The Importance of Quality Oil Seals for Transmission Rebuilds

The Importance of Quality Oil Seals for Transmission Rebuilds

Modern transmissions work hard, so shouldn't their oil seals do the same? Inferior seals are one of the most major diagnoses of transmission fluid leaks that can damage the unit beyond repair. When you're rebuilding transmissions every single day, it can be easy to forget how critical these small parts are, but in a system that operates under such high demands, the value well-made oil seals should never be underestimated. In today's post, we're here to discuss the importance of choosing quality when it comes to transmission oil seals.

Causes and Effects of Transmission Seal Leaks

A single transmission can contain dozens of sealing components, all with a specific purpose. If even one of those seals fails, the transmission in the vehicle can begin to leak transmission fluid. A transmission leak isn't simply an issue in itself, however; leaking seals can quickly lead to a multitude of other problems, including total transmission burn out.The purpose of an oil seal is to prevent lubricant leaks by closing in the spaces between a transmission's parts. The seals also prevent dirt and other contaminants from clogging up the unit. A static seal, such as a simple O-ring, fit between two stationary parts, while a more complex, dynamic seal has multiple lips and acts as a barrier between a stationary and a moving part.

Over time, due to varying pressures, stress, and heat inside a working transmission, seals will begin to break down — it's just a matter of time. However, depending on the quality of the seal, that time period can differ dramatically. Additionally, oil seals that accompany more active parts of the unit, such as the input and output shafts, experience a lot more wear and tear, and generally need to be replaced more frequently. And since several of these seals are located inside the transmission, they're tough to service without tearing apart the entire unit. Until a seal actually fails, it can be difficult to detect any sealing issues at all.

While proper maintenance and lubrication can aid in the longevity of an oil seal, seal performance is largely dependent upon the overall quality of the seal. Simply put, a poorly made oil seal cannot withstand the pressure fluctuations inside a modern transmission, and will cause more transmission leaks and issues in the long run. Therefore, it's important to choose the highest quality oil seals when rebuilding transmissions in your shop.

Quality Seals Under Pressure

To find oil seals you can truly depend on to hold up long after the rebuild is finished, there are a few key markers of quality you should be looking for. The material a seal is made out of is one huge indicator of quality. Cheap rubber seals don't have the same durability as more innovative materials like polyacrylate, ethylene acrylic, hydrogenated nitrile, fluoroelastomers, and more. Each of these materials has different properties that determine how they perform in different temperatures and environments.

Another true indicator of oil seal quality is its inclusion in the original unit as an OE component. OE seals for rebuilding are the exact same seals used by the original transmission manufacturer to build the transmission, so you can be confident that OE seals will have the highest level of performance as well as the best fit inside the unit.

While no oil seal can last forever, the quality of the seals you choose to install in your rebuilds affects not only the success of that job in the shop, but also the value of your work over time. Using well-made, high quality seals that are able to withstand the high demands of today's transmissions will only increase your productivity in the long-term.

Oil Seal Installation: A How To

One of the main principles of power transmission is consistent lubrication. Shaft seals play a hugely important role in this. Imagine a situation involving a shaft-mount reducer – electric motor prime mover, driven by belts, motion controlled by a torque arm – with an improperly seated seal. A blown-out input shaft seal is a nightmare situation, necessitating an entire breakdown and reassembly, not to mention re-aligning and re-tensioning the belts.

The oil seal is our first line of defense in regards to keeping lubrication inside the reducer. It might also be described as the last line of defense – keeping contaminants outside the reducer where they belong. The average seal is incredibly simple in design – made up of a case, a lip or lips, and frequently a garter spring. Of course, some are exponentially more intricate and are manufactured with unusual materials, but the majority are straightforward.

The care taken during the installation process will pay off by allowing the seal to work quietly and operate efficiently behind the scenes of your application.

Prepping for Oil Seal Installation

Before you begin the installation process for any power transmission component, the first goal is making sure everything is clean and free of any material flaws such as nicks, burrs, scratches, dents, et cetera. Most of these components have very tight tolerances, so maintaining this accuracy is important in their performance. This is especially critical for oil seals because of their function.

Begin with a thorough inspection of all involved surfaces: shaft sealing surface and housing bore, seal lip(s), and outside diameter. Maintaining the integrity of the sealing lips is “Priority 1″. The slightest tear or nick can develop into a more significant issue during operation.

Over time, the seal lip(s) will wear a shallow groove into the shafting due to the pressure the seal imposes upon it. Visible scoring on the shaft indicates a genuine possibility that the seal will not perform as well as intended. The potential for lubricants leaking out and particulates working their way through the seal drastically increases when placed over a worn location.

There are a few options to remedy this situation:

Using a spacer to move the seal forward is a possibility, assuming there is enough room in the housing bore to allow a shift. Ideally, the seal outside diameter (OD) should be in full contact with the housing.

There are also shaft repair sleeves that can add a “new surface” to the shaft. Measuring a few thousandths of an inch in thickness, they cover shaft flaws so the seal can make proper contact with the surface.

Probably the least appealing solution is to either replace or refinish the shafting. In some cases, this is not possible; in others, it could benefit the application in the long term.

Which option is best? This decision is left entirely to you. Whatever solution you choose, the seal needs a proper fit to function.

With the application cleaned and the components ready, you’ll begin your installation.

Oil Seal Installation

Many seals come with a garter spring, found within the backside of the seal. It provides contracting pressure against the sealing surface. Making sure the spring seats correctly within the seal is an excellent first step.

Next, apply a small amount of grease to the seal lip(s) and the area of the shaft in contact with the seal.  When using a double-lip seal, fill the small cavity between the two lips with grease as well. This both protects the lips during initial installation and break-in, and also acts as another barrier keeping contaminants out. When installing rubber-coated seals, apply lubricant to the outside diameter as well. This will help prevent the seal from rebounding or backing out from its mounting place.

Orient your seal the same way as the initial install. The sealing lip should face the lubricant that requires sealing. The second lip on a double lip oil seal is intended as a dust lip. The seal must be installed at a 90°, or perpendicularly, to both the shaft and housing bore. This is an issue in cases where the housing does not have a counterbore or shoulder the seal can seat up against.

When a seal is angularly misaligned – or cocked on the shaft – an irreversible process begins. Excessive pressure on one section of the seal, when not installed properly, can cause the spring to become dislodged or the seal to heat up and become brittle through excessive wear, both leading to a premature failure.

Some Tools Required During Installation

In situations where the shaft has splines or an integral gear on the end, you’ll want to take precautions. These gears and splines often have very sharp edges that are quite detrimental to the seal’s integrity. You may use an installation sleeve that will allow the seal to slide past these hazards undamaged.

The last step involves the actual pressing-in of the seal. There are tools and tool kits available that can help with seal installation. Their biggest benefit is that they apply a very uniform force to the seal case, eliminating the possibility of the seal seating in any way other than flush.

If these specific tools aren’t available, it’s entirely possible to correctly seat an oil seal in its housing using a hammer. Ideally, this hammer will be plastic or rubber due to it’s more forgiving nature. Using this and a strike plate that covers the entire seal will lend you accuracy while driving it in. The downside to this method is the inability to drive the seal any further than the strike plate will allow.

The small little oil seal has an outsized role in power transmission.

Proper techniques and diligence during oil seal installation will result in what seems like an unremarkable situation – a component holding its lubrication. When something you’ve installed works effectively and quietly, you know you’ve done it right.

Want to find an oil seal or shaft repair sleeve for your application? Visit the Durus website.