Transmission Problem??????

[shimmersky]

Hi guys
im driving a 1997 svx lsi with 158000 miles
wxternal trans cooler installed at 115000

im driving along on freeway at 90mph or 140 kph and at exactly 3000RPM
Cruise not engaged

funny thing happens

the rev counter just goes from 3-4 thousand rpm for no reason
no throttle input

maybe a slipping trans??

am i on a shift point??

how can i tell when the trans is about to fail??

any symptoms??

it does this intermittently

if the revs jump and i put more throttle it just keeps putting the power on
if i really put my foot down it kicks down and shifts

looking for advice on how to tell when a trans is about to fail

please help
shimmersky@gmail.com

[Blacky]

Sounds like the torque converter is locking and unlocking. This usually happens around 80kph.

[Tapani]

How's the weather? Cool?

If you have an effecient external cooler the fluid may get too overcooled and the torque converter clutch releases. After a few miles the fluid heats up (above the 150F threshold) and the TCC engages again.

Mine does this when the ambient temp gets below +10C.

With the stock cooling setup it happens at ambients below -10C.

Br,

Tapani

[Huskymaniac]

Originally Posted by Tapani

How's the weather? Cool?

If you have an effecient external cooler the fluid may get too overcooled and the torque converter clutch releases. After a few miles the fluid heats up (above the 150F threshold) and the TCC engages again.

Mine does this when the ambient temp gets below +10C.

With the stock cooling setup it happens at ambients below -10C.

Br,

Tapani

This sounds plausible. If you are trying to climb a decent incline at that speed it could just be the TCU unlocking the torque converter. If cool, Tapani could be correct. If Tapani is right, install a thermostat between the tyranny and the cooler.

[Blacky]

I don't think Las Vegas is cool at this time of year. It's 98°F there today. (43°F here today.) Unless he's driving in the mountains.

[shimmersky]

Im actually driving in Dubai UAE
Was in Vegas for the last few years though
its hot
100F every day

only happens in drive not 3rd at 3000rpm only

usually only straight and level highway speed

3000 rpm = 90mph =140kph

[Conn SVX]

Slow down. Problem solved. Next!

[Chucksta]

At 100 F, and 140 KPH, it's also possible that the trans is unlocking the torque converter deliberately, to cool itself off ( increased flow ).

Where is the trans cooler mounted? Because to be effective in those ambient temps, it needs to be in front of the rad, or, have it's own fan for a wheel well mounting.

As a side note, mine ( also a '97 ) unlocks the torque converter and then re locks about three times a minute, for a few minutes, then doesn't do it any more for a few minutes, and then does it again.... but only with the cruise on. without the cruise on, it might cycle once every couple of hundred kilometers. It could be aging electronics in the TCU, a bad line of code, or any number of reasons I know nothing about, but it definitely is related to the cruise circuit. Not even cruise being engaged, just arming the cruise control will trigger it.

One day, I'll actually get around to mounting my spare one and see if that changes it's behavior.

[Tapani]

Originally Posted by Chucksta

At 100 F, and 140 KPH, it's also possible that the trans is unlocking the torque converter deliberately, to cool itself off ( increased flow ).

If I understand correctly the heat generation with open TCC greatly exceeds the effect of the increased cooling flow.

This is the reason why the TCC is engaged even in third and at low speeds when the oveheat mode is on.

You may want to monitor the TCU with a lap top when all this happens. Can be done with the ECUtuner software + interface.

/T

[1986nate]

Your transmission is likely slipping in the extreme heat. Change the fluid and filter out and you may be able to save it.

The TC should stay locked up. The TC unlocked will generate more heat than any benefit of turning the pump quicker.

[Chucksta]

@ Tapani.. & 1986 Nate

I know what you mean about the heat from the TC being unlocked would seem to outweigh the benefits of the additional flow, but according to Subaru,

"ATF Temperature Sensor
When the ATF is hot (AWD only), the TCU shifts the transmission as if in the
POWER mode. This pushes the shift points higher which allows the engine to run faster. The oil pump then circulates ATF through the oil cooler more quickly so as not to overheat the engine coolant."

It would seem that the concern was engine coolant temp, perhaps the issue was localized boiling? And how to tell if it is indeed running in power mode if it's a newer one with no "power" light in the dash? Power mode would seem to exclude 3rd gear lock up.

A partially plugged filter might be a contributing factor.

It would also seem that not all TCUs' are created equal... Tapani's won't lock up below 150F. Both of mine will lock up from a cold start within a kilometer if it's 50F outside or warmer. But, neither of them has ever locked up in 3rd gear. Ever.

Just wondering.. since mine's never done it, when the TC locks up in 3rd, does it shift into 4th locked up, or does it unlock, shift into 4th and then lock up again a bit later?

an interesting read..

http://www.northursalia.com/techdocs...ssion/4eat.pdf

[Chucksta]

Oh yeah.... and, according to Subaru, cruise DOES affect shift points. That explains a few "idiosyncrasies"..