Dripping rear crank seal

[Cadillac Joe]

I am in a position to purchase a very nice 1966 Sedan deVille and would like some sound advice and opinions on a leak from the rear crank seal. The car is very well maintained, and not driven so much in recent years which may be the culprit, but has oil buildup coming from the rear bottom of the motor and the bottom of the transmission cover. The problem was addressed 8 years ago with a rear crank seal. I hear from both the cars mechanic and other Cadillac sources that this is common. The amount of wet oil seemed to be alot, ie, several drips, and such, mostly in the area of the transmission bottom. Motor oil though. The ropelike seal supposedly tightens when the car is used more regularly. Could it be something else, and either way, is this normal and a major problem. The motor runs very well. Some 15 plus miles later at speeds up to 90 mph and no blue smoke, the car is strong. I would appreciate any information and ideas  before I leave the state. Thanks.

[Bruce Reynolds # 18992]

Gday Joe,

The crankshaft seal problems have been the bane of the Auto Insustry and Mechanics since pressure lubrication was invented.

The problem is that at the rear main bearing, the oil being pumped to it is under high pressure, and when it squirts out, after doing its job of lubricating the bearing, it is thrown directly at the Oil slinger which is protecting the Seal.

These Oil Seals have a lot to deal with, and if the oil drain passage is not large enough, or partially blocked by sludge and the like, then the only way out is the oil seal.   An engine that isnt used much runs the risk of causing the buildup of sludge.   Whereas a constant-running, maintained engine will have less sludge.

The Rope Seals are doing a good job, but only if they are installed correctly, and that means that they are not too tight, or too loose.  The ends seal tightly and both seals are replaced at the same time.

To do the job correctly, the engine has to be removed so that the crankshaft can be removed, and then the top seal half fitted in with the correct tool.   But, the fitting can be done without the mandrel tool, when taking care.

Another killer of the seals is excessive clearances on the Main Bearings, allowing the crank to flop around.   No seal will work properly then.

Another problem with oil leakage is pressure building up in the crankcase due to Piston Ring Blow-by.   But, your car should have a Positive Crankcase Ventilation System to relieve any pressure buildup.   That could be partially blocked.

Before pulling the engine down, I would be recommending a couple of Compression Checks, an initial one, then a Wet one.   That is, squirting asmall amount of oil down the cylinders to create a temporary sealing of the piston rings.   If there is a remarkable increase in the readings, it indicates that the rings are suspect.

Sorry I cant be more helpful.

Bruce,
The Tassie Devil(le),
60 CDV

[Roger A. Zimmermann #21015]

The rear seal is not a rope on these vehicles, but a rubber lip. It can be replaced with the engine in place. The oil pan has to be removed as well as the oil pump and rear cap. The shop manual has a good description how to do it. Usually these seals are more tight as the old rope system, when correctly installed.

[denise 20352]

  If you suspect worn main bearings, a hot idle oil pressure check might be indicated as well.  If it has just a warning light, you know nothing about the wear in the engine.  Usually if an engine cant hold 15-20 psi at warm idle, I start dreading having to pull it out and overhaul it.  Even though that is within the manufacturors specs, which are usually something like 1 psi per 1000 rpm for the late 60s and 70s, you know it has some wear in there.  I had a knocking 425 with the crankshaft so worn out that I could almost fit the next size of bearings in there, and it still made 5 psi or so at idle most of the time, and 15-20 when cruising.

   Something to think about when youre pre-buying.

-denise

[denise 20352]

  I dont know the 66, but I remember reading that some engines might come equipped with either the rope or the neoprene seal, and that the neoprene seals are sometimes made to replace the ropes.  Ive never tried to replace a rope seal with the engine in the car, that I can remember, but I have done the neoprene seals.  I use a small punch, and a piece of brass rod, if I have to go in there further, to drive the top part of the seal around until I can grab it.

   A word of caution, though.  Ive rolled the bearings out and replaced them with the engine in the car was well, but, as with any time you have a cap off, be careful not to peck a crankshaft journal with a tool, because even a tiny burr will damage a bearing.  I learned that the hard way one time, before someone told me to put long pieces of fuel hose on my rod bolts before I knocked pistons in.

   Sometimes the directions are a little hard to understand when they talk about putting a little RTV sealant around the cap, but not on the seal itself.  The main thing is that you dont want any of it to seep into the seal when you tighten the cap, so use it very sparingly, and far away from the seal.

   And another thing about RTV, while Im rattling on.  I replaced a rear main seal one time only to find a massive oil leak there afterward, but when I sprayed it down with cleaner and looked carefully, it turned out to be an oil pan gasket that didnt seal, right in the center of the back part.  Something that I learned about gasket sealing is...look at how difficult an old gasket is to remove, when no sealant is used.  If it is that difficult to get off, then you know that it must have made a really nice seal when it was on there.  That is why I only use RTV in corners, and only tiny drops.  I never coat gaskets with any sort of sealant, unless the instructions say to.  Even putting a little oil on a gasket to make it easier to remove later on can keep it from sealing.

   I hope you enjoy the car, if you end up buying it.

-denise