Rear seal or pan gasket leak
 

I got the truck up on jack stands so I can find this leak. Started the truck and let it run for about ten minutes and no leak. As soon as I put the truck in gear, it started to leak. I’m guessing it’s the rear main seal, just wanted some other opinions.

And, why would it leak only when in gear?

https://youtu.be/LN0Hd24RXR4

Re: Rear seal or pan gasket leak
 

If it's leaking only in gear, that leads me to believe it's the transmission. As the gears are turning in the trans, the gear oil is moving throughout. If it's coming from the front of the trans, the culprit could be input shaft seal or shifter plate seal. I'm not sure if there's another place up front where it could leak from since I haven't worked on any truck 4 speeds

Re: Rear seal or pan gasket leak
 

I thought it would be the trans too. However, it’s dripping from the sheet metal piece directly below the crankshaft rear main.
I can see part of the trans input shaft and it does not look like anything is leaking there. How could the trans oil travel from the transmission to the crankshaft area?

Re: Rear seal or pan gasket leak
 

And, it continued to leak after taking it out of gear.

Re: Rear seal or pan gasket leak
 

There is a fair difference in smell and feel between engine oil and gear oil. Give it the sniff test. Between that and the trans oil being thicker (I hope), you should be able to determine which it is.

When you put it back together, did you use a rope rear main seal or neoprene (if that was an available option the gasket set)?

Re: Rear seal or pan gasket leak
 

Ok, I think I got it - valve cover gasket. I’ll be a son of a gun!

I removed the flat plate that covers the flywheel access and followed the stream up. I was thinking it was the rear main since the oil was dripping from the center of the cover plate, directly below the rear main. Once the cover was removed, it still dropped but not from the rear main. The oil trickled down the block and off to the side, then back someplace to the center.
Should have seen this sooner. I did think earlier that it might be the valve cover, I just didn’t think it was that simple. Saves me a trans removal or oil pan removal.

Re: Rear seal or pan gasket leak
 

Ha, that's great that was it. I always say about Chevy small block V/8 valve covers...." There's only two kinds of Chevy valve covers, those that leak and those that are gonna leak."

Re: Rear seal or pan gasket leak
 

Oil leaks used to be a lot of warranty work, back in the day. GM went to the RTV sealer for a reason. After I got out of the Navy, I worked as a mechanic. I used the best sealers we could get, because I didn't want the vehicle to come back for an oil leak. One of the guys called any kind of glue or sealer, "acka-pucky", and called me the "acka-pucky king". He also asked my about how much fun I was going to have scraping gaskets if the job came back. I told him that if it got fixed right, it wouldn't come back on me. :lol:

Re: Rear seal or pan gasket leak
 

Looks like I still have a leak.

I don’t think it’s the rear main seal, since there isn’t any oil around that area. It’s dripping from the trans mount, but not directly below the trans. Seems like it runs from the driver side of the trans mount down. This is going to be difficult to find.

Re: Rear seal or pan gasket leak
 

Have you tried leak detection dye?

Re: Rear seal or pan gasket leak
 

No. Didn’t think of that. Thanks.

Do they make dye for engine oil?

Re: Rear seal or pan gasket leak
 

Leak detection dye is made for and used in engine oil, transmission oil, gear oil, freon, gasoline, etc.

I have had great success with it - just make sure that all 'leaked' oil is gone and you start with clean dry surfaces. Upfront cleaning and prep time usually works best.

Re: Rear seal or pan gasket leak
 

It looks like you need a UV flashlight and glasses to see the leaks?

Re: Rear seal or pan gasket leak
 

that's the stuff!