YEAR 1984
MAKE Peugeot
MODEL 505GTI
ENGINE SIZE 2,2lites
MILEAGE 120000km (74500 miles)
Righthand drive
Automatic transmission (3 gears + reverse)
In certain situations, a noise can be heard under the drivers seat. I have heard this noise on every long distance trip (>=400km, 250mi) and no mechanic has managed to determine the cause or fix the noise. I would like to find the cause of this noise and stop it from reoccurring.
The noise is heard in the following situations.
1. Car is travelling at least 80 km/h (50mph), however normally the noise occurs at 110 km/h (68mph).
2. Or the car is in 2nd gear and is accelerating up hill. When the car reaches a high enough speed, the car switches to 3rd gear and at the moment the noise is heard.
3. In all situations, the road is smooth and level OR the road surface is tarred but slightly wavy due to heavy trucks.
What does the noise sound like ?
1. Two to 3 distinct bangs.
2. Similar to stones hitting the bottom of the car.
3. Similar to stones hitting a thin sheet of metal.
4. Passenger sitting next to the driver also clearly hears the noise.
Where is the noise heard coming from ?
1. The noise always originates from the drivers side of the vehicle. The noise does not originate from the center of the vehicle.
2. Frequently, directly under the drivers bum. OR
3. Frequently, near the pedals under the drivers feat
4. Rarely, from behind the driver from the boot.
5. A passenger sitting next to the driver hears the noise coming from the drivers side.
Can the driver stop the noise or reproduce the noice ?
1. De-accelerating the car gently, stops the noise.
2. Moving out of the wavy truck-tyre-depressions in the road, stops the noise.
3. Accelerating stops the noise, de-accelerating causes the noise, e.g. driving at 110km/h (68mph), suddenly the noise is triggered, then accelerating to 115km/h (71mph) stops the noise, slowing down to 110km/h re-starts the noise. This can be repeated nurmerous times.
4. Accelerating up a hill in 2nd gear so that the car changes to 3rd at a high enough speed, will always cause the noise.
Other (subjective ?) observations
1. The noise is not heard continously throughout a journey. The noise comes in burst, i.e. The noise will be heard (2 to 3 bangs) and then maybe for the next 50km (31mi) the noise is not heard.
2. When starting from cold and driving 400km (250mi), the noise is heard sometimes during the trip. Continuing to drive another 400km, the noise does not occur.
3. It also occurs that during a journey the noise occurs only once and then not again.
4. When the car is realy warm (that means after driving about 400km / 250mi) the noise is not heard.
5. It has also occurred that driving along a wavy-truck-tyre-depressed road, the noise is not heard. Then on a new smooth road the noise is heard.
The only cause for the noise seems to be the exhaust pipe hitting the underside of the car. Although this seems unlikely.
Approximately underneath the driver's seat runs the exhaust pipe. The pipe is close to the center of the vehicle but more towards the drivers side. This pipe has broken 5 times over the 1 year period that I have owned the car. The pipe breaks approximately every 800km (500mi). The pipe tends to break at the welding joints or there where the pipe is old and a little rusted. Although by now most of the old piping has been replaced and the breaks only occur at the welding joints.
The entire exhaust pipe including 2 silencers can swing to the left and to the right when I shake it with my hand at the back of the vehicle. When shaking the exhaust I cannot get the exhaust to hit the bottom of the vehicle.
When lying underneath the car, I cannot shake the pipe under the drivers seat to bang the bottom of the vehicle. I can also not see any scratches or dents where the exhaust pipe has hit the bottom of the vehicle.
The exhaust is mounted on brackets that have rubber cushions. Although I cannot be sure if the mountings and rubbers are correctly attached.
I am not sure if the frequent breaks in the exhaust pipe are linked to the noise. I have no other explanation.
On one occassion the exhaust broke. A mechanic wrapped a piece of thin metal around the crack which he attached with 2 pieces of wire. This gave the exhaust flexibility to move and reduced the noise. Afterwards I cannot remember hearing the noise. At least the noise occurred less frequently than before the break. I continued to driver between 80 to 120km/h (50mph to 75mph) over about 2000km (1242mi).
Questions:
1. What is causing the noise ?
2. Is the noise caused by the exhaust ?
2.1. If so, is the exhaust to rigidly mounted ? How can I tell ?
2.2. Will an exhaust flexible stop the banging ? And where should the fleixible be mounted: close to the engine before the first silencer or after the first silencer ?
3. Are vibrations from the engine, gearbox or propshaft causing the exhaust to vibrate and bang ? Perhaps the engine and gearbox mountings are worn out or the propshaft is bent.
4. What parts of the car, should I tell the mechanic to verify, to eliminate possible causes of the noise ?
Once more, I looked closely under the car and saw what could be a spot where the exhaust bangs against the body of the car. The place is near the front of the car, before the gear box, just there where the exhaust turns from going down vertically from the engine, to moving horizontally towards the back of the car.
I painted the spot on the exhaust and on the cars body in red. Then I drove 800km. The banging was heard regularly at 110km/h. Noise also heard when deaccelerating down to 110km/h or accelerating from 110km/h. At 100km/h or 120km/h no noise.
After 800km I looked under the car. There where the exhaust and the body could bang together the paint is faded but not completely gone. Away from the bang-spot the paint is not faded). The banging noise is fairly loud and I imagined the paint would be completely gone at the bang-spot.
So it could be the exhaust banging against the car's body.
If it breaks again, I'll get a flexible installed.
A new mechanic checked the 2 engine mounts in the front of the car and the 2 diff mounts at the back of the car. The mounts seem fine to him.
After removing the nuts holding the 2 engine mounts, he shifted the engine and the exhaust around with a large crowbar. That at least showed that the exhaust is banging at the underside of the car's body.
After tightening the nuts he told me to drive off and see if that's fixed anything ...
Not sure what the mechanic could do. Seeing that the exhaust is less than 1cm away from the car's body at that spot where it hits. Difficult to shift the engine to the left.
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Banging noise under 505
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jasanek
