4.5 Transmission Removal, Mounts, Leaks, and Overhaul Inspection (Shafts, Bearings, Reverse Idlers, Synchronizers, Cases)
Key Takeaways
- Eaton says frosted gear teeth are no threat and lightly to moderately pitted gears often have life left, but gears with advanced pitting must be replaced.
- Replace any gear or sliding clutch whose clutching teeth are abnormally worn, tapered, or shortened by clashing (Eaton).
- If a bearing outer race spins freely in its case bore, Eaton says the case must be replaced.
- Before replacing a rear output seal, Eaton says to confirm the leak is not from speedometer parts, the rear bearing cover gasket, rear countershaft bearing covers, or the shift bar housing.
- Eaton requires auxiliary countershaft bearing end play to be checked and adjusted whenever a countershaft, bearing, or housing is replaced.
4.5 Transmission Removal, Mounts, Leaks, and Overhaul Inspection (Shafts, Bearings, Reverse Idlers, Synchronizers, Cases)
Nearly half of the 25 transmission tasks on the ASE T3 task list are about service rather than operation. They cover: determining the cause of wear and failure before and during disassembly; removing and replacing the transmission and its mounts; fixing leaks at covers, gaskets, seals and vents; and inspecting the input shaft, main shaft, countershafts, output shaft, reverse idler, synchronizers, and cases. This section follows Eaton's overhaul inspection checklist for Fuller transmissions.
1. Failure Analysis Starts Before Teardown
A replacement part will fail the same way if the cause is not found. Before disassembly:
- Interview and verify: What gear, load, speed, and temperature? Grinding, slip-out, noise, overheating, or leaks? Recent clutch work, PTO installation, or engine re-rate?
- Check the oil: level, type (EP gear oil where Eaton calls for PS-386 or engine oil?), smell and color (burned or oxidized), water contamination, and metal on the magnetic plug.
- Check related systems: air pressure and regulator output for range complaints, clutch adjustment for clash, driveline angles and mounts for vibration and lever jump-out.
During disassembly, keep parts in order and read the evidence:
| What You See | What It Usually Means |
|---|---|
| Light frosting on gear tooth faces | Normal break-in; Eaton says frosting is no threat and often "heals" |
| Light to moderate pitting | Surface fatigue; Eaton says such gears often have considerable life left |
| Advanced pitting or spalling | Fatigue beyond limits — replace (Eaton) |
| Clutching teeth worn, tapered, or shortened | Clashing and partial engagement — replace (Eaton); look for clutch drag, clutch brake, or yoke problems |
| Blue or black heat discoloration, scoring | Lubrication failure: low level, wrong oil, or overheating |
| Sliding clutch yoke slot worn or heat-discolored | Yoke riding the clutch (driver resting on the lever, or a sprung yoke) |
| Partial engagement pattern on sliding clutch teeth | Clutch not fully engaging — worn yoke, detent, or linkage |
| Cracked or broken gray iron parts | Shock load or mounting stress — replace (Eaton) |
2. Removal, Installation, and Mounts
- Disconnect the driveshaft, shift linkage or shift tower, air lines, electrical connectors (speed sensors, neutral/reverse switches, AMT harness), cooler lines, and any PTO or PTO driveshaft before lowering the transmission.
- Support the transmission on a transmission jack. Never let it hang in the driven discs — Eaton warns this bends the discs so the clutch will not release. On Eaton ECA clutches, move the release yoke to its service position with ServiceRanger first.
- To reinstall, put the transmission in gear, keep the yoke fingers clear of the bearing housing, align the transmission square with the engine, and mesh the splines by rotating the output shaft. Seat the housings by hand before torquing the bolts, and never grease the input shaft splines.
- Mounts, insulators, and bolts: loose, cracked, or oil-soaked mounts let the powertrain move. That causes vibration and, per Eaton, shift lever jump-out. Torque the transmission-to-frame brackets and mounting bolts to the OEM value; Meritor's PM checklist includes them.
3. Leaks: Covers, Gaskets, Seals, and Vents
Eaton's preventive maintenance checks for leaks include:
- Checking all capscrews — especially those on PTO covers and rear bearing covers — for looseness that would cause leakage.
- Checking the PTO opening and rear bearing cover for leakage from a faulty gasket.
- Keeping fill and drain plugs tight.
Before replacing a rear output seal, Eaton says to make sure the oil is really coming from the seal. Check the speedometer parts, rear bearing cover gasket surfaces, rear countershaft bearing covers, and the shift bar housing first. Also inspect the seal surface on the output yoke, since a grooved yoke will cut a new seal. To remove the output yoke nut, shift into first or low gear (low range) to keep the yoke from turning.
Vents (breathers): Meritor's PM check is to verify the breather is not damaged and to clean dirt and oil from its screen. A plugged breather lets pressure build as the transmission heats, pushing oil past seals. Overfilling does the same thing — Eaton warns that excess oil is forced out of the transmission.
4. Shaft, Gear, and Bearing Inspection (Eaton Checklist)
| Component | Eaton Inspection Points |
|---|---|
| Bearings | Wash in clean solvent; replace any that are pitted, discolored, spalled, or damaged. Check axial and radial clearance and replace bearings with excessive clearance. Inner races should be tight on the shaft; outer races slightly tight to slightly loose in the bore. If a bearing spins freely in the bore, replace the case. |
| Bearing covers | Check for wear from the thrust of the adjacent bearing and for worn or oversized bores; replace if damaged. |
| Input shaft and main drive gear | Check the oil return threads (replace the shaft if the return action is destroyed), splines, pilot spigot, and drive gear teeth. |
| Mainshaft | Check gear axial clearance (0.006–0.015 in., corrected with tolerance washers). Check the splines — wear marks in the spline sides of sliding clutches or hubs mean the affected shaft is replaced. Replace washers that are scored or reduced in thickness. |
| Sliding clutches | Check yoke slots for extreme wear or heat discoloration, and engaging teeth for a partial engagement pattern. |
| Countershafts | Check gears, bearings, keys, and retainers or snap rings; verify timing marks. On tapered-bearing auxiliary countershafts, set bearing end play with the specified shims and gasket. Eaton notes that the compressed gasket thickness (0.011–0.012 in.) is part of the end play. End play must be checked and adjusted any time a countershaft, bearing, or housing is replaced. |
| Output shaft | Check bearings, gears, washers and spacers, the speedometer rotor, and the yoke seal surface. |
| Reverse idler assemblies | Eaton: check for excessive wear from the action of the roller bearings. Check the idler shaft, thrust washers, and end play against the OEM limit. |
| Cases and housings | Check gray iron parts for cracks and breaks; inspect mating surfaces, bores, dowel pins, studs, vents, and magnetic plugs. |
| Shift bar housing | Check yokes and blocks for wear at the pads and lever slot. Replace sprung yokes, retighten and rewire loose lockscrews, and check shift bar neutral notches for wear from the interlock balls. |
| O-rings | Replace any that are cracked or distorted. |
5. Synchronizers
- Fuller range synchronizer (pin type): Eaton says to check for burrs, uneven or excessive wear at the contact surfaces, and metal particles; check the blocker pins for excessive wear or looseness; and check the contact surfaces of the synchronizer cups.
- Synchronized medium-duty transmissions (blocker-ring type): Inspect the hub and sleeve splines and the sleeve's engagement chamfers, the keys (inserts) and their springs, and the blocking rings. Measure the gap between each blocking ring and its gear's clutching teeth with a feeler gauge and compare it with the manufacturer's minimum. A ring worn below the minimum no longer creates enough friction, so shifts into that gear grind. Broken springs or keys cause hard shifting and clash.
6. Reassembly Checks
- Time the drive gear set and the specified auxiliary gear set.
- Verify mainshaft gear axial clearance and auxiliary countershaft bearing end play.
- Turn the input shaft by hand through several revolutions in each range; any bind points to timing, a misplaced washer, or a bearing problem.
- Use new gaskets and seals, torque covers to specification, fill to the bottom of the fill plug hole with the correct lubricant, and verify air system operation before road testing.
During a Fuller transmission overhaul, a technician finds that a countershaft bearing's outer race spins freely in its case bore. According to Eaton's inspection guidelines, what must be done?
A technician is deciding which gears to reuse during an overhaul. Which statement matches Eaton's guidelines?
A tractor has oil around the rear of a Fuller transmission. Technician A says Eaton recommends confirming the leak is actually from the rear seal — checking speedometer parts, the rear bearing cover gasket, rear countershaft bearing covers, and the shift bar housing — before replacing the seal. Technician B says a plugged transmission breather can push oil past seals. Who is right?