Before disassembly, remove the inspection cover. This will allow you to observe transmission action. Shift the transmission into each gear, and, at the same time, rotate the input shaft while inspecting the conditions of the gears and synchronizers. The basic disassembly procedures are as follows:
1. Unbolt and remove the rear extension housing. It may be necessary to tap the housing off with a soft face mallet or bronze hammer.
2. Unbolt and remove the front extension housing and any snap rings.
3. Carefully pry the input shaft and gear forward far enough to free the main shaft.
4. Using a brass driftpin, push the reverse idler shaft and countershaft out of the transmission case.
5. Remove the input shaft and output shaft assemblies. Slide the output shaft and gears out of the back of the transmission as a unit. Be careful not to damage any of the gears.
After the transmission is disassembled, clean all the parts thoroughly and individually. Clean all the parts of hardened oil, lacquer deposits, and dirt. Pay particular attention to the small holes in the gears and to the shifter ball bores in the shifter shaft housing. Remove all gasket material using a putty knife or other suitable tool. Ensure that the metal surfaces are not gouged or scratched. Also, clean the transmission bearings and blow-dry them using low-pressure compressed air.
Always use protective eyewear when you are blowing the bearing dry with compressed air. Do NOT allow the bearing to spin. Air pressure can make the bearing spin at tremendously high rpm, possibly causing the bearing to explode and fly apart.
After all parts of the transmission have been cleaned, inspect everything closely to determine whether they can be reused or have to be replaced. The wear or damage to some of the parts will be evident to the eye. If brass-colored particles are found, one or more of the synchronizers or thrust washers are damaged. These are normally the only transmission parts made of this material. If iron chips are found, main drive gears are probably damaged. To check for damage or wear on other parts, it may be necessary to use measuring tools and gauges to determine their condition.
Any worn or damaged parts in the transmission must be replaced. This is why your inspection is very critical. If any trouble is NOT corrected, the transmission overhaul may fail. You would have to complete the job a second time, wasting man-hours and materials, as well as unnecessary equipment downtime.
Always replace all gaskets and seals in the transmission. Even though the seal or gasket may have not been leaking before disassembly, it may start to leak after assembly.
When replacing a main shaft gear either due to wear or damage, you should also replace the matching gear on the countershaft. If a new gear is meshed with an old gear, transmission gear noise will occur.
If new bolts are needed, make sure it is the correct thread type and length. Some transmission use metric bolts. Remember mixing threads will cause part damage.
All parts must be lightly coated with a medium- grade lubricating oil. This is done immediately after the inspection or repair. Oiling the parts give them a necessary rust-preventive coating and facilitates the assembly process.
After obtaining new parts to replace the worn or damaged parts, you are ready for transmission assembly. To assemble the transmission, use the reverse order of disassembly. Again refer to the service manual for exact directions, as well as proper clearances and wear limits of the parts. The service manual will have an exploded view of the transmission. It will show how each part is located in relation to the others. Step-by-step direction will accompany the illustrations.
Certain key areas of the transmission should be given extra attention during assembly. One area is the needle bearings. To hold the needle bearings into the countershaft or other shafts, you coat the bearings with HEAVY GREASE. The grease will hold the bearing in place as you slide the countershaft into the gears. Also, measure the end play or clearance of the gears and synchronizers and the countershaft and case as directed by the service manual.
Before installing, ensure the transmission shifts properly. This will save you from having to remove the transmission if there is still problems. Also, since the transmission is already out, this is an ideal time to inspect the condition of the clutch.Continue Reading