General Motors 4L60E

GM's four-speed automatic for rear-wheel drive, and one of the most-produced transmissions in history — behind small-block V8s, straight sixes and diesels in pickups, vans, SUVs and sports cars for two decades, in North America and in Australia.

Its name is a specification, and learning to read it decodes the whole GM family at once. The 4 is the number of forward gears. The L means longitudinal, which in GM's usage means rear-wheel drive — a 4T60E is the same idea turned sideways for a front-driver. The 60 is a strength rating on a scale that runs to 90, so a 4L80E is the heavy-duty relative rather than a different concept. The E means the shifts are commanded electronically by the engine's control module rather than decided hydraulically inside the gearbox.

That last letter is the whole history of the unit. It began in 1982 as the Turbo-Hydramatic 700R4, a purely hydraulic four-speed; the 700R4 was renamed 4L60 when the naming scheme arrived, and the electronic 4L60E was phased in from 1993 for trucks and vans and 1994 for rear-drive cars. The three names are one gearbox at three points in its life, and parts catalogues, forum advice and workshop manuals move between them without warning. The 4L65E of 2001 is the same unit with five-pinion planetary sets for higher torque, and the 4L70E follows it.

The torque converter's lock-up clutch is the first thing to wear and the cause of most of what follows. What it sheds contaminates the fluid, and the contaminated fluid clogs the solenoids and sensors that the E in the name depends on. A 4L60E with erratic or missing shifts is very often describing its fluid rather than its clutches, which is worth establishing before anybody drops the pan for the last time.

What is replaced, and roughly when:

• The torque converter and its lock-up clutch, first, and the source of the debris in everything below it.
• The valve body separator plate, and the separator plates of the overrunning, forward (input) and low/reverse clutches, which the trade reaches at around 150,000–200,000 km.
• The rear planetary set, which works hardest and is the routine replacement on a high-mileage unit.
• The clutch drum and brake band, which is where the heavier applications — the big-engined Hummers in particular — show wear the lighter cars do not.

One behaviour worth recognising rather than diagnosing: when the electronics lose confidence, the gearbox falls back to third gear and stays there. A truck that will suddenly only pull away sluggishly and will not change gear has gone into that failsafe, and it is telling you the control side has failed — not that four gears' worth of hardware has.