Mercury 40HP Input Shaft Seal Replacement | Mercury 40 Outboard Upper Seal Replacement |

Mercury 40HP Input Shaft Seal Replacement | Mercury 40 Outboard Upper Seal Replacement |

Buy your Mercury 40 seal kit and marine grease here:

Buy only the Mercury 40HP seal kit here:

See how to do an upper seal replacement on your Mercury 40HP in this video from

We’ve already removed the lower unit, and if you need to see how to do that you can check out this video:

John will start by getting the gearcase fluid out. Then, we’ll show you how to remove the prop and get the input shaft removed. During this process, we scratched the input shaft a little bit, and John will show you how to repair that.

With the input shaft removed, we’ll use our Mercury outboard seal kit to replace them. We’ll wrap up by reinstalling the input shaft.

See this diagram for a better look at the lower unit and input shaft seals:

Read how to do this job step by step:

See how to replace the prop seals here:

Draining the lower unit – 0:50
Removing the prop – 1:00
Removing the pinion gear – 2:00
Removing old seals – 3:00
Replacing the seals – 4:35
Replacing the input shaft – 6:22

Find Mercury outboard parts here:

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In the video we’re working with a 2003 Mercury 40HP 4-stroke EFI outboard motor, but you may have similar steps for your Mercury outboard. If you’re not sure whether these steps apply to your motor, leave a comment and we’ll get back to you.


Mercury 40 water pump replacement:

Mercury 40 HP outboard oil change:



carlos adame says:

What size is the pinion nut? None of my wrenches/sockets seem to fit?

Steve Kenney says:

You guys sent me a broken part.

Steve Kenney says:

Won’t this damage the upper driveshaft bearing because the seal carrier is being pressed on by the outer race?

Les Howell says:

Hi John,
Great videos, really informative and well done.
I may have missed this on a previous video.
On some parts that may required disassembly, why do you use red Loctite rather than blue?
Please keep the videos coming.
Thank you.

John Roberts says:

You do a fantastic job with your videos!

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