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Thread: MPS6 rear diff switch

  1. #1

    Default MPS6 rear diff switch

    This is a simple mod that allows you to turn off the rear diff. My motivation for doing this mod was to stop the resonant vibration that occurs in 6th gear at around 100 km/h.

    You might have seen my testing video that showed there is torque going to the rear diff all the time. This mod effectively tells the ECU and the 4WD control unit that the hand brake is applied which completely disconnects the rear diff, but without the disadvantage of dragging the rear brakes as would happen if you took the first notch of hand brake.

    When you throw the switch to put the car into FWD mode the hand brake light will appear on the dash as a useful reminder that you don't have AWD available.

    You'll need:
    1 x length of wire (length depends on where you mount the switch)
    1 x cable splice
    1 x circular cable terminal
    1 x switch
    2 x spade connectors for the switch

    What to do:

    Preparation: Grab the edges of the centre console cup holder section and pull it out. It's a press-fit, but be careful not to break anything.
    Step 1: Using the cable splice, attach one end of the new wire to the brown wire that goes to the hand brake position switch. Be very careful with this, it's a thin wire and if you don't align the splice correctly you could accidentally cut the brown wire.
    Step 2: Attach the circular cable terminal to the other end of the new wire and secure it somewhere that will give a good earth. I used one of the hand brake bracket bolts.
    Step 3: Cut the new wire at the appropriate place and connect the two ends to the switch using the spade connectors.
    Step 4: Re-install the cup holder by pressing it back in. You're done.



    I still haven't decided where to mount my switch so it's swinging loose inside the console compartment. I'll probably drill a hole and put it on the front face of the console compartment. If you do this mod you can put the switch anywhere.

    This is my loose switch, sometimes I hang it out the front of the console.



    Why would you do this mod? In my case it was only to turn off the vibration that was driving me nuts on long highway trips. But you may have your own reasons.

    Warning: DO THIS AT YOUR OWN RISK. When in FWD mode you could experience wheel spin, severe under steer and loss of vehicle control. So don't turn the DSC off when the rear diff is turned off.
    Last edited by kmh001; 27-04-2009 at 12:30 PM.

    Gone to Volvo


  2. #2
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    If only you could do this in reverse do you could make the car RWD...

  3. #3
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    EXCELLENT WRITE UP. Thanks very much. Cool little mod.

    Funny, I never though I had diff whine until I did the "one knotch handbrake test"...its annoying the crap outta me now.
    Last edited by EQ; 30-04-2009 at 03:43 PM.

  4. #4
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    Agree, excellent write up, well documented.

    My only question, as I'm considering this becuase I've got the dreaded resonant vibration and Mazda cannot seem to find a solution.

    When this is activated, does it actuate the electronic clutch pack which controls drive to the rear? If so if you were running in FWD mode for extended periods say a 4 hour highway run, would it cause added stress and wear to the rear clutch?

    Thanks
    Chris

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    Quote Originally Posted by kmh001 View Post
    Warning: DO THIS AT YOUR OWN RISK. When in FWD mode you could experience wheel spin, severe under steer and loss of vehicle control. So don't turn the DSC off when the rear diff is turned off.
    Wow, just like driving an MPS3

  6. #6

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    thats the real reason they want to do it... AWD is boring... to safe... haha

  7. #7

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    That's why I call it a MPS3 switch

    Shakes, the switch has the opposite effect that you've suggested. It cuts power to the rear diff coupling solenoid so the clutch pack disengages. Should run cooler too.

    Thankfully the Germans may have found the solution to the vibration.

  8. #8
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    Quote Originally Posted by kmh001 View Post
    That's why I call it a MPS3 switch

    Shakes, the switch has the opposite effect that you've suggested. It cuts power to the rear diff coupling solenoid so the clutch pack disengages. Should run cooler too.

    Thankfully the Germans may have found the solution to the vibration.
    Thanks Mate, that's exactly the response I wanted to hear, when I get back from Holidays I'm off to Dick Smiths to but me a switch

    I've just spent the last %#%$* 10 minutes under my rear end tightening the bolts on the forward diff mount - will post the story in a new Diff thread and what outcome transpires after Mazda have a look on Thursday!
    R36 - Just like an MPS6 except with a growly V6

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    It would be interesting to see if you had any power differences between 4wd & 2wd modes, a trip to a dyno could be in order for this one.

  10. #10

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    That's a good question. There's a guy in the US who is certain 2wd mode make his quarter mile times quicker. On the other hand people have theorised that regardless of whether the diff is turned on or off, all the the drive train components still turn so there is still power being consumed to turn them, hence no power difference.

    I tend to think the later theory sounds more plausible.

  11. #11
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    I bought all the gear from supercheap for $24.00. Goes in...when I can find ten mins.

    Is there a link to the germans?

  12. #12

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    Do you speak German? The google translator is a bit rough but you can get the gist of what they're saying. Go to the technology section and it's about the 12th thread down.

    Translated version of http://www.mazda-mps.net/

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    My brothers girlfriend may be of assistance here....

  14. #14
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    Hey all,

    Fitted my MPS3 switch today and after a short freeway run, it is definitely nice not to feel and hear the resonant vibration, thanks again kmh001, great write up and very easy to follow. Some pics of where my switch is.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  15. #15

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    Nice one. That's a classy looking switch. Where did you get it?

  16. #16
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    Super Cheap Auto $7.48
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  17. #17

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    Quote Originally Posted by kmh001 View Post
    That's a good question. There's a guy in the US who is certain 2wd mode make his quarter mile times quicker. On the other hand people have theorised that regardless of whether the diff is turned on or off, all the the drive train components still turn so there is still power being consumed to turn them, hence no power difference.

    I tend to think the later theory sounds more plausible.
    I think that even if the drive train components still turn, it doesn't particularly mean that it will limit performance to the same as AWD mode, because even though the parts are turning, there is absolutely no load on them. It's like having an Air conditioner unit installed in you car but not running, the belt still spins (like disconnected AWD diff) but the losses are not noticable when it is off, but when the AC is cranking(like rear diff connected) you will feel the power losses.
    I believe the guy in the US has a valid point. Besides, if he is getting quicker quarter mile times, it will be no thanks to AWD (because it's been disconnected) therefore it can only mean more power available to the front wheels.
    Last edited by mpsJOE; 31-05-2009 at 09:29 AM.
    .

  18. #18

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    I should qualify that comment; he uses 2wd after the launch, ie he turns the rear diff off when he is in 2nd and traction is no longer an issue. If he used 2wd mode from the start his quarter mile times would be horribly slow due to the lack of traction.

    Anyway, I got a nice switch like shakes to replace the original and attached it to the front of the console box where it's easy to reach between gear changes. I've been experimenting with turning it off more often and I'm convinced that I'm picking up around 15kw or so when the rear diff is off.



    I don't have any data yet but it's definitely noticeable. It's a bit like a KERS system where you can inject a bit more speed on the straights for overtaking when you're in third gear or higher.

    Trying to milk everything out of the car means switching it on and off rapidly (because the car is significantly quicker through corners in AWD mode) but between that and changing gears and steering I feel like a one-armed paper hanger. I'm starting to think that reprogramming the 4wd control module could improve performance almost as much as reprogramming the ECU.

    Gone to Volvo


  19. #19
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    Looks good Mal, the location you've picked is probably quicker to reach than where I've placed mine. If I was to try and use my switch to squeeze out maximum performance I'd need three arms!

    The idea of reprogramming the 4wd module is a good one!

  20. #20

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    Thanks for the link to the german site! Sort of useful but with 17 pages of half german to read its hard!

    Did anyone get to read what the fix was for the problem. ???????????????????????
    Mine seems exacatly like the 'OTTMAR's' problem... vibration through steering wheel aswell as shudder and whine.

    Thanks

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