Automatic tranny lost Overdrive

Dr_Doug · #1 05-24-2002, 01:08 AM

My 1991 Explorer with the A4LD tranny that has lost overdrive. The tranny shifts perfect and smooth, as always, but refuses to go into OD.

This first happened as I accelerated at a speed of 50 mph. The driveline hic-cupped and dropped out of OD. I suspect this hic-cup was the drive-line shocked when it dropped out of OD.

In addition, when in third or fourth gear and I let off the accelerator the RPMS drop to an idle. Could this be a locking torque converter issue?

There were ECM codes, other than "11", or fluid loss to the modulator valve.

Could this be a solenoid or a servo motor or broken band? The fluid is changed every 25,000 miles.

Thanks for your help!

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Mark Kovalsky · #2 05-24-2002, 10:02 AM

You say it won't go into overdrive, but it operates in third and fourth gears? Fourth gear *IS* overdrive.

I think you may mean the torque converter clutch isn't locking. It should lock in third and fourth gears. It is controlled by the PCM (Powertrain Control Module) and a solenoid inside the transmission pan.

If the electrical connectors on the transmission are dirty it can interupt the signal to the solenoid. The solenoid could also have failed. It is possible, but not likely, that the PCM is bad.

Mark

Dr_Doug · #3 05-24-2002, 10:11 AM

Mark and others,

I count three shifts. (1 to 2), (2 to 3) and (3 to 4). When I put the drive selector in D or OD, the results are the same. Does this sound like the torque converter clutch isn't locking?

Thanks for your help.

Doug

Mark Kovalsky · #4 05-24-2002, 01:48 PM

It could be. There should be one more "shift" which is the torque converter locking.

It's also possible that you are feeling the 1-2, 2-3, and the torque converter locking. I think you need a pro to drive it and tell you what's wrong.

Mark

hmustang · #5 05-24-2002, 02:15 PM

I don't know if you have a switch or just another selection but you should try and see at a highway speed have it in the overdrive then shift it to drive or 3rd gear and see what the RPM's do if they stay the same then you know that you don't have overdrive.