Ford Mustang Rear Main Seal Install

Posted 2/7/2017 by Tyler Rodriquez

A leaking rear main seal on your Mustang can cause not only a stain in your garage, but a headache if you don't fix it before it gets worse. Follow along as we walk you through this easy install.

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How To Install Mustang Rear Main Seal

The hardest part of installing a new Mustang rear main seal is getting to the actual seal. This is a part you will want to replace if you already have your transmission out even if it is not leaking. This is cheap insurance to prevent future leaks.

Tools Required:

  • Small Flat Head Screwdriver
  • Small Amount Of Fresh Oil
  • Quality Brake Clean
  • Hammer
  • Small Drift

How to install

  1. Remove the transmission, clutch, flywheel, & spacer plate. These steps can be found in our AOD To T5 Swap Stage 3 & AOD To T5 Stage 4 videos.


  2. Ford Mustang Rear Main Seal Install

  3. Using a small flathead, pry the old rear main seal from the engine paying close attention to the orientation of the seal.


  4. Ford Mustang Rear Main Seal Install

  5. Clean the area with quality brake clean and a clean towel and inspect for any damage or foreign materials that may be present.


  6. Ford Mustang Rear Main Seal Install

  7. Once the area is clean, apply a thing coat of fresh oil to the new seal and place into position.


  8. Ford Mustang Rear Main Seal Install

  9. Lightly tap the seal into place with a hammer and small drift until it is flush with the engine block.


  10. Ford Mustang Rear Main Seal Install

  11. Reinstall all of your transmission components and you are done!


  12. Ford Mustang Rear Main Seal Install


About the Video

How To: Mustang Rear Main Seal Replacement (1982-2004 3.8L, 5.0L)

Check out our YouTube channel for even more tech tips, installation videos, how-tos, and more. The best place to go for anything Mustang related!

Published on 2017-01-13
The rear main seal is located at the back of the engine block and has a very important job of keeping oil inside of the engine while the crankshaft rotates. Since the crankshaft protrudes from the back of the engine block, a seal is required to keep the oil inside of the engine where it belongs.

Most Mustang rear main seals feature a silicone, rubber or Teflon construction which wears out from age and the rotational forces from the crankshaft. Common signs of a failing rear main seal, is oil seepage around the bottom of the transmission, the bellhousing, or the spacer plate.

Replace the worn or damaged rear main seal in your 1982-2004 3.8L or 5.0L Mustang with this high quality rear main seal from Ford Performance!

Mustang Fitment: 1982-2004 w/ 3.8L or 5.0L

Item # LRS-6701A
MPN # M-6701-B302
Transcript
How’s it going everybody? Landan with Late Model Restoration. Today I’ll be discussing a rear main seal and how you go about replacing one in your Mustang.

The rear main seal is located at the back of the engine block and has a very important job of keeping oil inside of the engine while the crankshaft rotates. Since the crankshaft protrudes from the back of the engine block, a seal is required to keep the oil inside of the engine where it belongs.

Most rear main seals feature a silicone, rubber or Teflon construction which wears out from age and the rotational forces from the crankshaft. Common signs of a failing rear main seal, is oil seepage around the bottom of the transmission, the bellhousing, or the spacer plate.

The absolute best time to replace a rear main seal is when you have to service a manual or automatic transmission by means of removal. The rear main seal is an easy part to service, but the only downside is getting to it. Since transmission removal is required to service the rear main seal, most shops charge an arm and a leg for that reason.

Now, if you have a bit of mechanical experience and good selection of tools, you can do this in your driveway. I’m going to pick up with the transmission already removed from the car and will be performing the work on a 1988 Fox coupe. To view the general procedure of transmission removal in a Fox Mustang, click the link in the description or the card in the upper right hand corner on your screen.

With the transmission, clutch and flywheel or flex plate out of the way, locate the rear main seal.
Carefully use a small flathead to pry out the old seal.
Be sure and make a mental note of the seals orientation.
Clean the area with brake clean and inspect for any damage or foreign materials that could be present.
Once inspection is complete, apply a thin film of fresh oil to the outside of the rear main seal.
Position the seal into place with the back of the seal is facing towards you.
This will be the side doesn’t have the inner lip.
Lightly tap the seal into position until it is flush with the back of the engine block.
Double check your work and you’re all finished.

All that work in removing the transmission to spend ten minutes replacing a seal… it is what it is fellas! Like I said before guys, replacing the rear main seal can be managed in your own driveway. Grab a friend or two to speed up the process and make sure you have a decent set of tools. Other than removing the transmission, this installation procedure covers just about any Mustang with a one piece rear main seal.

For more tech related videos, subscribe to our YouTube channel if you haven’t already done so. Of course be sure and check out our wide selection of engine parts and accessories from the real Mustang enthusiasts, LMR.com!