Rear Main Seal Leak

in HUDSON Posts: 20
Hey HET,

I have a pretty significant oil leak on my '51 Hornet. It does not leak sitting or at idle, but when I am running down the road the oil is hitting the driveshaft and slinging all over the bottom of the car, so I assume it must be rear main seal. Any thoughts?
I am going to do some more checking, but if that is the case does anyone know of a readily available replacement? Is it a rope replacement or a modern rubber seal? 
Finally, if I am tearing into it that far, should i replace main/rod bearings or maybe even do a full rebuild?

Any thoughts and/or parts leads are greatly appreciated. 



  • Jon BJon B Administrator
    Posts: 6,445
    Hi, Jake, I'm no expert but first off:  are you sure it's motor oil and not coming from the transmission (or clutch, if you have a manual shift)?
  • charles4dcharles4d Expert Adviser
    edited May 17 Posts: 349
    Check the drain plug and your dipstick also you never know missing a little thing can be a big mess my two cents worth
  • Ken U-TxKen U-Tx Senior Contributor
    Posts: 3,227
    If it as a rear main bearing seal leak, it would be dripping out the gravel guard under the flywheel. If it is on the drive shaft behind the transmission, then it may be the rear main-shaft seal on the transmission. This seal is a typical oil seal that is one piece and pressed into the tail-shaft housing bore, after removing the driveshaft yoke.
  • Ken U-TxKen U-Tx Senior Contributor
    Posts: 3,227
    Is the oil rather thick and stinky like sulfur? If so ten that is gear oil from the tranny.

  • edited May 17 Posts: 20
    I know for sure its motor oil. It used 6 quarts to go on a 100 mile cruise up to a car show 2 weekends ago. I then looked under the car to find the oil everywhere from the back of the engine all the way to the bumper.

    I filled it back up with a synthetic blend (high mileage) which seemed to stay in much better (Only used like 1 pint on the way back) Either way pretty substantial loss

    I did do some updates to the dipstick, but i am uncertain if it is sealing all the way, it doesn't have a wiper seal or anything, i made a little grommet thing to seal it up better

    I also replaced the oil fill cap
  • onerare39onerare39 Expert Adviser, Moderator
    Posts: 916
    Perfect place to say this, WWFD... what would Frank do?

  • Geoff C., N.Z.Geoff C., N.Z. Senior Contributor
    Posts: 3,302
    You need to drop the flywheel cover and see exactly where the oil is coming from.  It could be the  sump gasket, or the seal, or the packing up the sides of the bearing cap.
    If you're stuck in a hole, stop digging.
  • Oldfarmer1947gmailcomOldfarmer1947gmailcom Expert Adviser
    Posts: 1,331
    There are also Welch plugs in the back of the block which are connected to oil passages
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