1994 Eldo Northstar tranny slips at 40 PMH

[mmares713]

121,000 miles, after a fluid change the tranny started slipping when in drive, drops into 3rd. 1sat and 2nd also work fine and so does 3rd up to about 40 MPH. No one has the OBD 1 or whatever it takes to read the codes, what do I do now? use the dash method?

[KHE]

read the codes, what do I do now? use the dash method?

Yes.

Then post any codes here.

[joeb]

Hmm, recent service and now issues? U did use the proper fluid? I see comments saying dex6 causes old trans to shift oddly. But perhaps u used dex3? Having no OD is usually not good. In that no shifting may be bad solenoids which may mean a less expensive fix. But no OD is usually not a cheap fix.

[KHE]

No 4th gear can be caused by a 4th gear servo piston seal that is torn/not sealing. Not too bad of a fix with the trans. in the car. Keep the gear selector in 3 so the trans doesn't attempt to command 4th gear and slip which is hard on the bands/clutches.

[Cadillac Jim]

I'm running Dexron VI in my 1997 ETC which uses a 4T80E and it shifts better than it did with Dexron III. Although the 1994 Eldorado also uses the 4T80E, the two transmissions may not be totally identical inside, but I don't believe that use of Dexron VI would cause any problem. In fact, if the transmission was conventionally serviced and not flushed, there should be no perceptible difference in the way the fluid works with the transmission.

What exactly was done? The words "fluid change" can mean a conventional service, where the pan is dropped and cleaned out, along with the scavenger pump screen, and the transmission put back together and topped off with fluid. It can also mean a flush, without dropping the pan or cleaning out anything. Or both. Or something else, like simply draining the pan and topping off the fluid.