Rear Mainshaft Seal

panhead_pete

panhead_pete

Senior Member
Hi all


Need some guidance please. Noticed today two things of concern with my 31 A Coupe. Its got new oil.



1) Oil dripping somewhat profusely from the (drain?) hole at the bottom of the bellhousing. Its my 1st A but not my 1st engine so Im guessing rear main seal??? .



2) Out of that same hole is a the long ends of a split pin. About 3/4"worth. Any ideas what that's off? Clutch is working fine.



So I guess Im pulling the engine or box to try and ascertain what is going on and if its a rear main seal what will be the best plan of attack? Motor our or box?



Thanks one and all.



On brighter news I got one step closer to getting it registered here in Japan, with it passing inspection. With 3 months of BS to get this far hopefully will have plates on it in 2 -3 weeks :)
 
Pete, the split pin is there for a reason, its purpose is to vibrate and keep the hole open. DO NOT REMOVE. They all leak oil from the rear main, its normal. Do not overfill oil, add 4 quarts only. No need in pulling motor, drive it.
 
Pete, There is no traditional seal for the rear main. There is a labyrinth which is a series of slingers that throw the oil into a catch groove and the oil drains back into the pan through a tube. All Model A's leak at the rear main to one degree or another. There is a school of thought that it keeps the ball at the end of the wishbone lubricated.

When the rear bearing becomes excessively worn the oil leakage at the rear will become excessive. Other things that can cause excessive oil leakage are the crankcase being over filled, the breather tube or cap being blocked, the flanges of the rear bearing cap not sealing, or something wrong with the little tube in the pan that drains back the oil. If the oil leakage gets excessive you need to check the clearance in the rear main bearing.
 
Thanks so much fellas. Quite the relief to learn about that pin and its role. Im kicking myself for not noticing it earlier as have spent quite a bit of time under the car sorting our wiring etc.



Also really appreciate the info about the rear seal or lack thereof. Its my 1st stock(ish) A and I have a LOT to learn but I do love it. Im wondering now if I did indeed over fill it a little when I serviced it. Hearing your comments @nkaminar is making me rest a little easier tonight but will go check breather tube etc. You would think after years of riding old HDs I'be ready for some oil on the deck :)



Thanks again!
 
Anything which increases air pressure inside crankcase will force oil out the rear main.

1. Breather cap slammed down so hard that tabs on cap are bent allowing cap to go down too far blocking airflow.

2. Anything stuffed into breather tube OR breather cap like a pot scrubber.

Recently there was a guy who had stuffed a chore boy into the breather cap.

Water vapor collects in chore boy and forms a white sticky substance. Sticky stuff dries out and blocks breather tube.

All of the oil was forced out the rear main and engine seized up.

He spent $4000 on new engine. Then he put the clogged breather tube on new engine and proceeded to force all of the oil out the rear main and seized that one up also.

Five quarts of oil will exit the rear main in about 70 miles of driving depending on how plugged up the breather is!

3. One of those accessory devices with flexible steel tube to direct fumes downward.

Many of these have tubes which are too small (1/2 to 2/3rds the diameter of breather tube) and increase air pressure in crankcase.
 
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Benson said:
Anything which increases air pressure inside crankcase will force oil out the rear main.

1. Breather cap slammed down so hard that tabs on cap are bent allowing cap to go down too far blocking airflow.

2. Anything stuffed into breather tube OR breather cap like a pot scrubber.

Recently there was a guy who had stuffed a chore boy into the breather cap.

Water vapor collects in chore boy and forms a white sticky substance. Sticky stuff dries out and blocks breather tube.

All of the oil was forced out the rear main and engine seized up.

He spent $4000 on new engine. Then he put the clogged breather tube on new engine and proceeded to force all of the oil out the rear main and seized that one up also.

Five quarts of oil will exit the rear main in about 70 miles of driving depending on how plugged up the breather is!

3. One if those accessory devices with flexible steel tube to direct fumes downward.

Many of these have tubes which are too small (1/2 to 2/3rds the diameter of breather tube) and increase air pressure in crankcase.
Click to expand...

Agree with all of this. Also be advised if it didn't leak it wouldn't be a Ford.
 
Keep the oil level closer to the "Fill" mark than the "Full" mark. Just like the radiator you must let the engine adjust the oil level to it's liking or the cycle will repeat over and over (of course, don't let it get below the "Fill" mark)
 
And yes, if it didn't leak at least a little than that would mean something was wrong. That rear main seal (which isn't a seal at all) takes a little different thinking than the type of seal you are used to. It will also leak some oil every time that you go uphill.
 
panhead_pete,
Having just gone conquered a massive oil leak in the rear main in my Model A, I can attest to the accuracy of the information by all of the respondents here. Thanks to their guidance, I was able to make what was a sizeable (and embarrassing) oil leak to just a few drops! Since I had NO shims left at the rear main cap, I had to sand off a few thousandths of the cap using a piece of thick flat glass and 180 grit sandpaper - but it worked! Hope that encourages you.
 
Keep the oil level closer to the "Fill" mark than the "Full" mark.
Click to expand...
This would be my normal. Ostensibly take 4 quarts (in the sump) but an additional quart is usually held by the "dipper tray" in operation. (Some dipper trays have "holes" made in the low spot by drilling or rust-thru.)

In operation MOST of the oil for the crankshaft moving parts is reservoir-ed in the dipper tray. As long as that is full, you've done about the best you can do for the major engine moving parts. The rest of the engine takes the sump as the source for oil (hence the oil pump) but this oil is introduced to the valve chamber which acts as its own "source tray" for the valve train.

The sump can be VERY low and still perform its function in supplying the oil pump.

So in my mind "running low" is acceptable.

Joe K
 
Here is my true story about a massive oil leak at the rear main. in the mid 1960's I went on a tour with some other Model A owners up the Big Sur coast from San Luis Obispo. One of the cars developed a massive oil leak and we dropped the pan to find the Babbett mostly gone out the rear bearing cap. As fortune would have it the owner found a leather sandal on the side of the road and cut the sole to fit the cap. He bolted it up and drove the 150 miles home, without the massive oil leak.
 
nkaminar said:
Here is my true story about a massive oil leak at the rear main. in the mid 1960's I went on a tour with some other Model A owners up the Big Sur coast from San Luis Obispo. One of the cars developed a massive oil leak and we dropped the pan to find the Babbett mostly gone out the rear bearing cap. As fortune would have it the owner found a leather sandal on the side of the road and cut the sole to fit the cap. He bolted it up and drove the 150 miles home, without the massive oil leak.
Click to expand...


Otherwise known as the "Grapes of Wrath" solution...


Joe K
 
Cheers all! So much great info and I really do appreciate all the help.



'28 RPU said:
Keep the oil level closer to the "Fill" mark than the "Full" mark. Just like the radiator you must let the engine adjust the oil level to it's liking or the cycle will repeat over and over (of course, don't let it get below the "Fill" mark)
Click to expand...


I think right there is my issue. I filled it to the 'full' mark, wondering at the time why it took more than 4 quarts. Thanks for explaining that!
 
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