Rear. Main. Seal.

[m_owing]

1988 stock 5.0L
Always dripped down the back, from the bottom of the bellhousing. Replaced the rear main a few years ago, started leaking right after putting everything back together. ZR and Zippy replaced the intake gaskets last year, also got a new PCV valve, screen and grommet. Valve covers are dry too. I've double checked the oil pan gasket and it seems dry also.

Talked about this in a thread last year and loved RedSN's comment about how even Ford considers a rear main leak as 'normal'
http://www.torontomustangclub.ca/forums/showthread.php?17153-87-93-Replace-Intake-Gasket

I'm ready to do it again and want all the insurance I can get to eliminate this leak. From my research this is what I've come up with:

- fel-pro crank repair sleeve 16250 (didn't know about these last time)
- green loctite between this and the crank
- fel-pro seal 40620 (or similar: Ford Racing M-6701-B302)
- fel-pro installation tool 16300
- grease (dialectric?) on inside of seal spring/groove
- RTV (of some kind) on outside of seal

Anything you think I could be missing?

[hammerhead]

maybe oil pan seal...?

[ChickenLips]

please document the job and update later with result. I have a fairly fresh motor on a stand waiting for install and this prompted me to consider doing the seal before dropping it in the hole.

I know you've done the PCV, but years ago I was certain I had a real main leak and it was the PCV not properly seated.

[ZR]

If leak is between crank and seal itself, yes opt for the Fel Pro repair sleeve making sure to use lock tite.
If leak is between block and seal, replace seal only. They make a standard and premium seals, neither have proven 100% reliable. When doing clutches, if seal is dry we've opted to leave as is and not replace seal.
Back side of the seal, I use white lithium grease to fill the cavity full to prevent spring from flinging out. Oddly enough just had a pick up in for axle seals, previously installer did not use grease, spring had popped out and did damage to the bearing / axle face when it became lodged in outter edge of the bearing race.
Not sure why Ford did not make the rear main seal more like an axle seal with a steel lip so it's for sure in perfectly straight.
When removing old seal, be x x x tra careful not to damage / mark the crank itself, very common to see when we get a persistent leaker in someone else has had their hands on.

[m_owing]

please document the job and update later with result. I have a fairly fresh motor on a stand waiting for install and this prompted me to consider doing the seal before dropping it in the hole.
I know you've done the PCV, but years ago I was certain I had a real main leak and it was the PCV not properly seated.

Will update. I'll also check the PCV again


maybe oil pan seal...?

Updated my first post. I've checked the oil pan many times and it seems clean and dry.



If leak is between crank and seal itself, yes opt for the Fel Pro repair sleeve making sure to use lock tite.
If leak is between block and seal, replace seal only. They make a standard and premium seals, neither have proven 100% reliable. When doing clutches, if seal is dry we've opted to leave as is and not replace seal.
Back side of the seal, I use white lithium grease to fill the cavity full to prevent spring from flinging out. Oddly enough just had a pick up in for axle seals, previously installer did not use grease, spring had popped out and did damage to the bearing / axle face when it became lodged in outter edge of the bearing race.
Not sure why Ford did not make the rear main seal more like an axle seal with a steel lip so it's for sure in perfectly straight.
When removing old seal, be x x x tra careful not to damage / mark the crank itself, very common to see when we get a persistent leaker in someone else has had their hands on.

When everything is apart I'll look to see where the leak is coming from. I'll buy everything and decide when it's time. Do you put any RTV or silicone anywhere?
How does grease prevent the spring from moving?

[LX89]

My rear main likes to leak in colder weather.
Warmer weather usually nothing.
Same seal since 92 when Ford rebuilt the engine under warranty.

I keep the PCV valve and screen clean.
Not going to touch it as it's probably a expensive job.
Might even leak more if some mechanic doesn't do the job right,lol.

[ZR]

Will update. I'll also check the PCV again



Updated my first post. I've checked the oil pan many times and it seems clean and dry.




When everything is apart I'll look to see where the leak is coming from. I'll buy everything and decide when it's time. Do you put any RTV or silicone anywhere?
How does grease prevent the spring from moving?

Back of the seal packed with grease prevents the spring from coming dislodged. Same technique with axle seals etc.
I install as designed, dry n clean on outter edge.

[m_owing]

Not going to touch it as it's probably a expensive job.
Might even leak more if some mechanic doesn't do the job right,lol.

When driving the oil either drips on the exhaust or the exhaust is close enough that it burns it up and stinks. That and I'm growing weary of always having to make sure there's cardboard wherever I park. By the end of the season I usually have to add almost a quart.


Back of the seal packed with grease prevents the spring from coming dislodged. Same technique with axle seals etc.
I install as designed, dry n clean on outter edge.

I get that's what it does, I'm curious how it physically does it. Does the grease fill in the space so the spring can't move, or create some kind of hydraulic pressure?

Thanks again everyone.

[hammerhead]

spring will pop if the seal isn't installed or pressed in evenly thru the install - too much twist can cause the spring to pop also...

[hammerhead]

one other thing to consider as well is crank case pressure can push oil out of weak areas as all mentioned above

[m_owing]

one other thing to consider as well is crank case pressure can push oil out of weak areas as all mentioned above

Right. I mentioned I have a new PCV setup. How else can I make sure there isn't an excess of crankcase pressure?

[hammerhead]

The cheapest thing is the PCV - could be clogged or incorrect valve or spring pressure in the valve - maybe a clog in the intake where the pcv goes thru - old engines will build up crankcase pressure with blow by from worn cylinders and rings and also worn valve seats - boost can also do it (i think your stock tho) - not much really will cause it - crank case pressure can be tested but I'm not sure many do that....gas or exhaust type odors from under the hood could indicate blow by (might be hard to tell if it drips on the exhaust as mentioned) - compression test could show weak cylinders... rough idle could indicate pcv stuck open - extreme cases head gasket or cracks in block - I don't think that would be your case - I would start cheap first with the PCV...

[1986stangfan]

Back of the seal packed with grease prevents the spring from coming dislodged. Same technique with axle seals etc.
I install as designed, dry n clean on outter edge.

This can not be overemphasized! When I was at the transmission shop we would have vehicles come in from other shops stating that axle seals or transmission rear seal has been replaced but still leaking. 9.9 times out of 10 the springs were not in place when the axle or driveshaft was removed

[m_owing]

The cheapest thing is the PCV - could be clogged or incorrect valve or spring pressure in the valve - maybe a clog in the intake where the pcv goes thru - old engines will build up crankcase pressure with blow by from worn cylinders and rings and also worn valve seats - boost can also do it (i think your stock tho) - not much really will cause it - crank case pressure can be tested but I'm not sure many do that....gas or exhaust type odors from under the hood could indicate blow by (might be hard to tell if it drips on the exhaust as mentioned) - compression test could show weak cylinders... rough idle could indicate pcv stuck open - extreme cases head gasket or cracks in block - I don't think that would be your case - I would start cheap first with the PCV...

I sprung for the motorcraft PCV and grommet. Fit together great. No rough idle. I tested cylinder compression a few years ago and it was fine, not to say something couldn't have changed. I run codes frequently too. No boost. ZR and 1986stangfan mention greasing the spring, which I didn't know about so didn't do last time. I ordered all the parts and the $60 plastic felpro installation tool (part# 16300). Hopefully I have some time to give it a shot before it's too cold.

[Jeff Esliger]

Make sure you get a good rear main seal.when l did mine l only use Ford Motorcraft seals

[m_owing]

Make sure you get a good rear main seal.when l did mine l only use Ford Motorcraft seals

I ordered fel-pro 40620 and was thinking about ordering a Ford Racing M-6701-B302 just to compare (though I'm sure they look the exact same)

Jeff, you were able to get a Motorcraft seal for an original fox 5L? Dealership?

The BIG question,
Is there anyway to tell if it will leak (replacement done poorly) BEFORE putting everything back together and driving it?

[RedSN]

………and the $60 plastic felpro installation tool (part# 16300).
I didn’t realize it was only $60. I made my own when I did the seal in my car.

https://photos.smugmug.com/94-Mustang/i-gQrkJQN/0/fa840a1c/M/C03167DC-9311-44A6-96AB-6ACF1AEBCD00-M.jpg
ABS cap
4” PCV pipe
JB Weld
and a couple of bolts.

[m_owing]

I didn’t realize it was only $60. I made my own when I did the seal in my car.

https://photos.smugmug.com/94-Mustang/i-gQrkJQN/0/fa840a1c/M/C03167DC-9311-44A6-96AB-6ACF1AEBCD00-M.jpg
ABS cap
4” PCV pipe
JB Weld
and a couple of bolts.

It’s not even this tool! It’s just the plastic cap looking thing. It has an ID and an OD, one for hammering on the sleeve and one for hammering in the seal. I did a lot of reading and apparently it’s well worth it.

[m_owing]

please document the job and update later with result. I have a fairly fresh motor on a stand waiting for install and this prompted me to consider doing the seal before dropping it in the hole.

I know you've done the PCV, but years ago I was certain I had a real main leak and it was the PCV not properly seated.

I got all the parts but it looks like the job won’t happen until next season. I’ll update then. Thanks again everyone.

[cudaboy]

Thought this was mainly a GM problem. Ive only had 2 GM cars and both had the problem. My 69 GTO needed the seal replaced 3 times during my ownership.