Your Top-Heavy Duty Clutch Questions Answered

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Your clutch system plays an indispensable role for your drivetrain. You have heavy duty questions about clutches. Wheelco has the answers.
Heavy Duty Mechanic

What You Need to Know About Your Heavy-Duty Clutch System

When it comes to your clutch system, there are a few things you need to know in order to safely operate and maintain your drivetrain. While clutch designs vary depending on light, medium, or heavy duty applications, the primary purpose of your clutch is to transmit torque from the engine to the transmission. It also facilitates the function of changing gears. It does this by interrupting or “breaking” the power flow between the engine and the transmission when the vehicle is at a stop (with the engine running) so you can shift gears. 

We’ll break down importance your clutch system has for your drivetrain. As we do, we’ll answer some of your top questions, which may include:

  • What are the main components of a clutch system?
  • How do heavy duty clutches work?
  • Pull type clutch vs push type – What’s the difference?
  • How can you increase clutch life?
  • Signs your clutch needs replacing
  • All New or Reman – What’s the best for you
Heavy Duty Clutches

Main Components of a Clutch System

Before we can explain how heavy-duty clutches work, let’s break down the main components of your clutch system and what they do. The main components are flywheel, clutch cover assembly, clutch disc, pressure plate, release bearing, and the release fork.

The clutch assembly has a similar setup and component, regardless if it is light, medium or heavy duty. However, in heavy duty applications there may be two clutch discs for the need of increase torque capacity. Light and most medium duty vehicles tend to only have one. The need for increased horsepower and tow necessities in heavy duty applications is why there is often two clutch discs. 

Flywheel

What does a Flywheel do? A flywheel stores the rotational energy from your engine, acts as the driving friction for your clutch disc, and provides a ring gear for the starter motor to engage upon. It is bolted to the engine crankshaft and to the clutch cover assembly

Clutch Cover Assembly

What does a Clutch Cover Assembly do? The clutch cover assembly applies an engineered plate load pressure needed to sufficiently engage the clutch disc(s) and pressure plate and provides torque power to the transmission. The cover assembly keeps these components from slipping, when the clutch is engaged. 

Clutch Disc

What does a Clutch Disc do? The clutch disc connects the power from the engine and to the transmission via a spline. The clutch disc contains a damper which absorbs engine vibration, gear rattle, noise, and uneven drivetrain power pulses. 

The clutch disc is positioned between the flywheel and the pressure plate. The clutch disc has a cushion plate (made of riveted friction material like brake lining) connecting the engine and the transmission. When the clutch is engaged (when your foot is off the pedal), the clutch cover assembly squeezes the clutch discs and the pressure plate, making a solid connection to the flywheel and engine.

Wheelco Quick Tip: Need More Torque for your big rig? The more paddles on the clutch discs and wider cushion plate can increase your torque.

Pressure Plate

As an integral part of the cover assembly, the pressure plate acts as the contact surface between the discs and the cover assembly. The pressure plate is activated to release the clutch when the driver depresses the clutch pedal. The pressure plate will then move away from the flywheel. This “frees” the clutch discs of both the pressure plate and flywheel.

Release Bearing and Fork

What does the Release Bearing and Fork do? The release fork engages and disengages (pushes or pulls) the release bearing, which connects or breaks the power flow between the transmission and engine. It is positioned in the center of the diaphragm springs

Diaphragm Springs

What do Diaphragm Springs do? The diaphragm springs press the pressure plate against the cushion plates on the clutch disc. Thus, it applies friction/force between the pressure plate and the flywheel. This locks the engine to the transmission, forcing them to rotate at the same speed. 

How Do Heavy-Duty Clutches Work?

The flywheel is bolted to the engine crankshaft. The clutch cover assembly, which is connected to the transmission via a spline, is bolted to the flywheel. Because they are bolted together, this keeps the engine and transmission turning over at the same speed.

When you press the clutch pedal down, the clutch linkage or hydraulic system pushes the clutch release fork (yoke) which in turn presses the clutch release bearing. This action activates the pressure plate, which moves it away from the flywheel, freeing the clutch disc of both the pressure plate and the flywheel. You can then shift gears smoothly.

When you take your foot off the pedal, engaging the clutch, the spring tension inside the cover assembly forces the pressure plate against the clutch discs. Because the assembly is bolted to the flywheel, this locks the engine to the transmission input shaft. They will once again rotate at the same rate, transmitting the engine torque to the transmission. 

Pull Type Clutch vs Push Type – What’s the Difference?

Clutches have been designed primarily into two types of friction-disc clutches, depending on the fulcrum point on the pressure plate. The two types are push type and pull type. The difference in the design is pedal effort and clamp load. Pull type clutches have an estimated 30% increase in clamp load using the same amount of pedal effort. Because of this, pull types are more common in heavy duty applications because of the extra need in torque and horsepower.

Push Type and Pull Type
  • Push type clutches are common in light and older model medium-duty vehicles. When you press your clutch pedal down on the clutch, the release bearing is pushed into the clutch and diaphragms springs, allowing you to shift gears. 
  • Pull type clutches are common in heavy-duty vehicles. When you press your clutch pedal down, the release bearing is pulled away from the clutch. This pulls on the diaphragm springs, allowing you to shift gears..

How to Increase Clutch Life

Replacing wearable parts in any clutch system is something that every truck owner encounters. At Wheelco, we recommend proper maintenance and inspections according to the manufacturer. Here are a few key takeaways you should do if clutch life is a concern: 

Don’t Ride The Clutch

This term is when you keep your pedal partially pressed down. When you do this, you pull on the release bearing and remove pressure plate load. This results in clutch slippage and wear.

Burning Your Clutch

This is a common occurrence when you’re towing heavy loads, especially if you’re pushing the limited to your engine torque range.

Use Clutch with Proper Torque Rating

Consider your engine torque rating and horsepower when choosing the proper clutch.

Signs Your Clutch System May Need Repair or Replacing

Clutch life can vary greatly, depending on the application, towing frequency, heavy hauls, stop and go traffic. However, clutch pedal behavior and clutch performance can help diagnose problems before the become dangerous to drive.

Here are some common signs and symptoms which indicate your clutch system may need attention:

  • The clutch pedal is spongy, sticking, or loose
  • Loss of clutch pedal free play.
  • Difficulty shifting gear
  • Difficulty shifting into reverse
  • Temporary acceleration loss or slipping
  • Any unusual noises when pressing clutch pedal 

If you notice any of these signs or symptoms, we strongly encourage you to make an appointment with your mechanic or give one of our service technicians a call. We will be able to properly diagnose and recommend repairs and replacements you may need. Your safety is our primary concern. Driving with a failing clutch is dangerous and can leave you stranded.

All New or Reman – What’s the Best for You

Ease of installation, performance, and reliability are surely your concerns if you are looking for replacing your clutch assemblies. Is All New or does Remanufactured suit your needs? There are many factors when considering the best assemblies for your specific needs. At Wheelco, we’ve put together a Quick Guide for those who are ready to replace their clutches and flywheels. 

Wheelco Brand Recommendations

If you are looking to repair or upgrade your drivetrain, we are ready to help you. Our experts can help you determine the parts and/or assemblies needed for your driving requirements. Mid-America and Eaton are a few brands we trust if you are in the heavy-duty market. Simply give us a call, chat online, or stop by one of our stores.

About Wheelco Truck & Trailer

At Wheelcobeing customer driven is more than just a motto we live by. It means that our employees will do everything we can to best serve you, our valued customer.

Customer driven is more than just offering you advice, giving time-honored service or contributing the latest tech-support. It’s about being there—whenever and wherever you need us—in-person, over the phone or online.

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