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EFV-8 Club Forum / 1940 Ford Discussion / Rear main seal

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Posted By Discussion Topic: Rear main seal -- page: 1 2     gwistrup 01-01-2026 @ 8:07 AM reply profile send p.m. Member Posts: 41 Joined: Dec 2022 I have a 1940 Ford Tudor sedan that has a rear main seal leak. It will leave a 2-3" spot wherever I park it. I would like to replace the rear main seal but some people have told me that even if I replace the seal, it will still leak. I'm asking the flat head experts if I can stop the leak with a new seal or am I wasting my time. If a new seal will fix the leak, who makes the best seal kit? Can you replace the seal successfully with the engine in the car or will your odds for success improve by removing the engine? I would imagine that an 80 year old rope seal is going to be pretty stiff and it won't come out very easily. Thank you for your advice, Gil carcrazy 01-01-2026 @ 10:46 AM reply profile send p.m. Senior Posts: 1987 Joined: Oct 2009 Unfortunately, Ford did not go to a rope seal for the rear main bearing area until late 1941 for commercial vehicles. All 1946 and later Flathead V-8s used a rope seal. Your vehicle, if it has the original engine, uses a labyrinth type of rear "seal" which essentially just throws the oil off of the crankshaft to be returned to the crankcase. If your rear main bearing clearance is larger than that of a new engine, the leakage past the rear main bearing will be worse. It is possible to have the crankshaft modified to use the later rope type of seal to greatly reduce or totally eliminate the oil leakage problem. To have the crankshaft machined for a rope seal you will have to remove the crank from the engine and take it to a machine shop to have the required work performed. In the meantime, you can reduce oil leakage past the rear main by not overfilling the crankcase. Use 4 quarts of conventional oil of SAE 30 weight viscosity. Be sure to use a good engine oil break-in additive with the required amount of ZDDP to minimize wear on the camshaft lobes which contact the tappets and the fuel pump pushrod. This message was edited by carcrazy on 1-1-26 @ 2:56 PM kubes40 01-01-2026 @ 4:40 PM reply profile send p.m. Senior Posts: 3580 Joined: Oct 2009 Um, well pretty much everything you had advised is correct sans one thing. It's five US quarts to fill. Mike "Kube" Kubarth carcrazy 01-01-2026 @ 8:54 PM reply profile send p.m. Senior Posts: 1987 Joined: Oct 2009 If you have the correct dipstick for the engine, insert the dipstick fully into the engine after you have drained all the old oil out and installed 4 quarts of fresh oil. Check the level indicated on the dipstick. If 4 quarts brings the oil level up to the halfway point or higher within the safe driving range, do not add any additional oil. If the engine has an oil filter, you can fill the engine with 5 quarts of oil which will bring the indicated level up to the halfway point of the safe driving range. kubes40 01-02-2026 @ 2:45 PM reply profile send p.m. Senior Posts: 3580 Joined: Oct 2009 I have to wonder where you guys still come up with four quarts. The owner's manual, the salesman's manual, any Motors manual or similar repair manual all state five (US) quarts. Heck, even the engineering release for the oil pan indicates five (US) quarts. An oil filter did NOT affect the specified amount. Mike "Kube" Kubarth gwistrup 01-02-2026 @ 3:09 PM reply profile send p.m. Member Posts: 41 Joined: Dec 2022 Thank you for the information. I'm sure the engine in my car is not the original. It has a Crab distributor and it does not have the drains on the lower oil pan rails of the block. I think it is a 1942 -1946ish block. Maybe this engine has a rear main seal? Aren't there more potential leak points in the bell housing area such as the oil pump and the aluminum rear main seal holders? JayChicago 01-03-2026 @ 10:38 AM reply profile send p.m. Senior Posts: 558 Joined: Jan 2016 Re 5 quarts capacity 5 quarts when new. When I drain oil from full on the dip stick (have verified dipstick is the correct one), only 4 to 4-1/4 quarts comes out. Can only get that much back in. Engine has 52,000 miles, never been rebuilt as far as I can tell. I assume there is 3/4 quart of sludge build-up in the pan and engine. gwistrup 01-05-2026 @ 3:06 PM reply profile send p.m. Member Posts: 41 Joined: Dec 2022 I consulted the article on how to identify your flat head V8 from the Fordbarn and I have positively identified the engine in my Tudor as a 1941-42 V8. It has the raised intake, it passes the pencil test, the exhaust ports are relatively flat, the coolant drains are angled, and there are no core plugs in the oil pan rails. The cylinder heads have "81T" cast on them. I believe this engine has a rope seal with the aluminum seal holders. Therefore, can I replace the rear main seal to stop the leak? Who makes the best seal kit? I assume engine removal would be the preferred method to fix this. carcrazy 01-05-2026 @ 3:50 PM reply profile send p.m. Senior Posts: 1987 Joined: Oct 2009 If you are sure you have a Flathead that originally came with a rope seal for the rear main bearing, you can simply purchase the Rear Main Rope Seal Kit from Dennis Carpenter under Part Number 91A-6347-ST for $34.95. He currently has this item in stock. The best way to accomplish this task is to take the engine out of the car and place it upside down on an engine stand. Get back with us later if you find that your engine has the earier type of labyrinth seal in which case installing the rope seal will require much more work. In addition to purchasing the lower and upper rope seal holders which fit into the rear main bearing cap and engine block, you will have to take the crankshaft to a machine shop to have rear slinger removed. kubes40 01-05-2026 @ 4:19 PM reply profile send p.m. Senior Posts: 3580 Joined: Oct 2009 Jay, I'd recently pulled the pan off of my '38 Tudor, original engine, 32,000 miles, great running. There was at least 3/4" of what appeared to be oil "paste" at the bottom of the pan. In my opinion, the engine is designed to run on five quarts regardless of the gunk in the pan. Oil not only lubricates, it cools. As an example: So, if a guy only fills it up to the dipstick and has a ton of cr-- in the pan, takes three quarts to get to dipstick "correct" you think that's a good idea? That cr-- in the pan isn't doing anything but laying there. Never witnessed a manual that called out for five quarts "new" and less when "used". Mike "Kube" Kubarth This message was edited by kubes40 on 1-5-26 @ 4:20 PM

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