Ongoing investigation with VW UK - Droning when slowing down

[john87]

Hi Folks,

Just wanted your opinion on this matter.

My R32 sometimes makes a droning/grinding sound when slowing down, more often when I have 3/4 people in the car, and I have good reason to believe that the drivetrain (rear diff to be more specific) is at fault. VW UK currently have a case open regarding the matter, as the car has a VW used approved warranty.

Previous to contacting VW UK, I took the car to a local VW dealership, who after test-driving the car and witnessing the sound, came to the conclusion that slowing the car through the use of engine braking (going down the gears) is causing the fault, therefore I should not do it. Please tell me I'm not the only one who think this is an unaccetable response? 

Considering they didn't even touch the car, other than put it up on their ramp, I am very disappointed with their 'diagnosis' and the fact that they are blaming my driving style rather than beginning to even look for the source of the fault. Rant over..... for now 

John

[Viking]

Ask them to point out in the handbook where it says engine braking must be avoided at all costs or damage to the drivetrain will result. 

[john87]

Ask them to point out in the handbook where it says engine braking must be avoided at all costs or damage to the drivetrain will result. 

Good point  they also said that it is not advisable to 'skip' a gear when changing, i.e. 3rd to 5th, 4th to 2nd etc.. nonsense 

[Stevie35]

Typical VW technicians, I had same trouble with VW when I had trouble with the clutch the flywheel had gone and I knew it but they said it was release bearing so they changed it and the noise was still there, then when the noise was still there, VW master technician told me it was gearbox chatter which is common on R32s however I knew otherwise and when we drove a similar car there was none.

Unless you get a mechanic who has been working at VW for over 20years your not getting a mechanic ur just getting a spam who can fit certain parts to a car and tick boxes. Mechanical knowledge and technical know how is few and far between.

As for engine braking causing the problem to the car and stop doing it, I hope you have given this diagnosis to VW UK and told them how unhappy you are. I would have slapped the guy!

[john87]

Typical VW technicians, I had same trouble with VW when I had trouble with the clutch the flywheel had gone and I knew it but they said it was release bearing so they changed it and the noise was still there, then when the noise was still there, VW master technician told me it was gearbox chatter which is common on R32s however I knew otherwise and when we drove a similar car there was none.

Unless you get a mechanic who has been working at VW for over 20years your not getting a mechanic ur just getting a spam who can fit certain parts to a car and tick boxes. Mechanical knowledge and technical know how is few and far between.

As for engine braking causing the problem to the car and stop doing it, I hope you have given this diagnosis to VW UK and told them how unhappy you are. I would have slapped the guy!

Hear hear!

The lady at VW UK admitted she 'knew nothing about the technical side of cars' but for some reason agreed with the technicians' 'diagnosis' which enfuriated me even more! 

I've now had two identical diagnoses from independent garages, who say the prop shaft bearings sound like they are worn out. I've booked the car back into the dealer where I originaly bought the car and told them I am confident that this is the problem. Watch this space!

[south]

Good point  they also said that it is not advisable to 'skip' a gear when changing, i.e. 3rd to 5th, 4th to 2nd etc.. nonsense 

No [advanced] driving instructor would ever tell you that... you select the appropriate gear for the speed. You should have pointed out that, according to them doing the exact opposite (ie. engine breaking) was causing issues.

[OEM+ DUB]

I appreciate you have had a couple of independents diagnose the prop shaft bearings but I just wanted to ask if the oil level in the rear differential has been checked?

Having some practical experience of the (Gen1) Haldex system on the MkIV R32/V6 4motion, I'm aware that the oil level in the diff can be woefully low without any external signs of leakage.  Some put this down to not being correctly filled at the factory and others down to inexperienced technicians draining the diff rather than the Haldex coupling when servicing and then filling the diff with Haldex oil.

The diff on the MkIV takes 1 litre of transmission oil and the Haldex coupling takes a cartridge of specific oil with far less volume.  As both the oils are designed and engineered to have different viscosities and do completely different things, if incorrectly filled the diffs can prematurely wear and have even been known to catastrophically fail - imagine running a gearbox with little/no oil.  When worn they can transmit all kinds of strange drones on light throttle and overrun as well as feeling like they are sticking and or groaning if reversing on lock.

This may be unrelated to your particular issue but a check of the diff level is relatively easy (remove the filler in the side of the casing - NOT the drain in the bottom - the oil when full should be level with the filler hole when the car is on level ground).  If it needs topping up, I would suggest draining and refilling with fresh transmission oil as this will also allow you to check how much metallic swarf has been trapped on the magnetic drain plug (a light covering of metal 'hair' is normal and shows the plug is doing its job).

Hope this helps and that you get it sorted soon!

[simonp]

The rear diff is pretty much disconnected from the drivetrain when no throttle is being applied, so how can engine braking be bad for it? 

[OEM+ DUB]

The diff will turn even when no throttle is applied as it is mechanically linked to the rear wheels by the rear driveshafts...  You're right though that engine breaking will have no effect - this is a complete 'red herring'.

[john87]

Thanks for the replies - I had thought about the oil level in the rear diff, as when I bought the car I asked the dealer to perform the Haldex oil change (as it was overdue by 5k miles according to the schedule).

The car's booked back in later month (at the selling dealership) to investigate the noise further. I still hear a droning sound when travelling at 70mph+, however the droning sound when decelerating has been solved - one of the rear tyres had 2mm less tread than the other and for some reason the 4wd setup didn't like this!

[john87]

Had the car in at a local indy today to have the tracking done, and asked his opinion of the problem I'm having. The first thing he did once the wheels were off the ground was turn each of the rear wheels by hand, which resulted in a clicking/rubbing sound from the rear diff  to which he said 'That doesn't sound good' and having around 20 years experience tuning and rebuilding Impreza's, I didn't take his opinion with a pinch of salt!

I'm now beginning to wonder whether the dealers have f**ked up the Haldex oil service as previously mentioned...

[john87]

Update..

Dealer phoned yesterday to confirm that rear diff is 'at fault' and they are in the process of submitting a warranty claim to VW HQ since the car has extended cover.

The noise only occurs while slowing down, particularly in the lower gears where engine braking has more of an effect... when slowing down, the gear teeth within the diff are loaded on the opposite side as the diff is effectively acting to slow the car down.

The noise sounds just like in this link..

http://youtu.be/pJ80oQhNy9Q

  I know it's a bus, but all diffs must be pretty similar in design...

[flashp]

It'd be interesting to see if they're prepared to determine what oil is actually in your rear diff. Watching this with interest....

[OEM+ DUB]

Update..

Dealer phoned yesterday to confirm that rear diff is 'at fault' and they are in the process of submitting a warranty claim to VW HQ since the car has extended cover.

The noise only occurs while slowing down, particularly in the lower gears where engine braking has more of an effect... when slowing down, the gear teeth within the diff are loaded on the opposite side as the diff is effectively acting to slow the car down.

I'm sorry to hear my suggested diagnosis looks to be correct but really pleased that they are taking it seriously and pursuing a warranty repair for you.  Fingers crossed that you get it replaced FOC!

[john87]

The dealership called this morning to confirm that VW have approved the repair and are shipping out a new 'final drive unit' (reportedly worth £3500) and should be fitted tomorrow 

When I asked what had caused the failure, they said they weren't 100% sure and that VW had not asked them to strip the unit down to determine the cause. Happy anyway that it's getting sorted!