This video kind of goes along with Tim and Sean's transmission videos. I filmed the quick and easy little job of replacing the rear main seal. Enjoy.
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Thanks for sharing this. In response to your question, why wouldn't somebody choose to replace this seal if they already have the transmission out, I'll give you a few reasons why Sean and I decided to pass on the replacement when replacing his transmission.
#1) You have to take off the flex plate to get to it and there have been reports that people have had multiple cracked flex plates after replacing their original flex plate. Now, maybe the reason why the flex plate cracked in the first place wasn't addressed like a worn crankshaft bearing but we decided we didn't want to mess with it because his seal showed no signs of leaking. Maybe the flex plate torquing sequence needs to be absolutely spot on so there are no extra vibrations that would cause it to crack. I guess what I'm trying to say is there was enough reports of cracking flex plates that we didn't want to risk it if his seal wasn't leaking.
#2) Just like you showed in your video to knock the new seal in, you need something with a very wide diameter to knock it in evenly. I don't have anything like that either. The technique you used is basically what you have to do if you don't have some sort of special tool or maybe a big enough pipe fitting to drive the seal in, but I probably would have opted to tap it in a little more gently going around the circumference using a brass drift and hammer to slowly and evenly seat the new seal in. So, since we would be taking out a seal that is doing it's job for a new seal that we can't necessarily guarantee we're going to be able to drive in properly, this was another reason why we opted to leave it alone, because maybe after we put everything back together, we find we now have a leaking rear main seal which would really suck.
#3) Sean only has 160,000 miles on his engine. We were also thinking that there's a very good chance he will never develop a rear main seal leak bad enough to force him to pull his transmission again. Now, if he had say 250,000+ miles on his rig and he was still planning on keeping it for a long time, replacing the rear main seal would have definitely been something to do.
Anyway, I figured I'd share our thought process on this because the way you sounded in your video you sort of imply you'd have to be pretty stupid to not replace it while you have the transmission out. Sometimes the smartest move you can make is leave shit alone. Like I quoted in our video, sometimes following the old saying, "if it ain't broke, don't fix it" will keep you from cursing and throwing shit when you f*ck up.