1996 Z71 after truck gets up to operating temperture and after shifting into overdrive there is a clunking or jerking
And it can't seem to make up its mind whether it should be in third or fourth gear at 55 mph, right? This noise is the torque converter lockup feature malfunctioning. This is very common in 4L60E transmissions, especially in trucks with over 125,000 miles, and even more so in trucks which have been used to tow while the transmission is in overdrive (an advertised no-no). A 4L60E transmission is really only good for about 120,000-150,000 miles. There are several factory parts inside which are too weak for the job any truck owner does with his truck. I speak from many years' experience (I have been a mechanic for thirty-five years), this transmission is almost dead. I have rebuilt MANY 4L60E's over the almost twenty years GM has been putting them in every rear-wheel-drive vehicle it makes, and the best way to be happy with your transmission after you have it rebuilt is to tell the builder that as a minimum over a stock rebuild you want: A new torque converter, a hardened input shaft, the Borg-Warner 29-element input sprag, The Beast sun gear reaction shell, the Sonnax .490" pressure boost valve, a new reverse drum, an extra-wide (2 5/8") Carbon Fiber power band, all Alto Red Eagle frictions and Kolene full-thickness steels, the Sonnax "Super Hold" 1-2 and 3-4 servos, the Transgo valve body separator plate, the Sonnax cast-aluminum pinless forward accumulator piston, the Sonnax heavy-duty 2-3 shift valve, and a 15,000lb capacity auxilliary transmission fluid cooler. This build will cost about five-eight hundred bucks more than a stock rebuild, but you will have a bullet-proof transmission that you can tow 10,000-12,000 lbs with, and it won't break.
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