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      04-18-2013, 09:35 AM   #1
ManiacGT
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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.
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Last edited by ManiacGT; 04-18-2013 at 09:37 AM. Reason: Typo
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      04-18-2013, 09:45 AM   #2
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pics?
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      04-18-2013, 10:53 AM   #3
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Maniac, you just live to fiddle around with your car! I think nothing would give you more pleasure than dismantling the thing and putting it back together the way you like it. More power to you!
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      04-18-2013, 10:57 AM   #4
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Quote:
Originally Posted by rking117 View Post
pics?
Yowzer man... you responded 10 minutes after I wrote it, where I mentioned I don't have any pics but I'll get some for you
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      04-18-2013, 10:58 AM   #5
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Quote:
Originally Posted by jparnes1 View Post
Maniac, you just live to fiddle around with your car! I think nothing would give you more pleasure than dismantling the thing and putting it back together the way you like it. More power to you!
You're probably right, its in my nature... and while I tried really hard not to say 'I'd make a better job than BMW did' I won't... oh damn, I just did
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      04-18-2013, 12:54 PM   #6
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Bravo! Nice thinking-cap fix. Interested to see Your pics.
I found a Jubilee pic that we also call a hose clamp, or worm gear clamp.

Just FYI, the JB4 tuner enables the driver to use the steering wheel controls to command the flap open and close, see command 4/4 and 4/5 on the list of JB4 commands. I read that it helps some people with noise abatement for early morning startup in their neighborhoods.
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      04-18-2013, 01:08 PM   #7
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It still rattles a tiny bit on start up but its nowhere near as bad as if left alone and lasts a few seconds. You also can no longer hear it when driving around as you could just before. I'd rather have a couple of seconds of tiny rattle over the full on BOOOOM for 30 secs when starting the car. Prob just needs a little more adjustment to make it silent...

Pic...



There are two to ensure the top one can't move when bumped against the actuator. The placement takes a little experimentation but they're easy to move around and tighten back up.

To make this completely quiet, my next test is to put a small spring between a hole on the actuator bracket (holes are there already) and the bottom clip I've put on. This should assist the vacuum actuator in pulling the flap 100% closed as it seems the spring inside the actuator overwhelms the vacuum part which is why the rattle exists. If I can take some pressure off that internal spring by putting an external spring on the clip, that should do the trick totally.
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Last edited by ManiacGT; 04-18-2013 at 01:20 PM.
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      04-19-2013, 03:46 PM   #8
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Is it easiest than put a cap into the hose?
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      04-19-2013, 04:00 PM   #9
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Good fix (and inexpensive).
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      04-20-2013, 02:08 AM   #10
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Quote:
Originally Posted by Frogg
Is it easiest than put a cap into the hose?
You didn't read my post then?

Capping the hose makes the exhaust very very loud at cold start. I wanted a louder exhaust but not too loud and this does the trick while also stopping the flap rattle some of us have.
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      04-20-2013, 05:30 AM   #11
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Quote:
Originally Posted by ManiacGT View Post
You didn't read my post then?

Capping the hose makes the exhaust very very loud at cold start. I wanted a louder exhaust but not too loud and this does the trick while also stopping the flap rattle some of us have.
Oh ok, excuse me i haven't all understand before your answer
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      04-21-2013, 07:30 AM   #12
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Quote:
Originally Posted by Frogg View Post
Oh ok, excuse me i haven't all understand before your answer
No worries... your English is better than my French
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      04-21-2013, 12:44 PM   #13
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dumb question but.. when does the flap open normally? Wide open throttle in sport / sport + ?
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      04-21-2013, 02:06 PM   #14
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Quote:
Originally Posted by nicknaz View Post
dumb question but.. when does the flap open normally? Wide open throttle in sport / sport + ?
I forget, it's either wide open on start up or when the engine is warmed up. but either way, sport or sport+ has nothing to do with it.
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      04-21-2013, 02:23 PM   #15
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It opens and closes constantly under different conditions.
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      04-21-2013, 02:55 PM   #16
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Quote:
Originally Posted by ManiacGT View Post
It opens and closes constantly under different conditions.
sooo..... what are those conditions? Search wasn't too helpful...

I ask because the stock exhaust on my 35i seems plenty loud on WOT / drones on freeway and I wonder if there has been a change cross model years (or if ManiacGT is fully embracing his inner ricer )
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      04-21-2013, 03:30 PM   #17
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Quote:
Originally Posted by nicknaz
Quote:
Originally Posted by ManiacGT View Post
It opens and closes constantly under different conditions.
sooo..... what are those conditions? Search wasn't too helpful...

I ask because the stock exhaust on my 35i seems plenty loud on WOT / drones on freeway and I wonder if there has been a change cross model years (or if ManiacGT is fully embracing his inner ricer )
You're looking for a definition.. There isn't one, its condition based.

It opens to allow full power breathing when required and closed to prevent drone when undesirable. Conditions are determined by the ECU.
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      10-28-2013, 01:07 AM   #18
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Smile Disabling the exhaust flap acutator solved all my problems rattle noise and power pro

I had been driving my 2010 3.5i for a few months with lots of weird noise, but after looking at some threads saying it was normal for new BMW for many weird noise, I didn't pay attention any more. It was not until when I stepped the gas to the floor once when racing up a slope on street, feeling and hearing the RPM seemed to be obstructed by something. I took much research online and compare the noise, I finally disable the acutator, and all the problem was solved. Basically, the noises have 3 types: (1) the 'click' noise when the flap closes hitting or rubbing the exhaust pipe, (2) another 'click' noise when the acutator moves the push rod and when the pivot points of the rod system seem loose, (3) shaking of the closed flap, hitting against the exhaust pipe, giving 'zeeee' noise.

Mechnically-wise, BMW's design seems to be simple for such an important thing. Shouldn't they have made it electronically controlled?

Last edited by shlai; 10-28-2013 at 01:13 AM.
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      10-28-2013, 06:24 AM   #19
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It is electronically controlled, the controller is inside the boot (trunk)... its just moved by vacuum actuator. Either way, its a crap design because it's well known to fail.
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      10-29-2013, 01:18 AM   #20
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Some said that the exhaust flap is important for non-turbo car to maintain power at certain RPM. How about our 3.5i? The turbo probably doesn't run probably after 2500 rpm I heard. Will disabling the flap affect the performance below 2500 rpm.
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      10-29-2013, 06:36 AM   #21
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Its to lower noise pollution... no other reason.
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      10-29-2013, 07:32 AM   #22
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Thanks for you reply. I have disconnected the pipe and acutator and capped them. Do you think I should also secure the push rod as well like some friend up in the thread above did? I notice the spring of the acutator is very strong in keeping the flap open, but in case the flay may still move during spirit drive on very bumpy road.
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