories of new ones failing quickly so I'm not sure if it's a problem you have or just cheap chinese **** rubber?

 

[JSIN12]

Without pulling it apart the only option is possibly the alloy coupling.

Welding? Not sure if it's a good idea but it would have to be pulled apart and welded and then machined true otherwise you are just creating more problems.

Strange that the centre support bearing is failing constantly. Maybe a sign of bad mounts? Have you tried different suppliers for those centre mounts? I've heard a few stories of new ones failing quickly so I'm not sure if it's a problem you have or just cheap chinese **** rubber?

There is still a bit of the spigot nub there hanging out. Just not enough to fully seat into a 3 bolt shaft.
I've used both kelpro and mackay bearings.
My first bearing failed very suddenly and violently, It was a few years old. My new one is less than several hundred km old again and it's already scrubbed out a layer of rubber from the bottom half of the bearing. Like there's rubber flakes everywhere all over it and clear to see where it's being eaten away. I thought maybe i didn't put the washers/spacers back in the correct places effecting the angle, or maybe my trans mount is sagging a bit. It's hard to tell not being able to see it in motion at higher speeds.
I'll have to have another close inspection on all that next time i go see the car (it's semi retired and stored at someone else's house in another suburb when not in use)

I've never had any problems in my other VX s that have the 3 bolt style shafts. The CV and double uni joints on the 4 bolt have always been so much of a headache and pain the whole time I've had it.

Well unfortunately it is broke, missing the original pinion spigot,
They are there for a reason to keep it centre
As you said, you don’t want to pull it apart,
But the only way I can see the tail shaft to run true, is to get a spigot welded back on, then re-assemble the diff.

If you try and do it any other way, you can possibly cause a lot of vibration in the tail shaft, because it’s not running/spinning true/dead centre,
Before you start, first I’d find a person with a lathe, with good welding skills,

Do it once, do it properly,

(Where is an action, there is always a recaction)

The 4 bolt VT style is just metal on metal with no spigot to keep anything centre. That's why i don't quite understand how it's going to have too much of a negative impact without it. Especially if instead of using the rubber donut coupling i use one of the allo billet ones, so then it would basically be like metal on metal.. i might be missing something, i don't know.
I'm just brainstorming ideas.

 

[losh1971]

I have heard the alloy couplings can cause unwanted vibrations. Something to consider when you fit something with less dampening.

Those aftermarket centre bearings you have used are not great. Try and find one which is a lot stiffer in the rubber, gen are very good but they might be NLA?

 

[Immortality]

The 4 bolt flange on the older models still has a shoulder that locates and centres the drive shaft on the pinion flange.

I've had Commodores with both styles of driveshaft and can't say the other style failed more. The older design was needed as the drive shaft moved in a range of motor with the articulation of the rear suspension. When they went to the IRS suspension the diff no longer moves so the drive shaft doesn't need to flex at the diff end and hence the reason they can use the rubber coupling instead of the older style uni joint.

The 2 drive shafts have to be set up differently however. On the IRS models with rubber couplings the drive shafts need to be inline with the transmission and diff where as the older type driveshaft with uni joints the drive shaft actually needs to be offset in the centre to create a small angle across the uni between the drive shaft and the gearbox as well as the driveshaft and diff to ensure a good working life for the uni joints.

I really can't say why the centre support is failing.

 

[Lex]

I'm wondering if the car is lowered?

 

[losh1971]

I'm wondering if the car is lowered?

Isn't that normally only a problem for cars with live axle? I wouldn't have thought the diff would rotate on an IRS vehicle?

 

[Lex]

Isn't that normally only a problem for cars with live axle? I wouldn't have thought the diff would rotate on an IRS vehicle?

@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?

 

[ephect]

My first bearing failed very suddenly and violently, It was a few years old. My new one is less than several hundred km old again and it's already scrubbed out a layer of rubber from the bottom half of the bearing. Like there's rubber flakes everywhere all over it and clear to see where it's being eaten away. I

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.