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Sherman Gearbox


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Does anyone know the history behind the gearbox used in the Sherman?


Is it the same, I.e dimensions and internal ratios as Grant/Lee? Was it a gearbox used for something else beforehand or specifically built and designed for the Sherman?


Does any one know the TM manual number for the gearbox? Or is there anywhere online I can gain more information on it?


Has anyone ever replaced syncros in these gearboxes, if so was it NOS parts used? As I have encountered a few lately that have syncro problems I.e. they just grind until you come to a halt and then go into gear. If I can't find a supply of NOS parts I am looking into getting the parts manufactured.


Also if anyone knows the design limitations on these gearboxes, I.e the manufacturers torque and horse power input.





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TM9-1750 covers "Power train unit, Three piece differential case, for medium tanks, M3, M4, and modifications". March 1, 1942

TM9-1750B covers "Power train unit, One piece differential case, for medium tanks M4 and related Gun motor cariages", August 16, 1943


I do not have TM9-1750A but I suspect it is just a revised version of 1750.


Both these TMs fully cover removal from vehicle, complete dismantling, rebuild and refitting of all parts of the power train forward of the propshaft.


The gearbox is virtually the same from the first grants to the last ultimate series Shermans although of course the mounting of the controlled differential and the brakes changed significantly. Also the arangements for lubricating the crown wheel and pinion were improved as time went on so later gearboxes have a built in oil passage from where the return oil hose connects, to the front of the box. The actual gears and shafts are I believe all interchangeable except that the input flange is different on very late boxes to accomodate the tacho drive being moved from the engine to the gearbox.


Early boxes were set up for the gearlever to the right of the box as Grants had the driver over the gearbox and he changed gear with his right hand. This stayed the same on Rams and Sextons as they were RHD and changed gear with the left hand. For Shermans the driver was moved to the left of the gearbox so a new linkage was designed but the internals were not changed at all.


The gearbox ratios did not change but M40 GMCs, M74 ARV and the 'Jumbo' assult tanks had lower final drive ratios.


I am not sure that anyone has found the limits to the power and torque capacity of a Sherman box. There have been many engine upgrade packages for Sherman but the gearbox was never criticised for short life, just for not being automatic.


As far as I know the design was not directly used before Lee/Grant but was a major development of the M2 medium tank gearbox with which it shares only its basic concept.


I have driven many Sherman family vehicles and as you say many are very reluctant to let you into gear. The worst ever was an Israeli Trailblazer which had had its transmission filled with EP90 on the principal that it was big and that is what you put in big gearboxes! As the syncro and the brakes require friction to work it neither steered or changed gear willingly. The official oil was 50 viscosity (same oil in the engine if a radial) but this took account of it thinning significantly as it got hot. Modern oils, even single grade oils, are far more stable and better lubricants than WW2 oils and you will find that filling the transmission (all of it, not just the gearbox) with a universal 15/40 oil as used in modern tractors will absolutely transform the steering and brakes without any harm to the gears etc.


It should be bourne in mind though that the synchro is having to do a lot of synchronising as there is a lot of momentum in the propshaft and clutch to loose. Do not expect to move the gear lever straight from one gear to the next. From neutral, 'lean' it into the next gear firmly, but not forceably. When it has synchronised it will let you in, you can not force it in by pushing harder and if you go back to neutral and try again you will lose whatever synchronisation that you had. Also, when accelerating try to change up early rather than holding out for maximum revs in each gear. There is plenty of torque and the gearchange will be far quicker if changing at lower revs so the vehicle does not loose as much speed while you change.


One last thing: if you remove the flange fitting for the oil return pipe from the oil cooler on the top LH side of the box, not the elbow but the actual flange to the casing, you will have to dismantle the gearbox because there is a banjo shape piece on the output shaft that should engage with the piece that you just took off but has dropped down under gravity and is almost impossible to get to re engage from outside. This is not good as there is then no internal lubrication.


Good luck, David

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I can help you with most internal parts for the Sherman controlled differential. We had great stocks of Sherman parts after the war and used the M4A2 right up until the early seventies. As well several companies continued using Sherman running gear for a variety of industrial machines. Send me a PM and I would be glad to see if I can assist.

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