Interested in learning more about automatic transmissions? Read about the transmission bushing in this article.
In the transmission industry, what we call a bushing is known by many names—plain bearing, solid bearing, slide bearing, and friction bearing all refer to this component. Compact, cost-effective, and lightweight, bushings into a housing or bore act as a bearing and provide a surface for a rotating shaft and support for a shaft that moves fore and aft. The primary purpose of a bushing is to reduce friction and wear on mechanical parts.
Read on to learn more about this critical component.
Why bushings instead of bearings?
While bushings and bearings perform similar functions, bushings are usually used over bearings for a few different reasons:
- Lower cost
- Lighter construction
- Less prone to damage
- Allow weight to be distributed over a wider area
When considering costs, bushings have a few advantages. Bearings can cost up to 400% more than bushings, and the tooling needed to manufacture bearings can cost up to 75% more than bushings. Bushings are also typically 50% lighter than other types of bearings and are less prone to damage from shock loads, which can lead to failure in bearings. Bushings can also handle greater shaft misalignment. Bushings allow for wider weight distribution than bearings.
Common Bushing Materials
Bushings come in a wide variety of materials, including bronze, steel-backed babbitt, cast iron, and plastic. The type of material usually depends on the application the bushing will be used in. Bronze is a durable material that works well in low- and high-speed applications. Steel-backed babbitt, which often comes at a lower cost than bronze, has excellent fatigue resistance with high load capacity and resistance to corrosion.
Common Bushing Features
Transmission bushings often come with some common features that enhance their performance. Coatings applied through a process called thermal spraying can reduce wear, corrosion, and abrasion and improve heat resistance. These coatings are applied to the surface that contacts the shaft. Some bushings also have grooves, channels, or holes to allow the lubricant to flow freely. Indents may also be added to the bushing surface to retain oil.
Common Types of Damage
Bushings, like any other transmission component, are often subject to different types of damage. More specifically, bushings can experience pitting and scoring from lubrication issues.
Pitting damage is usually due to lubricant cavitation, which occurs when pressure suddenly drops below the vapor pressure, forming bubbles or voids within the fluid. When the pressure rises again, these bubbles collapse, causing shockwaves that damage the bushing over time.
Scoring occurs when the lubrication barrier breaks down. When this barrier breaks down, the shaft and bushing come into contact with each other at high speeds, which causes damage.
Transmission Bushing Installation
It is critical to use the correct bushing driver when installing the component. Some technicians install the bushing by driving it into place, and others use a press. Pressing is usually the preferred method because it reduces the likelihood of damage to the components.