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Discussion Starter #1
Hello Everyone,

These boards have provided a wealth of knowledge working with my 2001 H6 VDC, but I've recently come across an issue that no manner of searching appears to be the case.

History:

Recently replaced the transmission due to a failed seal between the front differential and the gearbox. Resulting in very little oil in the diff, a horrible mix in the AT, and a very nice whine.

Currently having front left CV replaced (most likley irrelevant, but noting it for refernece)

Front O2 sensor showing fault on Check Engine Diagnostics (Still to be replaced)

Issue:

In previous driving, when either off-gas or on brake, the revolutions of the engine would typically drop. When going downhill I would typically lock 3rd to engine brake unless it decided to drop for me.

However, since replacing the transmission and doing a bit of driving, this no longer seems to be the case. Also, when downshifting (step-up on acceleration) there appears to be a high revving of the engine in-between the shift.

Doing some reading, I'm thinking this could be that the Torque Converter Lock-Up is staying engaged, and not releasing as it should under brakes/zero throttle? And therefore also causing a spin-up of the engine inbetween gears.

Does anyone know if the solenoid that controls the TCC sits dis-engaged when recieving no voltage? (I.e. if I unplugged the solenoid, would the TCC not engage?)

This won't help diagnose if the clutch is permanently engaged, but if it's engaging and then not releasing it may assist.
 

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So what exactly happens when you take your foot off the gas to coast? There is a solenoid that controls the lockup function. I don't remember which one it is. What happens when you brake and come to a stop? If the lock up is staying engaged the car will want to stall out.
 

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Discussion Starter #4
Yes there is a solenoid that controls the TCC, however I am struggling from the electrical & mechanical diagram to ascertain if it is engaged or disengaged with below 0.5v input.

With the foot off gas to coast it stays in gear, increasing in RPM if there is enough of a slope, or decreasing on the flats with visibile downshifting of the gears as it slows.
 

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Discussion Starter #5
And ps I'm pretty sure the fail mode is that there will be no lockup function. I have no clue on voltages.
I figured as much.

The other possibility is that the previous gearbox was giving me an abnormal function that I got used to, and this is indeed the intended function. However, the shifting doesn't seem as consistent as before which has led me to believe not.
 

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The VDC programming will control TCC lockup for a number of reasons. It will actually keep the converter locked up during decelleration to assist in stopping, using the engine torque to slow the vehicle, especially in emergency stops. On acceleration, say passing, there is a lag common to the downshift pattern. Every automatic Subie I've had did this. Mine does it, but not as noticeable all the time since the ROM rewrite.

However, since replacing the transmission and doing a bit of driving, this no longer seems to be the case. Also, when downshifting (step-up on acceleration) there appears to be a high revving of the engine in-between the shift.
If the engine is revving, and not accelerating, the TCC is not necessarily locked up. When it is locked, it is similar to a manual clutch allowing direct drive and 100% torque transfer and when the vehicle is stopped it stalls the engine. You may have damage within the transmission that is affecting clutch control overall. The actual clutch packs for the gearing.

So, a few questions:

Used or rebuilt transmission?

Was the torque converter replaced with the transmission? This is important, especially with the contaminates entering the system.

Was the valve body refurbished? Cleaned?

Were the cooling lines/radiator flushed? In line filter in the fender replaced?

If any contaminate or debris remained in the system, it is most likely effecting main line pressure which will adversely effect the torque converter function, as well as the clutch packs.
 

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Discussion Starter #7
Thanks for the info

- Used transmission (the second one, luckily buying from a wrecker who gaurentees the parts).

- The transmission was replaced including torque converter, differential and AT

- No refurbishing done on the valve body as far as I am aware (will ask tonight)

- The coolant may have been flushed as a number of other parts were serviced at the time, but I don't think this was done.

I'm used to the lag with the downshifting, but not the high engine RPM between the shifts like is currently occuring. CV has been replaced today so taking another drive tonight and will provide some further feedback.

Another thought is that some of this could be 'normal operation' and I am used to an incorrect operation from the previous transmission. Might need to arrange a sneaky test-drive at a dealership to see what I can find.

Could someone let me know the expected RPM while coasting (No brake, no throttle, flat ground) at 100km/h (apprx. 62 mph), and should there be a change when brakes are applied? (I.e. If the TCC is disengaging)
 

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Revs raising during a shift is never a good sign. It typically means that clutch slippage is going on. The TCC will typically disengage during a shift, but there should be no rpm flaring during shift, especially above the stall speed. I'm assuming that by high rpm during shift that it is well above the stall speed.

One way to see what is going on with the TCC is to use freessm and a vagcom cable. There should be a PID for TCC on/off as well as voltage to the solenoid. But what you are describing rules out a stuck TCC. You would have hard shifts, and possible stalling if the TCC was stuck, but definitely no rpm flaring during a shift.
 

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Discussion Starter #9
Thanks everyone for the feedback.. I thought I might be clutching at straws. After driving tonight the rev flaring appears to not be occuring.. although I need to get some more hill driving done before I can be confident that's gone.

It still stays in gear under deceleration/braking, but the more I look at this the more it looks like the previous transmission was the one at fault. The old behaviour was that the revs would drop right down until you accelerated, and it would then jump back up to the appropriate revs (either an overdrive gear, but I believe that's just 4th in these boxes, or into a neutral?)
 

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The reason I know about these things is I thought my transmission had an issue too because it also stays in gear and the RPMs stay up when coasting, but I think your right, that your new trans is the normal one and you were used to abnormal activity, as all the discussions I've had with people and things I've read suggest this is normal behavior. And when you mash the gas to accelerate the RPMs will spike as the TC is becoming unlocked allowing slipping.
 

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There is no overdrive, the TC lockup behaves as the overdrive in these transmissions, so from what that tells is your old transmission had no TC lockup.
 

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4th gear is indeed overdrive---0.694:1, not 1:1. The torque converter or lockup clutch can never produce input shaft speeds greater than engine RPM. . . only equal to or less than.

One thing to consider. . . the transmission controller for the H6 non VDC has changed a few times over the 5-year run. Not sure what the differences are or if any would effect operation of the TCC, but if you're running a used tranny, check the VIN or production date of the donor car to make sure it uses the same controller. . .or just swap the controller if it's available.

Ran into that little nuance when I swapped from a 2.5 to a 3.0 and lost the trans controller somewhere along the way. Believe it or not it would operate on the 4cyl trans controllers but the shift points were much higher than they needed to be, and no TCC operation at all. I plugged in the correct TCM (sourced off eBay for a paltry $50 shipped) and all's well.

I'm running a 2002 transmission, and the part number for the controller was actually different from the one for the 2001 LL Bean I also have. VDC TCM's are completely different animals, they've got an extra plug even. I have not swapped my TCM's between the 2002/2001 H6's I have. . . it's working and that's enough for me. :)
 

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Discussion Starter #13
Cheers for the point on the TCM. Given that it's a VDC model, if there weren't any changes it's less of an issue.. but given that it's a second replacement box I didn't check the model number myself. Still have the original box and the 2nd, so will have a look shortly at the model numbers and see what comes up.
 

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Guru,

I wasn't referring to flushing the coolant. I was talking about flushing the transmission fluid portion of the radiator. It might just be a good idea to install a separate transmission cooler in front of the radiator. They are inexpensive and easy to install. In the pic, the trans cooler is on the passenger side of the radiator in black. Hoses run through the side of the core bracket.

All other questions have been answered. I hope the checklist helped. If you still want the voltage specs, I may be able to locate and post them, but I don't think you need them.
 

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Discussion Starter #16
Thanks Cardoc, have done an install similar on a Toyota Hilux before so will certainly keep it in mind.

I've located the voltage specs already, just need to drive it a bit more and do some further testing.
 
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