Drop-in Corvette-style 2-4 servo for 4L60E and 700R4 with a 2-groove apply pin, updated return springs and fresh seals for firmer 2nd and 4th.
If your Silverado, Sierra, Tahoe, S10, Camaro or Astro shifts into second like it is wading through mud, or the engine flares when it goes into overdrive with a trailer behind it, the 2-4 band is probably not getting clamped hard enough. This Whatever It Takes (WIT) servo assembly, manufacturer part number R74900BA, replaces the stock 2-4 servo in the 4L60E, 4L65E, 4L70E and the older 700R4 with the Corvette-size apply piston. It comes already assembled with the pistons, a high-temp painted cover, a 2-groove apply pin, updated return springs, new D-rings, new O-rings and a new external snap ring, so nothing from the old servo goes back in.
The 4L60E holds second and fourth gear with a single band wrapped around the reverse input housing. The servo is the hydraulic piston that tightens that band. Second-apply oil from the valve body pushes the piston, the piston drives the apply pin into the end of the band, and the band grips the housing. Third-apply oil acts on the release side to let the band go for the 2-3 shift, and fourth-apply oil brings it back on for overdrive. Because the same piston handles both the 1-2 and the 3-4 shift, a servo that is undersized for the job, leaking past its seals or tired in its springs hurts two shifts at once.
GM built these transmissions with four different servo sizes depending on the vehicle, according to TransGo, and the Corvette-type piston has the largest second-apply area of the factory versions. It came from the factory mainly in the port-injected Corvette and the performance Camaro and Firebird. More area on the same line pressure means more band clamping force, which is why a truck that came with a smaller servo feels noticeably firmer on the 1-2 shift after the swap.
A worn 2-4 band rarely sets a dedicated trouble code, so a scan tool that shows nothing does not clear the servo. Our 4L60E common problems guide walks through how band slip differs from the 3-4 clutch and sun shell failures this unit is known for.
Pull the pan first. A pan full of dark band lining means the band and likely the reverse input drum surface are damaged, and a new servo alone will not save it. If the fluid is reasonably clean, check line pressure against spec, then drive it hot and watch whether the slip happens only in second and fourth. If you are chasing a harsh or late shift in a Camaro, the 4L60E Camaro shift problems guide covers the valve body and pressure control causes that can feel similar, and S10 owners can use the S10 shift diagnosis guide.
This servo fits the GM 4L60E, 4L65E, 4L70E and 700R4, which covers 1993-2013 4L60E trucks, vans and cars including Silverado 1500, Sierra 1500, Tahoe, Suburban, Yukon, S10, Sonoma, Blazer, Astro, Camaro and Corvette, plus earlier 700R4 applications. TransGo notes the equivalent Corvette servo does not fit 2006 and newer Corvettes, which use a different transmission. The servo bore is shared across these cases, but apply pin length is not universal, so compare the new pin to your old one. If you are unsure, send us your year and VIN before ordering. Browse every part for this unit on our 4L60E parts page.
If the band is already burned, do the job once: the 4L60E Super Master Rebuild Kit includes the frictions and band for a full overhaul. If you find worn valve body bores while you are in there, a 2003-08 4L60E valve body restores the pressure that feeds the servo.
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Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
Only if the band and drum are still healthy. The servo adds clamping force and fresh seals. If the band lining is burned off or the reverse input drum surface is glazed, the band has to be replaced too, and a Corvette servo will only hide the problem for a short time.
Yes. The servo bore and design carried over from the 700R4 to the 4L60E, 4L65E and 4L70E. Compare apply pin length to your original pin, especially on a case or band that has been changed.
No. The 2-4 servo is serviced from outside the case. You need a servo cover compressor to push the cover in and release the snap ring. Most owners use the job as a reason to change the fluid and filter anyway.
It gets firmer, which is the point. On a stock truck that came with one of the smaller servos, the change is noticeable but not violent. If you also install a shift kit, expect a crisper shift overall.
Use Dexron VI. It replaced Dexron III as the GM service fluid for the 4L60E family and is backward compatible with older applications.
There is no servo-specific relearn. If the transmission control module has learned around a slipping band for a long time, resetting shift adapts with a scan tool and driving through several full shift cycles helps it settle.
