Sherman A4A2 diesel 2-3 shift problem

[Malcolm Towrie]

Thanks for the great information, guys.

I should clarify. We have two Sherman's, one changes gear ok, this one doesn't, and it has been getting worse. The various guys who have been driving them for years agree on that. So I think it is more than gear changing technique.

But that is interesting what you are saying about short shifting from 2 to 3. Personally, I have being doing the opposite, taking it up to 2000 rpm in 2, pushing the clutch in, selecting N, letting the clutch up, and then waiting a while before dipping the clutch again to select 3. I guess that ends up being the same as short shifting as I'm just waiting in N to let the high rpm come down. I'll try the short shift.

One concern I had about short shifting is that lugging seems to be considered a no-no for screamin' Jimmies, even if they pull like trains at low rpm. Tough on the rod bearings, due to lower oil pressure I believe. Anyway we're putting maybe 30 miles a year on the old girls so we unlikely to wear them out.

By the way, the gearbox was originally synchromesh, but it sure isn't now. We have to double clutch up and down on this tank. Just worn out, I guess.

I don't know what oil is in the gearbox, or how old it is. I am just getting involved in these tanks. We should replace it with fresh SAE 50 or maybe 15w40 to see if that helps.

The engine with the slow dropping rpm doesn't seem to be burning oil, but that's a good point about oil burning keeping the rpm up. I'll see if this engine has a history of needing oil top-ups.

We have synchronized both engines by holding them at 1000, 1500, and 1800 rpm when disconnected (after confirming the tachs were accurate) but that has not resolved the difference in rpm drop between them.

We have almost confirmed both clutches fully disengage. When running each engine on its own with the clutch disengaged, the prop shaft could be turned by hand.

Malcolm