Bad Exhaust Vibration - 1.9 TDi Passat 1996

[Tom_Pattinson]

Hi - I am experiencing bad vibration through the entire exhaust system of my 1996 Passat 1.9 TDi. I thought that one of the exhaust boxes was disintegrating inside (it is THAT noisy), however, I have replaced both rear boxes. The vibration and noise (resonance) continues - are engine mounts to blame? The car has covered 130,ooo miles, regularly serviced. Any help would be very welcome! Thanks, Tom

[Jerry Stringer]

Tom,
From the TDIFAQ.
[ QUOTE ]
Rattles, buzzes, and resonances from the exhaust system:
- Many B4 (1995 to 1997) Passat models have a resonance in the exhaust system at 1200 rpm, and a lesser one at 2400 rpm. Several possible causes have been described but the problem appears to be inherent in the design.
- Some owners have reported that the downpipe (flex pipe) has become clogged with carbon build-up, thus causing noise to be transmitted through the rest of the exhaust system. In some cases this component has been replaced under warranty. In other cases, the problem was addressed by removing the flex pipe from the car and working it back and forth to loosen up the deposits.

- Some have had one of the mufflers (there are two) come apart internally, thus requiring replacement.

- Exhaust hangers can harden up and/or work loose over time, thus transmitting much more noise to the passenger compartment. These components are easily replaced.

- If this happens out of warranty, some owners may consider this to be an excuse to buy a performance aftermarket "cat-back" exhaust system. This might be the only way to eliminate the flaws in the standard system. The TDI engine is not loud even when operating with no muffler at all.

- Several owners have had success with getting a muffler shop to install an additional flex pipe downstream of the catalyst.

- Deteriorated engine mounts can increase the amount of noise and vibration transmitted into the vehicle.


[/ QUOTE ]

Jerry

[Chris Bell]

The solution is to add a 2nd flex-joint to the exhaust system.

[Tom_Pattinson]

Hi Jerry - this describes EXACTLY my issue, thank you so much! I am an engineer, and recognise resonance, though could not pinpoint the source. I am now in the process of having a replacement flex joint fitted, together with renewing the engine mounts - I hope this cures the noise! Would you advise fitting a second flex joint to the rear of the cat? Kind regards, Tom (UK)

[Chris Bell]

I would not replace the original flex-joint unless it is cracked. If you replace it with a joint of the same length, you will not cure the problem, only postpone its recurrence. The OEM joint is too short (and, thus, too stiff) to dampen the resonance after time and soot have stiffened the joint further.

Replacing the motor mounts will not cure the resonance either, although they may need to be replaced if the voids in the front and right rear mount are overly compressed. Worn mounts may increase the amount of NVH transmitted to the vehicle, but aren't the cause of the resonance that seems to be coming from the rear.

The beauty of the 2nd flex-joint installation is that it decouples the rear of the exhaust system from the front and allows the rear to pivot laterally in the opposite direction from that of the front which helps to eliminate the strong lateral component of the resonance.

Save your time and money on mounts and a replacement front joint and install the 2nd flex-joint first. Its also an easier, less costly job.

Now, I'm assuming that you have the typical resonance/droning that seems to come from the rear. If you have a more metallic rattle seemingly coming from the front, this solution doesn't apply...motor mounts and/or a new catalyst may be required.

[Jerry Stringer]

Absolutely! If Chris Bell says it helps then I would do it. I'll probably get around to doing this later this year myself.
Jerry