Transmission Problem??

Hello, everybody
I have a 93 with 107,000 miles, original transmission with cooler, external filter, and temp gauge all installed at 80,000 miles.
Here is my problem. For several months I have occasionally noticed a slight "stumble" when driving at highway speed. When it happens, it only lasts a fraction of a second, and I haven't been able to tell if it is caused by the engine or transmission.
Yesterday, I was beginning an Interstate trip of about 150 miles. The car had been parked outside for two days in the cold. It was 25 degrees when I left. Normally, I leave from a much warmer garage and the transmission has plenty of warm up time before I get to any 55 mph or greater zone. However, on this trip back home I reached a 55 mph zone soon after I left, and, of course, the transmission would not shift into drive. I believe it has to be at least 50 degrees? Anyway, I drove in 3rd for 5 more minutes or so and then put it in Drive again. This time it did a strange thing. It felt like it was hunting between 3rd and Drive, and the tach went up and down a few times. I put it back in 3rd until it had gotton over 100 degrees, which is the bottom end of the tranny temp gauge. Then it shifted into drive and felt "normal" for most of the 150 miles of Interstate travel back home. It did do a couple of those "stumbles" that seemed worse than normal.
Obviously the question is: Is my transmission starting to fail? If so, is it possible that something needs adjusting or should I start looking for a dealer to install a Subaru remanufactured unit? I will appreciate any help you can provide. Thanks.

[svxistentialist]

Hi Prof

Your stumble may not be transmission related. More likely fuel or ignition. I am assuming you have changed the timing belt, if not, do so. Stumble could be caused by a lot of things, like a loose connection at the ECU earth side, plug coil breaking down, maybe a bad MAF or O2 sensor. Give it to a good subie techie to troubleshoot.

You may not have a tranny problem, in fact, I don't think you have. You mention a tranny cooler, so I am assuming an additional or auxiliary cooler, right? These temps you are driving in are extremely low. Your tranny oil is not getting up to operational temperature, causing the hunting between 4 and 3. When it gets into 4, if the oil gets to lockup temp, the D range locks up. This in turn cuts out the TC use, so the oil is not heating up to compensate for the cool airflow, vicious circle, cools to a point where lockup drops out, maybe below where it looks for 3. 4 is a really high ratio.

If you have a valve to switch off the extra cooler in very low temps, then do so. If you don't, then use cable ties or something to put card or foil in front of the matrix on your aux cooler to keep airflow from going through it. Oil temps will rise, your problem will go away.

One last point: the oil temp sensor in your tranny might possibly have failed, and be sending bad or no signals to the TCU. However, maybe not, I would try shutting off the extra cooler in cold weather first.

If it works, you have saved a bundle!!

Best of luck,

Joe

Hi, Joe
It is a relief to hear that it is probably not the transmission. Yes, the timing belt has been changed (in fact, the water pump went out some time ago and took the timing belt with it). What you said about the TC makes sense to me. The tranny temp was between 135 and 150 degrees for most of the drive home. I think the TC doesn't lock up until 150 degrees or so. I can't cut off the cooler, but I certainly could block it, as you suggest. I'll also have the engine checked out for the "stumble". Thanks for your advice.
Bill

[svxistentialist]

You're welcome Bill.

Hope the problem is as simple as I suggest. While you are looking into it, check that your ATF is not spent, i.e. brownish as opposed to red on the dipstick, and with a bad smell.

If it is, flush and refill with fresh oil of the correct grade.

Good luck with it,

Joe

{Hey, and don't forget to remove the blocking sheet if the weather gets warm}

[SVXPILOT]

MY trans has been doing this for the last 50 thousand miles. recently has became much worse. trans shifts great with firm quick shifts. when driving at cruising speeds trans will drop from D to3rd than immediately back to D. doesnt matter whether at 50mph or 90mph. If im accelerating slightly it will stay in D. As soon as i coast with foot resting on gas it will shift. If I coast with foot of accelerater it will stay in D. Seems to act up more as the temperture drops. I thought it was trans cooler not allowing the trans to heat up enough for D. Now Im leaning towards a faulty TPS since if I select 3rd at lower speeds the trans wants to drop to 2nd than back to 3rd. If I press manual button on shifter it will stay in 3rd. I drive 300miles round trip daily cummuting and don't like driving 80mph locked in 3rd. although the car seems much stronger in 3rd.

Hopefully we can get this resolved as it seems many have had the same symptons.

[SVXPILOT]

Also my fluid is always clean. every 10 thousand miles I put 7qts mobile1 15-50 in engine, mobil 1 filter. And pull plug on trans to drain than add 4 to 5qts mobil one trans fluid.