Sherman Transmissions
Other Auxiliary Transmissions

By: John Smith of Old Ford Tractors

The introduction of the N-series Ford tractors and their high sales numbers created a huge market for add-on accessories for the tractors. Many companies started making products to "improve" the Ford's usefulness or make their operators more comfortable. But one stood out just by the sheer number of "goodies" they sold and that was Sherman Products. The Sherman brothers were insiders with Henry Ford and Ford's dealers would sell and service many of the Sherman's products. Front endloaders and backhoe attachments were popular. Some items such as the aluminum head and the live pto didn't go over as well. Far and away the Shermans' most popular add-on was the auxiliary transmission. By the introduction of the 8N, tractor buyers could order a Sherman transmission when they ordered their new tractor and Ford would ship the tractor with the Sherman attached to it. The dealer mechanics then installed the transmission before delivery. Their first offering was the Step-up transmission which gave the owner twice the gear selection he had before. Step-up first and step-up second gear was between the regular second and third gears. It was basically an overdrive unit for the transmission input.

Sherman step-up transmission Sherman step-up transmission sales literature

The Sherman Step-up

Click the ad above to see
the complete sales literature

Some Step-up units were sold that used a cable to shift the transmission rather than the usual lever on the left side. The cable came out of the right front of the tractor transmission case and mounted on the right lower dash with a large black plastic knob that was pushed in for overdrive or pulled out for normal position. The cables were prone to rusting and were soon discontinued in favor of the old reliable lever.

Sherman step-up cable shifter Cable type Sherman step-up transmission sales literature

The Sherman Step-up
cable type shifter

Click the ad above to see
the complete sales literature

Sherman Step-up parts drawing Sherman Step-up installation instructions

Rebuilding a Sherman Step-Up transmission [Click here]

Then came the Sherman Step-down transmission which worked the same as the Step-up except it lowered the gear ratios rather than raised them to give the tractor a slower ground speed. The Step-down used the same gear case as the Step-up transmission but was painted red instead of the gray like the Step-up. The Step-down transmission, available with cable or lever shift, is an extremely rare find today.

By far, the most popular and most useful transmission back then and still today is the Sherman step-up/step-down combination transmission.

Sherman Combination
transmission sales literature
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combination transmission sales literature

Sherman combination
transmission Sherman steering wheel info plate
Sherman combination transmission Steering wheel information plate

The Sherman combination transmission shifter and shift pattern

The Sherman combination transmission internal gear train

Sherman combination parts drawing [Click here]
Sherman combination installation instructions [Click here]
Rebuilding a Sherman Combination transmission [Click here]

The Sherman shift levers for the combination and step-up/step-down are unique and easy to tell apart from a quick glance.

Following the popularity of the Step-up/Step-down Combination transmission was the Sherman "special purpose" or "creeper" single Step-down transmission. The "creeper" transmission uses the same gear case as the combination transmission but uses a top cover with only one shifter rail. It was painted a copper or bronze color as opposed to the gray or red of the combination. It was an extreme step down with a 9:1 reduction ratio and is a very rare find today. Externally, it uses the same shifter lever as the combination transmission.

Internally, the creeper transmission uses all straight cut spur gears. All other models have helical cut gears.

In the later '50s Sherman offered the shuttle or reverser transmission that simply reversed the input to the regular transmission and gave you all the normal forward speeds when you were going backwards. This was handy for the Fords that were being used as forklifts or for loader work as one lever could change the tractor from forward to reverse at the same speed as the gear the regular transmission was in at the time.

The popularity of the Sherman transmissions induced other manufacturers to offer their versions of auxiliary transmissions. One such company was the Hupp Corporation who made excellent quality gearboxes to fit Ford and Ferguson tractors. Their "Dual-Drive" over/under transmission was similar to the Sherman unit but the shift lever was on the right hand side of the tractor. Hupp offered two models of the Dual-Drive with different gear ratios, the D59 and the D59-2. The D-59 offered a low gear reduction of nearly 2 to 1. They also sold a straight ovedrive (step-up) model, the O-49-C which was a "convertible" model. Buying and installing the upgrade kit could convert the overdrive to a Dual-Drive whenever the owner desired.

Hupp Dual Drive
transmission sales literature (courtesy of Ed Gooding)
Click the ad above to see the complete
Hupp transmission sales literature

The Hupp Dual Drive transmission shifter The Hupp overdrive transmission shifter
The Hupp Dual-Drive transmission shifter The Hupp overdrive transmission shifter

Hupp shift pattern
The Hupp Dual-Drive transmission shift pattern

For some applications such as trenching or running a rototiller, a lower ground speed was needed while still maintaining the higher pto speed. To accomplish this, some transmissions were made to install behind the tractor transmission rather than in front like the Sherman and Hupp. The Everett trencher transmission actually lengthened the tractor by a few inches when installed. The Everett transmission has such an extreme gear reduction at 98 to 1 that it's only logical use can be for running the trencher unit. The photo below shows an Everett unit installed in Marvin Baumann's 8N "Fourtrans", the world's slowest tractor. Marvin has four transmissions in his tractor, the Sherman creeper transmission, the standard transmission, the Everett trencher transmission, and the Howard gear reduction unit.

The Everett trencher transmission
The Everett trencher transmission

The Howard gear reduction unit mounts to the back of the regular transmission housing and has a shift lever on the side cover where the dipstick was located. The Howard did not affect the pto speed, it only reduced the tractor ground speed which makes it the only auxiliary transmission for the N tractors that is suitable for running a tiller . Gear reduction is about 3.5 to 1. These were originally designed to be used with the Howard Rotovator, a rear mounted rototiller. They were somewhat fragile if abused and broke gears easily. Complete Howard transmissions or replacement gears for these units are nearly impossible to find. The Howard transmissions for the NAA and hundred series tractors were redesigned with planetary gears and are much more durable.

The Howard transmission shifter
The Howard transmission shifter

The internal components of the N series Howard transmission

One of the more rare auxiliary transmissions is the F&T overdrive unit from the mid '40s. Basically the same as a Sherman step-up or Hupp overdrive unit, it apparently never sold well and it's unusual to see one today.

F&T overdrive transmission page 1 F&T overdrive transmission page 2

The F&T overdrive transmission. Click on the ads above
to see a larger (readable) version of the sales literature

The F&T overdrive transmission shifter
The F&T overdrive transmission and shift lever

There have been other manufacturers of auxiliary transmissions mentioned in Ford Tractor reference books, etc, but if they existed at all they are very, very rare. If you're thinking of adding an auxiliary transmission to your N-series Ford, the best bet today for availability is still the Sherman. Used Sherman transmissions and parts for the transmissions can still be found in salvage yards, at swap meets, etc.

Thanks to John Smith of Old Ford Tractor for allowing us to use this information.

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