Cause of Leaking Lubricants

Now let us review some of the reasons why the lubricant is likely to leak at any one or several of these locations.

First of all, a transmission (or almost any other gear case) will usually start leaking if the oil level is too high. To stiffen the oil used in gear cases, some manufacturers use soap and soda in the oil. As the gears operate, the oil is splashed all over the inside of the gear case. Because of the soap and partly because of the splashing and the heat, the oil starts to foam or fill with air bubbles. Thus the oil expands and takes up more room. This action creates excessive pressure inside the gear case. If the oil level is too high to start with, the pressure created inside the transmission many be more than the seals and gaskets can resist and the oil will start leaking out. Leaking can occur at any one or several locations. The transmission oil level should only be checked after the vehicle has been parked for several hours or overnight. During this time, the bubbles or foam will cool and settle as a liquid in the bottom of the transmission case.

With the transmission cold, remove the fill plug. The oil level should be at, or just below, the bottom of the till plughole.

If the oil level is too high, allow the excess oil to run out the fill plughole.

Even if the oil level is correct, it is possible that the foaming action of the oil will cause the pressure inside the transmission to become too high. To permit the excess pressure to escape, a vent valve is used. This valve contains a seat and spring-loaded ball, and has a dust cap over the valve assembly.

To check the vent valve, first make sure the area around it is free of dust and dirt.

Then try turning the dust cap with your fingers. It should turn freely in either direction. If it does not turn freely, replace it.

Gaskets or oil seals will always leak if the bolts securing the plates, covers, or retainers are loose. All of the bolts should be tightened uniformly with a torque wrench.

The bolts that secure the input shaft retainer, the gearshift housing cover, and the retainer seals should be tightened with a torque wrench to the manufacturer's specifications. If tightening the bolts fails to stop the leak at this point, the transmission should be disassembled and the source of the leak repaired.

Leaks around the threads of the fill plug, the drain plugs, or any of the bolts can usually be stopped by coating the threads of the plugs or bolts with a lead-based paint.

A loose gearshift retainer will also allow the lubricant to escape.

All of the seals need to be lubricated; otherwise, they will be ruined. Therefore, a little seepage around any seal is normal. A seal is not considered as leaking unless enough oil is escaping by the seal to drip on the ground and cause a small puddle.

Leaking Seals

With the power plant in the vehicle, you can inspect all seals except the input shaft retainer seal. If this seal is leaking, oil will drip out through the plughole in the bottom of the pan under the flywheel housing when the plug is removed.

If oil does drip out at the flywheel housing drain plug, examine the oil closely. It may be engine oil leaking from the engine crankshaft rear oil seal. The engine oil is much thinner (has less viscosity) than the transmission oil, so you should be able to tell which seal is leaking.

An oil leak, either from the engine or transmission input shaft seals, is serious, because the oil can ruin the clutch. An oil-soaked clutch disk will almost always slip or grab.

TESTING TRANSMISSIONS FOR MALFUNCTIONS

In addition to the leakage problems, there are other problems that can develop in the standard transmissions used in almost all trucks. We can classify these as mechanical problems.

The best way to locate mechanical problems in the transmission is to road test the vehicle. Before road testing, however, check for missing or loose bolts and be sure the oil is at the proper level in the transmission case. Check the parking brake mechanism for proper mounting and correct adjustment. Check all moisture seals or boots. Check the action of the gearshift levers.

The transmission is often blamed for problems that are elsewhere. For example, with the engine running and the vehicle standing still, disengage the clutch and move the gearshift lever into first or reverse. You should be able to shift into either of these gear positions without any gear clashing or without the vehicle moving. If the