MPS6 rear diff switch

[kmh001]

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.

[tricache]

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

[EQ]

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.

[shakespeare]

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

[MattMPS3]

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

[PaulG]

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

[kmh001]

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.

[shakespeare]

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!

[MattMPS3]

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.

[kmh001]

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.