Silencer question: 2009 2.9 987.2@ 90K miles.

[911hillclimber]

Simple question, has anyone had a light droning 'hum' in their 987.2 Boxster, bog standard spec all original system but 91K miles old?
Hum chimes in at 45 mph any gear, chimes out at 60 mph any gear.

 

[Motorhead]

If it’s speed rather than gear [i.e. engine] related, are you sure that it isn’t a tyre or transmission issue or something vibrating on the body Graham?

Jeff

 

[911hillclimber]

Nothing touching that I can see.
tyres? Could be..
diff, hope not!
cant hear it if I drop the widow down an inch or so.

all a bit wearing now.

 

[malarcy]

Can you dip the clutch and drop the revs when it happens - if it carries on then its "rotational" - so tyres or (wheel) bearing(s)

Play with tyre pressures? - see if you can "move the fault" to a higher or lower speed with 4 or 5 psi over your normal running pressures - not as a fix but as a diagnostic

 

[911hillclimber]

Thank you, good ideas.
The car has had this issue for 5 years now and has had a tyre change to no avail.
In 15K miles it has not gotten worse, so thought wheel bearing prob was not the cause.

It does not get louder from 40 to 60 mph, just there.
Dipping clutch to separate engine does nothing to the this low level humm.
Wife and I think it is from the driver's rear, so a few weeks ago swopped the rear wheels over side to side, noise still at driver's rear.

Had not thought of tyre pressure change to see if that might change things. Rear 19" Bridgestones are 34 psi, 32 front. Will add 5 psi to the rears to see if a change can be heard.
Will try that tomorrow. If no change, will drop to 32.

Jacked the rear up today (both rear wheels off the ground) and the wheels rotate so smoothly it's untrue, just the normal light scraping of the pads on discs, both sides.
No bearing feel, no play at all. Wheels run true too.

This humm was far worse until Zuffenhaus specialist found a crumpled plastic deflector up against the gearbox casing(!) which they removed. The noise was far less after.

I repaired this ducting and the noise is 50% worse, and the level I'm irritated by right now. I cannot see any issue with the repair, ie parts touching.

Below 40 there is nothing, rides quietly as my big Skoda. Above 60, tyre noise drowns out everything.

TBH, this is the only negative about this car which I've had 10 years.

 

[CLIFFWILKINS]

Have you tried changing the diff fliud if man box they share same oil.

 

[911hillclimber]

Yes, but about 5 years ago as part of the major service, and level checked last service at Zuffenhaus in March 26, at my request. It needed a minor amount. There no transmission leaks evident.
The Bridgestone tyres are 19" low profile but match the Porsche option spec for 19's, in fact I think the car was ordered new with these (non Porsche marked) wheels from Italy.

The tyres are N rated, and about 30% worn. All tyres are perfectly flat due to a demon alignment to Porsche road standard spec by Zuffenhaus.

A few weeks ago whilst checking the rear (again....) with wheels off I placed stiff sponge rubber between any panels I felt might vibrate while on the road, so exhaust heat shields and inner arch mud guards etc. Nothing changed.

The nature of this noise happened while on holiday in Austria and it was sudden. That was 4 or 5 years ago.
A wheel bearing would have got much worse in the 15K miles since, a transmission bearing/diff would have got worse too, but no, the humm is the same though a lot less now since Zuffenhaus spotted the broken and jammed wind scoop during the car's MoT in March.

The wind deflectors scoop air up right under the main body of the transmission, one scoop either side of the box attached to the rear suspension brace. The scoops for PDK and Manual trans are different. I presume they add cooling at 160 mph. They are not loose.

My mind has been all over this problem.
The driveshafts are silent, smooth deep plunge and feel tight.
Bar brakes everything on the suspension is original and tight and quiet.

 

[CLIFFWILKINS]

Might be worth changing again as 5 years ago last change with a quality oil.
Fairly inexpensive to possibly cure or rule out.
If not wheel bearings, tyres come to mind again.
Try to borrow a set from a friend or member just to try.

Have you considered a CV Joint ?
Just another thought are the tyres mounted correct the right way round with the outer side walls on the outer.

All the best

 

[911hillclimber]

Thank you Cliff, All tyres are orientated correctly.
Trans oil change a good idea, even just to tick it off the 'possible' list. (and to see if anything metallic comes out)
Have examined the CV joints best as I can by hand, but the components that are on the list.
Not a simple task to change though, silencer off etc I think.

I am rapidly getting to the point of expense test/ experiments etc, and will change the car soon if I can't crack it.

It will be soon good money after bad.

Have thought of simply buying a new 19" right size rear tyre and swop and drive. Messing about with the local tyre shop, but not too expensive a test.

Set of non-Bridgestone tyres: £1000
CV shaft change, £600 and much grief. (DIY labour)
Gearbox? Massive action.

Car value? About £10K tops.

If stuck, We Buy Any Car .com
Maybe buy another sport car, anything but a Porsche!

 

[CLIFFWILKINS]

I can understand your frustration had cars before where you just cant track an issue down, in the end your wanting something to go bang to get to the bottom of it.
Its can lead to start replacing parts especially if a garage has no idea expensive process .
I know you have done yours but Air separaters can hum so i have heard.
Maybe one last roll of the dice try another indie or email Steve Winter at Jaz
Good luck

 

[Motorhead]

[Lengthy] PM sent Graham.

Jeff

 

[911hillclimber]

Thank you for that Jeff, have responded.
We are competing at a big hillclimb this weekend, so little time to do things on the 987.2, but quality time next week to delve even further (if I can).

 

[Motorhead]

Message received. Thanks Graham, and just FYI I’ve added another message.

On the subject of PMs, I’m sure that we used to get a notification that a PM had been sent when logging-on. Maybe I haven’t switched-on the appropriate option?

Good luck with the hillclimb … hope the Lola [?] behaves itself!

Jeff

 

[911hillclimber]

Yes, my little Lola Sports Libre, air cooled of course!

 

[911hillclimber]

Back from the races, so good time to delve a bit deeper to this humming issue.
Taking the suggestion to add 4 or 5 psi to the rears to see what happens.

I use a simple pencil pressure gauge with the round slide that comes out under pressure, have used this for decades.

For some reason I decided to try to check the accuracy of this pencil gauge.
I have a battery powered inflator with a pressure gauge and set that to the standard 34 psi.
It took a long time to reach 34 psi suggesting the tyre was well underinflated.

Using my 911 front tyre I checked the pressure, and found the pencil gauge was 4 psi down on the electric pump, so at 25 psi I checked the tyre with my race car gauge (range 0 to 30 psi) and it gave the same pressure as the inflator pressure, 25 psi. The pencil gauge gave 21, 4 psi low.

So, set the Boxster to 32/34 using the electric pump and took it out for a 15 mile run.

Noise/humm is still there but less obvious, and seemed to not be present from cold, but started about 3 miles into the run.

Have now ordered a Ring pressure gauge as the reviews state the accuracy to very good and repeatable and I'll leave the pencil gauge in the tool box.

Net step is to now increase to 39 psi using the pressure inflator.

Whew, busy.
Many still think it is the tyre.

 

[Motorhead]

If you’re convinced that it’s a tyre issue Graham, as suggested in my previous PM definitely I’d be trying a nitrogen fill. Some Kwik Fit outlets offer it at low cost when purchasing tyres and I think that Porsche dealers can also provide a nitrogen fill, but your guess is as good as mine as to how much they’ll charge for that!

Jeff

 

[911hillclimber]

Yes, on the to-try list.
Going to try the +5 psi in the rears first once I have my new RING gauge here.
Have to say the 'dead' 'woody' steering feel has gone!

If all that comes to no conclusion will try the 'box oil. I think that is probably a DIY job, even I should be able to do that rather than bother Zuffenhaus.

I did check the plastic floor covers in case one part was 'beating' in the air stream, but all tags in place, all screws present (never been removed).

If though I had Zuffenhaus do the oil with the car high on the ramp could ask for a check of such things?

 

[Motorhead]

Interesting that you reckoned that the sound wasn’t present from cold but became apparent about 3-miles into the drive when the tyres were warming-up and the density of the air in the tyres will have changed [marginally?] along with the frequency of any tyre cavity modes of vibration … and the tyre pressures too of course, just to complicate things!

I’m not sure that a transmission oil change will have any effect, but probably worth a try if all else fails. As you say, if you hand-over the job to Zuffenhaus it’s an opportunity for them to give the whole underside a comprehensive once over.

Keep us posted on progress.

Jeff