Banging Noise, Cannot Resolve Despite All Efforts

[aiboart]

BAII XR6T A4

STD wheels, springs, engine and tune

Bilstein monotunes

dba 5000 front discs

A very sticky problem.

The car behaves perfectly when the weather is warm. It is just brilliant.

When the weather turns cool things change seriously for the worse.

Once the weather turns cool, any steepish downward irregularity in the asphalt, even liquid smooth asphalt frequently generates a massive bang that originates under the pedals, or in front of the driver. This is sometimes a massive impact that sends a wave through the floor into the driver and the rest of the car. It is exceedingly unpleasant.

More typically there is an extremely loud bang or series of bangs that sounds like someone is hitting the suspension or the cross member with a iron rod out in in engine bay. At other times the noise it has a metallic springy character.

The noise simply does not occur in warm weather under any conditions. It does not occur in summer, at all.

The noise will tend to occur at every steepish irregularity in the road where the drivers side goes in rebound. In weather such such as today (max say 18C) the noise will also occur on level but crazed asphalt. Once triggered, by even very smooth but undulating asphalt, the noises will continue to occur several dozen times per km for hours on end. At other times it disappears for hundreds of km, until a slightly larger break in the asphalt will trigger a large bang, and then we get the constant banking for hours on end with every crack or dip in the asphalt.

The noise often has a massive springy character to the bang. The noise is speed independent. It occurs in my driveway at 0.5kph when the front driver side wheel goes slowly over a 2cm drop. It is normally associated with the driver side when in rebound, albeit minor excursions though at it also occurs at bump.

Frequently in cold weather when the noise occurs, it is followed by several lesser bangs and gives every impression of something bouncing around.

Things done to date

2 dealerships, more than 10 visits.

Replaced lower ball joints, replaced engine mount (leaks and witness mark found), tightened steering rack (witness mark found), tightened all chassis bolts several times.

2 Pedders visits, the noise has a tendency to disappear for a couple of days after the car goes up on a hoist.

1 shock place

I have convinced myself over a period of 18 months that the noise is,

• sticking sway bar drop links
  
• sticking sway bar other
  
• sticking bush somewhere in the suspension
  
• loose bush somewhere in the suspension
  
• coil binding
  
• clinking two piece front discs
  
• exhaust hitting cross member
  
• exhaust hitting heat shield
  
• heat shield flexing and flicking
  
• heat shield fasteners hitting body
  
• under batter air pipe hitting the body
  
• undefined bind in the suspension causing crashing into road irregularities
  
• auto box smashing into something
  
• engine smashing into something
  
• body welds
  

I have all the above checked out many many times. The difficulty in is that once the car goes on a hoist the noise will disappear for a half a day.

Any ideas?

Regards,

aa

[Guest EGOXRT]

Ferrofluid bushes maybe. Dud Bilstein's, take them off and have them dynoed.

[aiboart]

Thanks for the help.

I had the Bilsteins dynoed on the car which showed nothing, nor did the problem occur during the dyno process. Then I bought a 5th Bilstein to replace the unit in the car and the problem still occured.

For the sake of completeness I will follow your advice and have the spare Bilstein dynoed off the car.

The presentation of this problem has a consistent temperature controlled component, a suspension speed component and a direction component (strongly favors rebound - down).

To my mind a hydraulic system would be most likely to behave consistently in those conditions. I will see to swapping out the Ferrofluid bushes as your suggest.

Regards,

aa

Edited 27/09/09 11:09 PM by tab
Quote removed

[senna_T]

Have you had the lower inner control arm bushes looked at john? That or the swaybar links as you have mentioned...

Feel free to drop past for a free safety sheck if you like

Cheers

Pat

02 4721 2112

[Dadowiz]

I'm certainly no expert but did have a similar issue in a Jeep Cherokee.

Basically when the weather would change (cold and rainy)the ABS module would start playing up causing the wheels to lock up. The front rotors on the Jeep were warped and when the fronts would lock up the combination of rotor shudder and ABS lockup would flex the monocoque body slightly causing the transmission to hit a cross member.

Very annoying!

Like I said I am definitely no expert, but maybe worth looking into?

Good luck!

[aiboart]

Thanks guys.

I appreciate your help. I am going to have another crack at the problem in a few days.

Just to illustrate the capricious nature of this problem, it was going nuts the other day with the gearbox or exhaust or bits of the suspension seeking, it seems, to come through the cabin floor or firewall.

Next day, nada, nothing at all. This was despite hundreds of km of open road and city driving over variable terrain. The car was so dam refined my self declared non rev head passanger decided he wanted to buy a XR6T.

The day after that, the high energy banging was on again over the slightest imperfection in the asphalt.

Pat, I would like to order some of your new Kiwi rear drop links. This will probably have to be via mail order, though if I can find the time I would certainly like make the journey to see you in the new workshop.

Regards,

John

[senna_T]

Definitely a tricky situation John.

If you can make the trip out to see us, we'll put the car on the hoist and check it over for you

[Erko]

what a pain the arse!

John I remember you had this problem last year and you told me about it when you came over to buy something. This sucks.......I too thought it might be worth putting the front shocks on the dyno but youve done that. Take it out to WSP, they can put it on the hoist and apply lateral loads and pitch and see if anything shows up.