Tailshaft - balance, vibration?

[uglyoldfatbastard]

Working on @PlenumBiscuit car today we got all the ECU & TCM sorted out to the correct year and calibrations although he did forget his second key so we could not program his keys
Engine runs great and no DTC's or misfires going up and down steep hill in 38C temperature and transmission show no pressure or heat problems and no DTC's either. In fact you could not fault it and we collected data and found nothing out of the ordinary which would be a good thing except for this slight shudder/vibration when car under load going uphill but it's not the engine or transmission it is more mechanical if that makes sense.
Now @PlenumBiscuit did notice when he was under the car that the rubber for the centre bearing was sagging a bit but it was still in one piece and it's possible/probable that it is the original tailshaft from the original LLT engine and 0BRA transmission that has done over 300k.
Somewhere in the back of my head I have this nagging thought that the transmissions and tailshafts were marked at the factory for assembly so they balanced correctly although this could all be a dream in my head.
I seem to remember a TSB to the dealers about vibration and turning the tailshaft 90 degrees to help stop the vibration.
Anyone confirm what the centre bearing rubber should look like with car parked or know more about the balance/vibration on these tailshaft as would be handy to know and might help him out as he lives in the hills and it is driving him mad.

 

[ephect]

Centre bearing should be centred with minimal sagging. How easy is it to move/shake the tailshaft up/down side to side?
It should move a bit but not half the radius

 

[uglyoldfatbastard]

Centre bearing should be centred with minimal sagging. How easy is it to move/shake the tailshaft up/down side to side?
It should move a bit but not half the radius

That is what I told him as well but it is to hot and no room to climb under the car for this old guy.
He should come online sometime today and fill in the blanks and but he did say it moved quite a bit.

 

[PlenumBiscuit]

Hiya @uglyoldfatbastard has rigged up this ECU and motor and trans so well has done enormous work and configured the car with its new lfx the way it should be.

Shocked that the car was able to run previously

Anyhow I've always noticed a light rumble sound by the drivers left foot when sitting on 1500 revs in low gears

I checked the centre bearing and although all the rubber is intact the tailshaft does rest in the bottom half of the bearing circle outer casing

As for the coupling at the front I tried to push that area up and down whilst laying under the car and in the small area I had found a slight bit of play pushing the coupling up and down...but only a millimeter. Maybe they wear inside the coupling bolts area

.....and that's wear the rumble/waddle is I'm hearing at 1500rpms

....and then the engine shudder up hills under load might be the same issue but just a more stressed enhanced version of it

But it's very random not always there under load as old mate learnt today

 

[Lex]

Hiya @uglyoldfatbastard has rigged up this ECU and motor and trans so well has done enormous work and configured the car with its new lfx the way it should be.

Shocked that the car was able to run previously

Anyhow I've always noticed a light rumble sound by the drivers left foot when sitting on 1500 revs in low gears

I checked the centre bearing and although all the rubber is intact the tailshaft does rest in the bottom half of the bearing circle outer casing

As for the coupling at the front I tried to push that area up and down whilst laying under the car and in the small area I had found a slight bit of play pushing the coupling up and down...but only a millimeter. Maybe they wear inside the coupling bolts area

.....and that's wear the rumble/waddle is I'm hearing at 1500rpms

....and then the engine shudder up hills under load might be the same issue but just a more stressed enhanced version of it

But it's very random not always there under load as old mate learnt today

Whats the engine mounts like?
Maybe all that rubber needs replacing?

When thet fitted the new engine, do you know if they fitted new engine mounts?

 

[losh1971]

Check your rear wheel bearings..

 

[uglyoldfatbastard]

Check your rear wheel bearings..

I thought wheel bearings but it's just different. It's like the older cars when a uni joint would go if you hold the revs steady and just drive no problems but let it kick back a gear and add some pressure and it rumbles but it's not there all the time like it would be with a older uni joint.
Easy enough to check the wheel bearings though but I still think tailshaft but I know it's not the engine or transmission as they never falter or fault at all.

 

[losh1971]

I've had wheel bearing problems and it was at 1500-1800 where it was noticeable.

 

[shane_3800]

I've had hundreds of cars with sagged centre bearing rubbers at my work over the years, it does not create vibration.
if there is vibration theres an issue elsewhere.
even the rubber couplings can have cracks and they still drive fine.

What tends to happen these days, is that people swap the centre bearing as it's worn out and the cheap Chinese crap that all auto parts stores fail.
But during the first rodeo someone puts a slight very hard to see dent into the shaft and it will vibrate until it's rebalanced.
Tail shafts and even hollow CV shafts have to be handled with high care to insure there is no dings that can put them out of balance.

Also lowered commodores from VT-VZ can bottom out the CV half shafts which can very rarely cause vibrations.
This is especially prevalent when you get dick heads that install camber bushes but don't understand how to adjust them correctly.

 

[uglyoldfatbastard]

I've had hundreds of cars with sagged centre bearing rubbers at my work over the years, it does not create vibration.
if there is vibration theres an issue elsewhere.
even the rubber couplings can have cracks and they still drive fine.

What tends to happen these days, is that people swap the centre bearing as it's worn out and the cheap Chinese crap that all auto parts stores fail.
But during the first rodeo someone puts a slight very hard to see dent into the shaft and it will vibrate until it's rebalanced.
Tail shafts and even hollow CV shafts have to be handled with high care to insure there is no dings that can put them out of balance.

Also lowered commodores from VT-VZ can bottom out the CV half shafts which can very rarely cause vibrations.
This is especially prevalent when you get dick heads that install camber bushes but don't understand how to adjust them correctly.

Ok so we know the sagging centre bearing is not the cause but what about the actual uni joints themselves?

So he needs to check wheel bearings, engine mounts and replacing the centre bearing is probably a good idea as well.

The car runs and drives really good it's a slight shudder/vibration only when under load uphill is when I felt it as nothing to hear just a sensation.

Very weird but hopefully something he can nail down.