A rear main seal will lose engine oil while causing a bad oil leak
Your car's engine rear main crankshaft seal is designed to give the engine
oil leak protection from between the crankshaft output flange and the
This seal is mounted in a steal plate which is bolted to the rear of the engine
block. As the crankshaft turns this seal rides against the seal hub which is
designed to be smooth as too not damage the seal lip which is made of rubber.
This seal is located between the engine and transmission just behind the
What Goes Wrong?
Heat and engine vibration is responsible for causing the rear main seal to
fail. This is because the seal is made of rubber and can become hard and brittle
causing the lip of the seal to fail allowing engine oil to bypass the seal and leak
outside of the engine. When this problem occurs engine oil will leak into the
transmission bell housing which will show up at the most downward part of
transmission near the flywheel. If the car is equipped with a standard
transmission is will contaminate the clutch disc causing the clutch to grab and
How Much Does It Cost?
This repair job is usual fairly expensive since the transmission and flywheel
will need to be removed. The seal itself will cost between $13.00 and $35.00 on
Amazon and that is pretty much all you will need beside maybe a small amount of
transmission fluid. If you are having the job done at a repair garage or dealer
you can expect to pay between $650.00 and $850.00 for the labor depending if the
car is front or rear wheel drive in most cases. A
main seal is much easier and less expense to replace.
There is a video of the job being done at the bottom of this guide.
Let's Get Started!
raising the car on four jack stands using a floor jack. Put the car as high
as possible to give you more room under the car which will help make the job
easier. Wear protective eye wear and gloves before getting started. This job will
vary depending on if it's a front wheel or rear wheel drive car. Some steps
like removing the exhaust system may or may not need to be done as well.
1. Disconnect the Battery
When removing the transmission you will need to
remove the starter in the
process so you should
disconnect the battery's negative cable to avoid short circuits.
2. Remove the Exhaust System
The engine will need to tip downward to allow enough room for the
transmission to be removed. Also, if the exhaust system is in the way of the
transmission coming out the
need to be partially or completely removed.
3. Remove the Driveshaft or CV Axles
No matter if the car is front wheel or rear wheel drive, automatic or stick
driveshaft or CV
axle will need to be removed to allow clearance for the transmission
4. Remove the Transmission
There is not that big of difference if the transmission is automatic or stick
shift when attempting to
remove the transmission. The main difference is an automatic transmission
will have two cooler lines running up the the radiator which will need to be
undone using a line wrench and the
torque converter will need to be unbolted from the
5. Remove the Flywheel or Flex Plate
A car equipped with a standard transmission will have a
that will need to be removed before replacing the rear main seal. A car
quipped with an automatic transmission will need to have the flex plate removed
which is easier because it just unbolts from rear of the crankshaft.
6. Remove the Rear Main Seal Housing Bolts
Now that those additional jobs are out of the way you can get down to replacing
the rear main seal. Like we said, most of the job is getting to the seal but now
that you have gotten this far let's continue with the job. The image below
shows what a typical rear main seal looks like pressed into its housing bolted
to the rear of the engine block. The cylindrical metal piece sitting in the middle of
the seal is the crankshaft which is the part that turns when the engine is
running. There is a smaller piece in the center of this crankshaft which is a
pilot bearing which will be included on rear wheel drive stick shift cars only.
This seal was not leaking too badly but since we where replacing the clutch
anyway we decided now would be the time to replace the seal.
Some application will have a thin metal plate between the engine and
transmission which will need to be removed before you can remove the rear main
seal. Use a large screw driver or pry bar to remove the engine plate
to clear access for the rear main seal housing.
There may or may not be will be two or four oil pan bolts that go through the
oil pan and up into the rear mails seal's housing. Remove these bolts 10mm, 12mm
or 13mm bolts and put them in a container for safe keeping.
The seal housing will have a series of 6 to 8, 8mm or 10mm bolts holding the
rear main seal housing to the rear of the
Remove the bolts by turning them counterclockwise and also put them in a
container for safe keeping.
Now the seal housing will be able to be removed. Using a large standard
screwdriver gently pry the housing loose from the engine block. As you work
around the edges of the housing lift with your other hand using a rocking
motion. It can be a little stuck because the housing is mounted on dowels in the
Now the housing will come loose from the engine block. Be careful not the
drop the housing because it is aluminum and can crack if it hits the ground hard
enough. This part will need to be cleaned before it can be reinstalled.
7. Remove the Rear Main Crankshaft Seal
Usually the seal will come off with the housing but sometimes they
can get stuck on the crankshaft. Without scoring the crankshaft gently pry the
seal retainer until its removed. This particular seal has a plastic retainer that is
meant to give an added layer of protection to the seal.
Here is what the seal retainer looks like when removed. It is a simple
plastic ring that pushes into place once the seal in installed. This retainer is designed
to keep the seal from moving while in operation. Now remove the rear main seal
by hand from the crankshaft hub.
8. Match the New Rear Crankshaft Seal
Match the new rear main seal to the old unit, they should match
identically in size. Some rear main seals can be redesigned from the factory and
might be slightly different in appearance but should still have the same inner
and outer diameters.
9. Install the New Seal into the Seal Housing
This part is important: The direction the rear main seal is installed will
mean the difference between the seal working or leaking. The lip of the seal must
go toward the engine and over the crankshaft without damage. Some seals will
come with an installation tool which is a thin plastic ring that the seal
sides over the crankshaft hub.
Use a gasket scraper and carburetor cleaner remove all the old gasket material,
oil and grime from the seal housing. Once the seal housing has been cleaned
thoroughly gently and correctly in place the seal in the housing. In the image
below the lip of the seal is facing upward.
Using a flat piece of mild steel and a hammer positioned above the seal, gently but evenly hammer the seal into place. You don't want to have the seal go
in at an angle because this will distort the seal and may cause it not to work
The seal will be completely installed when it is flush in the seal housing. Check the installation by running your finger around the seal
feeling for evenness against the housing.
Once the seal is installed apply a thin layer of sealant to
both top and side sealing surfaces. Before doing this step prepare the block for
the seal housing installation so the sealer does not start to dry.
10. Prepare the Block and Crankshaft
We must now prepare the block to reinstall the seal housing and the rear main
seal. Use a shop towel and carburetor cleaner to wipe clean the gasket surfaces while avoiding getting cleaner and debris into
the oil pan.
Position a cloth over the oil pan to avoid debris getting into the pan while
resurfacing the crankshaft seal hub. Use a small piece of emery cloth or fine sand paper,
about 400 grit.
Use the emery cloth to polish the crankshaft journal this step is used to give the
new seal a fresh surface to ride against.
Finish by wiping down both the crankshaft and gasket surface
free of oil and dirt and remove the cloth from the oil pan.
Recheck the oil pan and block for cleanliness. All surfaces
must be oil free to seal properly. While lifting the oil pan gasket slightly apply sealer to the oil pan
and gasket, and into the corner of the block.
11. Install the Rear Main Seal
Apply a small amount of engine oil over the crankshaft seal
hub surface before installing the seal. When installing the rear main seal housing along with the new seal, the
lip of the seal must be lifted over the end of the crankshaft. The lip wants to
fight it so push half of the seal onto the crankshaft then pull it down and around
to work the remainder of the seal into place. Do not use metal objects to
help get the lip over the crankshaft this can damage the seal. Some seals
are designed with an application sleeve which is removed after installation.
After pushing the seal housing into place, (sometimes tapping it with
a hammer helps) reinstall all block and oil pan mounting bolts by hand to avoid
Tighten the block side bolts in a star pattern first and torque to
manufactures specification which is usually 6 to 8 foot pounds.
Finish the installing of the seal housing by tightening the oil pan bolts
to about the same torque setting.
Place the seal retainer ring into place over the crankshaft seal.
Use a small punch and hammer and evenly install the retainer back into place. Do not over install this could push the seal out of the housing.
Then reinstall the engine plate.
The rear main seal job is now complete. Continue the reassembly of the
flywheel, clutch and transmission. It is recommended when doing a job like this to
change the oil and filter since the engine was open and a small amount of
dirt and grease could have failing into the oil pan.
Watch the Video!
Here is the complete job getting done including the exhaust, clutch flywheel and
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crankshaft main seal questions please visit our forum. If you need
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