35i/is Exhaust Rattle (Vacuum/Flap) FIX

[inkey$]

I thought BMW had sorted the issue after aout 2008/9.

[Maniac]

I thought BMW had sorted the issue after aout 2008/9.

I wish...

[Kryton]

I had the vac flap wired open on my 35iS for a few months, then got fed up with the drone/booming noise under acceleration so put it back to standard.

[Maniac]

So the car is in for its exhaust replacement today. This entire item is required below. Cost is £1075.01 http://www.cooper-bmw-parts.co.uk/index ... virtuemart for the part ALONE. That bit I'm not paying for. But its £252 for fitting, which I am paying for unfortunately. £252 to put a bit of gunk on, mount it. All that just for a £20 vacuum actuator failure. I've never had such an expensive rattle to fix. If only I wasn't so picky!

[TitanTim]

Out of interest is this a problem that afflicts the 35is exhaust only? I have a kind of metallicky resonating rattle on mine at cold start up and sounds quite raspy until it warms up. Its definitely exhaust related almost like a loose baffle but only when cold. I can't tell exactly where its coming from but sounds like its from the front of the exhaust system, even though the exhaust flap is in the right tip. Not sure whether to leave it now as will be taking the car off the road for winter end of the month

Maniac, hope it gets sorted

Tim.

[Maniac]

Not sure Tim, its a problem that's affected many 35i/35is/335i/335is owners over some years. I'm not sure if they fit this flap on the four pots as I think its a single exhaust? Can't be sure tho as I've never looked under an N20 car. If the N20 does have the flap then you'd hear it as a loud ticking from the rear silencer as each puff of exhaust gas pushes the flap open and it clangs back shut. Right old racket!

[TitanTim]

Not sure Tim, its a problem that's affected many 35i/35is/335i/335is owners over some years. I'm not sure if they fit this flap on the four pots as I think its a single exhaust? Can't be sure tho as I've never looked under an N20 car. If the N20 does have the flap then you'd hear it as a loud ticking from the rear silencer as each puff of exhaust gas pushes the flap open and it clangs back shut. Right old racket!

Cheers for that, the 2.0 does have the flap and the actuator in right exhaust tip but can't tell if it that that's making the noise. Will have to get someone to rev it up while i have a listen

Tim.

[Maniac]

The flap only operates at cold start, and under certain speeds/loads when driving to keep the drone down. Leave it until tomorrow morning so the car is cold, start it up and run round the back to listen. You can't miss the noise if its there...

Here's one from youtube. You can hear the metallic ticking noise at low revs. Its super loud on mine currently.

[Gizmo-R]

Sounds awful! That is not being picky about fixing it!

[Maniac]

Car is collected... no exhaust rattle as yet. Cold start tomorrow will tell. Final bill was cheaper than quoted (get that) at £219. Also gave me free hire car in the end. They do redeem themselves from time to time.

[Gargybloke]

Terribly poor design the exhaust being just one section

Lets hope this one lasts.

[Maniac]

So, shiny new exhaust, rattle free start up this morning

Well at least rattle free from the exhaust. I can now hear a quieter rattle from the waste gates so that might be my next quest

[Stark]

That's the exact sound of it being faulty. Mine was replaced, and all ok, apart from my ears always thinking there is a rattle and analysing every sound!!!

[Z4andy]

Is it possible that these flaps can get a bit sticky

I ask because today on start up I had to get out of the car again and when walking back heard a slow creak from the flap as it opened up.

If that makes sense.

[z4s4]

I am a new Z4 owner with a 2011 35is that has over 70K on it. The first thing I found on the cold start was this terrible rattle from the right rear. This forced me to design a better muffler flap solution that fixes the rattle problem completely and takes only 15 minute to make and install.

The issue in this design is that you have a large heat difference that could cause the flap to become tight once the exhaust starts to flow. The designers probably made the clearances a bit larger because of this. So the rattler is not from the vacuum actuator but the flap. The vibration in the muffler system is rattling the flap when the right frequency is present. If you simply apply a slight amount of pressure to the flap shaft it will stop the rattle at any frequency.

Using a ~2" length light coil spring with closed rounded ends can do the trick (You can find these at harbor freight). Bend the ends to form a round that is slightly larger than the flap shaft diameter on both sides. Attach the spring from one side of shaft to the other by stretching it and you now have tension on the shaft. Add a small amount of high temp thick grease to allow the flap to rotate freely and you are done...

Hope this helps....
Thanks z4s4
PS: Any one know where you can get a service manual for this car?