Hi all,

I have a Dana 44 rear axle, stock for the 1956 F100. It's running a 3.73:1 ratio if that helps. I recently installed it as a swap for the original 4.27:1 axle. Part-for-part replacement.

The problem is that it continually blows out its lubricant from the breather port on the top of the brake pipe banjo on the top of the driver's side of the axle.

My truck seems destined to leave trails of lubricant wherever it goes, from one source or another. Since stopping the oil pump major leak, the rear axle has now taken over the job. If the breather was blocked, surely nothing would get out, so a pressure build-up seems unlikely. So what else could cause it? I can't over-fill it because the fill plug location (in the lower half of the differential cover plate) kinda prevents that in the first place!

I'm stumped at the moment, any advice would be gratefully received.

I'd rather not have to remove the axle so soon after putting it in, but I have an ominous feeling that might be necessary.

 

Make sure that you have not overfilled the axle is the perhaps to obvious first step (sorry, but we never know). Then make sure that you have the right lubricant depending upon the differential type (Trak Lok, open, Detroit Locker, etc.). And finally do you have a hose with a check valve on breather tube nipple? It should be about a foot long with the check valve on the end mounted as high as possible allowing slack for axle movement. Now that check valve is to keep water from coming into to axle not preventing overflow, but it is important to have it. If the axle is warm and you go through water the air inside the axle contracts with sudden cooling and sucks air/water in through the breather. The check valve is meant to prevent that. A simple Google search will reveal lots of sources for these check valves.

The hose should absorb any overflow providing everything else is OK.

 

Where is the differential leaking from?

 

The only way I can see oil coming out the breather is if oil is trapped in the axle tube. Many years ago there was a thread about making a half-moon shape that fit the tube ID, attaching it to a 3' long piece of all-thread, and using it to scrape the crap out of the tubes. I did it to my D44 and was surprised at how much junk came out. You obviously have to remove the axle shafts to do it, and the brakes/backing plate (as a unit).

If you want to search for it, I think it was MTFlat who suggested it.

 

Just install a sintered bronze filter on the end of a long hose and be done with it.

 

I think Ross is on the right track. There should not be that much oil near the breather outlet.

 

I have sintered bronze filters on my excavator, bulldozer, and skid steer. Factory installed. No problems at all.

 

Thanks for your responses, guys.

Having investigated a bit more, the stuff coming out of the breather looks like it's an emulsion rather than pure oil.

So a good clean out and refill is this weekend's job, by the look of it!

By the way, the breather button is only sat on the top of the brake pipe banjo, not remotely mounted at the end of a pipe. The banjo is on the top of the driver's side of the axle, about 6 inches from the diff casing. I transferred it from the original axle which was on the truck onto the 'new' one when I swapped them over a few weeks ago.

To be honest, I was clearly sloppy with that job. I should have stripped the 'new' axle down first, before fitting it. Lesson learned.

 

Looks like a good plan.

 

I'm waiting on the arrival of a new diff casing gasket. In the meantime I have fitted a length of garden hose over the base of the breather, jubillee clipped it tight on, and looped the other end over the chassis crossmember by the nearby shock top mount. That can act as a sort of header tank for a while. So far so good.

Hopefully that will hold until the off-season when I already have an engine rebuid/refurb planned. I can do the axle at the same time while Fido is laid up.

Thanks for the advice guys - much appreciated.