"Houston, We have a Problem" Help!
 

Hello, everybody
I have a 93 with 110K on the original tranny. Tranny has external filter, cooler, and temp gauge. This weekend I drove on the Interstate for 150 miles one day and back 150 miles the next day. After warm up, the tranny temp gauge stayed between 155-170. After everything had warmed up, I would occasionally be aware of a "stumble" somewhere in the engine or tranny. Then later, while cruising at 65-70 mph, something would happen to make the tach momentarily "flare" from about 2300 rpm's to around 3000 rpm's and then immediately back, as if the torque converter had unlocked and then re-locked. This would happen several times in succession. Then everything would be fine for another 10-40 miles, until the next episode of several of the rpm flares. It did this periodically on both days of this trip. To my amazement, it went up a rather large mountain at about 65 mph without incident.
This may be only a coincidence, but the dash light array that lights up to indicate what gear the tranny is in lights in every gear except "D".
If anyone has had these symptoms or knows what's going on and what to do to have it fixed, please reply. I hope I've supplied enough information. If not, please ask. Thank you very much.

Tranny
 

Hi Professor, The bulb behind the"D" is proably burned out. After all, it's on when ever the SVX is doing forward. As for the tranny, as the weather gets cooler, sometimes it can't maintain the minimum temp to keep the torque converter locked up. Around 160 degrees. Moving in and out of lockup should be followed,as the weather cools, by not locking up at all. You either need a cooler with a thermostat or a bypass for the external cooler for the cold temp months. There are some beautiful diagrams on various ways to accomplish this in the how to's. Thanks for signing on and Take care, BOBB

Hi,Bobb

Thanks for replying.
So, you think it's definitely the TC unlocking and re-locking. That's what it felt like to me, but the temperature didn't seem cold enough to cause the symptoms.

Unless the outside temp is very hot or very cold, which it wasn't on this trip, my SVX's normal tranny operating temp on the Interstate is around 160-165, with the TC locked up.
My TC has always locked up at 150 on my tranny temp gauge, so I don't think that is the problem. The outside temp was around 60 and my tranny temp gauge was registering well over 150 on all of the incidents and over 170 when a few of the incidents happened. Are there any other possibilities?

Temp
 

Hi Professor, Well time will tell. I don't know were your temp gauge is located, but most are in the filter adapter. Ony part of the transmission fluid goes through the filter/cooler line. The temp may or may not reflect the true temp in the tranny. And there is always the "within factory tolerance" issue. If its a temp problem, its an easy fix. If not, it likely will run a few bucks. Take care, BOBB

TC will not unlock due to temperature until the tranny falls below 100°F. Were you using cruise control when that happened? I noticed that if you use cruise and your TPS is worn or not calibrated properly the ECU/TCU tends to unlock the TC rather prematurely (eg. going over an overpass).

If I don't use cruise then it's fine. You should also be able to tell if it is the TC unlocking or 4th gear slipping if you're not using cruise.

You mention that the RPMs immediately return to normal. When the TC unlocks it will not lock for at least 5 seconds (in my observations).

Hi, Earthworm
No, I was not using cruise control. So, how do I figure out whether it's the TC or something else? If it's something else, what might that involve? Thanks for your help.

Something else might be a slipping clutch.

Were you climbing uphill or accelerating when the flare occured?
How far did the RPMs go?

On my car the RPMs in 4th gear at 75mph indicated speed with unlocked converter would be around 2800 - clearly below 3000.
TCU does take a few seconds of steady cruising to lock torque converter back after unlocking, it is never momentarily.

I did have a slipping clutch problems due to low line pressure.
The symptoms were as follows:
Generally transmission worked fine, all shifts were fine.
Stall test RPMs were normal in all gears it could be tested (1-3 and R).
On 4th gear with locked converter if I slowly pushed accelerator the RPMs would jump up some amount depending on how much throttle is pushed (could jump 200 rpm, could 400), but if I released the throttle they immediately jumped back into normal for 4th locked. The only place I could really notice this was a long fast incline where normal cars have to downshift to maintain the speed.

I traced the problem to the line pressure not changing in response to throttle position, which was due to the worn Solenoid A.
Postmortem autopsy on the solenoid did not find any obvious problems - it was clicking, opening and closing. Apparently it just
got worn too much and fluid pressure pushed it open.

New solenoid pack solved the slippage problems, transmission still works fine a year later.

So my point is - if you suspect anything wrong, go do a line pressure test.

The temperature gauge I have is connected to the outlet flow pipe from the tranny. The lock-up of the TC and unlock occurs around 145F. Is that 100F you refer to in the pan?

The temp sender for my ATF temp gauge is mounted in the return pipe to the tranny, and my TC will start unlocking at 125F according to the gauge. My guess is that professor 56's TC is unlocking. The behavior he describes is very similar to what I experience when driving in the winter.

Here's some more information that may be helpful. It actually did the flare thing on one previous Interstate trip, which was last winter, with the outside temp between 40-45 degrees. My tranny cooler bypasses the radiator completely, so cold temps could well be the problem. I don't know exactly where the temp sensor is located; I'd have to check with my mechanic, who installed everything.

Also, the flare is very quick, e.g. a jump up from 2300 rpm's at around 65-70 mph to around 3000, and then immediately back. These flare episodes would come in groups and then everything would be fine for awhile. One sizable mountain at interstate speeds did not produce any of these symptoms. It hasn't been a problem in the last few weeks because I've only been driving around town. It shifts normally around town. I hope this helps. Thanks.

It sounds to me like the TC is just unlocking and relocking very quickly. Its easy to tell when the TC is locked because if you slowly increase the throttle position, the TC will not unlock and the rpm on the tach will rise linearly with the speed of the car. Also, when the TC is locked, when you let off on the gas, the rpm will not take a step decrease in value. They will drop linearly with speed of the car.

The fact that it didn't happen when you were going up the hill makes sense because more heat is generated by the motor, and the tranny stays warmer, even if the TC is locked (which is where much of the heat in an AT is generated).

I like this post and would suggest you try this. I think I'm going to do this test as well for my tranny.

I really don't think our TC's will unlock then quickly lock again.

My TC would only unlock on constant highway driving once the outside temps fell below about 15°F. Anything higher and the tranny was able to keep itself above the unlock temperature.

Now, I have many more questions. If it is a slipping clutch, why does it only happen in High Gear? What other things besides a bad solenoid could cause a slipping clutch?

What does a line pressure test involve? Would I have to take it to a Subaru dealer? What should it cost?
Also, if the solenoid has to be replaced, what does that involve? Subaru dealer? Cost?
Thanks for your help.

The RPMs with the TC unlocked are a bit dependent on the ATF temp and engine load. I've seen 3000 rpm at 75 mph. Just mentioning it so people don't think that 2800 rpm at 75 mph is a hard relationship.

That would be a question best for gl1674 to answer.