Rusted leaking rear differential cover

I'm in the middle of my repair. I'll follow up in a couple days with pix. Meanwhile, some observations so far. I believe [empty_lord nailed it]. The geometry of the cover is such that a crevice is formed between the bottom edge of the radiused cover where it meets the flat vertical housing. My leak originated there. No perforations above the lip. I'm convinced that any trapped moisture collecting in that crevice initiates corrosion and eventual leaking. A cover welded around the outside (stock) leaves that crevice inside. Root cause.

Thanks (again) to [NUDRAT for sharing the axle vent issue]. In my case thinner hot oil from use and internal pressure from clogged vent increased the leak rate. I got as far as an exploratory procedure in my GF's garage, then paused. I waited 'til I could book time at a buddy's garage to completely remove the axle from the truck. That dovetailed with other brakes & suspension issues. Since unclogging the vent and replacing nasty stank fluid I've recorded cover temps from 125 to 180F in recent weeks.

I started with [Jeffersonjohn's bolt-on replacement]. I prefer how forming a gasket can fill the crevice on bottom. No crevice, no leak initiation there. My stock cover may've been 14 gauge originally; compared to about 11 gauge on the Dorman replacement; considerably thicker. So, although I could've easily welded on a replacement, I like bolting better. But my version took some twists. In short, mods to the cover for a friendlier fill port and way to check fluid level better. Stay tuned...

 

Nice. That Jeffersonjohn method looks solid and I’d go that route if in the same boat. Look forward to some pics!

 

Interesting observation. I've always assumed the rust was coming exclusively from the exterior (which wouldn't be surprising given that it's exposed to some pretty harsh conditions). But you're saying you saw evidence of moisture accumulation on the inside in that crevice?

 

Good question.



Below the fluid level there's clearly more protection; presumably oil protection. The actual crevice was destroyed removing the old cover, unfortunately. Mine was solid above the crevice. Not even close to perforation.

 

Followup time. The old cover was cut off with a 4.5" disk. The housing was ground not perfect but flat enough.



I tried minimizing sparks and dust getting inside. Some did anyway so it'll get attention early and often going forward. (shrug)

The replacement cover was modified. The stock fill port was drilled out at roughly 45-deg angle using a simple guide.



The new hole was elliptical. A threaded coupler was welded in for an up-angle port. Not just for easier filling. It's alignment provides a clear path to the bottom of the housing.



The second port was added for a site glass. Eight 1/4-20 holes were made around the lip/rim to secure the new cover. The housing was wire wheeled. Both housing and cover were primed with Rustoleum Rust Reformer then painted with Rustoleum Rubberized Undercoating.



Scope creep included new brake lines from the T block to both sides; the old ones twisted off during removal. Rear brakes were completely replaced: drums, shoes, wheel cylinders, parking brake bell cranks. Saving the old U bolts wasn't worth it; they were cut off and replaced.

 

Nice work!


Where can I get one of those site ports to fit the OEM Plug?

 

LOL

 

Thanks my man! You can get them at McMaster-Carr or this one other place.

 

Cool bud. You are awesome.

 

Professional Hand Model, seriously, the oil eye I chose was 3/4" pipe thread (

Sydien 2Pcs G3/4 (Dia 26.2mm) DN20 Thread Air Compressor Fittings Brass Oil Level Gauge Sight Glass for Belt Driven Air Compressor

Amazon). Some other might fit the stock fill plug thread. But it'd be a tiny window. And one would have to somehow overfill the axle. Possibly through the breather? Creative. Do share if you make it happen.

 

In my research, there are 360° View Site Plugs. Now I’ll be able to monitor the health of the entire diff.

Where are my Crazy Pills?

 

Is that bung on the OEM diff cover metric, or pipe thread? The one @KamperBob used was a NON-OEM.

You may have to get crafty like KB did above. Great work!

 

A sight tube would probably work better than just replacing the plug but adds an extra leak potential.

 

I’m almost sure its BPPT. Yeah. Creative and I like it. Probably won’t do it unless ‘in there’ for something major which I never hope to be.

 

Thanks, Noah. Yes, 3/4" pipe thread. The larger, up angled hole is not only more funnel friendly. Having a clear path to the bottom of the housing means I can swab it with a telescoping magnet. Noninvasively! The drain plug has a magnet but one has to dump the oil to check/clean it. (Unless the truck is upside down of course. LOL)

 

Yes, I saw all that. Your work looks great. Fantastic upgrades "while in there" also.

The noninvasive pap smear is a wonderful idea.

 

This is the one guys! Sight Glass with Oil Monitoring Draw Off Capabilities to send off to the lab. I’m sure we could somehow magnetize the Butterfly Screw for @KamperBob Metal Catching Analysis.

 

I know I was pedantic but some might appreciate that.

 

That's not crazy, dude. It's insane! Love it.

 

Yeah. You’ve inspired it.

 

You're welcome.

 

Make sure it's not just a failing weld. I had two dealerships look my 2006 Tundra Double Cab over and both told me the cover was failing but they could only replace the whole axle since they don't do any welding at dealerships.

I got a buddy who is an expert welder to cut off the old cover and weld on a new Barnes 4WD cover. (He was impressed by the thickness of the Barnes cover by the way). We didn't inspect the original differential cover to make sure the "experts" at the dealerships were correct. We just had a local mechanic drain it and pull out the guts. Then we cut off the cover.

Once the cover was off, my buddy called me over to show me that the original cover was just fine all along. No perforations. The factory weld had failed. He traced out a small little line on the housing's surface showing me where the oil was leaking. "If I had known this, I could have repaired it in 15 minutes. We wouldn't even have had to bring it into this shop. We could have drained it and I could have simply ground out the failing section and re-welded it. We wouldn't have needed to pull the gearing because that little bit of welding wouldn't have heated it up at all".

The story gets sadder because shortly after having everything put back together, I started hearing a faint whine from the differential. The mechanic was confident it must be road noise from a wearing tire or something else but not the differential. Turns out the shop didn't have the tools needed to do that job and they shouldn't have taken it on. One mechanic there retired, the other left during pandemic. The owners won't do anything to help me out other than offer to have their new guy (who was honest enough to explain why he couldn't work on my now failing differential), bolt on a salvage axle for just a little less than Toyota wants to put on a remanufactured one.

Now Toyota is likely to get a nice payday because their guys never actually inspected the leaking cover like they said they did. I now believe they eyeballed it and assumed they knew the problem and solution. And yes, I bear responsibility for trusting and not verifying.

Hence this precautionary post to all others. Power wash the daylights out of your cover and then climb under there with a wire brush, clean it up, and look at the seam. These covers are not that fragile. I live in rust belt city. My truck was 14 years old at the time. The cover was solid. One small portion of the weld was bad and my pipe fitter buddy would have fixed it for a pack of homebrew.

 

If the axle is now failing all it should need is old 3rd member to be unbolted, everything inside cleaned out to make sure no metal fragments, and a new 3rd member put in. Of course you must pull axles out slightly to do this. Unless the noise is coming from a wheel bearing or similar. If it's the differential itself just swap it with a known good unit.

 

Okay well here's your chance for me to learn. I have only minor theoretical knowledge of differentials. I was skeptical when I saw the guts of my axel lying on their grubby shop floor but decided to stay quiet and trust the guys that were helping me out. That acted like they had done this before and they were letting us use their lift to weld the new cover on. The new guy at this shop told me he doesn't have a special tool required to put it back together after pulling it apart and repairing it but that a transmission shop would. He would be able to swap out the whole axle with a new/used one though.

It's definitely a whine coming from the differential. Louder under load but also there slightly when coasting. The transmission shop he recommended has not returned my call and the best mechanic shop in the city nearby is NOT interested in taking it on. I watched a two hour university class on YouTube with a professor who went through quite a procedure using shims to make sure the gears meshed perfectly in a particular differential housing. I was under the impression when finished that each set up was unique.

The shop that damaged my good differential wants to replace the whole thing with a scrap unit for 3600 dollars. For 1000 dollars more Toyota would replace it with a remanufactured unit (conceivably with a warranty). That was their fix for the differential cover. I have not asked them to look at it now that I had it "fixed". Any thoughts you have would be appreciated. Especially before going back to the dealership.

 

If they just pull out the old 3rd member (differential gear assembly) they don't have to take any of the differential components apart. They just need a known good 3rd member to put in place that is already assembled. If it's already assembled you just remove the driveshaft then you need to pull both axles out at least slightly. Then unbolt old 3rd member and remove then install new and reverse all other tasks.
Many people like to do wheel bearings, axle seals, and backing plates when pulling the axles but it is not a necessity if you do not want to spend the money.

 

If you and your buddy can pull the axles and 3rd member, I would do that. Just get another one to throw in. It'd be the cheapest option and can be done in a garage/driveway.

Your location may help. If you were near the Sacramento, CA area I could probably sell you my spare once I pull it. (If 2wd OR it matches your gearing if 4x4. Has 4.10's and OEM LSD.)

East coast gear has a swap out program, where you buy an assembled 3rd member and provide yours as a core. West coast diff (differentials.com) may also be able to do the same (they're local to me and who I buy parts from).

 

Wow you guys make this sound like replacing a light switch. (A very heavy light switch) I wonder why I'm getting all the drama from the shops around here? I wish I had more time (and talent) to mess with it this year, but I already have so many irons in the fire. Probably can't drive it to Sacramento from Michigan to watch you do it. But you have inspired me to look into getting a complete 3rd member shipped here and paying someone with the tools to do it right. You see after we replaced the differential cover, I was motivated to have the rust on the frame dealt with (my 06' fell outside the recall). After needle scaling, painting, cutting and welding, I can't say goodbye to her yet. Thanks. This might take a while to solve, but I'll keep you posted.

 

My truck goes in tomorrow to a different shop from the one that messed it up. I drove it on a short 120 mile round trip and by the time I got back I was hearing the noise even when coasting. My new guy ordered a remanufactured 3rd member from Jasper. It comes with a three year 100k mile warranty, parts AND labor for 3000 dollars. That beats Toyota and the it beats the price the other shop quoted for a scrapped rear axle.

We'll see how things go. Hope to get it back in a few days, maybe even with a report on how it got goobered up to begin with.