TCI 29-element forward sprag for GM 700R4 and 4L60E input drums. Replaces a worn or rolled-over sprag behind no-drive-in-D and slipping complaints.
A Silverado, Tahoe, S10 or Camaro that will not move in Drive but pulls in manual Low or 2 is one of the clearest patterns a 4L60E gives you, and it usually points at the forward sprag. The TCI 373600 is a 29-element forward sprag assembly for GM 700R4 and 4L60E transmissions, made by TCI for builds that see more torque than stock. It goes inside the input drum and replaces a sprag with rolled, chipped or worn elements. It weighs under half a pound and ships from the USA.
The 4L60E input housing carries the forward clutch, and the forward clutch drives the outer race of the forward sprag. The sprag's inner race connects to the input sun gear. In Drive, first through third, the sprag locks and passes engine torque from the forward clutch into the gear train. When the truck coasts, or when it shifts to fourth and the input sun gear outruns the forward clutch, the sprag freewheels so nothing binds. In manual Low and 2 the overrun clutch applies alongside it and locks the input sun gear to the housing directly, which is why a dead sprag still lets the truck pull in those ranges and gives you engine braking.
The sprag sees full launch torque in first gear. Sonnax's 4L60E build tips single it out as a part that carries launch load, which is why upgraded and towing builds go to more elements. TCI's 29-element design spreads that load across more contact points than the earlier 27-element style, so each element is less likely to tip past center and roll over.
Note that this pattern differs from the 3-4 clutch burnout or a stripped sun shell, which leave first gear alone and take out third and fourth instead.
Check fluid level and condition first, then do the range test: no Drive with good manual Low points at the sprag, while no movement in any forward range points at the forward clutch, its piston seals or the forward accumulator. Our 4L60E forward clutch and sprag wear guide walks through that split. With the unit on the bench, hold the input housing and turn the sun gear by hand: it should spin freely one way and lock solid the other. If it locks both ways, spins both ways, or feels notchy, the sprag or races are finished. The input housing and sprag failure checklist covers what else to inspect while the drum is apart.
TCI lists the 373600 for GM 700R4 and 4L60E transmissions, so it covers the 700R4 era and the electronic 4L60E used in 1993-2013 Chevrolet and GMC trucks, SUVs, vans and performance cars. Some 4L60E-family units, including later builds, used different input housing and sun gear combinations. Count the elements in your old sprag and compare race diameters before you order. If anything looks different, send us your year and VIN. For a lower-cost 29-element option, see the 4L60E forward input sprag, 29-element or browse the 4L60E parts collection.
| Part Number | TCI 373600 |
| Type | Forward sprag, 29-element |
| Fits | GM 700R4, 4L60E |
| Brand | TCI |
| Product Dimensions | 5.8 x 5.5 x 1.9 in |
| Weight | 7.7 oz |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
That is the classic forward sprag pattern. In manual Low the overrun clutch locks the input sun gear to the housing and bypasses the sprag. If nothing moves in any forward range, look at the forward clutch first.
More elements share the torque, so each one carries less load and is less likely to roll over. It is aimed at towing and modified engines that put more launch torque through first gear.
Yes. TCI lists it for both the GM 700R4 and the 4L60E. Compare element count and race size with your old sprag to confirm.
Only if your existing races are pitted, scored or heat-tinted. Inspect them closely. A new sprag running on damaged races will not last.
Hold the input housing and turn the input sun gear by hand. It should turn freely one way and lock the other, as in the factory direction check. If it locks the wrong way you will have no drive in D.
