Technical What's that new droning noise?

[Zardo]

Hi,

I accelerated hard (probably was in fourth gear) and suddenly a droning noise appeared out of nowhere and just stays.

The noise has a dominant frequency which:

- seems to be faster than wheel RPM
- is independent of the selected gear
- is independent of the clutch pedal depressed or not
- is indepemdent of engine RPM
- increases linearily with speed
- get's louder with speed
- doesn't change in frequency nor volume when cornering
- does not generate vibrations on the steering wheel
- appeared with about 249000 km on the clock (approx. 155 k miles)
- impossible to localize the origin, the noise seems to come from everywhere

ChatGPT thinks it's the pinion gear of the differential.

Is that the most likely diagnosis?

Does the differential share the oil with the gearbox?

Could examining the gearbox oil for metal be helpful?

Thanks

(I'll record the noise and do a frequency vs speed analysis)

 

[AnthonyH]

Can you attach an audio/video file so we can hear it?

 

[Pugglt Auld Jock]

Hi,

I accelerated hard (probably was in fourth gear) and suddenly a droning noise appeared out of nowhere and just stays.

The noise has a dominant frequency which:

- seems to be faster than wheel RPM
- is independent of the selected gear
- is independent of the clutch pedal depressed or not
- is indepemdent of engine RPM
- increases linearily with speed
- get's louder with speed
- doesn't change in frequency nor volume when cornering
- does not generate vibrations on the steering wheel
- appeared with about 249000 km on the clock (approx. 155 k miles)
- impossible to localize the origin, the noise seems to come from everywhere

ChatGPT thinks it's the pinion gear of the differential.

Is that the most likely diagnosis?

Does the differential share the oil with the gearbox?

Could examining the gearbox oil for metal be helpful?

Thanks

(I'll record the noise and do a frequency vs speed analysis)

Hi Zardo. Sorry if I'm a bit late to this "party". Chat GP seems to make a plausible suggestion. However I think something like this is far too difficult to diagnose without being there. How experienced are you with car repairs? If you don't have much then i think seeking professional advice would be wise - Gearbox work is often expensive so you need to be sure about a course of action before you start. By the way, yes, the gearbox and final drive are all in one and share the same oil. My Ibiza suffered a final drive bearing failure - most probably one of the crown wheel bearings - didn't bother stripping it down as, when we drained the oil, it was full of "glitter" so obvious an exchange box was the best option. In my opinion, if you have a transmission failure like this, especially a transaxle, then little bits of metal will be distributed throughout the box. to effect a satisfactory repair which is likely to last, the whole box needs to be comprehensively cleaned out so you can be sure there's no contamination anywhere, and that is best done by completely dismantling the box. Unless you're doing this yourself - and it's not a task to be undertaken lightly - an exchange box is often the best solution.

Of course that's not going to be cheap, so you need to be sure of the diagnosis before proceeding

 

[Zardo]

Can you attach an audio/video file so we can hear it?

yes, I'll do that (a first attempt at recording the sound wasn't successful, it's clearly audible to me but the phone didn't really record it).

 

[bugsymike]

Drive shaft support bearing where mounted to engine?
Independent of engine speed or gears or load, but may change slightly going from a left hand bend to a right as slightly different shaft/road wheel speeds.
If you had it safely mounted on a wheel free ramp then at those sort of speeds some underneath would feel it if hand on bearing support or a stethoscope to the bearing. Not common but I have fitted a few in the past.

 

[Zardo]

I was mistaken, the noise actually does decrease when unloading the left side (when steering to the left) and slightly increases when cornering right (loading the left side).



The spectrogram starts at 0 Hz and has 100 Hz intervals with horizontal lines. It goes up to 700 Hz (on the very top of the picture).
Speed was about 78 km/h for the first test.

I see a base frequency at around 160 Hz, another line at 240 Hz, a harmonic at 320 Hz, another line at about 385 Hz (with 78 km/h in 6th gear). Engine noise was very faint.

 

[bugsymike]

I was mistaken, the noise actually does decrease when unloading the left side (when steering to the left) and slightly increases when cornering right (loading the left side).



The spectrogram starts at 0 Hz and has 100 Hz intervals with horizontal lines. It goes up to 700 Hz (on the very top of the picture).
Speed was about 78 km/h for the first test.

I see a base frequency at around 160 Hz, another line at 240 Hz, a harmonic at 320 Hz, another line at about 385 Hz (with 78 km/h in 6th gear). Engine noise was very faint.

So could be worth checking on a safe wheel free ramp for that drive shaft centre bearing on engine. If possible try to position supports so drive shafts horizontal to road wheels as when normally on the road (not hanging down)
Having said all that, it may be worth checking wheel bearings on front as I have had them with the hardening gone from one side of the bearing giving similar affect. Wheel bearing may not show on ramp as no road loading.

 

[Zardo]

Since the noise doesn't change with engine power (and even persists unabated when switching the engine off and gears in neutral) but will abate when unloading the left side when driving wouldn't that point to the left-side wheel bearings (maybe the left front one) rather than the gearbox, differential or axle?

It totally doesn't sound like this:

 

[bugsymike]

Noisy diffs also change sound depending on or off the accelerator.
My thoughts are what I said re driveshaft support bearing , but try and check wheel bearings also.

 

[AnthonyH]

Noisy diffs also change sound depending on or off the accelerator.
My thoughts are what I said re driveshaft support bearing , but try and check wheel bearings also.

I agree with this, I think it's driveshaft related, wheel bearings don't sound like that in my opinion.

 

[Zardo]

https://eper.fiatforum.com/en/Drawings/Detail/F/C/GPABR/4B/274/2/20/1/SubGroup

so that bearing would be item nr. 2, I guess (or is that the bearing of the front wheel)? I changed the rear wheel bearings twice on this car, but never the front ones. Anyway, I don't think I'm proficient enough to do anything drivetrain related on the front except maybe the brakes and the suspension, so if the noise doesn't come from the left rear wheel bearings, I'll probably have to take the car to the dealership.

There is also this differential gear bearing, nr. 7:

https://eper.fiatforum.com/en/Drawings/Detail/F/C/GPABR/4B/212/20/10/0/SubSubGroup

 

[Pugglt Auld Jock]

I agree with this, I think it's driveshaft related, wheel bearings don't sound like that in my opinion.

But it varies when he's steering side to side? I agree it's not quite what I would expect a wheel bearing to sound like but I've heard wheel bearings making unusual noises more than once so I'd want to be taking a close look at the front wheel bearings, especially the left front as the noise is louder on a right lock. Only once I'd definitely ruled it out would I spend time looking at other "suspects".

 

[bugsymike]

https://eper.fiatforum.com/en/Drawings/Detail/F/C/GPABR/4B/274/2/20/1/SubGroup

so that bearing would be item nr. 2, I guess (or is that the bearing of the front wheel)? I changed the rear wheel bearings twice on this car, but never the front ones. Anyway, I don't think I'm proficient enough to do anything drivetrain related on the front except maybe the brakes and the suspension, so if the noise doesn't come from the left rear wheel bearings, I'll probably have to take the car to the dealership.

There is also this differential gear bearing, nr. 7:

https://eper.fiatforum.com/en/Drawings/Detail/F/C/GPABR/4B/212/20/10/0/SubSubGroup

None of the above.
This photo is from a Fiat Doblo but I trust the principle is the same.
I am thinking the bearing in a three bolt housing screwed to side of engine to support the drive shaft.
It involve dropping bottom suspension wishbone, hub nut off, the three bolts on the centre mounting and pulling shaft out of gearbox, look out for the oil,
then hopefully you can get a new bearing fitted in the centre mounting.

 

[jackwhoo]

I think it's going to be front left wheel bearing if noise increases when steering right therefore loading front left wheel more heavily

 

[Pugglt Auld Jock]

I think it's going to be front left wheel bearing if noise increases when steering right therefore loading front left wheel more heavily

My thinking too Jack, now just watch us be proved wrong!

 

[bugsymike]

My thinking too Jack, now just watch us be proved wrong!

We can't always be right from 1000s of miles away, but considering some get it wrong when standing beside the vehicle and getting paid for it!!!

 

[AnthonyH]

We can't always be right from 1000s of miles away, but considering some get it wrong when standing beside the vehicle and getting paid for it!!!

Its a mechanic shoot-out. Me and Mike in one corner, Jack and Jock in the other!!!

Jack and Jock has an uncanny ring to it!

 

[Pugglt Auld Jock]

Its a mechanic shoot-out. Me and Mike in one corner, Jack and Jock in the other!!!

Jack and Jock has an uncanny ring to it!

Name for a film? - Thelma and Louise but from the male perspective perhaps? Just in case you've no idea what I'm on about, Lookee here folks:-



Or maybe Easy Rider? Bags I be Dennis Hopper, always thought he was "super cool"

Sorry for the deviation from subject, I just couldn't resist. I'll be good now.

 

[AnthonyH]

I asked AI to write me a film synopsis called Jack and Jock, here it is!


For the film Jack and Jock, the story follows two unlikely partners whose love for classic cars is matched only by their disdain for each other. Set in a small, weathered Scottish town, the film is a humorous and heartfelt tale about friendship, family, and the power of a perfectly restored engine. When a new mechanic comes to town Jack and Jock must work together to prove their skills, save their legacies, and perhaps even build a friendship along the way. The film unfolds in a tense final showdown that tests their mechanical abilities and newfound trust, culminating in a spectacular, mud-splattered race through the breathtaking Scottish countryside.

 

[Pugglt Auld Jock]

I asked AI to write me a film synopsis called Jack and Jock, here it is!


For the film Jack and Jock, the story follows two unlikely partners whose love for classic cars is matched only by their disdain for each other. Set in a small, weathered Scottish town, the film is a humorous and heartfelt tale about friendship, family, and the power of a perfectly restored engine. When a new mechanic comes to town Jack and Jock must work together to prove their skills, save their legacies, and perhaps even build a friendship along the way. The film unfolds in a tense final showdown that tests their mechanical abilities and newfound trust, culminating in a spectacular, mud-splattered race through the breathtaking Scottish countryside.

Love it dahlin'