406oc.co.uk

Hi guys,
Got a 2001 2.0 HDI estate and today had a new cat and flexi hose fitted as the old one blowing in several places.

Patten part as main dealer want £800 + labour!

All fitted and no blowing but now at certain revs there is a huge vibration/resonance through the entire car. The mechanic who fitted it had it back on the ramp and tried to find the vibration but with no joy. He's sent me on my way saying it might be that flexi where it's not as flexible as the original. Says to drive for a week then report back.

At the same time he also replaced both front suspension coils as one had snapped (although I never knew it had).

Any thoughts or advice please before I vibrate away into pieces.


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Take it back I can't see why running it for a week will help.

Try banging on the tailpipe and listen for the vibration then (engine off).....chances are the cat is faulty or a heat shield is loose.

Could be the flexi hasn't tightened up properly on the pipe.

Thanks Jasper. The only issue is I have to get the revs just right for the vibration to announce itself.


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Banging on the exhaust should make it rattle somewhere, if there is something loose it will show with a bang, that's how i've been fixing exhaust rattles for too many years.

The flexi-joint can often fail due to worn engine mounts, the vibration from which can be softened by the knackered flexi-joint. Replacing the flexi-joint in this case can cause the excess movement from the knackered mounts to become apparent. Or it could just be the bonnet not resting properly on the supports, which it turns out can produce similar symptoms

Interesting stuff. The old flexi did have a huge split in it.
Why could this affect the engine mounts out of interest?
Definitely a vibration and not a rattle.


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You've not read mjb's reply properly, he stated that worn engine mounts can cause the exhaust flexy to fail . Not a worn flexy causing the engine mounts to fail
It's the two steady mounts that stop the motor moving for & aft to much (top one near the cam belt cover & bottom one at the back of the sump near the turbo with a driveshaft going through it .
As the exhaust flexy degrades it becomes weeker & fail steady mounts will excelarate this, when you fit a new one it'll be loads stiffer & could cause this.
I.M.H.O, I think it it needs to go back on the ramp loosen all the exhaust mounts / clamps & make sure that the exhaust is not strained or under any tention as it is tightened up,
start at the down pipe & work your way back first doing it all hand tight/just nipped followed by making sure it's good & tight or torqued up if you prefer.
Hope this help's & best of luck bud, Oh by the way welcome to the forum DDD.

Ahhh ok. Sorry get what you mean now. I've just been for a 75 mile drive and it's awful around the 1200rpm and 2100rpm. The vibration goes through the whole car and makes everything vibrate inside. Gutting as it used to be a very smooth drive.

The guy who fitted it did undo a few clamps to test but the exhaust was too hot so I reckon he didn't go as far up as the flexi. He told me to take it back after the weekend if it's still like it and he'll send the cat and flexi off to be replaced.

Is there anyway to prove otherwise without loosening the clamps etc?

I've tried hitting or moving the back of the exhaust. Made no difference.

Pushing down on the bonnet next to the wing makes the car resonate more at idle. But raising the bonnet and slightly twisting makes no difference so I think this is not the issue.


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And thanks for the welcome :-)


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406HDi3 wrote:Pushing down on the bonnet next to the wing makes the car resonate more at idle. But raising the bonnet and slightly twisting makes no difference so I think this is not the issue.

Shame; it's about as quick and easy as fixes come

I'm thinking "rear lower engine mount" a worn mount lets the engine move far too much...which bends the eggsauce flexi....which eventually breaks. I surmise that the engine is pulling greatly at the eggsauce system under acceleration and forcing a 'tightness' giving this vibration and noise.

Run the engine at idle with the bonnet up, blip the throttle, and if the engine lurches forward by a few inches then the mount is goosed. Many things improve with a new mount in place including the gear and clutch action and less vibration/shakes under load.

Not saying this IS the fault but the mounts are VERY common.

Thanks for the tip although I'm not sure how I'd tell if the engine lurches forward because any blip rocks the engine


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406HDi3 wrote:Thanks for the tip although I'm not sure how I'd tell if the engine lurches forward because any blip rocks the engine


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Yet again not reading / understanding the quote above ,
IF THE ENGINE MOVE EXCESSIVELY : ie back wards & forwards more than 25mm / 1" then your bottom steady / mount is F.U.B.A.R'D

+1 on the bottom engine mount. It causes all sorts of problems with rattles and vibrations. A bit of a pain to replace so get the garage to do it. Top engine mount can also go but easy to replace yourself.

Ok. Well the garage is going to try replacing the flexi/cat for another one as apparently some are too stiff from manufacturer. You can feel the vibration substantially when just touching the cat with the tips of your fingers. As for the lower mount, this was replaced a few years back so I'd have to very unlucky for it to have gone yet again.
Will check for movement in the morning but I'm still going to insist that the engine moves no matter what.


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