How is reverse?
In reverse the VB sends full pump pressure to all the involved circuits, which are the L/R band and the Hi-drum. There is zero pressure regulation.
In all forward gears, the forward Clutch is engaged and one of; either the Second gear band for Second, or for Third gear, the Hi drum. In Drive, to get First gear, the rear one-way (sprague) clutch gets the job done. But in manual Low, the L/R band is applied.
Thus, with a little detective work, it's fairly easy to diagnose what went wrong.
BTW for future reference, to do a first-gear blast-off, with a stock A904, it is customary to shift the trans into manual low, because the sprague is not designed for that.
To make matters worse, the sprague does not come in a rebuild kit, and must be ordered separately.
As for my guess, I'll chose the Forward clutch, which is a bit unusual.
