Running gear flush

[rcsteuer]

I have a '49 CJ3A that I rebuilt (complete) and put on the road in April. I want to drain and flush the running gear but not sure what to se for flushing.  the transmission has yellow parts, and I don't want them damaged.

Any suggestions?

[Rus Curtis]

Do you have a Service Manual (SM)?  It gives you guidance on fluid, interval and the "how-to" steps, Sec B, Fig 14 and para B-15.  It doesn't really dictate flushing but drain and refill.  Is there indication the gears need flushing?

I've read of others using Kerosene, diesel and even auto transmission fluid.  I'm not sure I'd use any of these if there's been no damage or you don't drain out a lot of water.  IF there's a lot of water that comes out (oil floats) then your gears may have some rust damage.

So, inspect the fluid as it comes out.  Post what you see and maybe you can save some money/time.

[rcsteuer]

Thanks for the response. More of a precaution than anything.  I rebuilt both the transmission and transfer case about a year ago.  The fluid change is much earlier than suggested but want to do a flush just in case there was anything left in them that I didn't get cleaned out. Dumped the fluid and, although it doesn't look contaminated, it's cheap enough to run something through it to be on the safe side.
I was considering diesel but need to check to see if it'll harm the non-ferrous metals in the tranny.

Thanks again for the reply.

[Rus Curtis]

Not to my knowledge.  The danger to the yellow metal comes from the additives in the hypoid rated gear oils, i.e. GL-4, 5, etc.  Those additives deposit and stick to the surfaces to ward off shearing wear.  With the softer metals, the additives stick and actually remove some of the surface of the metal.  The GL-4 additive is low enough to not damage the softer metals.

This is all based on what I've read.

The advice on using diesel came from the CJ2A Forum.  There they suggested not driving with it in the gear boxes.  Instead, they recommended to let it idle in gear for a for a short period and drain.  Their suggestion was to have the transfer in neutral and wheels chocked.  If I were doing this, I'd flush both boxes by having the jeep up on axle stands so the wheels could spin. 

Here's the link:

https://www.thecj2apage.com/forums/water-found-in-tranny-and-transfer-case_topic38077.html?KW=flushing+gears

scroll down to SE Kansas post @ 10:02pm

Sounds like you know the history of your gears and probably won't have anything in your gear oil.  If you were curious, you could run a magnet through it or strain it through a filter to see if you catch anything coming out when draining.

[rcsteuer]

Yep, when I first rebuilt both, I was looking for GL-1, which is basically mineral oil, which would have been fine for the transmission, but digging a bit further into this, it became apparent the transfer case should have GL-4, so that's what is in it.  GL-5 contains sulfur which will tear the brass in the transmission apart. The GL-5 is good for the differentials.

The engine is back at the rebuilders because the rear main has leaked since day one.  Since the vehicle is garage bound, I thought I'd run something light through it, like 10W motor oil just to drag anything that might have been remnants of the rebuild. Actually, I expect there's nothing there but thought it would be a good precautionary step.