Change rear main seal while trans is off?

[The motor guy]

Personally, I say don't touch it unless it's leaking. How do you know they'll install a new one correctly? Opinions? This is my 6.7 cummins 2007 model, 230k miles 12,000hrs. There aren't any leaks at all on this engine, other than the hydroboost is a bit damp, but doesn't leak yet

 

[burbguy82]

Tough one. Not sure. No good answer either way. You are going to feel bad if:

you change the seal, and it leaks

or

you dont change the seal and it leaks in 5k

 

[BrendanC]

change it EVERY single time you have access to it.

OEM only seals.

 

[CarlB]

All depends on which do you believe is most likely.

A) Old seal eventually leaks
B) New seal is a dud and leaks

I believe A happens more often than B, so I change them accordingly. But you can go the other direction.

 

[The motor guy]

Tough one. Not sure. No good answer either way. You are going to feel bad if:

you change the seal, and it leaks

or

you dont change the seal and it leaks in 5k

change it EVERY single time you have access to it.

OEM only seals.

I think it's funny my 99 5.9 cummins leaks from every seam imaginable, but this 07 6.7 cummins is dry as can be underneath

 

[wlk]

I think it's funny my 99 5.9 cummins leaks from every seam imaginable, but this 07 6.7 cummins is dry as can be underneath

I was looking at a truck recently w the 5.9l and noticed the same, leaks everywhere. Road horribly stiff but man that motor was powerful. Ended up not buying, didn't like how the tranny felt.
Oh, my vote is change them if you have access.

 

[slacktide_bitog]

If it's automatic, you don't really have to.

If it's a manual transmission, changing it is a good idea because a bad rear main seal means oil on the clutch.

 

[The motor guy]

I was looking at a truck recently w the 5.9l and noticed the same, leaks everywhere. Road horribly stiff but man that motor was powerful. Ended up not buying, didn't like how the tranny felt.
Oh, my vote is change them if you have access.

The 5.9 has a catch can and the 6.7 actually creates a vacuum with the ccv filter being routed back to the intake, I think it makes a big difference when it comes to blowing seals out

 

[The motor guy]

I was looking at a truck recently w the 5.9l and noticed the same, leaks everywhere. Road horribly stiff but man that motor was powerful. Ended up not buying, didn't like how the tranny felt.
Oh, my vote is change them if you have access.

Try driving a 6.7 even bigger difference

 

[wlk]

Try driving a 6.7 even bigger difference

Well, I ended up buying a 94 Ford dually w the 460. So no more rosd testing but by the time I need a new one, maybe the 6.7s will be affordable for me.

 

[cptbarkey]

Yes. At that mileage and age it’s inevitable.

 

[Lubener]

At 230k miles and that seal just staring at you, I would replace it with an OEM part.

 

[demarpaint]

I did a clutch job, on my 88 E-150 a little over two years ago. The internal slave cylinder was leaking. The RMS was not leaking but was in service for 35+ years. There was no way that transmission was going back in with the original RMS. I also changed the original front and rear seal on the transmission. So far so good.

 

[Trav]

No way in Hades am I not changing it at that age and miles with it looking right at me.

 

[JavierH19]

Definetly, Is this even a question. Oem only and inspect the new seal. I've gotten bad seals and gaskets with defects that I could see.

 

[The motor guy]

The 5.9 has a catch can and the 6.7 actually creates a vacuum with the ccv filter being routed back to the intake, I think it makes a big difference when it comes to blowing seals out

No way in Hades am I not changing it at that age and miles with it looking right at me.

It's not looking at you. The flex plate still has to come off

 

[JavierH19]

It's not looking at you. The flex plate still has to come off

The flexplate comes off, rms gets replaced, and back on goes the flex plate in 40 minutes or so once the trans if off. Wasn't hard when I did the rear main seal in my old manual f350. Taking the trans out was.

 

[TazzySpazzy]

I would change it out. The rear main is definitely a "while your in there you might as well do it" kind of thing. But rear mains don't tend to leak that bad and if you have a gravel driveway like I do you'll never see the leak spots!

 

[D60]

I find this debate fascinating because no one ever considers HOW you'll be doing it -- or rather, operates on the assumption that the job will be performed as well as humanly possible.

If you do it properly and use a quality seal, yes, replace it.

If you rush through and claw it out with a screwdriver, scratching the wall or the crank along the way, skip it.

Because I'm paranoid I never just "eyeball" seal depth unless it bottoms against a seat. Some float and then I find a way to make a tool so I drive it flush with a surface.

If you envision how a seal works, being cocked even a couple thousandths gives you an oval or ellipse trying to seal a circular crank.

So do it right and do it carefully, or let sleeping dogs lie.

edit: depending on cost I'll often order TWO seals. Having a second guarantees the first one goes in well. But if I don't have a spare, I'm left thinking I don't like my first attempt and wish I had another for a second try

 

[TazzySpazzy]

I find this debate fascinating because no one ever considers HOW you'll be doing it -- or rather, operates on the assumption that the job will be performed as well as humanly possible.

If you do it properly and use a quality seal, yes, replace it.

If you rush through and claw it out with a screwdriver, scratching the wall or the crank along the way, skip it.

Because I'm paranoid I never just "eyeball" seal depth unless it bottoms against a seat. Some float and then I find a way to make a tool so I drive it flush with a surface.

If you envision how a seal works, being cocked even a couple thousandths gives you an oval or ellipse trying to seal a circular crank.

So do it right and do it carefully, or let sleeping dogs lie.

edit: depending on cost I'll often order TWO seals. Having a second guarantees the first one goes in well. But if I don't have a spare, I'm left thinking I don't like my first attempt and wish I had another for a second try

Of course you are making an assumption about other people's assumptions. We all hope to being doing things correctly but yeah sometimes we miss a step through ignorance or forgetfulness and things go sideways, but there is no better lesson learned than those from our own mistakes.