Monthly Archives: December 2015

#36 The Transmission, Differential, and Final Drives: Called the ‘Powertrain’ and It Was Great On The Sherman!

The Transmission, Differential, and Final Drives: Called The ‘Powertrain’ The Sherman’s Was Very Well Designed.

Sherman transmission

The Transmission, differential and final drives on the Sherman were very robust from the start of the Sherman design and proved to be rugged enough to take all the upgrades the Sherman had thrown at it over the years. As a combined unit, along with the steering brakes, with the armored differential housing they were referred to as the ‘powertrain’. In most cases a whole powertrain unit would be swapped if any of the major components needed serious work, since it was relatively easy. There were three types of armored covers, a three piece bolt together type, and two cast types. Powertrain units incorporating any of the differential covers could be swapped into any Sherman in place of any other type of powertrain unit. The internals of the three types of differential covers where different though and parts in some cases do not interchange. Hydraulically powered steering was tried on very early M3 Lee tanks, but it was discarded for an all mechanical long lever system used throughout the Lee and Sherman run.

latemodeel powertrain diagram

The final drives and differential had a gear ratio of 2.84:1, limiting the tanks top speed by RPM to 26 miles an hour in the M4A3 version of the tank, and that for only short burst. The RPM limit varied with engine model, and in the Jumbos case, a slightly higher gear ratio of 3.36:1, limiting its top speed to 22 miles an hour but giving the drivetrain a little more mechanical grunt to get the extra weight moving. This was the only modification major enough to be mentioned in any publication I’ve read so far. That says ‘damn good design’ to me. I’ve read several accounts of Sherman restorations being done, where after years on a firing range, or just rotting in a field somewhere, the final drives and differential units needed no mechanical restoration.

M4A2 differential cutaway
Cutaway of an M4A2s differential
M4A2 Final Drive cuttaway
Cutaway of a Sherman final drive.
Sherman final drive herringbone gears and shafts. This image is from the American Fighting Vehicle Vehicle Database.

Now a bit about gear ratios, for those who are not gearheads, before we get into the transmission since it’s going to have even more confusing gear ratios talked about. The meaning of the gear ratios in the above paragraph is, for every rotation of the drive shaft coming out of the transmission and going into the final drives and differential has to spin 2.84 times to spin the sprocket output shafts one turn.  What determines the Transmissions output rpm is what gear it is in, and what ratio that gear is.  The higher the number, the more mechanical advantage is transferred to the final drives, but lowers the top tanks tops speed in that gear.  If you have driven a manual transmission car, this is why first gear climbs in RPM so fast and each further gear the RPM climbs slower, but the car goes faster, same for the Sherman tank. If you really understand this, you will always get a laugh at the Hollywood portrayal of nitrous oxide; something used in WWII aircraft engines because they always show it as making the cars top speed faster, when all it can do is improve the acceleration to the mechanically limited top speed.

This M4A3 Powertrain is about to go back into its hull

The Sherman transmission has a “Granny” first gear ratio of 7.56:1, the tank isn’t going to be moving faster than 1 or 2 miles per hour before the driver would have to shift.  The next gear up, second is 3.11:1, on level ground, gear two is used to start the tank and drive it at low speeds. Say up to 5 miles an hour, on road and rarely off road third rarely you would then get into third gear, 1.78:1, and up to 8 to 10 mph.  Fourth would be the last gear to see regular use, coming in at an almost one to one, 1.11:1. This is your driving like a bat out of hell 13 to 19 miles an hour gear. Fifth gear is actually an overdrive gear, at 0.73:1, meaning .73 of a turn to spin the tranny output once. Meaning, this has to be taken to into account in calculating the tanks top speed and it could only reach its top speed on good roads in fifth gear! Reverse gear, 5.65:1, was almost as tall as first and really limited the tanks reverse speed. If you understand what be just covered, you can understand the gear ratios listed on your next cars window sticker.  On our example, M4A3 at would be screaming along at 2800 rpm, at the tanks 26 mph top speed.


Now that you understand gear ratios you may wonder what the term “Granny” gear means. The ‘Granny’ gear refers to a really high gear ratio gear, almost always first. The Granny gear was used for getting a vehicle started while hauling a big load, trying to tow another tank to get it started or heavy vehicle for the same reason, climbing a steep hill or obstacle, driving through thick mud or deep water or getting another tank or heavy vehicle unstuck from mud or another obstacle. This gear could also be used to slow the tank when going down a steep hill.

Powertrain early, from M4A4

The Sherman Transmission was fully Synchromesh in gears 2 through 5 with first and reverse not needing it.  Synchromesh means you did not have to depress the clutch twice, once to get it into neutral, the next to go to the next gear, or “double clutching”. This, in theory, made the Sherman tank, though a manual transmission that used a clutch, much like any car that has a manual, relatively easy to drive. If you could drive a car from the 30s you could drive a Sherman. There are several Sherman museums that will let you drive one if you have the right amount of money.  From what I understand, the key to how easy the Sherman is to drive comes partly from the motor in it and partly from how much you’re really willing to drive the thing and not worry about breaking it. It’s an American tank people, you can abuse it, it can take it, it’s not a Panther, it was designed with the American young adult of the 40s in mind. Hell, these things were used to tear down buildings post-war! They are not delicate.  Anyway, back to what I’ve read about driving a Sherman. The easiest motors are supposed to be the Diesel and Ford GAA, then A57 if it’s running right, then the R975 powered tanks. The R975 because it likes to get up into its higher RPM power band, and stay there for a while, it helps burn off carbon and keeps the plugs un-fowled, is supposed to be the hardest to drive. In contrast, the few places that have running Panther tanks have to be extremely careful who they let drive it since using some of its design features could destroy the transmission or final drives.

powertrain brake adjeuxtment

The Sherman powertrain was a very tough unit. I know of at least two restorations where the transmission needed little mechanical work. This same transmission, and for the life of me I don’t think I’ve ever seen a name for the original designer/maker, stayed largely unchanged through the full life of the tank. The Israeli Shermans used into the 70s were using original Sherman Transmissions, though probably overhauled. That they could be, and continue to be on overhauled for restored Shermans, kept working, and working well after all those years also screams “DAMN GOOD DESIGN” and it’s a little sad I don’t, we don’t know, who made them or designed them.

rear firewall m4a3 late
The oil cooler shown in this diagram was found in all Sherman models.
This powertrain out of an M4A3 76w tank sat for years, after being abused in a tank used in the demolition of houses. It only needed cosmetic restoration.

#35 Shermans In Motion

Sherman Related Videos 

This is the Post I’m going to put interesting video content I find on the Internet.

The Motors: All The Sherman Production Motors Being Run

Video of all the major tank motors running. I’ll add more videos as I find them.

R975 running.

GM 6046 running.

A57 being run.

Ford GAA being run up.


Tanks in motion: Sherman Tanks on Film, Either Modern Restorations or Period Videos. 

Here is an older video of an M4A1 that was restored and had new tracks installed.  They really put this tank through the paces and it’s worth it even if the music is a bit dated.


Here’s a short video of an M4A4 driving around.

The M4 105 Dozer, a video dedicated to just it! bonus includes Sherman drifting! They look like they are having so much fun in this video! Well until they bust it! This video is a BLAST!!!!

Shermans and a M31 ARV gutted and made to look like a M3 Lee again.

This was a Normandy Memorial day in 2013 I think. In this video, we see an M4A1 75 start up and then drive off, almost stalling.  Then later we get to see an M4A1 76w driving around.  Interesting how close they let people get to moving tanks.  Parked nextr to it is an M10 tank destroyer.

This is another Normandy D-Day Memorial, 2014. The Video starts off with an mid production small hatch M4A1 75, with a later production M10 behind it and then an M18.  After that an small hatch M4a2, and then the Fury M4A2 76 HVSS tank.

Ontario Regiments Museum’s M4A2 76 W HVSS tank driving around!

A video of a restored M4A1 driving in circles firing off its main gun, I’m sure modified to fire on propane as a noise maker.

A very long video, POV from the co drivers spot, on a restored, small hatch M4A1.

Restoration Videos

Here is a video of a restored Firefly Vc, a Sherman M4A4, with the a working A57 multibank motor, getting new tracks.  This may not look tricky, but these men are all risking losing fingers or toes, or worse, if someone messes up.

Video of a Very nice looking M4 105, with dozer blade being used to recover a M4A4 in very bad shape.

A start to finish ‘flower pot’ restoration on an M4A1.

A resto mod on a M4A1, with more footage of that nice M4 105 dozer.

A restoration going on in Texas.


#34 Israeli Shermans: The Most Powerful Shermans Ever To See Action.


Israeli Shermans: These Modifications Kept The Sherman Relevant Into The 70s!

Israeli use of the Sherman tank would be long and glorious, with updated models using extremely upgraded guns, seeing action for decades after WWII. They would use the chassis for more things than the US Army did. They also went with their own strange naming system, making trying to figure out the Israeli Shermans even harder. There is also not a lot of good books in English on the subject, and Hunnicutt only has a little info on them and I think it’s a tad out of date. This section will be updated as I find out more info on the subject and or correct what is here, based on newer better info.

In the dark early days when Israel was struggling to become a nation, they managed to get ahold of a few Shermans. Three or so were acquired from the British, probably M4A4s. They also managed to get de-milled Shermans from Junk vendors in Europe. They had to re arm some with an old German 75mm field gun, they were called Sherman (Krupp). When they managed to get ahold of a Sherman armed with a M3 75mm gun the tank was called a Sherman M-3, when it had a 105mm gun, it was a Sherman M-4. As you can see already, naming convention confusion has commenced.

Sherman M1 from the x littlefield collection33
Sherman M1 that used to belong to the Littlefield collection
Sherman M1 from the x littlefield collection
Sherman M1 that used to belong to the Littlefield collection
Sherman M1 from the x littlefield collection2
Sherman M1 that used to belong to the Littlefield collection

In the later fifties Israel was able to get more up to date Shermans. The tanks were M4A1 and M4A3 models with the 76mm M1A1/A2 gun, probably from France. These Shermans were called Sherman M1s, regardless of what motor or hull they had. If they had HVSS suspension, they were called Super Sherman M1. Some of these tanks had an upgraded engines, probably late in their careers, and with Cummings diesels.

The Story gets more interesting, and slightly less confusing in the naming area, when they started to rearm the tanks.

M-50 based on a large hull Sherman, probably an M4A3.
M-50 Sherman based on an early small hatch hull, probably an M4 from the looks of the wheel spacing
Another view of the same small hatch M-50
Another view of the same small hatch M-50
Another view of the same small hatch M-50
Another view of the same small hatch M-50

IDF M50 Super Sherman 75mm [LIMITED to 500px]

The M-50: In 1954 Israel and France went to work on a project to fit the excellent French CN 75-50 75mm gun to the Sherman 75mm turret. This gun could shoot an AP round out 3200 feet a second. To fit the gun they added an extension to the front, and rear of the turret, the front one to fit the gun, and the rear one to add counterbalance weight. The first fifty tanks were based on the M4A4 hull that had been converted to use the R975 radial motor. This motor, though less powerful than the A57, was much more numerous, and easy to repair, and the French specialized in this conversion.

These M4A4 hulls with R975 radials still had their VVSS, with 16 inch tracks. The added weight of the new gun on the already larger and heavier hull made for a very sluggish tank with poor off road ability. These early M-50s also had early split hatches on the commander’s cupola. I think these tanks had a loaders hatch installed.

They solved this by installing HVSS, and in many cases a Cummings diesels motor. Once production got rolling, they were installing improved all around vision cupolas and HVSS on all the converted tanks, but some seem to have retained the R975 radial or in rare cases the maybe the Ford GAA? I’ll have to look into this more. One thing is clear from looking at pictures of the tanks in action, and survivors in museums and private collections, is they were not picky about what hull they used, as long as it had a 75mm turret. I’ve seen M4A4 hulls, and other early small hatch hulls in photos, they could be M4, M4A2 or A3, and pictures of a large hatch hulls, that could have been M4 105 tanks, (the only large hatch hull M4 tanks), or M4A3 75 or 105 tanks or even M4A2 75s. I have seen very little evidence that M4A1 hulls were used, I’ve only seen two clear pictures of the M-50 turret on M4A1 hulls, and one was on a non HVSS M4 and you couldn’t see the front of the hull to tell if it was large or small hatch hull.

M51 Sherman at the Latrun tank museum
M51 Sherman at the Latrun tank museum
M51 Sherman at the Latrun tank museum
M51 Sherman
M51 Sherman
M51 at the Kubinka tank Museum Russia


The M-51: In the early 60s the Israelis went to the French for help shoehorning an even bigger gun into the Sherman. They took a shortened version of the 105mm Model F1 gun; this was a modification of the gun used in the AMX-30. The gun retained a stabilizer, I’m not sure if it was the original Sherman one or a more advanced design.  This gun could fling an AP round at 2969 feet a second and had a HEAT round that could penetrate 14 inches of steel.  They chose to use M4A1 76 W tanks exclusively. These tanks had the larger T23 turret and they was helpful in getting the guns to fit. The French prototype retained its VVSS, and R975, but the Israeli production modifications had HVSS and the Cummings diesel fitted to the M-50 models. This was a 950 cubic inch diesel that put out 460 horsepower. This was enough horsepower along with the HVSS, to keep the tanks reasonably mobile, but they were no hotrods.

Both these tanks saw extensive combat use with Israel all the way into the 70s, and then a lot of them were sold off to collectors and museums or used as range targets.

Coming soon! Other stuff the Israelis used the Sherman chassis for!!! 







Wooden mockup CDA
Wooden mockup CDA




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M4 Improved M4 Improved2 M1 improved and M7






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Chrysler’s A65:




General Motors Corporation V8-184 diesel engine:





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Odds and ends: Weird stuff I couldn’t fit anywhere else.


Let’s start with…






