Sherman A4A2 diesel 2-3 shift problem

[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.

[jdmcm]

Poor steering in the Sherman that gets worse over time can be the fault of poorly adjusted brakes or a poor operator. If the brakes are dragging they will get hot and end up glazing the pads and brake drums, if someone likes to keep pressure on the levers or make long turns with the lever applied instead of shorter chopping motions the drums will get very hot, I have even seen them crack. Drums can be removed and resurfaced but pads will need to be replaced.

[Malcolm Towrie]

Originally Posted by 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.

Yes, it's Bart that is having these problems. Thanks for the info about the linkage bearings in the cover. I had the right hand governor apart, which is the side acting up the most and the cover bearings felt snug and free, so we'll focus on the obvious linkage problems but keep that in mind.
Malcolm

[45jim]

At no time should a driver of any tracked vehicle (with a controlled differential) make "choppy" movements of the tiller bars to steer the vehicle. Smooth applications of the required force that result in gradual loading of the brakes are the most efficient. Sharper turns require more force and consequently more throttle - but smoothly.

The brakes shoes never apply perfectly evenly around the drum surface as they are attached to each other by pins that wear that allow from some out of phase movement. Gradual application allows the shoes to settle on to the drum and spreads the braking action over the whole braking surface greatly reducing wear and tear. Quick pulls on the tiller bars can cause overheating in localized areas of the shoe surface and induce glazing.

Having taught many tracked drivers from M113 to Leopards over the years the ones that drive smoothly with care and attention to the vehicle rarely are the ones buying cases of beer for RCEME recovery crews. The best loved drivers of wrench benders were the ones that understood their vehicle and drove it with due care, not like something they stole.

When we restored our Sherman and Centurion in Calgary the old hands came out to give us some pointers and they overwhelmingly agreed that driving them firmly but smoothly was the key to long life. No different than a modern tank.

One of the problems for most private owners of tracked vehicles is that they rarely get a wide open area to drive the vehicle at high speed (relatively) so are not that familiar with its driving characteristics. Tip toeing around a display area at minimum throttle trying to preserve rubber track shoes does not teach one how to drive a tank!

Your brakes will last much longer if you are firm but smooth in their use.