Rebuilding a Sherman Combination Transmission
Page Two




Next is the extremely important inspection of the sliding collars. The sliding collars must be in good shape or the Sherman will not stay in gear. While the two sliding collars may look alike at first glance, they are not alike. Don't mix them up when assembling. The dentals on the collar in this photo are chipped on the ends, probably from someone trying to shift gears without stopping the tractor first. The sides of the dentals still look pretty good. While it's not the best, one like this would probably work ok if you can't locate a better one.



The dentals on this collar are badly worn and came from a transmission that would not stay in gear. You can easily see why. This collar is junk along with the step-down gear it mated with.



The dentals on the outside of this collar are excellent, just like new. We'll use this one.



The rear sliding collar (hi/lo) engages the step-down gear on the outside dentals and engages the step-up gear on the inside of the opposite end. This collar shows badly worn inside splines. It's junk, as is the step-up gear it mated with.



A good one looks like this which shows almost no wear and is nearly perfect. We'll use this one.



The front sliding collar (direct) has no dental chamfers on the inside splines because it only mates to the front input shaft with the external dentals.



A glance at the inside splines will tell you which collar is which. The one on the right is the rear hi/lo collar.



The hubs for the sliding collars are also different. The longer hub is for the rear collar and the shorter one is for the front collar.



Next we inspect the step-up gear. The dentals should look like these which are in excellent condition. The bore should be smooth and round and be a good fit to the output shaft. This bore is very good but has a couple of tiny rust pits. We will chuck it up in the lathe and polish it lightly with a fine emery paper before installing it.



Place the longer hub and the rear sliding collar over the output shaft in the case. Next, install the step-up gear onto the shaft, dentals to the rear. You should be able to slide the collar freely between the step-down and step-up gears and engage either one.



Install the front hub and collar and install the snap ring to keep it all in place.



Install the brass washer and a new needle bearing and we're ready for the front input (clutch) shaft.



The front end of the clutch shaft is supported by the pilot bearing in the flywheel. If the pilot bearing goes bad it can wear the bearing diameter badly on the input shaft and you'll need to replace the input shaft or repair the bearing diameter. This one shows signs that it has spun inside the pilot bearing at some time or other but it has no measurable wear and will be just fine. Check the clutch splines for wear also. The clutch splines on this one look like new.



Next, check the seal diameter on the shaft. It should have no measurable grooves or wear. If it does, the seal will never be able to keep the oil in. This one has just a very slight line where the seal rides. It's good.



Check the dentals closely on the inside rear of the input shaft gear just like we did for the dentals on the step-down gear. These dentals engage with the front sliding collar for the direct range on the Sherman. Also inspect the bore in the back of the gear. The mainshaft needle bearing rides in this bore and it has to be good. Here we've lightly polished the bore to remove some rust staining.



Remove the snap ring and press the old bearing off the input shaft if it needs replaced (they nearly always should be replaced).



Press the new bearing on and replace the snap ring. Always use the heavy duty version of the bearing here and not the standard duty. The heavy duty bearing has more balls to carry the heavy radial load from the input shaft.



Remove the old seal from the nose cone with an inside puller or a pry bar.



Install the new seal with a suitable driver. The seal lip goes toward the inside of the case.



Install the input shaft into the front nose cone. Make sure the bearing seats all the way into the pocket.



Install the 3 set screws that keep the bearing in place in the nose cone. Inspect them to be sure the cone point is still intact like the one on the right in this photo. If the point is sheared off like the one on the left the set screw needs replaced. The point is the only thing that holds the bearing in place as it protrudes just above the outer bearing race. Do not tighten these set screws more than "snug" as you can distort the bearing race and cause premature bearing failure by over tightening.



Put a new gasket on the flange and install the nose cone and input shaft onto the case.



That finishes the main Sherman gearbox which brings us to the top shifter cover. The top cover needs to be completely disassembled and checked over closely. Lots of shifting problems are caused by simple problems in the top cover.



To disassemble the top cover, remove the 2 tower caps and remove the detent springs and balls. The shift rails should now move freely. Cut the safety wires from the set screws in the forks and remove the set screws. The shifter rails will now come out either end and the forks can be removed. Remove the snap ring on the shifter shaft and pull the shaft out of the shift finger and out of the case.



Remove the set screw on the side of the cover and slide the interlock pin out.



The disassembled top cover and all the parts.



Check the interlock pin. Both ends should be round like half a ball and smooth, not gouged or sheared like the one on the left in this photo. If it's bad, replace it. This pin is what keeps the transmission from going into 2 gears at once. When you shift one rail, the pin slides over and locks the other rail in the neutral position. Lubricate it with some 90w gear lube and install it back in it's bore, making sure it slides freely from side to side.



The shifter shaft should be polished and checked for straightness. Make sure the Woodruff key slot and the snap ring grooves are good. Check the shift finger for cracks, straightness and excessive wear on the business end.



Replace the Woodruff key. The key always wears on the sides and a little bit of wear on the key translates to a lot of play at the end of the shifter lever.



Install the shifter shaft, key, shifter finger and snap ring back into the top cover. Make sure the shifter shaft moves freely back and forth and rotates freely side to side. Lube everything with 90w gear lube when assembling. Removing and installing the snap ring is easier with a set of snap ring pliers with a 45 degree bent nose.



The two types of shift rails are shown here. On top is the later rail that has a detent for the neutral position (a nice addition). The lower one is the early style. Polish the rails and inspect for straightness and any damage such as rust pitting, scoring or galling. Watch for grooves from the detent ball wearing into the rail.



Slide both rails into the top cover and make sure they work freely back and forth and rotate without any binding or tight spots which could indicate a bent rail. Remember the single groove end of the rail is for the interlock pin and the 2 or 3 groove end is installed under the detent ball towers.



Inspect the shifter forks for cracks, straightness and wear. The fork above is badly worn. It's junk. Do not try to use something that looks like this one in your Sherman.



This is a forged steel fork used in the earlier Shermans. It's in very good condition with only the slightest sign of wear.



This is a later style cast steel fork from a Ford built Sherman. They are interchangeable with the early style. This one is also in excellent condition with almost no wear at all.



This is the dog point set screw that keeps the shifter fork lined up with the small groove in the center of the shift rail. It's this little guy that causes a lot of shifting problems. Only the shear strength of the dog point on the set screw keeps things aligned and they can shear off as you can see on the one in this photo. Make sure the dog point is good, not worn on the sides or bent or broken. Replace with new ones if there is any doubt. If one of these dog points shears off, the shifter fork will move with the lever but the rail will not and the interlock will effectively block your other gear range until you replace the set screw. The one on the right is good.



Place the shifter forks into the cover, slide the rails into the forks, align the center groove in the rail with the set screw holes, and install the set screws finger tight. Turn the set screws until snug then back them off slightly until the fork moves freely side to side without the rail rotating. The fork must be retained to the rail by the dog point only and not by pressure from the screw. Do NOT tighten the set screws with a wrench.



Once the set screws are where they belong use safety wire to keep them in place. You should now be able to shift the forks through the 3 different gear positions and everything should move smoothly and easily.



Inspect the detent springs for breakage or mushrooming on the ends and replace them if needed. The detent balls get rusty and develop flat spots. Always replace them - they only cost a few cents each. Be sure to lube the detent tower bores and the balls and springs with 90w gear lube when you install them.



Everything in the gearbox should have a light coating of assembly lube. Install the new gasket and the top cover. Be sure to get the shifter forks lined up with the grooves in each sliding collar and lower the top cover into place.



Leaving the detent caps a little loose will make it easier to shift the transmission while you are bench checking. Don't forget to tighten them when you're done.



When the Sherman is installed in the tractor the output shaft is held secure because it's loaded against the tractor transmission main shaft. Do not try to shift the Sherman before it's installed without putting some pressure on the output shaft end. For testing, place the output shaft end of the Sherman down on the workbench so the weight will help keep the output shaft in place when you shift it. In this position you can shift gears and turn the Sherman case around while observing the input shaft. In the high range the input shaft will appear to turn faster than you are turning the case. In low range the input shaft will appear to turn backwards from the direction you're turning the case, and in direct range the input shaft will not move at all while you turn the case.



With the output shaft held in place be sure the oil slinger is not rubbing on the case. It can be gently "adjusted" for clearance if necessary.



The last item is a new gasket for the mounting plate surface. Make this gasket from 1/64" gasket material. Be sure to check the mounting plate for flatness and for cracked or stripped threads.



All finished. Once you've refurbished your Sherman in this manner, have it installed with the correct shims for bearing load, and have it filled with fresh gear oil, you can rest assured it will shift correctly, run smoothly and quietly, and provide reliable service for another 50 years.

Bearings used in the Sherman combination transmission -
Input shaft bearing - ND 3210
Mainshaft needle bearing - Hyatt 93316
Output shaft cup - Timken 25820
Output shaft cone - Timken 25877
Countershaft bearings - Hyatt 93516
Late style top cover shifter shaft seal C/R 6720
Other parts available from New Holland dealers -
Front seal 8N7052A
Front nose gasket C0NN7C251B
Top cover gasket C0NN7223D
Shifter fork C0NN7231B
Shifter fork setscrew C0NN7B360A
Output shaft C3NN7015D
Cluster gear C0NN7113B
Front countershaft thrust washer C0NN7119A
Step-up gear C0NN7A062A
Front sliding collar C0NN7A061A
Detent spring C0NN7C349A
Detent ball 72387
Most other parts are no longer available new and must be located used.

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Copyright 2006 John Smith & www.oldfordtractors.com