I've been having shifting issues with the automatic transmission in my 300D for quite some time. I've made all adjustments that are possible, including the modulator and bowden cable. The vacuum is within spec. The problem that continues to irritate me is that the transmission has a tendency to skip 2nd gear when accelerating from a rolling stop. It'll rev to nearly 5K before it finally shifts and it jumps into 3rd. If I come to a complete stop it will shift normally. Downshifts into 2nd are another problem. It will not downshift from 3rd into 2nd for any reason whatsoever. It will only downshift to first. The rise in rpms worry me about it throwing a rod in the process.
I've heard about a K1 or K2 piston that needs replacing but I don't believe it to be the problem. I've actually swapped an entire valve body from a spare transmission last week and that did not change the shift/downshift issue. It does shift better overall than it did before the swap.
I feel this may be something a professional transmission tech may only be able to solve. I have a manual transmission with all the required components to swap in. I just wish I had the correct flywheel. I feel to just go ahead and swap rather that spend the big bucks it'll probably cost to fix the transmission right.
Should I just dump the automatic for the manual?