[roy@gambitmotorsport]

I have never been a fan of the 335i's seatbelt-assistant. It activates slower than I'd like, failed to deliver the belt every few days, and required "intervention" to fix about once a month. After driving an M6 without it and hearing the new M3 is the same, I considered it time to abort. Other people absolutely love it, so to each his own. I found a DIY to disable them some time ago and was happy with the results.

http://www.e90post.com/forums/showthread.php?t=31248

I occasionally have a minor rattle, like a rock or small plastic piece rolling around under hard cornering and braking. Thinking it may have been something breaking off on one of my previous seatbelt-assistant "repairs", I decided to open things up and go to town. Seeing no way to the bottom I immediately gave up on this, but decided to physically remove the seatbelt-assistants, was then surprised and pleased by the difference sound quality coming from the rear, so am retroactively posting a DIY. Hope you enjoy it or at least find it interesting - the results of following anything herein are completely your own.

[roy@gambitmotorsport]

According to the previously mentioned DIY, remove fuse 25. It's been a while since I did this, so check the original thread and your fuse box "map". This will disable the seatbelt-assistants' activation. According to my experience and others', this will not interfere with safety systems, as things like "no seatbelt" warning still function and no airbag warnings go off.

[roy@gambitmotorsport]

If you care not for the future of your seatbelt-assistants (i.e. possibly during resale), do what it takes to rip the arm out. Just pull straight out, it hurts nothing other than the unit itself. Otherwise, deal with the minor complications in motor removal a bit later.

[roy@gambitmotorsport]

Dislodge the door-trim lining covering the sides of the rear panels.

[roy@gambitmotorsport]

Pull the side out - see picture. It takes some force, but comes apart before you really feel you're going to break anything.

[roy@gambitmotorsport]

Pull out all of the foam surrounding the two speakers. This is not required to remove the seatbelt-assistant motor, but lends to the sound quality by adding resonance and an air passage out once the motor is removed.

This picture is taken afterwards. Beforehand, you can't really see the speakers.

[roy@gambitmotorsport]

Then, remove the motor. It's held in by three nuts. The upper front one should be removed. The other two can just be loosened. There are two sets of wires running to it. One is a sensor, which can be pulled in-tact, and left to hang freely. The other is a set of four wires running to the motor. I ended up cutting and taping these. If you may want to revert this someday, you could do the same, but leave about 1/2 inch connected to the motor, in order to fit male/female fasteners to reconnect in the future. Disassembling the motor itself to get at some "plug" proved useless.

[roy@gambitmotorsport]

Ok - close up and do the same for the other side. Here's a picture of the end result.

[roy@gambitmotorsport]

All done! The removal of these units may seem silly and may have originally been an act of annihilation at a stupid engineering concept. I was planning on putting the arm "hands" back in by some means to make it look the same, until I turned on the radio.

I used to have a car whose radio was the same as mine in the highs and mids, but with slightly better bass. Now, the 335i exceeds it a bit in all three areas. I truly don't believe it's just in my head (except the pleasure), because I've listened to several of my favorite CDs in all three environments, always noting the difference. Honestly, I never knew where the top of this cars volume was, as I never turned it up all the way previously, because the sound would degrade. No more. For the record, my fader is at v4 rear.

If anyone else goes for this, I'd like to know your impressions. Also, if you live in the SoCal area and would like to hear the difference, drop on by. It's not "night and day", but it's a little more noticeable than the golf tee mod was to exhaust enthusiasts, IMO.

[roy@gambitmotorsport]

I may put a thin, air-passable, fabric screen in place sometime in the future. Nothing more though, as I think the improvement in sound is a function of both the added posterior space through foam removal and air passage for resonance.

Can't wait for the "I can't believe..." and "That's ghetto..." strings, though.

If anyone out there is a sound engineer or has just built really good speaker enclosures before and can explain why this could be sounding better in more definite terms, I'd appreciate the insight.

[XPO186]

interesting...

I think ppl would complain about this thing less if it was built more robustly,

like circa E30

[XPO186]

btw, cool DIY

[roy@gambitmotorsport]

Originally Posted by XPO186

I think ppl would complain about this thing less if it was built more robustly,

I tried lovin' them, but after the third or fourth time stopping what I was doing to try to get them to work properly again, I said bye!

[roy@gambitmotorsport]

Originally Posted by XPO186

btw, cool DIY

Thanks! I wasn't planning on a DIY, as I wasn't expecting the sound difference. But, afterwards, it kind of reminds me of replacing the 5 1/4" with 6x9" in my first car (a '79 320i - hope I'm remembering the rear deck sizes right). With the same stereo and amp, it's not like you're booming the block now, but everything's just a little deeper and more precise.

[RiXst3r]

Interesting... probably sounds like when you port a speaker box... lets the speaker move easier and you get some deeper reverberations from the rear of the cone as well

[roy@gambitmotorsport]

Just played some more CDs and FM radio today - definitely an improvement. Basically, everything used to start sounding a little cluttered when I turned it up, where now it's crisper and deeper.

[roy@gambitmotorsport]

Originally Posted by Brisk

nice DIY..

just a question as im trying to fix my own arm...
there is the main seatbelt arm and than there is the smaller plastic that leans up aganist it... it has some grooves and seems to catch onto something within the motor assmebly, anyway u can take a picture or describe to me how i can get this secondary palstic piece back onto its track or groove?

thanks alot.

I'm sorry, there's not much left of my original units.

If you're talking about how the inner (thinner) arm fit into the outer (fatter) arm and motor unit, I couldn't say. Except that the fact that they kept popping out of place was one of the reasons I deleted. Pushing it back in seemed to do the trick most of the time - not offering guarantees.

I heard in a post somewhere here I think that the dealer covers fixes on these units, as they have issues and it's accepted. I'd say that's your best bet if the car's leased. Otherwise, how about more bass?

[roy@gambitmotorsport]

I revise this.

The difference is "night and day" in sound response. Just heard "In the air tonight" by Phil Collins on the radio today - nothing at all like stock sound response with radio (which is especially muffled compared to CD), with my new set-up.

If turning your volume up past a certain point results in anything but *better feelings*, this mod will turn it to gold with no cost. If you're leasing, sorry - for this and other things.