Leaking Differential…Sept. 2011

I spotted a spot of oil under my RV while in Alaska in August 2011. I don’t remember seeing it before that. There was a bunch of road crud around the axle tube to differential junction on the passengers side that was soaked with oil. That’s the side opposite where I had the broken spindle the year before. I topped it off with 80W90 gear lube and didn’t think much about it until I hit Spokane where a mechanic was looking at my parking brake issue and mentioned it. A couple days later, I check fluid level and it was down so I topped it off again, and cleaned the upper plug and breather. The breather did seem to allow me to blow a little air though it (or it got opened when I cleaned it). A differential has zero pressure so with the breather pinhole open the oil shouldn’t be pumped out of the leaking area too fast, I hoped. A plugged breather can cause an atmospheric caused positive pressure in the differential which could cause more oil to leak out faster.

Then, a few days after that, I spotted a little puddle under that part of the rig when I stopped for grocery’s. Not good. I was on my way to Arlington and I was only 100 miles from there so I just crossed my fingers and hoped it wouldn’t run dry.

Arriving in Arlington, I ask around and find a mobile tech/mechanic. For a few days, we both tried to come up with a solution to my differential dilemma, using our brains. I spent most of my time on-line and I’ve found my differential for $1400 used. Shipping would probably be $400 or so. Then if the used one is bad, shipping back. A new hub to hub axle assembly is $5900, before shipping. This style differential uses a ‘sweated’ on axle tube and it’s leaking around that, so it’s not really repairable. Or there is a crack in the differential case. Don’t know yet. Anyway, the mechanic is willing to do the job if I decide to replace the assembly, but doesn’t want to help if I just clean it and slather on RTV. Which is what I think I should do. We’ll see after I clean and inspect it.

Eventually, I crawled under the rig and using a putty knife cleaned off the leaking section of the axle. All that caked on crud came off easily, then I scrubbed it with a brass wire brush. Checked for cracks but didn’t find any. Liberally sprayed it with brake cleaner and it all looked great. No dripping gear oil to contend with. Not sure if that means I’m almost out of gear oil in the differential, or that I cleaned up the wrong place (don’t think that’s possible, because I could see the seep pattern on the road grime in that area), or if the temperature is playing a role in sealing it up for me! If it’s just a case of barometric pressure and temperature keeping it from dripping, I lucked out, because I didn’t have to contend with oil during the clean up or application of RTV. This morning, I ran a bead of RTV Red all around the seam and will give it another two coats today. RTV tube says it only takes an hour to skin over and I’ve given it two…allowing for the lower temperature outside this morning…60°F. Now it’s 67°F so I’m off to give it another coat of RTV. Fingers crossed that this will work.

OK, 2nd coat of RTV is on. 1st coat wasn’t as tacky as I’d hoped, so I’m going to forgo the 3rd coat until it’s cured, 24 hours according to the instructions.

Update: (Oct. 18th, 2011) I didn’t see much need to add a third coat of RTV Red and today I took it out on the road for a quick test. Checked it first and found the RTV nice and dry and no evidence of any seeping oil. Topped off the gear oil and rechecked it for any leaks before getting on the road. Drove around 20 odd miles and after getting back to the RV park and checking it again for any leaks, found nothing. Looks like it’s going to work! Wasn’t looking forward to pouring another $4,000 into this rig…which I plan on selling next year.

Update: (Feb. 10, 2012) I checked it for leaks a few times on the road, but there was never any drips or seeping I could see. So now I’m down in Mexico and when my mechanic was under there fixing the parking brake problem, he asked me if I knew that the differential was cracked. I said no, and could it be welded? Sure, he says. So now I’m waiting for him to arrange the work on that. Further update: He never found anyone to do the welding.

Update: (Nov. 2015) The RTV Red patch I did is still doing the job of ‘slowing’ the leak and I’ve not had to really worry about this leak much at all. Every 6 months or so I’ll crawl under (or pay someone to do it for me) and top off the differential.