4L80E/4L85E Low-Reverse Roller Sprag, 8-Leg, GM 34727

This is the low/reverse one-way sprag that lives behind the rear planet in a GM 4L80E or 4L85E. It is the part that has to hold the low/reverse clutch pack stationary so the transmission has reverse and a solid first-gear engine-braking hold. When it fails it either rolls over under load or lets go entirely, and the symptoms are unmistakable on the bench and on the road: no reverse, delayed or weak reverse, a ratcheting noise when you back up, and low/reverse clutches that come out burnt on teardown. OEM reference 34727.

It is a roller-type sprag with eight legs that key into the planet carrier, which is the design most rebuilders prefer over the older mechanical-diode style because the rollers wedge harder and are far less prone to rolling over in a high-torque truck or a tow rig. Fitment covers all 4L80E and 4L85E transmissions from 1995 to current, which puts it behind Chevrolet and GMC Silverado, Sierra, Suburban, Tahoe, Yukon and Cadillac Escalade among the common applications.

On a rebuild it goes in with the rear internal gear and low/reverse support; check that the eight legs seat fully into the carrier and that the rollers and springs move freely before you stack the clutches. If you are in this transmission for a no-reverse complaint, replace the sprag on principle rather than reusing a marginal one, because a second teardown to chase it costs far more than the part. Ships from the USA.