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      04-18-2013, 09:35 AM   #1
ManiacGT
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Drives: Z4 sDrive 35i
Join Date: Jan 2011
Location: Manchester, UK

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

Well I've been running with a disabled exhaust flap in my 35i for some months as last summer it started the dreaded flap rattle just like the 335i etc..

While the extra drone on the motorway is acceptable, and overall there are some louder pops etc that are quite nice. I was getting a bit fed up with the loud noise at cold start up as the flap was disabled.

So, thinking cap on, I determined that the issue was the fact that the vacuum actuator on the exhaust flap was simply not closing the flap fully and this caused the flap to rattle against the exhaust pipe internally on each exhaust pulse. You can't adjust the actuator and you can't easily replace it, you have to replace the entire muffler/silencer on that side.

Well I'm not about to replace half my 3.5 year old exhaust so after more thought I came up with the idea that, if the actuator cannot reliably hold the flap fully closed under vacuum (perhaps due to a leak or whatever) then perhaps it can hold it reliably closed around 80% or so.

More thinking required on how to do this, one option being to place a small self tapping screw through the exhaust where the flap rests against the tube to stop the rattle. Problems with this were a) drilling in a confined space b) the toughened metal ring around the flap mechanism and c) the flap may still rattle against the screw.

So, the next idea was Jubilee clips.. not sure if that's what you call them in the US, and I'll get some pics on here when I can, but this has done the trick. I placed two clips around the rod from the vacuum actuator, so that, when the actuator pulls the rod up to close the exhaust flap, the clips prevent it from pulling it closed to 100% but instead leave the flap a few mm away from the wall of the exhaust so it closes say 80/90%. This is enough to make the car much quieter on start up, while reducing the rattle to near nothing at all.

Having tested it on the way to the office this morning, the car exhaust is now somewhere between normal and loud (GolfT) mod. Quieter on cold start up so I don't annoy the neighbours/sound like a ricer(chav), but still louder than stock to make me smile a bit.

Job done for mere pennys.

Last edited by ManiacGT; 04-18-2013 at 09:37 AM.. Reason: Typo
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