A/T - C5 Slipping On 1-2 Shift After Rebuild
TECHNICAL BULLETIN # 261DATE: 1994
TRANSMISSION: C5
SUBJECT: Slipping Shifts
APPLICATION: Ford
Slipping on 1-2 Shift After Rebuild
When a C5 transmission is rebuilt with a disabled torque converter clutch (dummy lock-up), the shifts may be very soft or slip. This is because there is typically more torque transmitted through the geartrain when the torque converter is not locked up (torque multiplication).
If a check of the vacuum drop and line pressure rise is okay, try installing a C4 intermediate servo spring, piston and cover assembly.
Use a piston and cover with a casting code of "A" or "H" for in-line six cylinder and V-8 engines. Use a piston and cover with a casting code of "W" or "Z" for 4 cylinder and V-6 engines. These servos have been found to offer the best results for the given applications. However, other servos and covers can be used if necessary. The larger the apply surface of the piston, the firmer the 1-2 shift will be.
Note
The servo sizes from largest to smallest are C, H, A, R, B, Z, K, W, (C and K are very rare).