jdm svx trans, will it work?

[oab_au]

Originally Posted by b3lha

You need the JDM TCU to properly control the JDM trans. It should plug straight into the USDM loom. The wiring is the same except that the JDM cars have an extra wire for the power mode switch.

The USDM TCU will not control this box properly even if you do swap in a US-type solenoid. There are substantial software differences between a JDM and USDM TCU.

If you cannot get hold of a JDM TCU, it is possible to reprogram a USDM TCU with the JDM software. I'm pretty sure the circuit board is the same. Try sending a PM to Longassname. He might be able to make one for you.

Hi Phil, I am sure there are differences in the two maps, but the objectives of the two programs, will be the same, regardless of the AWD that is used.

First they will detect a difference in wheel speed between the two ends, and apply the clutch, in line with the difference, to stop any wheel spin.

Secondly they will apply the clutch to prevent wheel spin, depending on, Throttle opening, road speed and gear position. 1st gear, low speed, full throttle will apply the highest pressure. 4th gear, high speed, light throttle, will apply the lowest pressure.

The torque split between the two boxs, does not come into it. The VTD will do the most variation, but this is due to the epicyclic ratio difference, not to the maps.

I agree, using the appropriate TCU for the type of box, is the best, but there are some combinations that are not that easy to match. The wiring, and speed sensor differences, can make the swapping of the solenoids, the most cost effective option.

Harvey.

[Alex-svx]

Yes i have to go back on the old plan and swap the tranny. Now i just need the parts.

[NiftySVX]

Originally Posted by oab_au

Hi Phil, I am sure there are differences in the two maps, but the objectives of the two programs, will be the same, regardless of the AWD that is used.

First they will detect a difference in wheel speed between the two ends, and apply the clutch, in line with the difference, to stop any wheel spin.

Secondly they will apply the clutch to prevent wheel spin, depending on, Throttle opening, road speed and gear position. 1st gear, low speed, full throttle will apply the highest pressure. 4th gear, high speed, light throttle, will apply the lowest pressure.

The torque split between the two boxs, does not come into it. The VTD will do the most variation, but this is due to the epicyclic ratio difference, not to the maps.

I agree, using the appropriate TCU for the type of box, is the best, but there are some combinations that are not that easy to match. The wiring, and speed sensor differences, can make the swapping of the solenoids, the most cost effective option.

Harvey.

Sorry to just jump in here, but is the solenoid's little valve body identical in the two setups? I really wish I had known this before I spent all the money on my USDM trans. I would have just put the US speed sensor and the US solenoid and rebuilt burnt up VTD box and put it in my car instead.

[Trevor]

Originally Posted by oab_au

Hi Phil, I am sure there are differences in the two maps, but the objectives of the two programs, will be the same, regardless of the AWD that is used.

First they will detect a difference in wheel speed between the two ends, and apply the clutch, in line with the difference, to stop any wheel spin.

Secondly they will apply the clutch to prevent wheel spin, depending on, Throttle opening, road speed and gear position. 1st gear, low speed, full throttle will apply the highest pressure. 4th gear, high speed, light throttle, will apply the lowest pressure.

The torque split between the two boxs, does not come into it. The VTD will do the most variation, but this is due to the epicyclic ratio difference, not to the maps.

I agree, using the appropriate TCU for the type of box, is the best, but there are some combinations that are not that easy to match. The wiring, and speed sensor differences, can make the swapping of the solenoids, the most cost effective option.

Harvey.

The above vague statement, is to say the least misleading and partly incorrect, refer preceding post #48. Adding to the confusion, Posts #5, #16, are entirely incorrect.

Consider the way the transmission actually functions. ---

USDM System. An increase in the length of the 50 cps PWM signal pulses, or a constant signal, opens the normally closed C bleed solenoid valve. As a result pressure to the centre transfer clutch is reduced and the rear drive can be interrupted to a point where drive is only to the front Wheels.

Reducing the length of the pulses, or a near zero signal to the normally closed C bleed solenoid valve, results in the solenoid closing. As a result pressure to the centre transfer clutch is increased, so that drive to the rear can be applied together with the front, to a point of lock up.

Alteration of the pulse length provides front rear torque control. Unfortunately this system does not allow drive force to the rear to exceed that to the front. Hence reports of understeer.

JDM VTD System. An increase in the length of the signal pulses, or a constant signal, closes a normally open C bleed solenoid, increasing pressure to the parallel multi plate LSD clutch, therefore over riding the LSD to a point of lock up.

Reducing length of the signal pulses, or no effective signal, opens a normally open C bleed solenoid, reducing pressure so that the clutch is released. Drive is then via the centre differential with a split of 36.4% front, 63.6 rear, due to the included LSD gear ratio.

Alteration of the pulse length provides front rear torque control, up to a point of lock up.


The very different arrangement USDM/JDM, explains the reason for problems involving front rear binding, if the appropriate TCU and or matching solenoid is not fitted. Refer report by Steve in post #14, as follows:-

“I have an update, everything is installed, tranny, rear gears with SVX LSD. I drove the car down the road and all was well at low speed, when i needed to turn it felt strange, kinda like a 4x4 truck in 4wd on pavement. So i believe the center diff is locked or something.”

I commiserate with Steve. Alex and now Nate. also require a thought. This now horribly confusing and misleading thread, is of no credit to the network.

[NiftySVX]

If that transmission is trashed then I could simply use the extension housing and its contents to make my trans a VTD. this excites me greatly. I wonder How much it would cost to have the necessary parts shipped, assuming the owner has no use for them.

[svxistentialist]

Originally Posted by NiftySVX

If that transmission is trashed then I could simply use the extension housing and its contents to make my trans a VTD. this excites me greatly. I wonder How much it would cost to have the necessary parts shipped, assuming the owner has no use for them.

Language barrier here Nifty.

When you say "trashed" you mean it is broken, unsuitable for use, not fully working.

I think when Alex says "trashed" he means the people who took it out sent it away as trash to be scrap metal. I don't think he physically has the original gearbox any more.

Joe

[Alex-svx]

Originally Posted by svxistentialist

Language barrier here Nifty.

When you say "trashed" you mean it is broken, unsuitable for use, not fully working.

I think when Alex says "trashed" he means the people who took it out sent it away as trash to be scrap metal. I don't think he physically has the original gearbox any more.

Joe

Yes thats rigth. And now i have send a mail to Subaru Norway and the price on the part i missing is verry expentive.

[NiftySVX]

OH MAN! FML!

I was so excited there, briefly. I will get my hands on a vtd setup, soon though. I have plans for my FWD trans to become a VTD unit with the 3.70 rear ratio. This goes along with my policy to never throw any part of an SVX away no matter how badly damaged or useless!

[b3lha]

Originally Posted by TomsSVX

A USDM TCU will fix the issue and be a lot easier to install. This would be suggestion

Tom

A US TCU will not work correctly with a non-US ECU. The US TCU requires an atmospheric pressure signal from the sensor in the ECU. This sensor is only fitted to US ECUs. The TCU will report an error code.

You can work around this by wiring a potentiometer to the Atmospheric Pressure pin of the TCU. You can then vary the aggressiveness of the shifting by turning the potentiometer. It will select the Normal, LowPres1, LowPres2 or Power shift maps as described in the Gear Shift Maps thread. It's like having a 4 position power mode switch.

[TomsSVX]

No Baro sensor in the other ECU's??? Thats a surprise. That would be interesting to do though with the pot.

Tom

[NiftySVX]

I'm just gonna guess that everyone is assuming or knows that the programming in the TCU just goes ahead and applies the clutch if there is a different value from front-rear that qualifies as a slip, like if speed one does not equal speed 2 then apply, but, in ACT-4 there is no possible way that the rear wheels would ever rotate faster than the front when power is being transmitted from the engine. If the computer compares rear wheel speed as a value expressed as a difference from front wheel speed that can only be 0 or negative, then who knows how it will act when the rear wheel speed is greater than front wheel speed.

[oab_au]

Originally Posted by NiftySVX

I'm just gonna guess that everyone is assuming or knows that the programming in the TCU just goes ahead and applies the clutch if there is a different value from front-rear that qualifies as a slip, like if speed one does not equal speed 2 then apply, but, in ACT-4 there is no possible way that the rear wheels would ever rotate faster than the front when power is being transmitted from the engine. If the computer compares rear wheel speed as a value expressed as a difference from front wheel speed that can only be 0 or negative, then who knows how it will act when the rear wheel speed is greater than front wheel speed.

I don't think it it makes any difference, how it finds where the difference is. Thats for Phil to find out.

Maybe read the two speeds, subtract one from the other, the result, either positive or negative, is the amount of pressure that is sent to the clutch. I believe that more than 20% difference is considered 'wheel spin'. Under this amount, the car is turning, and the US transfer clutch will allow slip. The VTD clutch will allow the difference, as the torque will shift to the front wheels, due to the rotational difference of the epicyclic gear ratio.
This is where the main difference is between the two drives. The US Transfer system will always maintain the same torque split between the two ends through a corner, as long as the throttle is constant. The VTD will vary the torque between the two ends, increasing the torque feed to the front as the car turns into the corner. Any body that has driven a VTD car will know how that, turning into a tight turn, the front wheels pull the front around the turn, with no sign of understeer.

Harvey.

[NiftySVX]

Any rear wheel speed that exceeds the allowance for turning will result in full line to the transfer clutch until the two speeds become equal. You can observe this with a line pressure test at the extension housing. From my tests and experiments with the transfer clutch, which is fun to watch, is really dynamic in nature and is always changing the pressure as you drive it. However, when i had it rigged up, slipping the front wheels would override the predictive modeling logic and just try and lock the clutch up as best it can with available line.

as a side note: This is one major area that is drastically improved by a throttle body mod that raises base line. The AWD is much more even split when the line is higher.

[Trevor]

Originally Posted by NiftySVX

Sorry to just jump in here, but is the solenoid's little valve body identical in the two setups? I really wish I had known this before I spent all the money on my USDM trans. I would have just put the US speed sensor and the US solenoid and rebuilt burnt up VTD box and put it in my car instead.

Unfortunately you have not had the courtesy of a direct reply to your query.

The outer case/body of the two solenoids i.e. normally closed and normally open, is the same, which makes them interchangeable.

However, understandably you may have become confused by incorrect statements within this thread. A US type N/C solenoid must not be used with a VTD box.

[Trevor]

I don't think it it makes any difference, how it finds where the difference is. Thats for Phil to find out.

Maybe read the two speeds, subtract one from the other, the result, either positive or negative, is the amount of pressure that is sent to the clutch. I believe that more than 20% difference is considered 'wheel spin'. Under this amount, the car is turning, and the US transfer clutch will allow slip.

But only at the rear, which is the point being emphasised.

The VTD clutch will allow the difference, as the torque will shift to the front wheels, due to the rotational difference of the epicyclic gear ratio.

The clutch does not enter the picture. The difference is compensated for, rather than shifted, via centre the differential, which reacts in its normal front/rear function. The special ratio has no intended purpose in this instance.

This is where the main difference is between the two drives. The US Transfer system will always maintain the same torque split between the two ends through a corner, as long as the throttle is constant. The VTD will vary the torque between the two ends, *increasing the torque feed to the *front as the car turns into the corner.

* On what evidence is this true?

Any body that has driven a VTD car will know how that, turning into a tight turn, the front wheels pull the front around the turn, with no sign of understeer.

Harvey.

In this instance, it is not a matter of the front wheels pulling the car round a corner. This happens in any event with front only drive under moderate application of power. As has earlier been pointed out by NiftySVX, it is clutch application preventinfg excessive front drive over rear drive which is the determing factor.

The understeering reported in respect of the US cars is the result of excessive front wheel bias, as it is not possible under any circumstance, for rear torque to exceed that at the front. Front wheel drive causes under steer, when the slip angle at the font increases due to the power being applied.

This characteristic doe not occur in respect of VTD models. Power can/will be applied to the rear in excess of the front, when power is used in a corner, resulting in the increase in any slip angle occurring at the rear rather than the front.