Beware: Common Problems of the 4T80E Automatic Transmission
Posted by Regis F. on Thursday, January 17th, 2013
The 4T80E is a four speed transmission made by General Motors for use in cars with the engine mounted transversely. It also incorporates a transaxle to allow its use in front wheel drive vehicles. The 4T80E is a heavy duty transmission designed to be used in cars weighing up to 8000 lbs. It was introduces in 1993 and phased out of production after the 2005 model year. It was used in big, heavy, V8 powered vehicles such as the Cadillac Deville, Eldorado, Seville and DTS as well as in the Oldsmobile Aurora, the Pontiac Bonneville and the Buick Lucerne.
Although this is a heavy duty transmission, it still has its share of problems. Here are a few things you should look for the next time you’re dealing with a 4T80E equipped car that needs to be serviced.
All sorts of problems can result from bad shift solenoids. The vehicle might not shift, it might shift too hard or it just might slip a little or a lot. It can happen in any of the forward gears. Use an ohm meter to check the resistance of the wires in the solenoid. The resistance for a properly functioning solenoid should be between 20 – 30 ohms. If you get a different reading or none at all replace the solenoid. Solenoids are nothing more than a fancy electric magnet. The winding inside the solenoid create a magnetic field when voltage is applied. This causes a valve to move which either opens or closes a hydraulic port.
Transmission leaks. All types of leaks are common with this transmission, especially those that sit for long periods of time without being driven. What happens is that the seals and gaskets dry up from lack of use and start to leak. One place to check for leaks is the front seal that stops fluid from coming out of the transmission where the torque converter hub enters the front pump assembly.
Another area to look at is the transmission pan gasket. Sometimes a leaking transmission pan can result from someone over tightening the transmission pan bolts. Doing so causes the gasket to be squeezed out and the result is a leak. You might also want to take a look at the seals that keep fluid from coming out of the transaxle where the two front wheel drive shafts enter the transmission.
Failure of the modulator. This is another pretty common problem with this transmission. If it’s shifting oddly, locate the modulator and pull the vacuum line off. If the line has fluids in it, then replace the modulator. In older vehicles that sit for long periods of time the diaphragm inside the modulator can get old and dried out, causing it to crack. The vacuum from the motor will pull transmission fluid into the line, in the same way a straw pulls soda from a soda can.
These are a only a few of the more common problems with the 4T80E transmission. Sometimes units get too damaged for simple repairs – when this is the case, I recommend picking up a remanufactured transmission.