How To Replace A Rear Main Seal Without Removing The Transmission

How To Replace A Rear Main Seal Without Removing The Transmission: A DIY Approach

Here’s one simple engine component, but nevertheless very important to the lifespan of your engine. It’s so essential, in fact, that your engine can not operate efficiently without it. Unfortunately, it is one of the most overlooked parts, even by the auto repair experts when carrying out routine service on engines or transmissions. For you, we’ll help along with a guide on how to replace a rear main seal without removing the transmission.

Which component then, are we referring to? This would be the rear main seal. It’s a tiny piece of rope-like or rubber component in your vehicle’s engine that could make you break the bank to get it fixed. Any driver would not hesitate, preferring to quickly get off the road and have the car fixed ASAP in the case of a faulty rear main seal.

This article focuses on how to replace a rear main seal without removing the transmission. It also outlines the causes of rear main seal failure, and the cost involved to replace a worn-out rear seal.

What Is A Rear Main Seal?

This is a very simple but very important engine part that is usually made of synthetic rubber. Just as the name suggests, rear main seals are installed at the back of a car’s engine. It’s always found somewhere sandwiched between the engine and the transmission.

A rear main seal is designed to last, this being as long as a cars’ total lifespan. Rope or Wick seals are commonly found in older engine models. New vehicles manufactured using modern technology usually come installed with synthetic rubber rear main seals.

Functions Of Rear Main Seal

The major role performed by the rear main seal is to prevent oil from leaking between the block and the crankshaft. By preventing oil leaks, the rear main seal enables the crankshaft to perform well and enables the engine to work properly with other components such as the transmission.

When the rear main seal becomes faulty, oil leaks fast. The leaked oil may dry up within the system, stay there, and end up destroying the entire system. A rear main seal leak is one of the worst things that can happen to a car. Why? This component is buried somewhere deep inside the engine.

Replacing it means dismantling the entire engine so that it can be accessed. It’s a minor component, but it’s very hard to reach. Replacing it takes a lot of time, is labor-intensive, and is very expensive.

Types Of Rear Main Seals

There are three types of motor vehicle rear main seals.

  • Rope or wick seal.
  • Split or Neoprene seal.
  • One-piece seal.

Old vehicle models are mostly fitted with rope wick seals. A few of the old model vehicles have a split seal. Most of the newer and modern models are fitted with a one-piece seal to improve their performance.

The rope and the split seals are kinds of universal seals in nature. This is because they can be installed on any engine, be it an old or new model. One-piece main seals are the best to use in your car because they are not prone to leakage.

1. Rope Or Wick Seal

They are given the name because they resemble a rope or a lamp wick. These seals handle the impact of intense crankshaft rotations and friction, as well as fluctuations in temperature. Wick or rope seals fail either by shrinking in low temperatures and expanding in high-temperature conditions.

Rope or wick seals are often lubricated with a small amount of oil that shields them from drying and also helps them to keep firmly in their place next to the crankshaft. One sad thing is that modern vehicles nowadays are fitted with very weak rope seals compared to older vehicles which had effective seals that were highly efficient in sealing oil leakage.

These compromised quality standards are because of the more strict environmental regulations that have restricted the use of asbestos, a material used to make more effective rope or wick seals.

Such regulations have forced some vehicle manufacturers to try lowering the cost of production by producing low-quality seals that are not strong enough to comprehend with crankshaft contact and engine speed. This created a need for the seals to try matching the engine RPM requirements.

This makes them perform poorly and leads to oil leakage. You can avoid buying counterfeit rope/wick seals by purchasing them from reputable dealers like Amazon.

2. Split Or Neoprene Seals

These seals are made from a rubber-like material. They have a lip shape design and are fitted in one direction to prevent oil leakage. They are also prone to leakage over time, just like rope seals.

3. One Piece Seals

These are the hardest to service but are also the most effective seals for your car. One-piece seals are round in design. Their disadvantage is that they only work on a specific design of crankshaft. To install this seal on older vehicle models, you need to replace the whole crankshaft.

Material Choice Of The Rear Main Seal

Nitrile rubber is used in many older engine applications where heat resistance (up to 250° F) is not a problem. Most synthetic rubber, two-piece rear main bearing seals are made of polyacrylate. It offers good heat resistance (350° F) and tough abrasion resistance at a reasonable cost.

Silicone is often used in higher temperature (480° F) engine applications. The drawback of silicone is that it is fragile and requires careful handling during installation.

Viton combines the abrasion resistance of polyacrylate and the heat resistance (450° F) of silicone–at a premium price. It is required on many high-temperature engines.

Polytetrafluoroethylene (PTFE) rubber is the ultimate in rear main seal design and material. It offers the best in fluid and high-temperature compatibility, and the unique “laydown lip” contact sealing surface can run on undersize shafts, seal minor shaft imperfections, and virtually eliminate shaft wear.

Symptoms Of A Faulty Rear Main Seal

Identifying if your car has a faulty rear main seal can be such a daunting task. This is because the part in question is unknown to many drivers. It is hidden underneath the car, hence it becomes very hard to identify the symptoms. Similarly, this part is found right inside the vehicle’s engine.

The hard-to-reach location is already a clear sign that the rear main seals are never intended to be repaired or replace but meant to last for a car’s lifespan. Though, there are two major issues to look for if your car might have a problem with its rear main seal.

1. Black Stains Along The Drive Way Or Parking Lot

When your car has left black puddles of oil on your driveway or parking lot, then something is wrong with the situation underneath the car and urgent attention from a qualified service mechanic is needed.

2. Aggressive Oil Loss

Another sign is finding yourself always in a need to top up your oil at a higher frequency than before, despite driving the same way as before. For instance, if the oil pressure light turns red just a few days or weeks after a fresh change of oil, then there is a strong possibility that you have an engine oil leak caused by a rupture of the rear main seal.

Causes Of Rear Main Seal Failure

Several reasons usually lead to the failure of the rear main seal. Below are some causes that you need to look for.

1. Worn Out Seals

When the rear main seal is worn on, this makes the crankshaft move excessively. This eventually stretches the rear main seal and makes it slip off its position while the engine keeps running. This allows oil to leak. The biggest dilemma is being able to identify if your seals are worn out.

It’s a tiresome task that involves removing other components to access the rear main seal. In such a scenario, it’s most likely that a full engine rebuild is necessary. The rebuild process involves replacing many components, including the rear main seal.

2. Clogged Or Blocked PVC System

The rear main seal comprises lips that normally ride on the crankshaft surface. Pressure buildup on the crankcase can push the lips into the shaft. Extreme pressure ends up stretching the seal leading to leaks. When the Positive Crankcase Ventilation (PCV) gets blocked, pressure increases in the crankshaft and eventually pushes the seal out.

Alternatively, a supercharged or turbocharged engine produces excessive blowby because of faulty piston rings, this eventually increases pressure in the crankcase and ends up damaging the rear main seal leading to oil leakage.

3. Engine Oil Condition

Low oil levels or using the wrong type of oil can lead to rear main seal failure. Some motor oil contains chemical additives that lower the efficiency of the seal. The seals’ conditions are eventually depleted over time with the buffers in the oil.

The lips that ride over the crankshaft become stiff and cannot seal themselves against the crankshaft. Engine oils should also be changed regularly to improve the rear main seals’ lifespan.

4. Crankshaft Condition

As stated previously, the lips of the rear main seal always ride on the crankshaft. This means the condition of the crankshaft’s surface will influence the effectiveness of the oil leakage sealing ability of the rear main seal. Any fault or wear on the crankshaft can cause leakage. Sleeve kits are often installed on the crankshaft to help restore its surface.

5. Misalignment Issues

Any misalignment with the engine compartment can lead to leakage too. When the bell housing or the input shaft of the transmission are misaligned, it can cause stress on the rear main seal and eventually lead to oil leakage.

It’s always advisable to inspect for any misalignment in the engine and transmission. For automatic transmissions, always check the flexplate for a lateral run out or damage. For manual transmissions, check the input shaft for any misalignment.

6. Seal Coating

Some rear main seals come coated with polytetrafluoroethylene (PTFE) on their lips. This means they are supposed to be installed dry with no oil and should also run on a dry crankshaft surface.

The seal normally transfers the PTFE layer to the crankshaft surface the lips ride on. The transferred layer prevents wear while it also seals better than Silicon and Viton materials. If such seals are installed with oil, they definitely start leaking after a few miles.

Replacement of rear main seal without removing the transmission

Effects Of Rear Main Seal Leakage

A leakage in the rear main seal is normally one of the most dangerous things that can happen to your vehicle. It can result in costly and unprecedented consequences mentioned below.

1. Fast Leaks And Permanent Engine damage

Rear main seal leakage can be very dangerous because it can lead to a fast leak which will lower the engine oil to dangerous levels. Low oil levels can lead to permanent engine damage. Fast leaks can also happen when the rear main seal cracks or tears.

The crankshaft’s continuous rotation on an already faulty rear main seal can tear it completely and lead to a fast leak. For manual transmission vehicles, a fast oil leak can allow oil to penetrate the clutch, causing slipping and chattering.

2. High-Risk Leaks

The rear main seal is always highly likely to develop a leak. This is because it is subject to both high oil pressure since it is right by the rear main bearing and the spinning crankshaft, which is constantly wearing on the inside of the seal. No matter how often you change your oil, eventually, the spinning metal crankshaft will wear down the seal enough to cause a leak.

3. Expensive Repair And Replacement

The rear main seal inspection and replacement are labor-intensive and a very expensive affair. It involves disassembling the engine because of its location. It is at the back of the engine and seals the crankshaft as it exits the engine.

The flywheel or the flexplate is then bolted onto the crankshaft flange, sandwiching the rear main seal between the engine and the transmission. To replace the seals, either the engine or the transmission has to be removed for the oil pan to come out and enable access to the seal.

The Cost Of Replacing Rear Main Seal–Why Is It So Expensive?

On average, the cost for a rear main seal replacement is between $650 and $900. Labor costs are estimated between $450 and $700, while parts are priced between $25 and $35. The estimate does not include taxes and fees. This cost may vary depending on the model of your vehicle and where you purchase spare parts.

Labor is supposedly a tedious 8-hour job, and that influences the general cost. Therefore, the cost of labor is much higher than the cost of parts combined. This entire process is usually very expensive because of several factors described below:

1. Job Complexity

Replacement of the rear main seal is a very complex affair. It involves disassembling the engine because of its location. The job itself is labor-intensive and time-consuming. In most instances, the cost of labor is always higher than even the cost used to purchase replacement parts.

2. Special Tools Required

Specialized and costly tools will be required to do the job. These tools include; engine hoist, transmission jack, a wide range of torque wrenches, an engine support bar, and a bunch of other specialty tools which you will be charged to use.

3. Other Entailing Services

At the service shop, the vehicle may encounter other maintenance like a clutch replacement, crankshaft removal, oil replacement if the pan gasket has been removed, or it may be time to rebuild part or all of the motor. This will mean an added cost.

4. Mechanical Parts

You may be obliged to change some mechanical parts. These may include changing seals or gaskets and doing engine rebuild. All these will end up adding to your initial bill.

How To Replace The Rear Main Seal Without Removing The Transmission

Replacement of the rear main seal at an automobile repair shop is a labor-intensive and time-consuming activity. Basically, it may involve removing the transmission and even sometimes disassembling the engine too.

But do you need to go through all this while there is an alternative way you can fix your rear main seal without removing the transmission? Here is a step-by-step procedure for how to do that.

Step 1. Detach The Battery

This comes as the first step on how to replace a rear main seal without removing the transmission. It is necessary to remove the battery from the engine. Although this is not involved in removing the transmission, it is necessary to ensure your safety is your priority.

You will need to take the battery out by disconnecting both negative and positive terminals that are attached to the main circuit. This will help you to create more working space. You can also proceed to disengage the exhaust system too to help you do the job in a more comfortable environment.

Step 2. Remove Driveshaft And Flex Plate

The driveshaft is also known as a propeller shaft. It is that long rod that transmits torque from the output shaft of the transmission to the rear differential in a rear-wheel drive, four-wheel drive, or all-wheel drive type of vehicle.

Before replacing the rear main seal, you will need to take the driveshaft off. After that, you will need to find the flexplate. This is a round metal disc with many holes in it. You can use a wrench and a screwdriver to assist you in the removal of the flexplate. This process will enable you to reach the rear main seal easily.

Step 3. Remove The Rear Main Seal Hood

At this point of removing all the additional parts, you are almost done with the process of how to replace a rear main seal without removing the transmission. The rear main seal is pressed into the hood through bolts into the engine block. Here in the middle, you can see the crankshaft that comes into action when the engine is running.

At the center of the crankshaft, there is a tiny piece, which is a pilot bearer. The seal hood normally has 6 to 10 mm bolts that you must take off. After removing the entire set of bolts, remove the hood of the seal. Take caution while removing the housing of the seal as it is made with fragile aluminum that is prone to cracks and dents.

Step 4. Remove The Crankshaft Seal

This is the last part of this process. The seal normally comes out with the hood, but if it does not happen, you have to do it by yourself. Sometimes the seal is stuck into the crankshaft. You can cautiously poke at the crankshaft to remove the seal.

This seal is the rear main seal you need to take off. Remove it and install the new one. This is the procedure on how to replace a rear main seal without removing transmission easily in no time.

Rear Main Seal Leak–Troubleshooting

Since the rear main seal is in a position that is difficult to inspect directly, try using a process of elimination once you find stains in your parking yard. If you keep losing oil but there isn’t any noticeable drip, you may be in the early stages of a leak.

1. Idle The Engine

It’s the simplest way to test for oil leakage. Idle the engine for 15 minutes to see whether oil appears on the surface underneath. The car’s movement and other car parts sometimes hide oil leak symptoms, making it difficult to notice.

For example, oil could get splashed along chassis components as you drive. Running the car at standstill helps get a better indicator of how oil is consumed when driving.

2. Using Dye

If you find oil stains or experience excessive oil loss, it may not be the rear main seal leakage. On most engines, oil leaks can occur above and below the rear main seal. It could be a leaking oil pressure sensor, oil pan gasket, or galley plug near the seal that causes oil to leak from the bell housing. Adding dye to the oil can help reveal where the oil is actually coming from.

3. Check The Transmission And Oil Pan

Check the transmission and oil pan if you notice oil leaks. If oil appears in front of the transmission and at the back of the oil pan, it may be a rear main seal leak, but there are other possibilities. It’s important to check further up the engine compartment for drips. You might discover a critical yet different problem that would be easier and cheaper to fix.

4. Check Valve Cover Gasket And Valley Pan

The valve cover gasket and valley pan can also be inspected for leaks. They are easier and less expensive to replace than the rear main seal. You’ll need to get under the vehicle with a flashlight to check these parts. Ensure you put on the right protective gear when doing this.

How To Replace A Rear Main Seal Without Removing The Transmission–Conclusion

Do have your faulty rear main seal replaced immediately, as the symptoms developed will be key for the lifespan of your engine. Fail to do this, and there will be a risk of permanent engine damage because of low oil levels if fast leaks are caused by faulty rear main seals that aren’t diagnosed accordingly.

Despite the high cost involved in replacing the rear main seal, seek the services of a qualified service mechanic to fix your vehicle if a problem involving your rear main seal is noticed. It can be so tempting to do the job on your own to cut costs.

This is not a pleasant route to take if you don’t have the skills and the tools required to do the job. You may get hurt badly or cause more damage to your vehicle.

Approved Tools

These tools have been tried and tested by our team, they are ideal for fixing your car at home.

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