Mechanics

HOW TO CHANGE AUTO TRANSMISSION FILTER?

1998 Mercury Mystique • 4 cylinder 2WD Automatic • 153 miles

My Haynes book does not give any instructions about changing the automatic transmission filter on this car, it only instructs how to drain, flush, and refill.

Are there any instructions on how to replace the filter, or it is not accessible in this particular car without removing the entire trans unit?

Thanks!
Avatar
Ben Lee
January 17, 2011.



Not accessable in this trans design. You would have to remove trans.

Tiny
Fixitmr
Jan 17, 2011.
Thanks for checking. I guess I'll just try a regular flush and see if that helps my shifting issues.

I'd also like to check the throttle position sensor, but can you provide any tips on the procedure? Do I leave the TPS in place, but just detach the electrical connector to tap into the TPS wire connectors? What values should I expect to see when pressing the accelerator petal with the TPS hooked up to a voltmeter?

What other sensors should I check (and their normal values?) As possible causes of transmission shifting issues?

Thanks!

Tiny
Ben Lee
Jan 17, 2011.
What are your shifting issues? Any slipping? You should get codes read. I have a 98 contour with tranny problems. Which is why I knew the filter answer.I read TPS with plug off with ohm meter. I dont look at values other than no gaps/jumps 0 readings. Smooth increase/decrease.

Tiny
Fixitmr
Jan 18, 2011.
I suppose slipping is what it is. I should also add that the last two days coming to work (7am) it had NO issues whatsoever, but on the way coming home from work around 3: 45pm (when it's more like 75 degrees or so) it starts happening about halfway home, so around 20 minutes of driving (about 10 minutes of that is freeway). So now I'm wondering if the issue only happens when the trans gets hot.

To explain exactly what's happening: it will be shifting just fine on surface streets and getting on the freeway, and I'll be crusing along around 65-70mph at the most, then suddenly the rpm will go from around 2700 up past 3000 (a few times as high as 3500), then the trans will***** back into gear very roughly. Then for the next 10 minutes or so on the freeway it will randomly raise the rpm's and***** back into gear. Sometimes it will do it several times in a row, and sometimes not quite as rough, rasing the rpm's only a little before******** back into gear. It seems to start happening when I'm crusing at a steady rate, but then I do lower my speed once it starts happening to make sure I'm in as much control as possible, and over in the slow lane.

There's no way I can afford $1,000 and upwards in transmission work, so I'm hoping to exaust all other possibilities, especially things that I can test myself.

Oh, almost forgot, I checked for codes about a week ago and there were no stored codes and no pending codes, but I'll check again since more time has gone by now. But still no check engine light to indicate stored codes. I also have the ability to view live data, in case you have any suggestions in that area.

Thanks so much for your help, I really appreciate it!

Tiny
Ben Lee
Jan 18, 2011.
I guess I should add that I just drove it for a short outing, all streets, no freeway, and keeping to 40mph or so, and had some slipping. I suspect I was at operating temperature by the time I got to where I was going, and barely over idle in the parking lot it was slipping in first gear, not in gear change or anything, just barely over idle in first gear.

Tiny
Ben Lee
Jan 18, 2011.
These transmissions are known to act up in the range of 150-175k miles. Mine went at 166 or so. It started slipping in drive from stop but worked in manual mode just fine. Try yours starting in low instead of drive and see if yours slips. But 3 weeks later it also slipped in low. Now if I can get it over 20MPH it works fine. Just cant get to 20MPH! Unfortunately, I am not a trans mechanic. Although if I was told what the problem is, I could likely fix it. I know it's an electronic control problem or a hydraulic leak. Or both.

Tiny
Fixitmr
Jan 19, 2011.
Do you know of any way that I can access diagrams for this transmission?

Also, I'd like to find out how the trans cooling lines are routed and I'd like to try flushing out the lines. I may also want to install a separate trans cooler unit.

I realized that the issue was only happening if the engine/trans was hot. The issue stopped for two days when I tried my drive home (warm afternoons) with the heater blower on high, but the 3rd day the issue was back the same, except it may have started a little further along my drive home (actually started at pretty much the exact same place on the freeway the last two days in a row).

Thanks again for your input!

Tiny
Ben Lee
Jan 26, 2011.
The question is whether you have an electronic failure due to heat. Or its a heated fluid viscosity issue. Just for fun you could remove your engine thermostat and see what effect this has as it will lower radiator temp and trans fluid temp. You might want to pick up a digital infrared pocket temp sensor to read trans temps. They sell 1 at harbor freight for under $20. Quite a useful little tool.

Tiny
Fixitmr
Jan 26, 2011.
Hmmm, both good ideas. HF is my favorite store anyway. I was just there yesterday in fact. I can always use an excuse to make a trip there.

Would I just point the pocket thermometer laser at one of the trans cooler lines?

Any possible adverse affects to removing the thermostat? (I know it is only temporary)

Tiny
Ben Lee
Jan 26, 2011.
Heater may not blow hot air especially at higher speeds? Gas mileage may go down a bit. Hard to predict for any 1 car. Outside air temps have an effect on answer to that. You can point it at trans and lines. You have to be careful that you point at lines with no other object behind them as meter likely reads wide/deep area. You could isolate with shield of some sort?

Tiny
Fixitmr
Jan 26, 2011.
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