Trying to diagnose what may be causing my 78 to jerk hard into gear when going from park or neutral into drive or reverse, or from reverse to drive. The car will feel like it lunges into drive and somewhat feels like it drops down or jumps back when going into reverse. Once in drive it shifts smoothly. I changed my transmission fluid and rear diff fluid this week and no change to how the car goes into gear. I'm wondering if U-joints possibly? But I don't have a vibration when driving. The car only has 33k miles.
My idle is around 8-900 in park, 550 in drive. Fast idle is at 1800.
78 Y88 400 TH350
Thanks for any help!