The TH400 on our 70 L34 shifts OK until it gets warmed up good. Then the first shift grabs 3 times rather than once. It seems to do it worse when going slow rather than tromping on it. We have tried adjusting the modulator. Any other suggestions? Thanks

Not a real expert here, but I would check two things:
1. Fluid level after it's warmed up. Check on flat surface with engine running.
2. Check vacuum hose going to Modulator for cracks and/or tranny oil inside the hose. If you've got fluid in the hose, you'll need a new modulator.

sounds like you have some worn internals the cold oil is thicker and can make the seals work ok untill everything warms up then the thinner oil will seep past any seal that is worn out causing the shudder when the clutch pack is actuated :eek:

The shift to 2nd, if it is in D, relys on the intermediate sprag to hold, along with the intermediate clutches. If in manual 2nd, there is a braking band applied as well. If you manually shift to 2nd(and keep it in 2nd) and it still seems exactly the same, I would look to seal issues. If the problem goes away when you manually shift to 2nd (not to D, just 2nd as above stated), then look to the sprag. These are the most common things that come to mind.