Low speed prop shaft vibration

Legin · Nov 25, 2018

I have seen this before with Audi , VW and BMW 4wd. To cut a long story very short it was the oil in the DSG in some cases and the transfer box , centre diff oil in other cases.
This took me a VERY long time and a lot of pain to figure out (Audi and BMW were clueless ) especially a problem when turning a corner combined with a plate lsd.
Its the friction modifiers degrading in the oil in the case of transfer boxes - fix is to change the oil worked in both my Q5 and my X3. Basically its clutch judder.
With DSG gearbox its more difficult. There was (is ) an issue with synthetic oil in the transverse DSG box,s causing plates to judder when the oil gets hot my passat awd did this.
The transverse DSG uses same oil for clutch packs and gears so its compromised either way. In the upmarket Audi and Porsche inline DSG the transaxle actually has two seperate lubricants one fo the gears and one for the clutch packs.
Haldex units run seperate oil also.
I changed the DSG (passat) oil but it only helped didnt fully fix because it was synthetic oil. However it s a well known issue with DSG (wet clutch version) in hot countries and the VW fix is to put in a mineral oil however VW to my knowledge never did this in UK. Guru ?

It seems all those reporting the issue are auto , if thats the case then it rules out the 4wd and diffs. On the cali my money is on the DSG oil affecting the clutch packs. Mostly though its the diffs and transfer box,s

Suggest changing all the transmission and diff lubes then take it rom there. This was a 100% fix on the Audi and BMW

Legin · Nov 25, 2018

Oh the balance is unlikely as the speed is too low plus it goes away as you go faster which means its not a 1x rev vibration.

flying banana · Nov 25, 2018

parrot2 said:
Hi a shot in the dark but no one has mentioned the drive shaft itself Old prop shafts had to be balanced or they vibrated. ?Could this produce this vibration.

True there mister parrot. Props usually have balance weights fitted. A missing one would stand out if you can get under and have a look? Might be worth having the prop off at a specialist for balance checking and peace of mind

VW Guru · Nov 25, 2018

H

Legin said:
I have seen this before with Audi , VW and BMW 4wd. To cut a long story very short it was the oil in the DSG in some cases and the transfer box , centre diff oil in other cases.
This took me a VERY long time and a lot of pain to figure out (Audi and BMW were clueless ) especially a problem when turning a corner combined with a plate lsd.
Its the friction modifiers degrading in the oil in the case of transfer boxes - fix is to change the oil worked in both my Q5 and my X3. Basically its clutch judder.
With DSG gearbox its more difficult. There was (is ) an issue with synthetic oil in the transverse DSG box,s causing plates to judder when the oil gets hot my passat awd did this.
The transverse DSG uses same oil for clutch packs and gears so its compromised either way. In the upmarket Audi and Porsche inline DSG the transaxle actually has two seperate lubricants one fo the gears and one for the clutch packs.
Haldex units run seperate oil also.
I changed the DSG (passat) oil but it only helped didnt fully fix because it was synthetic oil. However it s a well known issue with DSG (wet clutch version) in hot countries and the VW fix is to put in a mineral oil however VW to my knowledge never did this in UK. Guru ?

It seems all those reporting the issue are auto , if thats the case then it rules out the 4wd and diffs. On the cali my money is on the DSG oil affecting the clutch packs. Mostly though its the diffs and transfer box,s

Suggest changing all the transmission and diff lubes then take it rom there. This was a 100% fix on the Audi and BMW

Hi @Legin yes your correct there was never a change to mineral oil in the uk.

B J G · Nov 26, 2018

Legin said:
Oh the balance is unlikely as the speed is too low plus it goes away as you go faster which means its not a 1x rev vibration.

My past experience of prop balance issues was that it just changes with speed and can be felt as a vibration through the floor. Was worse off load as no torque to dampen it. Just my past experience to confuse.

Legin · Nov 26, 2018

B J G said:
My past experience of prop balance issues was that it just changes with speed and can be felt as a vibration through the floor. Was worse off load as no torque to dampen it. Just my past experience to confuse.

An out of balance is always there and 1 x each revolution and increases with speed. This can be easily measured with a spectral analyser (by a professional) if people really want to see whats going on.

What confuses things is that the out of balance frequency changes with speed and at certain points this frequency coincides with the natural frequency of the system and thus creates a resonance.

The parameters that influence system resonance are stiffness and mass. So your torque experience would happen because the mass changes as the gears join the party under torque and hence the mass increases.

Its why an out of balance wheel tends to only create a wobble at certain speeds even though the out of balance is always there.

In industry we frequently stiffen a system or increase it mass to move harmonics apart from natural frequency but its easier because most times the equipt only runs at one speed.

Another fix is to add a harmonic damper that is tuned to cancel out the resonance (anti phase), you sometimes see these on vehicles a steel weight mounted on a rubber - dual mass and crank dampers are an example.

So most times you feel the resonance not the out of balance that excites it.

The first post in this thread is an oil issue imo. The 50+ mph ones quite possibly a different problem. I think there are folk with different issues in this thread but only my opinion.