About... The background...

Before I start, I'd like to bring to your attention that you will notice that I will not go through the details relating to components of the drivetrain such as the CV joints, etc; the reason is that such component design and issues tend to be universal and very common. Information about the diagnoses of relating problems, and replacing such parts, can be readily found online, among many other reliable sources. If you still would like for us to help you, at Grease Pit Garage, please do not hesitate to reach out via our community forum!

At the beginning...

For 1991 GM introduced the 4T60-E which was a 4T60 with electronic controls, first seen on the new Buick Park Avenue. One benefit was that the cruise control was integrated into the gearbox' electronic control module, improving the ability to maintain a set speed while avoiding needless shifting, thus lowering fuel consumption and noise levels.^[1] By the mid-1990s, the 4T60-E was the transmission of choice in nearly every front-wheel drive GM vehicle with the exception of compacts. A heavy-duty 4T60-E HD was produced in 1996 for the supercharged GM 3800 engine and reused in mid 2005 to 2009 with an LS4 5.3 liter V8 in four different models the Buick Lacrosse Super, Chevrolet Impala SS, Chevrolet Monte Carlo SS, and Pontiac Grand Prix GXP. The 4T60-E was phased out in favor of the 4T65 beginning in 1997.

As discussed in the powertrain page, this transmission was a compromise! Yep... as stated before, Hydramatic had its own challenges to conquer in providing GM with a transaxle that can handle the 275hp, plus, output power of the 3.4L v6 DOHC that was to be mated to this machine!

The THM 440T-4 four speed auto debuted a few years earlier, but was prone to valve body and erratic shifting problems. The 440T-4 also had this quirk of self-destructing if the owner happened to get stuck in snow! Not much to build from. An all new FWD O/D trans was needed. When it came clear that the all-new trans wouldn't be ready for production by mid-1990, there was only one thing to do. Redesign the 440-T4 as best as they could.

Will the resulting transaxle take 275HP? NO! Will it take 250HP? NO! How bout 225Hp?... Cut the horsepower of the 3.4L to 200hp with an automatic, and a 210hp on a stick!! As said before, it makes a guy want to cry, especially knowing that Oldsmobile pioneered the automatic transmission! The redesigned THM 440-T4 was designated the THM 4T60E, with an early RPO code of MXO. Internals were beefed up, a heavier drive chain, a better pump, and best of all, Electronic shifting!

Now, instead of a finicky hydraulic valve body, all shifts and timing ere controlled by the ECM. The same one used by the motor. Big, beefy drive-shafts were installed into the W cars to take the power. By this time, tooling up was underway for the '91 model year. While there were a supply of motors, the trans were still being built a few at a time. Delco Electronics solved the horsepower "problem" by cutting the fuel delivery and spark advance curves of the motor; this weakened it to a 6250 shift point, and 6500 rev limiter. Free-revving was limited at 3000RPM.

The 4T60-E featured a 245 mm (9.6 in) torque converter with varying stall speed and gear ratios. For example, a 1995 Beretta features a 1650 rpm stall converter as opposed to a 1999 Century converter with a stall of 2095 rpm. In the 4T60 family of transmissions, the combination of drive-chain sprocket ratios and the differential gear ratio together offer up to 12 different possible final drive ratios to allow the transmission family to cover various engine and vehicle applications.

I read, from  a gentleman, who goes by "JJ" (Koehler, I believe) who was a driver of a 1996, W-Body, Grand AM GTP, and who stated that, and I quote: "I have put a few hundred passes on my 4T60E on the dragstrip. I race SCCA autocross regularly. I drive at high speeds. I live to beat someone from a stoplight or leave them halfway around the on-ramp. My GP gets driven hard, if not harder then it was intended. It now has 174,000 miles and will run with any 3.4L out there. The trans has never been apart. I am a firm believer in changing the trans fluid and filter every 20,000 miles. Flush it if needed. The biggest enemy of the 4T60E is dirt and oxidized fluid"... so, there you go!

Replacing a complete transaxle should only be done if a unit is verified to be the same as the unit it replaces, as in addition to the up to 12 variants of the final drive ratio, different applications and years can and will have incompatible electrical connectors. The use of an incorrect transaxle will result in undesired operation, up to and including total non-functioning of the transaxle.

Gear ratios (4T60E):

1	2	3	4	R
2.921	1.568	1.000	0.705	2.385

Anatomy... Taking it apart... How it works... Common issues...

The basic operation of the 4T60E... the A, B, Cs:

 

Common issues with the THM 4T60E/65E transaxles... understanding the differences, too. Keep in mind that, till 1993, these vehicles didn't have ODB-II):

  This is a teardown of the THM 4T60E... to follow, below, will be a teardown of the THM 4T65E for those who are interested. I've priced units that are rebuilt at around $1295, with a core deposit around $350 (I'm not compensated to advertise)... if any reader has leads to better deals via reputable rebuilders, then please let us know in the discussion forum.

 

 

The THM 4T65E model... this is an excellent series of "how to" vids (1-9):