1989 Buick Lesabre transmission problem
 

Well my little brother has a 1989 Buick Lesabre with a 3.8 v6 and it's fwd, its an automatic (of course) he's been having a problem of when you drive it in over drive it sometimes just kicks into neutraual, when you shift it from 1-D like a stick it works fine the car has about 175,000 miles on it and its on its second tranny (gm reman brand) the tranny probably has about 60k on it. We did change the fluid as scheduled. I was wondering the following problems, what is the problem, and the second is what model of tranny is in it?

THis is really general but; If its an electronically controlled tranny (it may be), there could be a problem with a relay when in overdrive causing it to go into nuetral. not sure about that but it may be worth looking at.

will not be electric, second 4 speed automatics are controlled by only 2 shift solenoids, and no relays.

transmission may be an old 440, 4t40 or most likely a 4t60. slips in overdrive maybe the 4th gear clutch pack, a burnt up TCC, a couple of things. however my first check would be of proper fluid level and condtion (color + smell) and then to check to make sure your getting vaccum at the modulator. these setups were notorius for the vaccum elbow at the throttle body leaking and the trans not getting proper vaccum at the modulator.

My 97 century does the same thing. I just ignore it since it's never been a safety issue and it only happens every few months.

Does it drop into neutral as you're going down the road, or in between shifts? If the latter, what gear(s) does it happen in, and is it on up/down shifts, or both?

I'm not as well-versed with GM trannies. I know the non-electronic Ford automatics use a cable mounted on the throttle which regulates line pressure in the tranny. On those if that cable breaks or becomes disconnected, it'll slip when it shifts because there's not enough pressure on the clutch packs. Might be something to check out if it's set up the same way.

Irseg, his tranny would have a TV cable (throttle valve).

to adjust it follow it up from the transmission, to where it goes by the throttle body. press in the black button at the retainer and pull the cable back towards the transmission. then rotate the throttle to wot and release it.

Mrselfdestruct, you would have a 4l60e, but still is prone to the vaccum leak.