rear Main Seal noobie question

[70Dart340V8]

I have a sort of noobie question about the rear main seals on our cars. I have a 1970 Dart 340. I've had a small oil leak coming off of my flywheel cover now for a good while. A while ago I replaced the Oil pan and oil pan gaskets (Front and rear rubber pan gaskets as well) in hopes it would fix the leak, it didn't. I've been looking into how to replace the rear main seal on my 340. From what I'm seeing it looks as if all I need to do to replace the rear main seal is remove the pan, remove the rear main cap, and use something to push/pull the upper portion of the rear main seal out while rotating the crank and install the new one the same way with some RTV where the ends of the upper and lower seals meet. From what I'm reading and seeing in pictures it doesn't look like I NEED to remove the transmission. Am I missing some big part of this or do I have this down for the most part? Like I've said I've already removed the pan in the past so I know everything that goes into that job, I'm more concerned about after I remove it. More specifically if I NEED to remove the transmission. I understand it may be easier to remove the engine/transmission, but that's not an option for me right now unless there is no other way possible to do it. Thank you for any help

 

[Inertia]

You don't need to remove trany,, you pretty much seem to have a handle on it..

BUT,, you need to be absolutely sure the oil leak is the rear seal.. Oil can migrate down from the oil sender/dist,, or leak from the oil filter/adapter,, valve covers,, fuel pump and along the pan to rear, with fan and gravity moving any oil to the back of the pan..

So were I you,, I'd wash the begeebees outta the engine with "brakeclean",, and then watch very, verry carefully to see where it's originating.. my $.02

hope it helps

 

[TrailBeast]

That's about it, and no you don't have to split the engine and trans.
One suggestion I would make is just to offset the ends of the seals from the main cap and block about 1/4 inch (where the main cap and block meet, rotate your upper seal half so you have about 1/4 inch sticking out above the block surface and match that with 1/4 inch in the cap) like the picture.
Then just a touch of RTV where the seals meet, and a small bead (a film basically) where the red lines are in this picture so oil can't get out between the bearing cap and block.

 

[Inertia]

Just to emphasize something TB mentions,, about the RTV at the red lines,, just a very thin film if any,, some folks think if a "little" is good,, then "more" is better..

I don't use any,, my concern is too much rtv would open the tolerance of the main bearing,, but more important is the main oil gallery from the pump passes thru that joint,, and any clearance created by RTV may cause oil pressure to blast outta there ,, causing other probs..

Check mating surfaces for any imperfections..

hope it helps..

 

[70Dart340V8]

Ok I was just making sure on all this. That offset idea is one I'll make note of when I do it. I'm positive it has to be coming from the rear main seal. I replaced the factory oil pressure sending unit with a line to an aftermarket mechanical gauge and recently replaced all the upper and front gaskets. I can visibly see there's no leaks coming from the upper portion of the engine. The only reason I didn't do the rear main seal is I'm used to needing to pull the tranny off to access it. If I had known it would have been so easy I would hav just done it when I had everything apart.... I guess hindsight is 50/50 though

 

[Inertia]

An easy mistake with the modern 360* rear seal being more common these days.. lol

At least you got some sperience takin the pan off..

Check the oil filter adaptor to block,, is common leak..

 

[TrailBeast]

Just to emphasize something TB mentions,, about the RTV at the red lines,, just a very thin film if any,, some folks think if a "little" is good,, then "more" is better..

I don't use any,, my concern is too much rtv would open the tolerance of the main bearing,, but more important is the main oil gallery from the pump passes thru that joint,, and any clearance created by RTV may cause oil pressure to blast outta there ,, causing other probs..

Check mating surfaces for any imperfections..

hope it helps..

The cap bolts are well away from that area and there is no place for any RTV to get trapped causing clearance problems, and I have never had a problem doing it.
(never had a rear main area leak after doing them that way either)

Just a light smear that you can almost see through does it, and the reason I do that is because of the oil pressure right there and that it can easily go around the seal and between those mating surfaces. (seen it happen more than a couple of times)

 

[Inertia]

The cap bolts are well away from that area and there is no place for any RTV to get trapped causing clearance problems, and I have never had a problem doing it.
(never had a rear main area leak after doing them that way either)

Just a light smear that you can almost see through does it, and the reason I do that is because of the oil pressure right there and that it can easily go around the seal and between those mating surfaces. (seen it happen more than a couple of times)

Yep, not diss-agreeing,, just trying to avoid someone with a caulk gun chugging a 1/4 inch bead across there, thinking any excess will "sqeeze" outta there... lol

Hence "more isn't better"..lol..

 

[TrailBeast]

Yep, not diss-agreeing,, just trying to avoid someone with a caulk gun chugging a 1/4 inch bead across there, thinking any excess will "sqeeze" outta there... lol

Hence "more isn't better"..lol..

Oh no, I didn't think you were.
Just trying to make the OP feel better about it.

LOL, 1/4 inch bead.

 

[70Dart340V8]

Thanks for the help guys. I saw on one of the forms that the 360 magnum rear main seal also can work and it's a tighter fit? The person who posted it said he had a leak he just couldn't fix until he used the 360 seal. Anyone heard of this trick? I'm probably still going to go with the 340 seal but just in case that doesn't work...

 

[TrailBeast]

Thanks for the help guys. I saw on one of the forms that the 360 magnum rear main seal also can work and it's a tighter fit? The person who posted it said he had a leak he just couldn't fix until he used the 360 seal. Anyone heard of this trick? I'm probably still going to go with the 340 seal but just in case that doesn't work...

I have never heard that about using a 360 seal because it was tighter, but then I'm sure I haven't heard everything yet.

 

[70Dart340V8]

I don't remember what post I saw it on. Apparently you just use RTV in place of the "ears" of the rear main seal and it's a tighter fit. Figured I'd ask. Once again thanks for all the help guys. I'm never disappointed when I come here for advice/help.

 

[jimjimjimmy]

Thanks for the help guys. I saw on one of the forms that the 360 magnum rear main seal also can work and it's a tighter fit? The person who posted it said he had a leak he just couldn't fix until he used the 360 seal. Anyone heard of this trick? I'm probably still going to go with the 340 seal but just in case that doesn't work...

I cant see how a 360 seal would work since 360 mains are a larger diameter than a 340.