Oil Leak at Back of Engine - Rear Main Seal or Oil Pan Gasket?

Can you do it with the engine in the car - is your chassis cross strut removable ? Is there enough room or do you have to pull the entire unit out to drop the oil pan?

My car's chassis cross strut is removable as well as the parking brake plate.  I can pull the oil pan from the bottom of the car.  My oil pan is a 10 quart aluminum by Dennis Quella.  It is a great oil pan although it can be challenge to seal.  There is very little clearance between the back of the pan and the flywheel plate.  I have the transaxle out of the car at the moment for the CV axle conversion and I will probably pull the flywheel and inspect the rear main seal since there is easy access at this time.

That is a substantial oil pan !

I think the removable cross strut modification is one of the most desirable changes from a serviceability point of view. It is on my list if the engine has to come out for any reason.

After having the recent misfortune while leaning over the engine bay of accidently dropping a spring washer out of my shirt pocket into the open timing inspection port on the bell housing and then spending much time ( and very luckily ) retrieving it, I can confirm there is very little clearance anywhere to be found on a Pantera flywheel and bell housing !  It is tight!

Inspection port cover is fixed in place now!

You can remove the chassis cross strut with the engine in the car.  It is significantly easier to do so with engine out but it can be done.  The same with the parking brake mount.

Thanks for letting me know - I would not have tried it with the engine in.

I was thinking of removing the old parking brake mount as well , as I have installed the Tesla/Brembo Electric park brakes combo and the controller offered by PE. They are super effective. Absolute confidence that the car is going nowhere when they are applied. And getting rid of that bracket would further clear up access to the sump.

It could be just the pan or it could be the rear seal. You need to at least drop the pan to look at it.

There is a change over by Ford from a rope seal to a viton two piece seal. Somewhere in the 1971 to 1973 time frame.

The rope seals to me are better but the issue with them is that if the engine sits for a VERY long time, they can dry out and begin to disintegrate.

If it is the crank seal then you need to remove the ZF and flywheel/clutch to get at it.

I think it is more common for the pan seal to leak but I have seen it both ways. Probably 60/40% pan v. crank.

I removed the flywheel and it looks like the oil pan gasket is leaking and not the rear main seal.  I have dye in the oil and you can see it where the pan meets the block.  There is no oil on the back of the flywheel which may further exonerate the rear main seal.  What do you guys think?

How much oil does it leak Steve?  Oil is cheap if not a big leak :-)

The leak in the photo is the lesser of two leaks.  There is a similar leak at the front of the pan.  It is just too messy.

A pan gasket is MUCH easier to do then a rear main seal. Consider yourself lucky.

Make sure that you put sealent on the bolt threads on both the pan and the flywheel

Yes- hard to tell whether it's the rear pan seal or rear main seal leaking. FYI, there are also two (maybe three) different rear main bearing seals. Choices are the OEM 2 piece rope seal, a neoprene 2-piece seal, or a one-piece 351-W seal (requires block machining). On stone-stock Panteras, oil pan removal means cutting the welded under-pan crossmember and e-brake bracket out for clearance. Making these removable was a post-Ford factory upgrade.

The seals all have their difficulties and all can leak from one or both sides of the main cap to block where the little square inserts go, or if the sheet metal oil slinger (to direct excess oil away from the rear seal) is left out. Most builders stagger the seal ends (either type) a little so the seal joint does not line up with the cap-to-block joint.

Rope seal- Can leak at the ends without some sealant on both ends where they get hand-trimmed to size with a razor blade. Easy to underestimate the size needed. High crank drag until broken in.

Neoprene seal conversion- Can leak at the small hole left in the cap when an OEM rope seal locating pin is driven out, unless the main cap pinhole is filled with something (early blocks). Seal can also leak if the crank journal is worn or ground undersize more than about 0.001". No break-in necessary.

One piece neoprene or Teflon seal- can leak if the crank journal is worn or ground undersize more than about 0.001". Also takes block/rear cap machining oversize about 1/4" to fit the large Windsor seal (I've only done one and that's been a decade or two....).  So a 1-piece seal is not a cure-all.

Finally, BOTH the two-piece main seals can be changed with the engine AND ZF in place. You just use a popsicle stick or something similar to not scratch the crank when lightly tapping the seal around the journal. The one-piece seal absolutely needs the ZF pulled to change it.  Good luck, all.

The oil leak is fixed.  I made a strap that presses the rubber seal against the engine.  I put Right Stuff on the seal before strapping it in place.  After it cured I applied a bead of Right Stuff to the entire gasket surface as seen from the bottom of the car and carefully installed the pan.  I made some 2” studs and temporarily put them in the side rail bolt holes to help guide the pan into place.

Have you used The Right Stuff before?  RTV based?

Yes, I have been using Right Stuff for a while.  It is similar to RTV but it dries much faster and is easier to remove if needed.  It seems to seal just as well as RTV.

If you are building an engine, you can have the machine shop do the necessary machining so you can use the one piece rear main seal used on the Windsor motors.

that should greatly diminish the chances of a rear main leaking. But your engine assembly tech needs to install it correctly without putting a half inch gash in the rubber seal. Ask me how I know this. 🤬🤬

Larry