Rebuilding an MTD snowblower auger differential
This auger, on a 1995 MTD Yard Machine snowblower, hit a heavy electrical cable, hidden under a foot of snow. It immediately broke the differential gears without shearing the shear bolts. For those who like to tackle their own repairs, here is how I did it. The parts cost $170.
You will be working on equipment that has sharp edges, gasoline in the tank, and a spark plug. Appropriate personal protection equipment should be used and the spark plug wire should be removed from the plug.
Remove the three nuts on each side of the auger housing which hold the housing to the main body of the snowblower. The nuts have been removed and the welded studs are seen to the left of the V belts. Pull the auger housing away about three inches and unhook the tensioning spring.
Remove the spring. Note that the open end of the spring is facing the motor.
Prop up the snowblower body.
Remove the plastic chute from the auger housing, noting the position of any steel reinforcing plate under the chute. Remove the center bolt of the pulley. It will probably be necessary to put a block of wood into the impellor to hold the pulley stationary while breaking the bolt free. Remove both pulleys.
The bearing securement plate is held in position by three bolts and nuts. There are three holes in the impeller to access the bolt heads. The nuts face the motor. Remove the bolts and nuts and the plate. Alternately, you can leave the bearing in place and when you withdraw the complete auger assembly, the shaft will pull through the bearing. I removed the bearing for inspection.
Note the position of the bearing. It just sets in there and is held in place by the bearing plate.
Looking in the housing from the front, mark the augers left and right and the outside position. Remove the three bolts and nuts on each side of the assembly. The bolt heads are on the outside of the housing. Pull the auger assembly forward. The rear shaft will pull through the bearing if you�re lucky. Otherwise some penetrating oil and gentle persuasion with a hammer may be necessary.
Note the parts positions on the outward end of the auger assembly: Large bushing in the steel cup, shim, and then small bushing in the end of the auger.
Note the small bushing and two shims on the inward end of the auger assembly.
Remove the two roll pins that secure the impeller only if that shaft is to be replaced. Use a file on the area where the sheer pins pass through the auger shaft so as not to damage the rubber oil seals when removing them. Remove the bolts that hold the two halves of the differential together. This differential has no gasket between the halves and is glue-bonded together. Use a sharp chisel carefully to pry the halves apart.
This unit hit an electrical cable hidden under the snow. In the case on the right side, you can see all the brass shavings in the grease.
The brass gear took a good hit. The worm gear was damaged and the key elongated the shaft slot. Replacement parts are $170 for both shafts and brass gear and a few incidentals.
Note the position of the parts. From the left is the bronze bushing and two shims. A new roll pin is pressed in.
The key is put into the shaft keyway. There is one shim on each side of the brass gear. The gear is centered over the key. The shafts have been greased so as not to damage the seals which are slid all the way along the shaft. The seal�s lips face inward towards the grease. The solid side of the seal with the numbers, faces outward to the environment.
One case half is coated with a light coating of Permatex silicone sealer and the differential is bolted back together. I torqued the bolts to about 7 foot pounds. Note the black plug on the top of the differential. This is where you add the lube. Good luck. I filled the case with an appropriate amount of OO Snapper-type grease. Some other brand's cases use Lubriplate lithium grease. I made a device to force grease through a thin hose using low air pressure.
Reassemble the augers again, noting the position of the shims and bushing.
Note the position of the bushings and shim.
Instead of using the roll pins to secure the impeller, I used two sheer pins. Install the new sheer pins in the augers and use your previous markings to properly assemble them. The shaft goes through the rear of the auger housing. Secure both ends of the auger shaft to the auger housing using bolts and nuts.
The shaft is not seen here because I installed the bearing first. Push the bearing onto the shaft. Alternately, you can loosely install the bearing assembly first, insert the finished auger assembly, and tighten the bolts and nuts once the shaft is passed through the bearing.
If you haven't yet done this step, you can now install the bearing plate. The shaft will self-center the bearing. Once you are sure the bearing is centered, tighten the nuts. The bolt heads can be held in place through the three holes in the impeller
Install both pulleys and I torqued the bolt to 30 foot pounds, not having a reference chart.
Place the completed auger housing close to the snowblower body and reinstall the spring with the open end facing the engine.
Position the belts on the bottom of the pulleys and attach the housing to the body with six nuts. Make the final adjustments and you�re done.