BMW M3 Forum (E90 E92)

BMW Garage BMW Meets Register Search Today's Posts Mark Forums Read


Go Back   M3Post - BMW M3 Forum > E90/E92 M3 Technical Topics > DIY Guides/ Discussions
 
MINHS Automotive
Post Reply
 
Thread Tools Search this Thread
      03-06-2015, 06:40 PM   #1
warranty
New Member
2
Rep
28
Posts

Drives: 2008 M3 sedan
Join Date: Jan 2010
Location: California

iTrader: (1)

DIY 6MT engine start without clutch pedal modification

Background
All modern manual transmission cars apparently have a clutch interlock safety feature which prevents the engine from starting unless the clutch is fully depressed. On other vehicles I have owned, repeated starts with a fully depressed clutch causes unnecessary crank/bearing wear since there's essentially no oil pressure under such conditions, especially with aftermarket clutches equipped with high-pressure pressure plates (which exert more lateral pressure on the crank). Such unnecessary mechanical wear leads to the so-called "crank walk" (lateral crank movement).

Objective of the modification
Since I'm a careful driver and I always check that my 6MT transmission is in neutral before starting the car, I want to prevent unnecessary engine wear by bypassing the clutch interlock feature WHEN I CHOOSE TO. I also want to retain the factory clutch interlock feature (if it's possible), while keeping the mod stealthy or "invisible" if possible. After much research and testing, I think I've found the perfect solution to accomplish my objectives on my 08 6MT E90 M3.

Theory of operation
While older cars have mechanical clutch switches: typically one at the fully-depressed position for clutch interlock, and one at the slightly-depressed position to disengage cruise control, etc., BMW has gone to a single, more advanced magnetic solid-state clutch switch that replaces the two separate mechanical switches. A magnet is embedded in the clutch master cylinder that causes the clutch switch (which is clipped on the master cylinder) to trigger the signals needed for clutch interlock. You can see the circuit diagram of the BMW clutch switch and an illustrated picture of the actual clutch switch connector below.





Signal 1 (brown/black): Ground
Signal 2 (blue/brown): This signal is triggered when the clutch pedal is depressed just slightly--it goes to DME for cruise control, idle-up such as when you push in the clutch to prepare for take-off, etc.
Signal 3 (purple/yellow): This is +12V supply for the clutch switch
Signal 4 (blue/black): This signal is triggered and goes to +12V only when the clutch pedal is fully depressed--it goes to CAS for clutch interlock.

Basically, what my mod does is that I use an additional momentary-on tactile switch to simulate signal 4 of the clutch switch; this is done by using the tactile switch to short signal 4 to signal 3 (+12V) as long as the switch is depressed. Simple, right? Instead of pushing in the clutch pedal, I simply depress my switch AND the engine-start switch to start the car. The factory clutch interlock feature is fully retained: meaning a valet, who is unaware of my modification, still has to push in the clutch to start the vehicle. Other features like cruise control and automatic idle-up are unaffected since they use a different signal on the clutch switch.

Since all modern manual BMW's (and Mini's) since E46 seem to use the same exact clutch switch, I suspect the same mod will work on all other BMW's but of course you'll be responsible to verify this yourself if you don't happen to have an E9x. And, perform the mod and accept the consequences at your own risk, yada yada.

To keep the mod stealthy, on my E90 M3 since there is no factory front fog light, I decided to use the blank fog light switch as my "invisible switch." Instead of modifying the headlight switch circuitry (which is possible), I added a tactile switch behind the blank foglight button and added some wires which you can see in my description later.

Parts--and talent--needed
- Basic electrical/soldering skills
- Momentary tactile switch (Digikey part #CKN1860CT-ND): this one can handle more than an amp of current @32V so it should last the life of the car. Of course, you're free to choose whatever momentary-on switch you want and you can install it anywhere you want.
- Miscellaneous wires, connectors, and heat shrink wraps to keep your work neat and tidy

Step 1
You'll need to remove the driver-side lower dash cover and remove the clutch switch from the clutch master cylinder. Pelican parts happens to have an excellent step-by-step tutorial with pictures here. The clutch switch easily unclips from the master cylinder.

Step 2
Identify wires #3 and #4 on the clutch switch, and solder on 2 wires that will lead to the additional tactile switch. The tactile switch will short signal 4 to signal 3 (+12V) to simulate clutch pedal being fully depressed. Sorry, I didn't take pictures here but it's easy enough.

Step 3
(Only do this if you choose to implement the "stealth button" like mine. Otherwise you can put the tactile switch of your choice anywhere you want)
Remove the headlight switch and open it up. There's plenty of DIY out there, such as this excellent one. I used a piece of double-sided tape to affix my tactile switch on top of the LED under the factory foglight button and soldered 2 wires to it. Then I routed the wires through a small hole I drilled behind the headlight switch body. Similar to the el-cheapo rear foglight mod, I used a few Lego pieces to allow the blank foglight button to actuate my tactile switch as you'll see later. Finally, connect the tactile switch wires with the wires that come from step 2 and voila, you're done!

You can see a close-up picture of my tactile switch in the picture below. Notice it is affixed on the little silicone plateau on top of the LED for the factory foglight:


In the picture below you can see the lego pieces I used on the left. These are el-cheapo Chinese knock-off Legos so I don't feel bad raiding my kids' drawer. The socket on the bottom lego piece fits perfectly over the tactile switch I chose (by design). I also did the poorman's rear foglight mod while I opened up the headlight switch, and you can see the lego pieces I used for that on the right..


It takes a little patience to put the headlight switch back together but it's possible. I would take pictures of the finished product but you know what? It just looks like a factory E9x M3 switch (as that's my intention) so there's not much to look at.

Enjoy!
Attached Images
    
__________________

2008 6MT M3 sedan
Appreciate 2
      03-09-2015, 03:13 PM   #2
IlChengis
once Treppiede
IlChengis's Avatar
Italy
16
Rep
888
Posts

Drives: 2012 E92 M3
Join Date: Aug 2008
Location: Miami and Atlanta

iTrader: (4)

I am surprised this DIY hasn't gotten any love in three days, as it's written very well and illustrates something I had been wanting to investigate for some time.

Thank you for investing the time to put this together man, great work!
__________________
2013 E92 M3 | 6MT | AlpWhite | SilverNovillo | CarbonTrim | ZCP | PremiumPkg | Alarm
2009 E92 335i | 6MT | AlpWhite | CoralRed | AlumTrim | M-Sport | Nav | Logic7 | Alarm (sold to a friend - still in the family)
Appreciate 0
      03-09-2015, 04:16 PM   #3
whats77inaname
Native Texan
United_States
83
Rep
2,149
Posts

Drives: when at all possible
Join Date: Aug 2011
Location: Tx

iTrader: (17)

Dude, as a DIYer, this is pretty awesome, especially when considering adding remote start.

This company
provides remote start BMWs, incorporating it into your OEM keyfob....just not for 6MTs. Seems like your mod would allow this to work for those of us w/a manual.

www.m3post.com/forums/showthread.php?t=869327

Last edited by whats77inaname; 03-09-2015 at 04:31 PM.
Appreciate 0
      03-09-2015, 07:50 PM   #4
Law
Captain
Law's Avatar
Taiwan
65
Rep
636
Posts

Drives: E46 M3 6MT | E90 M3 6MT
Join Date: Jan 2009
Location: Los Angeles, CA

iTrader: (0)

Garage List
2004 BMW M3  [5.00]
Awesome write up, this is going to help a lot of people
__________________
2011 E90 ///M3 6MT (Current)
| RAYS | EIBACH | AKRAPOVIČ |
2004 E46 ///M3 6MT (Past)
| HKS | KW | RECARO | RAYS |
Appreciate 0
      03-10-2015, 02:00 AM   #5
warranty
New Member
2
Rep
28
Posts

Drives: 2008 M3 sedan
Join Date: Jan 2010
Location: California

iTrader: (1)

Thanks guys. I actually bought a spare clutch switch so I could play with it and verify its operation so that I know for sure the modification is safe and effective, and I thought others would benefit from this information. As @whats77inaname pointed out, a remote starter that can use a relay to temporarily "short" pins 3 & 4 of the clutch switch can remote start a 6MT that wouldn't have otherwise been possible. I had contemplated the remote starter at one point and that was indeed one of my motivations for performing this mod.

I'm not sure how easy it is for thieves to hotwire and steal these modern cars with smart keys, but another idea for a theft-deterrent feature is to use a toggle switch to turn off the 12V (signal 3) going into the clutch switch. Without +12V, the clutch switch cannot send the "clutch depressed" signal 4 to the CAS, and therefore the engine cannot be started.
__________________

2008 6MT M3 sedan
Appreciate 0
      03-10-2015, 09:35 AM   #6
isherdholi
Private
isherdholi's Avatar
0
Rep
93
Posts

Drives: M3
Join Date: Oct 2012
Location: London, UK

iTrader: (0)

Excellent DIY, but I'm pretty sure you can achieve the same thing using NCSExpert to "code out" the clutch
__________________
Appreciate 0
      03-10-2015, 10:46 AM   #7
whats77inaname
Native Texan
United_States
83
Rep
2,149
Posts

Drives: when at all possible
Join Date: Aug 2011
Location: Tx

iTrader: (17)

Quote:
Originally Posted by warranty View Post
I'm not sure how easy it is for thieves to hotwire and steal these modern cars with smart keys, but another idea for a theft-deterrent feature is to use a toggle switch to turn off the 12V (signal 3) going into the clutch switch. Without +12V, the clutch switch cannot send the "clutch depressed" signal 4 to the CAS, and therefore the engine cannot be started.
Thieves were breaking into cars using keys they cloned on the spot once they had access to the OBDII port. There was a big bru-ha-ha about it about a year ago or so, and BMW offered a coding fix to the EU market, but didn't do anything here, IIRC.

We have the same car ('08/6MT) so if someone wanted it, all they have to do is break the glass, pull up the hand brake and roll it onto a truck. I don't know if you have the OEM alarm, but if you don't, your car comes pre-wired for it (only the '08s do), and you just have to buy the OEM alarm kit, install it, and have it coded in, which I did. The OEM alarm does have a tilt sensor, which is pretty nifty, but no shock sensor, so I followed this DIY to detect glass breakage and did a little something extra to go along with it.

Quote:
Originally Posted by isherdholi View Post
Excellent DIY, but I'm pretty sure you can achieve the same thing using NCSExpert to "code out" the clutch
Cool. Handle that and report back to us, as I haven't seen anyone do that across any of the other BMW forums. I'm always interested in seeing/learning about new options

Last edited by whats77inaname; 03-10-2015 at 12:06 PM.
Appreciate 0
      03-10-2015, 11:14 AM   #8
Craigy
Sporty Puristic 6
Craigy's Avatar
5
Rep
317
Posts

Drives: '09 M3
Join Date: Jun 2013
Location: Louisiana

iTrader: (0)

Quote:
Originally Posted by warranty View Post
Such unnecessary mechanical wear leads to the so-called "crank walk" (lateral crank movement).
Are you a DSM guy?
Appreciate 0
      03-10-2015, 11:19 AM   #9
whats77inaname
Native Texan
United_States
83
Rep
2,149
Posts

Drives: when at all possible
Join Date: Aug 2011
Location: Tx

iTrader: (17)

Quote:
Originally Posted by Craigy View Post
Are you a DSM guy?
Or a 2JZ-GTE guy?

BTW, OP, I wired my 5MT truck to bypass the clutch on start, so I have a special appreciation for what you did here.
Appreciate 0
      03-10-2015, 03:08 PM   #10
e92zero
Captain
21
Rep
673
Posts

Drives: 2011 E92 BW
Join Date: May 2010
Location: somewhere in US

iTrader: (0)

Thanks for the OP for this for the idea of a hidden switch to prevent the car from being started. I did a hidden starter bypass switch before on my integra. This is the first I heard about the wear on the lateral support bearing for the crank-walk. But I guess it make sense. I think I found the 'option' that can be coded in NCS. I will switch it to the brake pedal instead of the clutch and see how it goes and report back here.
Appreciate 0
      03-10-2015, 06:09 PM   #11
warranty
New Member
2
Rep
28
Posts

Drives: 2008 M3 sedan
Join Date: Jan 2010
Location: California

iTrader: (1)

@Craigy ....haha my expert knowledge of "crank walk" gives away my DSM roots eh? My first performance car was indeed a 2GT "wrong wheel drive" DSM which I had modded to hell and back. No crank walk with 230k miles on the original bottom end though!

@whats77inaname....yup, I'm also a 2JZ-GTE guy. In fact, my M3's stable mate is a hardtop 6MT TT Poopra.

Attached Images
 
Appreciate 0
      03-10-2015, 06:45 PM   #12
whats77inaname
Native Texan
United_States
83
Rep
2,149
Posts

Drives: when at all possible
Join Date: Aug 2011
Location: Tx

iTrader: (17)

Quote:
Originally Posted by warranty View Post
@Craigy ....haha my expert knowledge of "crank walk" gives away my DSM roots eh? My first performance car was indeed a 2GT "wrong wheel drive" DSM which I had modded to hell and back. No crank walk with 230k miles on the original bottom end though!

@whats77inaname....yup, I'm also a 2JZ-GTE guy. In fact, my M3's stable mate is a hardtop 6MT TT Poopra.
*lol* I was planning on getting an Alpine White 6MT TT MKIV w/black interior to match my AW 6MT N/A w/black interior M3 for a long while. In fact, I was shopping for one during the time I picked up the M3 (decided that 4 doors are more practical and I can get a coupe later). Always wanted to single turbo one of those....recently (a few months ago) decided to pick up a Noble M400 instead of a Supra. Still one of my all time favorite cars.

To give you an idea of how long I've enjoyed them, that poster you have on the left in your garage? I have that in a shirt that has been unworn for about 15 yrs now and my MKIV model collection numbered well over 200 pieces. I've been trimming it lately
Appreciate 0
Post Reply

Bookmarks

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -4. The time now is 05:20 PM.




m3post
m3post
Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2015, Jelsoft Enterprises Ltd.
1Addicts.com, BIMMERPOST.com, E90Post.com, F30Post.com, M3Post.com, ZPost.com, 5Post.com, 6Post.com, 7Post.com, XBimmers.com logo and trademark are properties of BIMMERPOST