MPT clutch capacity?

[Tapani]

How many of you guys with force fed engines suffer from any substantial front wheel spin? What is the torque handling capacity of the MPT clutch? Mine spins all wheels on gravel, but only the front ones on paved surface - even when launching in manual second. Just trying to figure out if the AWD system does what it should, do not want the break anything (see the cracked dront diff thread). Thanks, Tapani

- edit: I did a number of stand still launces on gravel. Starting in "Drive", "2nd manual" and "1st". I just let the brakes free and then pushed the other pedal down w/o building boost against the brakes. The turbo spools below the converter stall speed....

We know that the solenoid C map is different for selector "1st" position and thus more torque should go to the rear wheels "faster". This is clearly demonstrated in the attached image (based on raw 10 msec g-force data, measurement start is triggered by 0,01g so all trends start from 0 time).

It takes well over a half a second for the MPT clutch to apply both in "Drive" and in "2nd manual" while it transfers torque "immediately" when the selector in is "1st". This can also be seen while looking at the wheels - all spin from the "go" when in "1st".

So my conclusion is: Launching the car with full power while the selector in any other position than "1st" could be very rough on the front diff. Same thig while cornering and over powering the grip at either or both front wheels.... the MPT will react quite slowly.

Has anyone installed a switch to max out the MPT torque handling?

I haven't tried on paved surface yet.

[oab_au]

As far as I know!
The Transfer clutch will be applied based on,
1. gear position, the lower the gear the higher the pressure.

2. road speed. The lower the speed the higher the applied pressure.

3. Throttle position. The higher the throttle position the higher the pressure.

1st and reverse selected, uses a higher throttle pressure component.

In drive, the box is in 1st, the road speed is low, and the throttle position is low. So the applied pressure is low.
You floor the throttle, as the throttle position is increased the pressure is increased also. The electrical signal is instant increased, but the line pressure to the clutch has to rise to apply the clutch.
This is where the lag is found. This is not like applying the brakes, as there is not a maintained pressure in the system. The oil has to flow through restrictor holes in the transfer plate, through the lathe cut sealing rings on the mainshaft, to the piston in the rear case. with all the associated leaks, to apply the transfer clutch.
Hence there is a delay in engagement, depending on the condition of the box.

I have set up a Quick Change with a switch to lock the clutch for a particular member that does bracket racing, to ensure the clutch will not lag on the drag strip. You need a 39 ohm resistor connected in series with the C solenoid, that can be switched out for normal driving.

Harvey.

[Tapani]

Ok, thank you.

I guess the first thing to do (before going VTD) is to tear the transfer clutch apart and refresh if needed. Also the solenoid C and the valve body. Even on gravel the front wheels spin faster than the rear ones - this can be seen visually from the tracks......

Are there different type of plates available (other than thickness for adjustment)? The 4.444 box is out of an 1997 Outback - are the SVX parts the same or do they have a higher torque capacity? How about the turbo Foresters?

Tapani

[Tapani]

An update for those who are curious,

After yesterdays trials the MPT clutch works actually better. No binding (quite a bit before), except just a little if the selector is in "1st".

It also seems to "bite" a bit stronger on gravel, in "1st" the rear wheels really throw sand quite a bit :-).

I hooked up the ECUtuner to check the TPS signal vs sol C duty cycle. Please find results in the attached image. The TPS voltage formula in the ECUtuner tranny definition file is incorrect, so closed throttle is 10,196 and fully open is 80,384. Percentage of 5V?

On idle in "P" the duty cycle is 95%. At 2000rpm indicated (against brakes) showed 20 for TPS and 35% for duty cycle in "D" and 22% in "1st". While doing that I checked the stall speed - 3200rpm @ 5PSI... I do not know whether there is an Outback or a SVX converter installed.... probably from the Outback, because the original tranny broke and that would have been contaminated.

All other numbers are with ignition on, but engine off.

From this respect it would probably help a lot to load the engine to 2000 -2500 rpm before releasing the brakes - the MPT would be more enganged to begin with (not to mention spooling the turbo).

Tapani

[Tapani]

I browsed thru all service manuals I found.... it appears, that the SVX MPT has 6 sets of plates, the outback 1997 tranny has 5, a n/a 2006 Forester has 5 sets and a turbo again has 6.

So, the torque handling capacity of the MPT in the 1997 Outback 4.444 tranny I have may not be on par with the torque available ...... there are similar differences in the other clutches too - even the 2.0 (4.11) and 2.5 (4.444) Outback trannies (in 1997) had different number of plates for example in the high clutch - the transfer clutches were the same, though.

Does anyone know if the Phase 2 parts are compatible with the Phase 1? Can I just swap the plate set or do I have to swap the basket and other parts too? If the basket has to be replaced then the reduction gears must be changed too.

Anyone?

I attached an image showing some g-values from a stand still launch in 1st gear. Interesting things can be seen.... the blue line is just releasing the brakes and then rather slowly pushing the loud pedal down. The red line includes raising the revs to 2000 rpm prior to releasing the brakes (stall is 3200rpm). The first sharp increase in acceleration is due to the converter doing its job - multiplying the torque. The first tip is where the coupling point is reached (stator starts to rotate with the impeller and the turbine), the following further increase is the turbo finally spooling . This delay could be drasically shortened or even eliminated by stalling the converter fully prior to releasing the brakes. See the difference between the red and the blue lines - just by featering the throttle to increase the revs to 2k.

The chatter under full boost in first is, again, due to front wheels reaching the limit of traction.... this is on dry pavement. The tires are 6 years old Michelin Pilot Sports, 40 degrees F temperature. New tires for next summer are called for.

Also, the drastic decrease in torque before shift into second can be clearly seen..... too small a turbo . The butt dyno supports the graph too.

BTW, I just left the selector in "1st" to fully load the transfer clutch and let the TCU force the shift at 6800rpm engine rev limit (programmed in the TCU, not the ECU).

Tapani