Rebuilding a Sherman Step-Up Transmission
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Three styles of top shifter rails used in the step-up transmissions. The one on the left was the latest, the one on the right was the earliest. The earliest design used a narrower mounting for the shifter fork and must be used with the correct fork to match it. The two on the left are interchangeable. The shifter rail for the cable shift transmission is similar but is without the two end rings for the lever shift arm.
Minor wear on the shaft from the detent ball is common. Excessive wear such as this is not good and the shaft should be replaced.
The most common shifter fork (left) and the early (narrow mount) shifter fork (right). You must use the correct fork for the shift rail you're using.
Inspect the shifter fork ends for wear. This one is badly worn and should be repaired or replaced.
A good shifter fork with almost no wear.
The shifter fork on the left is the most common style. The fork on the right is normally found only in cable shift transmissions, but they are interchangeable and either style can be used.
Once the case has been cleaned and inspected, assembly of the cluster gear and shaft can begin.
Put the cluster gear and 2 thrust washers into the case, large gear to the rear.
Use some assembly lube and install the countershaft pin using a soft hammer
Turn the case over and install a new seal for the shifter rail.
Oil the shifter rail and it's bore and insert it into the case.
Install the shifter fork onto the rail, angled toward the front. The sliding collar can be tricky to get in place later, so you might want to place it in the fork now. Long end of the collar to the front. Install the castle nut onto the fork and rail but do not tighten it more than finger tight. The fork has to be able to swing side to side freely without turning the shifter rail shaft. Put a cotter pin through the nut to secure it.
Install the front input shaft. The outer snap ring on the bearing should fit down flat against the case.
Inspect the nosecone for any damage or wear. The brass bushings for the shifter cross shaft can be replaced if they are worn.
Remove the old input shaft seal. A prybar like this one makes removing the old seal simple and easy.
Press the sharp end of the hook into the soft area on the seal.
Pull back on the bar to pop the seal out.
The proper orientation to install the new neoprene lip seal. The open lip always faces the oil you're trying to keep in.
Install the new seal with a suitable driver.
Make a new gasket for the nosecone and install it onto the housing.
Drop in a new detent ball and insert the spring and cap. Make sure you have the correct length spring. A little too short and it won't hold the rail in place. A little too long and it won't shift at all.
Pop the shift rail forward to engage the collar onto the input shaft dentals. This will keep the collar securely in place until the rear output shaft parts are installed.
Lube the shifter cross shaft and slide it in place.
Install the correct size cotter pin to keep it all together.
Install the new bearing cup into the rear mounting plate using all the original shims behind it. Leaving these out or not installing enough of them can mean you won't be able to get the proper bearing load when installing the Step-Up into the tractor.
Next, assemble the oil slinger and new bearing onto the output shaft.
You can heat the bearing to expand it, or use a press to push it into place.
Insert the output shaft into the rear plate and assemble the rest of the parts.
The step-up gear, hub, snap ring and oil baffle plates are installed.
Make a new gasket and the mounting plate is ready to bolt on to the case.
Stand the finished Step-Up on end and rotate the case around as you shift it between ranges to make sure everything is working ok.
All finished and ready to go to work.
Bearings used in the Sherman Step-Up transmission -
Input shaft ball bearing - MRC 208MG
Mainshaft needle bearing - Torr BH 1412X
Output shaft cup - Timken 25820
Output shaft cone - Timken 25877
Countershaft bearings - Torr BH1616X
Top shifter shaft seal C/R 6203
Front seal 8N7052A
Internal parts such as gears and shafts are no longer available new and must be located used.
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Copyright 2009 John Smith & www.oldfordtractors.com