4L80E Intermediate Sprag Clutch, 34-Element Heavy Duty

This is the intermediate sprag that sits inside the center support of a GM 4L80E or TH400. It is the one-way element that holds the intermediate clutch drum against rotation so the unit can make second gear. When it rolls over you get a flare or a complete loss of second, a bang into third, and on teardown the sprag races come out chewed and the intermediate clutches come out burnt. OE reference 8633173, industry number 06763AM.

This is the 34-element version, not the early 16-element unit. GM ran the 16-element sprag in the early 4L80E and in the TH400 before it, and it is the piece that gives up first in a truck that tows, runs a tune, or sees any real torque. The 34-element sprag more than doubles the number of load-carrying elements in the same package, so holding torque goes up without changing anything else in the center support. It is a straight drop-in for the 16-element part and is the standard upgrade on any 4L80E rebuild that is going behind a diesel or a built gas engine.

Fitment covers 4L80E and 4L85E from 1991 up, and TH400 / 3L80 units using the same center support sprag. Common applications are Chevrolet and GMC 2500 and 3500 trucks, Suburban, Tahoe, Yukon, Express and Savana vans, Hummer H1, and the TH400 behind big-block applications.

On the bench it installs into the intermediate sprag race in the center support. Watch direction: the sprag has to lock in one rotation and free in the other, so set it in, then check it by hand before the center support goes back in the case. If it spins both ways it is in backwards. Replace the sprag races at the same time if either shows the polished witness marks or brinelling from the old unit letting go.