When Does A D18 Low On Oil Become A Problem?

While doing my 4 speed swap, I really thought I checked to see if the hole in the Dana 18 for clutch linkage was a blind hole or not. Perhaps there ‘was’ a glob of sealant still in there. After a trip up and down the road, then out for an hour; I have a bunch of fresh 80-90 chassis undercoating.

This morning I pulled the drain plug and filled half a solo cup. I didn’t see anything alarming in the oil. Is it likely to have roasted my intermediate shaft and bearings? Should I fill and go, or disassemble and inspect?

Not one of my most proud moments…

 

If there isn't any glitter in the remaining oil and it's not making any funny noises (well, any more than it did when you started out on your trip), I'd run it.

 

As long as there is enough oil to reach the high side teeth it *should* be ok. The biggest concern I would have is of the intermediate needle bearings rubbing each other while dry.

Toss some oil in with a magnet and run it a little while then drain and look at the glitter.

I'll admit I've done worse. I flat towed mine on the interstate with a dry rear diff. Now it is always glitterfull, runs hot, and howls.
It's motivated me to go to 4.27 gears and ditch the overdrive with 5.38s. That should also reduce my rpm in the transfercase for a given speed.

 

It was 17 miles (half hour) each way for a total of 34 miles. Most of the ride was 45-55 mph, with one straightaway at 60-65 for no more than a few seconds.

 

Sounds like you ran it maybe half dry.
The splash should lube things plenty well enough.
Sounds to me like you was quick to notice it.
I think it will likely have little effect on anything.
Much like running your engine 2 quarts low for a few miles.
No real damage just that the oil gets hotter and gets dirty a whole lot faster.

 

I poured the oil into a clear soda bottle so I could shine a flashlight through it. Looks pretty clear with only trace particles. The oil does look darker than I would have expected for an hour’s ride. May have gotten hot.

 

It would not have been low for the entire trip. Not that hard to drop the pan for extra assurance.
Good that you do not have an overdrive. I use that hole to add a couple extra pumps of gear oil into.

 

As to when low oil becomes a problem.

About 50 years ago I was driving my uncle's old Dodge pickup for a 50 mile trip to pick up some lumber in town. When we got to the where we were to turn into the lumber yard I could not down shift, nor could I even get it into neutral. I had to push in the clutch and coast to the side of the road and shut off the engine. We noticed a strong smell of hot gear oil, and burnt rubber. Crawled under and saw smoke coming out of the tail shaft which was hot enough to be glowing red, the seal was the source of the burnt rubber smell.

 

Or like when I blew the pinion right out of the rear diff on my Volvo 240. It was red-hot, lying on the street. Had been "making a noise" for weeks though.