A week ago yesterday I drove my Macho Power Wagon from my home in Ontario, Canada to my best other ever in Rochester, NY. 205 miles. Went to a couple car shows there and drove home today. This truck is a 79 MPW clone, 78 cab on an 83 chassis. It has a 77 block 440 with a rear main seal leak that I just can’t solve. So I stopped a couple times each way to check oil and add as needed. This is the first extended trip I’ve done with the truck and, aside from the oil leak, I am both pleased and excited by the way it performed. It rolled down I-90 at 70-75 like it was born to be there. Today was cloudy and not too hot so with the window, vent and sliding rear window open it was just very comfortable. Got a few thumbs up, honks, etc which just sweetened the ride. Just wish I could get the rms figured out.

 

definitley a nice truck, I have not yet cut my teeth on an old mopar engine, is that a typical modern style rear main or an older design? bent crank comes to mind, bad crank thrust bearing is another

 

Not sure what you mean by modern style or older design. When and where does the difference lie? It’s a two piece seal, the lower half sitting in a two bolt retainer, the upper half slides into a channel in the block.

 

The difference is the old design is a "rope" seal where the newer ones are rubber. It's called a rope seal because it looks like rope. Another issue can be the grooves in the crank surface. They where put there to help keep the oil from escaping when running with the rope seal. If you use a rubber seal they can cause it to leak. You need to have a look at what you have.

 

It was not a rope seal the first time I changed it. I don’t know what it was originally. I didn’t build the motor, it was in the truck when I bought it. Not sure about the grooves in the crank. I didn’t know about that and don’t recall seeing them when I changed the seal last winter but then I wasn’t looking for them either. My feeling is that the solution is to pull the crank and replace it. I’ve been fighting with this for two years and I’m tired of it.

 

If it was a two piece I would assume it was the rope style originally but years of redesign provided something better, in theory? I remember doing a rear main on a newer jeep, late 90s maybe even 2000's model must have still been an AMC design motor because it was still a 2 piece but as I recall correctly it was not a rope design specifically either.

I figured the term came from them literally using rope at one point. I did a reseal on an older Cat fork lift when I worked there. It was a gasoline or LPG powered motor and not built by cat directly, 4 cylinder, possibly GM? The rear main on that was literally two pieces of rope.

 

I’ve wondered about trying a rope seal because some have said that it solved the problem. But others have said that it didn’t.
Last winter the truck just sat in the shop. The oil was over the full mark and the floor slopes slightly. The oil level had to at least be up to the bottom of the crank because it would leak just sitting there and drain back into the bell housing. Every week I would wipe oil out of the bell housing and the engine had never ran.

 

I would expect it to have more give/flex then your typical seal, might be torn up easier by imperfections in the crank. Also might be more sensitive to what oil you use? Have you confirmed its not the oil pan?

 

If it’s the pan how could the oil get into the bell housing? It would have to flow upwards.

 

https://board.moparts.org/ubbthreads...1852151/1.html

here's someone else to has felt your struggles, lots of good theories in the thread, and links to other people struggles.

Looks like the 440 rear main is problem child for some

When was the engine built? by you? Line bore would also come to mind which I believe was mentioned here.

Is it in the bell housing just sitting or after driving? air current both from torque converter rotation and driving puts oil anywhere and everywhere