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I put some ATF on just to help and and tap it in. I've never used RTV on any press fit seal like this on anything. I didn't even know some people do. I doubt that's advised in any manual worth a lick. I could be wrong, it's just I've never of it. I guess it probably couldn't hurt anything....but I highly doubt it does anything either.......Well put it this way, if it were needed, the seal wouldn't be made properly, so.
Last edited by FORDF250HDXLT; Mar 4, 2026 at 01:45 PM.
I replaced mine right after knocking it out, so I just copied it, not thinking much about it. It's been too many months to recall exactly now though. Hopefully someone else chimes in to confirm. Don't see any photos anywhere or youtube vids? Really seemed like it goes in from the outside, not the inside like that, but I sure don't remember. I was so many hours changing stuff over from engines it's all a blur. I was right in the middle of a very large tree job and I was hustling to get that truck back on the road.
I replaced mine right after knocking it out, so I just copied it, not thinking much about it. It's been too many months to recall exactly now though. Hopefully someone else chimes in to confirm. Don't see any photos anywhere or youtube vids? Really seemed like it goes in from the outside, not the inside like that, but I sure don't remember. I was so many hours changing stuff over from engines it's all a blur. I was right in the middle of a very large tree job and I was hustling to get that truck back on the road.
A couple things regarding this rear seal..
1) I noticed, as soon as I got mine, that the rubber lip seemed wrinkled or "wavy". I asked CDD about that and they said it was normal but I am still doubtful (see pic 1).
2) I have sourced 2 different pictures that appear to show the seal going in, in both directions, one pic is the way I did it the other way has the lips facing towards engine not towards trans. My way is lips facing towards trans(see post 138 to see how mine is). Pic 2 is facing towards engine (Nick PIsca).
Anyway I have decided to get a new rear main seal just for peace of mind and I'm going with the National 3893V everyone seems to like. Im almost positive I had a leak there and I know this is the PITA to access without removing the enjoy so why not? Just kinda frustrated with the way it's supposed to go in??
It has been many years ago the last time I replace a rear seal on a 6.9. The direction when installed correctly the lip points towards the oil source, in this case the crankshaft. You normally press a seal in from the side that is closed or in this case the side that has the words on it. If it is going into a hole that does not have a bottom to it then you could press the seal in backwards. As long as the lip is point to the oil source it will be correct. Some seals have a secondary lip that faces the opposite direction so those can be a little more interesting. The main seal lip should be the larger one and normally also has a spring around the inside of it. Again that goes to the oil side. Hope that helps and makes some sense. If you have ever repacked wheel bearings think of those seals. They can only be driven in one direction and the lip of the seal points towards the grease and bearings.
It has been many years ago the last time I replace a rear seal on a 6.9. The direction when installed correctly the lip points towards the oil source, in this case the crankshaft. You normally press a seal in from the side that is closed or in this case the side that has the words on it. If it is going into a hole that does not have a bottom to it then you could press the seal in backwards. As long as the lip is point to the oil source it will be correct. Some seals have a secondary lip that faces the opposite direction so those can be a little more interesting. The main seal lip should be the larger one and normally also has a spring around the inside of it. Again that goes to the oil side. Hope that helps and makes some sense. If you have ever repacked wheel bearings think of those seals. They can only be driven in one direction and the lip of the seal points towards the grease and bearings.
That makes sense, thanks. What's a little surprising to me is doing research in this and seeing so many pictures and posts of people installing it the opposite way and no one really catching it unless you look at it closely. These same people don't seem to report back with issues of leaks in this area.
How's things going? Back on my main pc again, I have access to my records. For the replacement engine in my F450:
Felpro Rear Main seal Kit BS 15868-1 - rubber (advance auto locally had it in stock. Had I thought of it, I would have
ordered and used the higher end Fluoroelastomer seal instead though, like Precision Multi-Purpose Grease/Oil Seal - 3893V or MAHLE Rear Main Seal - 68028)
Although my notes show I researched options too late, I bet the rear main doesn't leak for decades. I'll eventually need to have a fresh reman trans put in this truck, and I doubt I'll bother updating the rear main seal at such time, that's how little I'm concerned.
MAHLE GS33679 Engine Oil Cooler Mounting Kit
Last edited by FORDF250HDXLT; Mar 6, 2026 at 05:55 PM.
How's things going? Back on my main pc again, I have access to my records. For the replacement engine in my F450:
Felpro Rear Main seal Kit BS 15868-1 - rubber (advance auto locally had it in stock. Had I thought of it, I would have
ordered and used the higher end Fluoroelastomer seal instead though, like Precision Multi-Purpose Grease/Oil Seal - 3893V or MAHLE Rear Main Seal - 68028)
Although my notes show I researched options too late, I bet the rear main doesn't leak for decades. I'll eventually need to have a fresh reman trans put in this truck, and I doubt I'll bother updating the rear main seal at such time, that's how little I'm concerned.
MAHLE GS33679 Engine Oil Cooler Mounting Kit
I ordered a new rear seal. Went with the national. Waiting for that to show up. I installed Speedy sleeves on the rear crank and will be installing one on the harmonic balancer for the front seal, waiting for that one to show up. I removed the front plate cover to have better access when pressing that seal in. Now that I have the water pump out and the main front plate out, I will be doing all those gaskets as well. I ended up getting my heads resurfaced, glad I did. Everything is in a in between/ almost there stage.
No one could've prepared be for how much a PITA it is to remove all this old fossilized gasket. I'm using that CRC gasket remover with a razor blade and the wire brush on the grinder so it helps but wow.
The front plate seems to have a good amount of pitting on the surface where the water pump bolts on to. Is this normal? Did a quick ebay search to see what they may cost - lots of rear plates but not a single front plate, not just on ebay but anywhere...scary
Last edited by steelholder; Mar 6, 2026 at 11:13 PM.
Could you guys help me locate exactly where these go? The bottom right gasket with blue seems to go on the oil cooler but mine isnt shaped like that or I cant find that spot. Did they make more than one type? Which of these is the oil pick up tube gasket and where is that located? I know one or couple of these is related to the thermostat ( which I didnt replace for now). Is the top left the diptstick o-ring? Not sure where on the tube that goes, how about the bottom left? Thanks all.
Last edited by steelholder; Mar 7, 2026 at 05:12 PM.
