auto transmission problem

[Bob]

My wife has a 1999 Legacy Wagon, 4-cyl. with 80K. When it has been
driven at least 15 minutes, within a period of no more than a half
second, the speedometer and tachometer needles will drop to about half
and return to their original setting, the AT TEMP light will come on
and the car will jerk as if it momentarily shifted or tried to shift
gears. It returns to normal (light goes off), but will continue repeat
the above on a random basis from a few seconds apart to a few minutes
apart.

If you shift to third, the light blinks on and the speedometer drops,
but the tach doesn't move and the car does not jerk.

If you are running cruise control and it does the above, it turns off
cruise control.

We've had the fluid changed and 2 of 3 speed sensors replace with no
change. My mechanic says the remaining speed sensor is located at the
top of the transmission and would require dropping trans. He's not
hopeful that would fix the problem. Any ideas?

 

[Edward Hayes]

Me thinks it is a loose electrical connection so I would start removing
fuses to clean and check for corrosion.

 

[Jim]

As Edward Hayes noted, suspect electrical problem. They can manifest
themselves in some odd ways:

Anecdotally: I had an 72 Saab, with electronic fuel injection, and
when you flashed or turned on the brights, in its later years, the
EFI apparently would briefly cut out as the car would lose all
power. It felt like something with the transmission. I had a wiring
diagram that seemed to point to a relay clump (for lack of a better
word) common to the EFI and the lights wiring, although I don't think
internally they should have been connected. I always assumed
there was a short somewhere in the relay, although I never did
have the problem fixed.