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How to Replace the Rear Main Seal on a Chevy 350?

How to Replace Rear Main Seal Chevy 350
Last Updated on Aug 16, 2023 By Lillian Kazmierczak

The rear main seal is one of the most important parts of your engine that needs good care. It protects the engine from oil getting on its parts.

When the seal breaks or wears down, it will lead to even worse engine damage. Replacing the main seal is both expensive and a lot of work.

Here, we’ll be showing you two easy ways to replace the rear main seal in a Chevy 350.

How to Replace the Rear Main Seal on a Chevy 350?

Things to do before you replace the main seal

The rear main seal is surrounded by quite a few other parts and you have to remove parts of the engine to properly access the rear main seal. Although time-consuming, it is important to do to prevent other damage to your engine.

  • Remove the battery and starter. This prevents any electrics from getting to you while you work.
  • Remove the transmission.
  • If your car is a manual, remove the flywheel and the clutch.
  • If your car is an automatic, remove the flex plate.

Once done, you are ready to remove the rear main seal.

The process

Before you begin, gather your tools. You will need a wrench that fits 10 to 12mm bolts and a flathead screwdriver.

  1. Take your wrench and take the bolts off
  2. Remove the housing of the seal with your flathead screwdriver
  3. You’ll need the flathead again to remove the crankshaft seal. The seal may be stuck in there good, so use some strength to get it out
  4. Place your old seal on top of the replacement. If they don’t match, you will need to buy the right size before continuing
  5. Clean out any dirt that’s stuck on the seal’s housing. Use your scraper and a rag to wipe up any excess
  6. Cover the new seal in a thin layer of oil
  7. Install the new seal into the housing
  8. Spray sealant spray on the seal
  9. Re-place the crankshaft housing, then the seal’s housing
  10. Tighten the bolts and your new rear main seal is good to go

How to Replace the Main Seal Without Removing the Transmission?

It will take quite some time to replace the main seal using the traditional method. If you want to save time and skip doing the extra work, it’s possible to remove the rear main seal without removing the transmission.

Note: Your car will need a two-piece seal for this method and it won’t work if you have a one-piece seal.

For this method, you’ll need a wrench, a floor jack, a Philips head screwdriver, and a set of needle-nose pliers.

  1. Lift your car up using the floor jack
  2. Take your wrench and loosen the bolts holding the oil pan up. Before you completely loosen it, find something to hold the oil pan in place
  3. Remove the sway bar for more space to push the oil pain forward
  4. Use your wrench to remove the bolts of the seal housing
  5. Take your screwdriver and push the old seal out to one side
  6. Grab the end of the seal with your needle nose pliers to pull out the seal
  7. Lubricate your new seal
  8. Make sure the grooved part of your seal is facing the engine, then put the new seal in
  9. Screw the seal housing back on and tighten the bolts. You have successfully installed your new rear main seal

When Should You Replace the Rear Main Seal?

There are clear signs if there is a problem with your rear main seal. Check to see where the leak is before replacing the rear main seal.

  • Oil spills

This is the most common sign you need to replace the rear main seal. Check under the car to see if there is any oil on the ground.

  • Dirty engine parts

If there is a lot of debris on your engine parts, there’s a good chance that’s being caused by an oil leak. Oil is sticky, so anything that falls on it will get stuck.

  • Smoke coming from the tailpipe

When oil drips onto the exhaust, it will burn and start to smoke. If the smoke is coming from your tailpipe, the leak is coming from where the rear main seal is.

What Causes Your Rear Main Seal to Break?

What Causes Your Rear Main Seal to Break

  • Misalignment

This can cause damage to the transmission. Your flex plate or crankshaft can cause cuts. This will lead to your seal breaking and oil leaking out of the pan.

  • Dirty or old oil

Motor oils contain additives that act as seals for your engine parts. If the oil is old or dirty, those seals can deteriorate and leave your rear main seal at risk of damage.

  • Faulty or dirty PCV system

The PCV system provides ventilation for your crankshaft. If it gets clogged or malfunctions, your crankshaft will feel more pressure from the engine running. The crankshaft can break the rear main seal.

  • The main bearing is worn down

Your crankshaft will become loose if your main bearing is starting to wear down. When that happens, the crankshaft will move around and hit the seal. This will cause an oil leak. If this is the problem, you will need to make a lot of repairs to your engine, in addition to replacing the rear main seal.

  • Worn crankshaft

The crankshaft is the part of the engine that holds the rear main seal. If there is a problem with the crankshaft, it will definitely lead to your seal breaking.

  • The seals didn’t stick

If you don’t let your lubricant oil dry before you apply sealant, the sealant will fall off the seal and cause leaks.


1. How much to replace a new rear seal?

Ans. A new rear main seal can cost between $600-900 dollars and a mechanic will cost you an additional $500-800.

2. Do I have to replace a broken rear main seal right away?

Ans. You should replace the seal as soon as you find a leak. The crankshaft rotation will make a leak bigger. Oil leaks can cause fires and engine failure from too much friction.

About the author

Lillian Kazmierczak

As far as I can remember, I would say I have been a car nut for my whole life. My father was a car dealer who used to change and repair his cars himself. This gave me the opportunity to get around all sorts of cars and get my hands dirty repairing vehicles from an early age.

A great fan of Japanese quality and German preciosity, my deep passion lies in older models that I believe have a flair that takes me back to my childhood! I also love their extraordinary durability and reliability when compared to today’s modern models.

When not out taking a ride, I enjoy socializing with fellow motorheads online and consuming any car facts and figures I can get my mind on!

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