WTF! Rear diff rusted and leaking?!

175000 miles. Good shape. Runs strong. Hardly had to do any maintenance in last 80,000 miles. Just changed timing belt. Crawled under truck to inspect the other day and my rear diff was covered in oil on the backside. I popped the fill plug off and was only about a 1/4 q low so I topped it off. Wasn’t really sure where it could be leaking from. The whole front side was dry. I then started to inspect more and there was a lot of rust built up and am assuming it’s rotting out!!? I would think this would be a large hunk of metal that would be the last place to rot out. I have a 89 yota pickup that looks 100 times better with almost 50,000 miles mor plus 13 years. I don’t know what to do? The rear brake backer plates are rusting out as well.

 

Find another axle at a scrap yard and swap it in. This is why you should inspect everything under there with every oil change. How often do you change your engine oil, gear oil, transmission fluid, transfer case, and just do a general look over?

 

Interesting. But I'm from the old school.

 

I do my own oil changes ever fall. I leave Alaska for three months in the winter. My wife is the primary driver and puts about 3000 on in the summer. I look under there prob once a summer but never in depth. Last gear oil change at 120000. Was going to do it again in a few weeks and looked under there the other day and saw oil dripping. Def never saw the oil before. Didn’t look too terribly rusted and to be honest never thought if my diff rusting out. I would think it would be there way after everything else was long gone. My 89 yota pickup has hardly any rust on the diff housing and is not garaged. I don’t think this is something that should happen. I do however regret not staying more on top of the rust. But now I will and have a lot of work cut out for me. The rear brake backer/dust plates are rotting out as well. I feel like this has all happened relatively recent due to the fact I took it to the shop last year and just had the di a full undercarriage inspection and change out the rear shocks. I would have thought they might have mention the need for cleaning things up or given me a heads up? Frustrating. Trying to find a scrap yard in Alaska with a rear axle assembly will be near impossible. Especially one that won’t be trashed. Thanks for the input.

 

Not sure what you're getting at here lol? Old school or new school, housing is still rotted. What's your "old school" solution?

 

You should be under there more often for sure especially in such a harsh environment. When I bought my 4R brand new, I was under it within a week greasing everything and painting literally everything. I'm under it 3-4 times a year with a can of black spray paint coating everything in sight. May be overkill but it'll never rust and if something does rust i'll catch it right away. Where exactly is the rot? There are other backyard fixes but they have to be done "properly" to avoid causing other problems.

 

How do you repair this leak. I have same issue. Looks to be leaky through the “pumpkin”. Not the drain or the fill. I was thinking some JP weld??? Leaks when it’s hot mostly. Can’t imagine a junk yard replacement would be any better.

 

“Rotting out” wha?

 

This is what I’m dealing with

 

Is it repairable.

 

That looks like the titanic

 

Personally with that amount of rust I would just top off the diff fluid occasionally and drive it.

 

Garbage.

But if your rear diff is that bad, it's safe to assume your frame is even worse.

This vehicle has neen neglected all its life.

 

Its a common issue. That cover is actually pretty thin. Anything is repairable, if you have time, money or welding skills and equipment. I've heard of people welding new covers, which can't be too terribly expensive. But I'd definitely check the frame out carefully before investing any money in it. You could also replace the housing with one from a rust free state

 

Not 100% sure, but it may be coming from the breather valve. Will update when I can get under it.
Frame isn’t bad. Lots surface rust. At this point I was told to “fluid film” the entire thing to at least stop it.
Any other products out there that will be better??

 

How long do you want to keep the vehicle? Because fluid film is a preventative step not a treatment for rust that already exists. What you see is the result of rust getting between the diff housing and the axle and compromising the gasket that is between them. While the axle does rust a little easier than the rest of the frame, that didn't happen suddenly.

People weld the diffs to prevent leaks like this, but that is so rusty you'd need to fix the rust for any lasting affect (it'll keep compromising seals if not removed). You'd want to remove the axle, separate the diff housing from the axle, and sand and repaint the whole axle and housing. I have repaired rust on my differential, the time it takes to remove the axle will be made up for by not having to work at odd positions with crap raining down as you sand.

I can't imagine that'll be easier than finding another axle in better shape, but if you insist that is what you'd do. And you should fluid film the rest of the truck, rust is inevitable on 3rd gens.

 

Fluid film, wool wax, etc., are all about the same. In any case it might be too late. Have a qualified mechanic check it over. You might be next in line to star in an epispode of "Just Rolled In".

 

Thx for the advice. And the driver side axle seal is being done as well. Will be sanding and attempting to control the rust. Will probably use JP weld on it as I’m sure the leak may start there as well.

Not easy. Not really a daily driver but the truck doesn’t owe me much. Fun in snow. Afraid to hit the trails without a tow company on standby!!

Only 183k on it. Still drives smooth. Mechanic thinks replacing the rear shocks is next, and says it’s just average rust. So hopefully it’s an easy job…..

 

This is a common issue with 3rd gens.....maybe something like this?

https://barnes4wd.com/products/toyota-pick-up-heavy-duty-differential-cover#tab-2

 

Nice. If it’s that bad Great option. Need front and rear black bumpers. What after market company do you recommend.

 

I only started using it last fall so it's too soon for me to form an opinion based on experience, but my understanding is that fluid film does stop existing rust from progressing. So in that sense it is a "treatment" if indeed what they claim, and what I have read from others, is true.

 

Nah.. nothing stops rist

 

Might not stop it completely, but many people think it prolongs their vehicle's life by a lot.