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Eaton Fuller 18 Speed Transmission Troubleshooting - PartsXP

eaton fuller 18 speed transmission troubleshooting

This Eaton fuller heavy-duty transmissions troubleshooting guide will help you with your transmission problems fixing, locating the issue of transmission trouble, analyze the cause of the problem, and make necessary repairs for your transmissions. Let's have a look at this updated Eaton Fuller Transmission troubleshooting & diagnostic guide.

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The general transmission function is to transfer the engine's power in terms of torque to the vehicle's rear wheels efficiently. Torque is the circular force delivered by the engine's flywheel. The gear ratios of transmission will increase or decrease torque based on the requirements that are needed to start or move the load. The transmission should have low ratios that meet the vehicle's requirements to maintain movement upgrades and to keep the engine’s operating in peak efficiency range.

Eaton Fuller Heavy-Duty Transmissions Troubleshooting Guide

Here, you can see common Eaton fuller transmissions problems and their solutions.


Vibration usually starts somewhere in the drive train and it will hear by the driver. Some Eaton transmission problems due to train vibration are

  • Gear and shaft splines.
  • Gear rattle at idle.
  • Continuous loosening of cap screws, brackets, and mountings.
  • Worn universal joints (It's not a transmission symptom, but an indicator of vibration).
  • Worn Shaft Spine Wear.
  • Fretted Bearings.
  • Broken or loose synchronizer pins.
  • Repeated rear seal leakage.

The main causes of this vibration problem are driveline imbalance or misalignment, unbalanced brake drums or wheels, rough running engine, broken or worn engine mounts, and worn suspension.

Gear Slip out and Jumpout

Front section

The mating teeth should be parallel when a sliding clutch is moved to engage with the main shaft gear. As the gears rotate, tapered or damaged clutching teeth may attempt to walk apart. Under the right circumstances, it can result in a slip out. Some of these conditions are:

  • Eccentrically mounted transmission with engine flywheel pilot.
  • Clash of excessive gear which shortens clutching teeth.
  • Remote shift control linkage incorrect adjustment that results in partial engagement. Also, you need to check for any loose connections and worn bushings.

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Causes for Jumpout

Extra heavy and long shift levers that swing from working on uneven ground, pendulum fashion. The whipping motion of the lever overcomes the voltage of the detent spring.

Mechanical remote controls with the master fixed on the frame. The relative movement will push the transmission out of the gear between the engine-transmission kit and the frame. The consequences of this circumstance are enhanced by worn or broken engine mounts.

Auxiliary Section

Slip out in the auxiliary section will be done by the clutching teeth being worn, tapered, or not completely engaged. As gears move, these conditions will cause the clutch gear to walk out of engagement.

Causes of these types of clutch defects including clashing or normal wear after a long life. Vibrations will set up by an improperly aligned driver line and low air pressure that add to the slip out a problem.

Jumpout usually occurs in the auxiliary section with the splitter gear set. The sliding clutch gear may not have enough time to complete the shift until the torque is reapplied to the gears if the torque is not properly broken during splitter changes. The partially engaged clutch gear "jumps" out of the splitter gear when torque is reapplied. Damage can be done to the grasping teeth of the mating gears because the gears have torque applied to them.


The operating temperature of the transmission should not exceed 250°F for an extended period. If it extended, then the oil will breakdown and shorten the transmission life.

Because of the friction of the moving parts, transmissions produce a certain amount of heat. The normal temperature is 100°F (40°C) above ambient. Heat dissipated through the transmission case. If that proper dissipation of heat prevented by some conditions, then it causes overheating.

Moreover, you have to inspect the oil temperature gauge and sending unit readings before checking the possible causes of overheating.

Causes of overheating are:

  • Improper lubrication.
  • Oil level too high or low, wrong type of oil, or an operating angle of more than 12 degrees.
  • High engine RPM.
  • Operating consistently under 20MPH.
  • High ambient temperature.
  • Exhaust system too close to transmission.
  • Coasting downhill with the clutch depressed.
  • High horsepower and overdrive operation.

You can use an external oil cooler kit to correct the overheating problems caused by the above symptoms.

Transmission Noise

There will be always a noise during the normal transmission operation. However, excessive noise or unusual noise like a whine, growl, or sequel sound indicates some kind of problem.

Causes of transmission noise are:

  • Engine operating noise.
  • Rough idling engine.
  • Unequal joint working angles.
  • Driveline out of balance.
  • Loose or worn center bearings.
  • Worn crosses in universal joints.
  • Worn or pitted teeth on the ring gear and pinion of driving axle.
  • Wheels out of balance.
  • Rear-axle bearing failure.
  • Worn spring pivot bearing.
  • Brake drums warped or out of balance.
  • Loose “U” bolts.

Eaton Fuller Heavy-Duty Transmissions Service Manual Instructions

Following is the basic procedure for troubleshooting Eaton fuller 10 speed transmission problems.

Preliminary inspection

  • Personal observation - Look for misuse like broken mounts, fittings, brackets, etc.
  • Based on the condition of the vehicle operating, you have to contact the operator.
  • Gather information such as maintenance and lubrication process, previous failures, etc.

Disassemble transmission

  • During disassembly, you need to check for missing parts, incorrectly installed parts, and not OEM parts. Also, clean each item closely.
  • After that, determine the failure type.
  • Next, find out the correct cause of failure and troubleshoot it.

Find out the problem and troubleshoot carefully. You may get a troubleshooting chart in your Eaton Fuller heavy-duty transmissions service manual along with Eaton fuller heavy-duty transmissions installation guide. So, get a possible correction for each problem and fix it.  

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Hope this Eaton fuller 18 speed transmission troubleshooting guide will help you to fix the issues. If you need any Eaton parts for the replacement of broken or damaged parts, choose PartsXP. We stock genuine Eaton replacement parts for all Eaton products. You can buy instantly from us!

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