This symptom is very common in 3 speed rear wheel drive Ford transmissions that are several years (8 years +) old with high mileage (100,000 +), but can happen with any make. The symptom is caused by heat traveling from the torque converter through the input shaft to the forward clutch drum. The o-rings, particularly the inner, that seal the forward drum piston in the forward drum become hardened over time and mileage. They loose their ability to seal properly, so when the fluid pressure is applied to the drum, the piston doesn’t move to apply the clutches.
The delayed engagement starts at several seconds and progresses to several minutes. If the inner o-ring breaks, there will be a sudden increase in the delay. After the transmission comes up to operating temperature, it works well until it sets long enough for the symptom to occur. The C-4, C-6, and FMX transmissions are the units that will usually exhibit this symptom, but can happen in others. Front wheel drive and overdrive units rarely exhibit this symptom.
If the delay becomes intolerable, the cure is to overhaul the unit. I do not recommend using an additive that will “soften” the seals. This may help in the short run, but cause other major problems in the long run. A transmission with the accumulation of miles and time for this symptom to occur will undoubtedly has significant wear in other areas.
