29-element forward input sprag for GM 4L60E, 700R4, 4L65E and 4L70E. Replaces 29236AM and 8654441A when the unit has no drive or slips in first.
If your Silverado, Sierra, Tahoe, Suburban, S10, Blazer, Camaro or Corvette revs up in Drive but will not pull, or slips on takeoff and then catches with a thump, the forward input sprag inside the 4L60E is one of the first parts a rebuilder suspects. This is a 29-element machined steel forward sprag assembly, the stock element count, and it drops into the input housing of the 4L60E as well as its 700R4 predecessor and the 4L65E and 4L70E that followed. It is listed against OE and aftermarket numbers 29236AM, 8654441A, A74658B, A74658C and 77725B.
The 4L60E has two one-way devices: a low roller clutch at the rear and this sprag at the front. The sprag rides between the forward clutch hub and the input sun gear. When the forward clutch applies in Drive, it spins the sprag outer race, and the tilted elements wedge against the inner race so engine torque reaches the input sun gear in first, second and third. When the sun gear needs to run faster than the forward clutch, for example on the shift into fourth or while coasting, the elements roll back and the sprag freewheels. In manual 1, 2 and 3 the overrun clutch applies and locks the sun gear directly, which takes the sprag out of the load path. That detail is the key to diagnosing it. Because the sprag carries launch torque every time the truck leaves a stop, Sonnax notes that clean fluid and a fresh sprag with good races matter a great deal to how long a rebuilt unit lasts.
A bad sprag normally does not set its own code. If the scan tool shows P0741 or P0748 on a 4L60E, those point at the converter clutch circuit and the pressure control solenoid, not at the sprag, so do not let an unrelated code steer the diagnosis.
Do a range test with the fluid hot and at the correct level. Slips or no movement in D that disappear in manual 1 or 2 point strongly at the forward sprag or forward clutch, since the overrun clutch bypasses the sprag in those ranges. A slip only in first with manual 1 holding is more likely the low roller clutch. On the bench, GM's unit repair procedure has you hold the assembly and turn the hub: it should spin one way and lock the other. Any lock in both directions, or freewheel in both, means it is done. Our guide on 4L60E forward clutch and sprag wear walks through the range test, and the input housing and sprag failure guide covers what else to inspect while the housing is out.
The listing covers the 4L60E from 1993 through 2014, the 700R4 from 1987 through 1992, the 4L65E from 2001 through 2007 and the 4L70E from 2006 through 2009. The 29-element count is the factory design for these units. Before ordering, measure your old sprag and races against this one and match the element count; if you are unsure, send us your year, model and VIN and we will check it. You can browse every part for this unit on our 4L60E parts page, and if you want a name-brand version, the TCI 373600 29-element sprag is the same count at a higher price.
Builds that see high horsepower or heavy towing often move to a 34-element sprag for more holding capacity; for a stock engine the 29-element design is the correct match. For background on how the sprag and roller clutch fail differently, read 4L60E sprag and roller clutches: where they fail.
| Elements | 29 |
| Fits | 4L60E (1993-2014), 700R4 (1987-1992), 4L65E (2001-2007), 4L70E (2006-2009) |
| Replaces | 29236AM, 8654441A, A74658B, A74658C, 77725B |
| Material | Machined steel |
| Weight | 9.9 oz |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
The listing covers the 700R4 from 1987 through 1992 as well as the 4L60E, 4L65E and 4L70E. Compare it with your old sprag and races, and send your year and VIN if you want us to confirm.
Both cause no-drive or slip in D. On the bench, the sprag should freewheel one way and lock the other. If it does, look at the forward clutch plates, piston seals and accumulator piston instead.
Yes if they show pitting, flat spots or wear marks. A new sprag running on a damaged race will slip again quickly.
The 4L60E family takes Dexron VI. Refill and check the level hot in park after the repair.
For a stock or mildly modified engine, the factory 29-element count is correct. High-power or heavy-tow builds often step up to a 34-element sprag for more holding capacity.
