Rear. Main. Seal.

[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.


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.


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.