A/T - 700R4 Shifts In Manual Low
BULLETIN # 196TRANSMISSION: 4L60/700-R4
SUBJECT: Shifts in manual low
APPLICATION: GM
4L60/700-R4
SHIFTS IN MANUAL LOW
It is normal for a 4L60/700-R4 to upshift in manual low when the engine approaches redline. An early upshift in manual low is usually caused by a mismatch between the valve body and separator plate, or a missing # 9 checkball. Example: 1988 valve body with 1987 separator plate and a missing # 9 checkball. Make sure you check this first. See ATRA bulletin # 188 for valve body interchange information.
If you desire a later shift in manual low (above 400 RPM), use a D2-Lo/Rev boost valve which has a small land that measures .283" in diameter. If you don't have one readily available you can get one from your local GM dealer (Part #...8648958).