4EAT MPT Clutch assembly

Liberty Valance · Post by **Liberty Valance** » Mon May 21, 2012 7:48 pm

Vehicle: 1990 Liberty GX AWD Auto Sedan

I was experiencing torque bind so went straight in for the Duty C solenoid and what I found was very surprising.

Please view the attached photo.
The extension housing on the left is from my car.
The one on the right is from the same model car.

Both are standard TZ102ZG1AA auto transmissions which match the compliance plate on the vehicle but that's where the similarity ends. They have a completely different MTP assembly. I can't even find rear transmission mounts to suit my car as the extension housing is also a different shape on the outside.

Every automatic first generation AWD Liberty I have looked has a MPT clutch and extension housing on the right. My suspicion is that the box on the left is from an imported vehicle maybe bought unknowingly from a wrecker or left over from a front cut?

I have tried to solve this problem myself and have had some of the best Subaru minds look at it. We are all stumped. Does anyone on this forum have a suggestion about what type of transmission I am looking at here or what vehicle it may have originally come from?

Thanks in advance, Scott.

Gannon · Post by **Gannon** » Mon May 21, 2012 8:19 pm

Have you got more photos with the rear transfer units removed. The one on the left has a gear visible, if it makes up a planatery gearset, you have yourself a VTD or Variable Torque Distribution gearbox, or at least rear end. But to my knowledge, these didnt come out till the 2nd generation turbo models

Liberty Valance · Post by **Liberty Valance** » Mon May 21, 2012 8:51 pm

It's a shame I didn't take a photo of the rear end of the transmission with the extension housing removed. If I try to describe it I would say there is a clutch basket with three planetary gears visible behind still attached to the output shaft when the housing is taken off. That could be a match to what you are describing.

The only other photo I have is of the extension housing still in the vehicle.

If it is a VDT that could explain why I'm still getting torque to the rear with a full 12V on the duty C solenoid. From my brief reading they seem to be performance oriented with rear wheel torque bias.

Gannon · Post by **Gannon** » Tue May 22, 2012 6:36 am

This is a vtd diff

In open mode, it operates as a normal, open differential with a slightly biased torque split of 40 front /60 rear. When locked it gives a 50/50 split or the ECU can vary it anywhere in between.
But I cant remember if it is open or locked when the ECU is giving 100% +12v on duty C. I have a feeling its opposite to the normal multi plate transfer clutch which is why it should need the ECU to match.

The SVX would have been the only Australian delivered model to have VTD in this transmission because starting in Gen3, the auto box was updated and its a little different.

In the Gen3 Liberty, H6 Outbacks and B4 auto's as well as a few Heritage 2.5's optioned with VDC got VDC

Liberty Valance · Post by **Liberty Valance** » Tue May 22, 2012 11:11 am

Thanks mate, this is golden information and is starting to explain a lot of the unusual torque split behaviour I am getting from this transmission. I am still getting some rear wheel drive with the FWD fuse installed.

Almost certainly someone has put a Australian Delivered SVX transmission or perhaps an imported Automatic RS turbo transmission into my car. I can't confirm if the TCU was also swapped but I have studied the TCU wiring diagrams of both models and all the inputs and outputs match even though the colour coding is different.

I want to use this car off road so was planning to put switch on the TCU output to Duty C in order to achieve full lock up on demand but may need to reconsider how I go about that now. Initially I was was cursing this strange box but I am starting to realise it could be a very good thing. Surely the 'performance' orientation of the VTD is going to be a stronger set up that the regular MPT to handle the higher output engines?

One thing remains which is really annoying me:
With FWD fuse installed and the cruise control set at 100km/hr the transmission locks up in fourth at 2500 RPM and has enough torque to pull up long hills without unlocking.
In regular AWD mode (without FWD fuse installed) and the cruise control set at 100km/hr the transmission runs slight higher at 2750 RPM and kicks down at the slightest incline.

Gannon · Post by **Gannon** » Tue May 22, 2012 5:31 pm

So did you notice binding of the driveline when turning sharp corners with the FWD fuse in our out?

Liberty Valance · Post by **Liberty Valance** » Tue May 22, 2012 8:44 pm

I purchased the car at a heavily reduced price because it had torque bind knowing that it would be an easy fix. At that time it had permanent bind with the FWD fuse either in or out. Pretty much gauranteed the duty c solendoid wiring was faulty or the solenoid itself.

This was confirmed when I replaced the duty c solenoid and the torque bind disappeared. Of course during replacing the solenoid I began to realise this was not the original transmission for the vehicle. Through your help I now know it is VTD rather than MPT probably from an SVX or an imported RS.

Tonight I wired in a series of switches to control FWD and Duty C from the drivers seats in order to run a number of experiments. I also wired in a digital multimeter to the Duty C output on the TCU.

Comment on the TCU: I believe this is the original TCU for the vehicle. It has the large letters 'EG' marked on the front. I have seen the same lettering on other liberty TCUs from the same year. I have seen an SVX TCU for sale with the lettering 'FG'. I believe this is a different model computer.That may explain some of the weird behavour of this transmission in this car. I would be very happy to buy the correct TCU if someone could offer one.

As I understand it in a 'standard' 4EAT with MPT clutch normal behavour is:
0 Volts on Duty C = 50/50 split
12 Volts on Duty C - Front Wheel drive.
Normal driving varies volts delivering up to 90% torque to the front wheels.

In this car with 12V on duty C the wheels won't spin on wet dirt under full throttle launch.

Amazingly with Duty C switched out (0 volts) it behaves like a rear wheel drive and pulls fantastic donuts on the spot.

While this is completely opposite to what I would have expected it is also a nice suprise and great fun for offroad driving. I can live with having a switch that turns the car into rear wheel drive. Some people would kill for a feature like that in their subaru!

I'll do more testing tomorrow at highway speeds and notice the effect of switching the FWD to see what happens to TCU output volts. Still unsure why the I can't get the torque converter to lock up in AWD mode.

Another interesting observation is that the shift points in the VTD must be higher than the original box as when left in drive the car will bounce off the rev limiter in every gear under hard acceleration.

Once all this sorted my plan is to make nice daily driver which is quite capable on the beach. Mods will include X-series Forester struts and springs, 15 inch Forester rims with all terrain tyres and 50mm body and strut lift. If I can ever understand this transmission I'll wire in a couple of switches to have more control over the torque distribution.

I'm starting to get ideas that this transmission would be possible to have three modes:
1. Rear Wheel drive only
2. AWD with rear bias.
3. 50/50 split lock

Just a few teething problems to overcome first....

Cheers, Scott

Gannon · Post by **Gannon** » Tue May 22, 2012 10:26 pm

Its impossible to have RWD only. The reason you are getting rear wheelspin is because of the biased torque split and because the rear is lighter than the front, so the rears are the first to break traction.

So with VDT, by varying the duty cycle to duty solenoid C between 0% and 100%, you can have anywhere between a 40/60 open diff to a 50/50 locked one.

So, how did you wire these switches?

RSR 555 · Post by **RSR 555** » Wed May 23, 2012 7:35 am

Not that this will help much but what I found years ago on my friends Imported RS Legacy was the rear gearbox mounts were a different shape to the aussie Liberty ones, plus the aussie RS never came in auto. We had to buy a set of SVX ones to fit it (so this is making sense now to me), so from then I, I'd always look at the rear mounts before buying a secondhand box even if the numbers were close or the same.

Gannon · Post by **Gannon** » Wed May 23, 2012 3:50 pm

Wow I have never heard of VTD in a Gen1, but I guess that proves it

vincentvega · Post by **vincentvega** » Wed May 23, 2012 4:00 pm

there was no gen1 VTD boxes. this gearbox is not original.

They didn't appear until gen2 TT / early WRX / SVX

Thats not to say you can't bolt a VTD rear end onto a gen1 auto box. Just never came from the factory this way

If you want to use the car offroad VTD is brilliant. I run mine open 99% of the time, and lock it as required. I noticed a HUGE improvement over the original MPT clutch setup.

Edit: repco had SVX mounts last time I checked (18 months ago)

RSR 555 · Post by **RSR 555** » Thu May 24, 2012 3:02 am

I can tell you this car was (whilst my Friend owned it) totally original and it was a fully imported VZ model. It was an EJ20 non turbo with quadcam and varible intake setup (can't remember what they call it) and it was a gen1 series1 wagon. I'm not saying you're wrong just what I've experienced when having to replace his gearbox mounts.

Liberty Valance · Post by **Liberty Valance** » Thu May 24, 2012 8:03 pm

Gannon wrote:Its impossible to have RWD only. The reason you are getting rear wheelspin is because of the biased torque split and because the rear is lighter than the front, so the rears are the first to break traction.

Yes, I now believe you are correct. I must have getting mostly rear wheel spin with very little front. With lots of throttle the car will over-steer on loose surfaces.

Gannon wrote:So, how did you wire these switches?

1. Interrupted TCU output C3 with an on/off rocker to control Duty C.
2. Installed an on/off rocker which grounds TCU output A2 to control FWD.
3. Connected a Voltmeter between Duty C Solenoid and Ground.

Liberty Valance · Post by **Liberty Valance** » Thu May 24, 2012 8:13 pm

vincentvega wrote:there was no gen1 VTD boxes. this gearbox is not original.

Agreed, I did say that earlier on.

vincentvega wrote:Thats not to say you can't bolt a VTD rear end onto a gen1 auto box.

I honestly don't believe this would be possible as they have a very different mechanical set up. You would also need the 4EAT transmission from a car which came with VTD standard.

vincentvega wrote:If you want to use the car offroad VTD is brilliant. I run mine open 99% of the time, and lock it as required. I noticed a HUGE improvement over the original MPT clutch setup.

This is nice to know. When you say 'locking' are you referring to obtaining 50/50 torque split by disabling duty c solenoid?

vincentvega wrote:Edit: repco had SVX mounts last time I checked (18 months ago)

Thanks, haven't tried REPCO yet. Can get original Subaru parts ex:Japan for $270 which is robbery.

Liberty Valance · Post by **Liberty Valance** » Thu May 24, 2012 8:29 pm

Can anyone comment on TCU differences between:

Gen 1 Liberty AWD Auto 4EAT with MPT
and
SVX Auto 4EAT with VTD

I am certain the original TCU isn't correctly controlling the newer transmission properly.

Happy to buy a SVX TCU if anyone has access to one from a wrecked car.

Last resort I will get this one from the US Ebay TCU for SVX

Gannon · Post by **Gannon** » Thu May 24, 2012 9:07 pm

Well the SVX was a much heavier car with a much more powerful motor, so the brake bands and clutches are gonna be different. The take up point of the torque converter is likely different too.

Have you compared the SVX and Liberty TCU pinouts?

Liberty Valance · Post by **Liberty Valance** » Fri May 25, 2012 5:59 am

Gannon wrote:Have you compared the SVX and Liberty TCU pinouts?

I have traced out the transmission wiring diagram for a 1990 Liberty and a 1992 SVX and found the TCU I/O to be exactly the same on both model vehicles.

I am prepared to say that I believe my car has the original Torque converter and Final reduction sections. Only the automatic transmission section and transfer section have been swapped. I think this would have been done to maintain diff ratios. The SVX has a 3.55 final drive ratio while the liberty has 4.11.

Just had a though while writing this. I wonder if VSS 2 operates at a different frequency on the VTD transmission? This might explain why I am always getting a very low duty c cycle in AWD mode.

Gannon · Post by **Gannon** » Fri May 25, 2012 6:20 am

The rear output shaft speeds between the 2 systems will be the same compared to the front, but can you compare the 2 toothed wheels that VSS2 reads? I have a feeling that they are different.

Can you supply more photos of your diffs, I'd like to see if they are different to the later series 2 4EAT used in the Gen3 Libs and onwards

Liberty Valance · Post by **Liberty Valance** » Fri May 25, 2012 7:12 am

Gannon wrote: can you compare the 2 toothed wheels that VSS2 reads? I have a feeling that they are different.

I think you may be correct. I have a spare MPT clutch to count but for the VTD that would mean opening up the extension housing again. I'll have to wait until I can get a new gasket.

Gannon wrote: Can you supply more photos of your diffs, I'd like to see if they are different to the later series 2 4EAT used in the Gen3 Libs and onwards

I could only provide photos of the rear diff housing and the final drive housing of the transmission. Would that help? Don't really want to go pulling diffs apart just for photos!

Cheers, Scott

Edit> looking at your photo on page one... perhaps the VTD has less teeth. Did you have a photo from above?

Liberty Valance · Post by **Liberty Valance** » Fri May 25, 2012 4:06 pm

I'd like to continue this discussion but I think the subject line has lost a bit of meaning. I will start a new thread to discuss VTD transmissions.