Sherman A4A2 diesel 2-3 shift problem

[Maurice Donckers]

another warning about changing oil , don`t put modern class 5 oil in a synchro box , this oil is not good for brass parts . use straight 50 in this case .

[David Herbert]

As Maurice said, any oil with EP additives will attack brass and bronze parts very aggresively. Almost any WW2 gearbox has bronze selectors so synchro or not, do not use EP / class 5 oils at all.

A Sherman gearbox shares its oil with the controlled differential steering system and the final drives. If you put EP into the final drives (as used in most modern tracked vehicles) it will migrate to the steering and main gearbox so no steering, brakes or synchro !

David

[Kirk Armitage]

If both those 6 L's by themselves, linkage disconnected from each other, idle down properly, I would have a hard look at the connecting linkages for play,binding when the motors are torquing etc. Those two rack are literally one when connected together, affecting both motors. If one motor seems slow to come down , disconnected by itself, I would look at ,a sticky injector, hi - low spring pack in the governor is sticking from condensation, and or a buffer screw in to far ( if those early govenors had them)
Love those old Detroit's. K Armitage

[Malcolm Towrie]

Thanks for the warnings about the modern GL-5 EP gear oils. Since the original manuals spec SAE 50 oil, I suspect that is what has always been used, at least here at the museum. Mind you, the brake steering isn't anything to write home about either, especially in first gear.

Kirk, I don't think we checked each engine idling down after hand operating the speed control lever with the linkage disconnected. I'll check that. The low speed and high speed springs look in good shape with good idle speed control and max rpm limited to about 2200 rpm. The buffer screw each side is just snugged up enough to tame the idle hunt so I don't think it's screwed in too far.

Malcolm

[Malcolm Towrie]

Today, we tested the slow responding engine with the governor completely disconnected from the rack control tube rod, so just hand operating the rack tube. Throttle response was great, very fast. So that seems to rule out oil burning or sticky injector.
Then we tested response of both engines with the linkage disconnected from both governors. So hand operation of the speed control lever on the governor of each engine. Again it was good for both engines. Raising rpm to 1500 and snapping the lever back to idle showed both engines idling down fast.

Connecting the linkages showed problems. Despite syncing both engines earlier, they're were now badly out of sync, with one revving to 1500 and one barely coming off idle. I found one clevis pin badly loose in the clevis, and the bushings supporting both ends of the throttle cross shaft that connects the two engines badly worn. So as Kirk said, that may be the culprit. We'll fix the looseness and go from there.

Thanks again.

Malcolm

[David Herbert]

Well done, you are getting there. This has defeated many people but as you are demonstrating it is fixable.

David

[45jim]

I wonder which A2 that is? I hope its Bart.

You have already established the engines are fine separately so follow the instructions on page 258 of the manual which cover the throttle linkage adjustment and engine synchronising.

Basically, disconnect the throttle linkage and then progressively reconnect the linkage from rear to front checking each section as you go to isolate the problem area.

The linkage bearings in the governor case are also a known problem area in the 6-71. The lever often moves easily when not connected to the rest of the linkage, but when connected up the side load binds the bearing. If its not Bart, we had changed out the governor covers and bearings to cure a similar problem. But that was a long time ago.