Packard Forum Index » Pre-War (1899-1942)

I have a pretty good rear main seal oil leak on my 37 "120". The engine was rebuilt a few years ago, I got it running last year, probably have 2-3 hours of run time on it. I was wondering if anyone has ever used any type of sealers such as "Blue Devil Rear Main Sealer" or any other product or advice?

I'm pretty sure the '37 120 has no rear main seal per se. There is a front seal. I doubt if any pour-in sealer will be effective. Oil can leak from the cam bearing plug or perhaps an oil line plug into the clutch housing. Leaking oil from the oil pan or valve chamber covers can often work its way back to the area around the clutch housing and mimic a rear main leak. The 120 rear main appears have an oil slinger running in a circular groove and a drain passage at the bottom of the groove that allows oil flung off the shaft by the slinger to drain back to the pan, and if the parts get clogged with sludge or gasket sealer, it can cause excess leakage. The crankshaft behind the slinger may have shallow threads designed to pump oil back toward the oil pan. It takes very little sludge or gasket sealer to foul these. Removing a valve chamber cover should reveal any serious sludging, and if it is present, using a quality detergent oil and driving the car on the road may improve the situation, but removing the oil pan and cleaning out sludge, if present, is the correct solution. Excess bearing and piston ring wear can also promote leakage. Over-filling the crankcase with oil can also cause leakage.

See my post on slingers on prior forum topic:packardinfo.com/xoops/html/modules/newbb ... 9453&post_id=284819#forumpost284819

I go through a rebuild story that sounds very similar to yours. If you suspect it is similar you will need to drop the oil pan and the clutch bell housing cover and possibly the rear main cap to inspect the oil slinger to verify.

Most modern rebuild shops have only seen rear main seal type configurations and never have experienced an oil slinger, so they often ram packing in there out of lack of knowledge...as stated by TxGoat, any blockage, sludge, packing, etc will exacerbate a leak at the slinger...cleanliness is next to Packard-ness.