'68 289 rear main seal

I just rebuilt my 4.7L 289 out of a 1968 mustang and initial start/warm-up went smooth except my rear main seal doesn’t seem to be holding. I don’t own a engine or car lift and i was wondering is the a feasible way to replace the seal without pulling the motor again?

The rear main seal is a split type seal so you’'ll need a Sneaky Pete to replace it. http://www.sjdiscounttools.com/kdt492.html

Remove the oil pan. Remove the rear main bearing cap. Use the Sneaky Pete tool to remove the upper part of the seal. Use the Sneaky Pete tool to install the upper part of the seal. Sometimes rotating the crankshaft while removing/installing the upper part of the seal makes the job a lot easier.


You will probably have to lift the engine out of the car somewhat to get the oil pan off, so you may need a shop crane to do this job. Before you do this, though, you may want to perform a leakdown test to make sure you (or whoever built the engine) didn’t botch the rebuild. I have seen engines that were rebuilt poorly or were not broken in properly produce so much crankcase pressure they would systematically blow out seals and find any way it could to purge the oil out of the engine. I once saw a Chevy 350 that was flogged from day one after a rebuild that would puke oil through the oil pan gasket and through the breathers in the valve covers due to blow-by. The owner refused to believe that it was blow-by caused by abusing the engine from day one and claimed the oil puking was due to a high-volume oil pump he installed during the rebuild. He stopped 80% of the original leakage with a Perma-Dry oil pan gasket and a crazy-looking homemade breather setup that raised the breathers higher than the carburetor (and this engine had a tunnel ram on it!)

I would recommend pulling the engine. That seal is very difficult to position correctly when working on the bench and doubly so from under the car.

If the rear main seal was the rope type, it may stop leaking on its own in a few days. It needs to get saturated first and then seated, just like rings.

I think the Sneaky Pete tool that Tester referred to can also be used to replace a rope type seal.

I am fairly certain that the 289 used a split rubber seal that required some very close attention to its lay up and proper trimming to get the ends to mate up with enough pressure to seal at the joint. The sealing lip must be pre-lubed while the mating ends must be trimmed nearly perfectly square and coated with an adhesive. If cut too short the seal would leak at the joint. If not cut short enough the seal would push out into the main bearing mating joint and prevent the cap from fully seating which would result in a massive oil leak.

You could always pull the tranny and get to it?

I think Rod Knox is correct about the rubber seal and the way it’s fitted but I know Ford did use rope seals up until whenever. (Vaguely remember doing a few rope seals on 70s era Ford pickups with the 351 but the memory is too fuzzy as it’s ancient history.
You can’t access the rear main seal with the transmission out. The pan has to come off and the rear main bearing cap removed.

I’ve generally removed the rear cap and loosened all of the other main cap bolts. This can allow the crankshaft to drop a hundreth or so of an inch and make removing and installing the upper seal half a little easier.

Really OK4450…is that true…sure seems odd doesnt it? Im not doubting you just definitely confused there…

Rope seals? Jesus you mean like in a stuffing box on a boat prop shaft? LOL… man the stuff they would do back in the day…and wouldnt you know it…IT WORKED TOO…

Roper seals were very common through the 60s. It was much easier to install than split rubber.

No kidding? Wow… Eventhough I know how to work on the older engines I guess I really dont see many anymore. Funny how they went about things in the early days (early for me anywhay)… I somehow got to grow up at a time when I encountered both the pre-smog era engines and the Dark days of Smog…all the way to present day… I got a pretty good education that way…some guys still to this day say that they cant work on todays vehicles…I think thats a cop out tho as you should be able to draw many correlations

Rope seals were very common through the 60’s, rubber seals rare. You have to remember that most of the engines used throughout the 60’s have designs dating back to the late 40’s and early to mid 50’s. The only new V-8 engines that I recall being designed in the 60’s was the small block Ford (221, 260, 289, 302, 351W) and the 'new" A block Chrysler.

Back then, I remember seeing any rubber rear main seals, though I recall an incident where Ford had to recall some engines because the spiral grooves cut into the crankshaft to funnel oil back to the engine were cut in the wrong direction, causing oil to be pumped out of the engine through the rear main seal. I think it was mentioned in the recall that the seals were rubber and it was a new design.

Did you “rebuild” this engine without replacing the seal or was the seal installation somehow not done correctly…Testers method works if you can get the oil pan off with the engine in place…

Leon hasn’t responded yet, but I still suspect that the seal just needed to swell up to seal and the problem went away on its own.

If you don’t grease that seal when you install the crank, the dry crankshaft will destroy the new seal in short order…

The word rebuild can mean different things too. If rebuilt is defined as reusing a crankshaft with a badly scored and pitted seal surface then it’s going to leak oil no matter what unless a Speedi-Sleeve is used.

Some may remember that getting those old petrified hard as stone rope seals out could be a real bear too. :slight_smile: