I've got a 2005 f150 XLT with 48,000 miles. Obviously doesn't get much driven much. I have got a fluid leak in the middle of the rear diff cover. I've had it undercoated since new with ziebart. Their lifetime warranty is only 10 years. I scraped off the years of coating and cleaned it with brake cleaner and found a real rusty spot in the middle of the cover. Service manager said it's from excessive heat. I think it's either their coating or sub-standard metal used by Ford. Anybody have a leaking rear diff that comes from the middle of the cover?

 

Here's my theory on that... could be right, could be wrong:

I think moisture got built up with the rubberized undercoating and attacked the diff cover.

It gives you a good reason to upgrade to a fancy diff cover. There are a ton of options out there.

 

That is exactly what happened. In their "examining/inspection phase" they didn't scrape off the peeling stuff and coated over it. When that eventually failed it had nice pockets to collect water, salt and anything else that goes to corrosion. That's what I discovered when scraping it off. Just wondered if Ford might have used faulty metals or something in those years. I've worked on a lot of different cars and never saw a cover like that.

 

Yep, the type of metal Ford used on the diff covers will rust very quickly. Usually, the dealers keep the diff covers in stock because of the huge demand for them. Getting rust under rust preventive coatings is not that unusual in any case. I worked in the frozen north a lot after buying my new 2000 F150. On one stay at home in NC between jobs, I noticed how rusty the cover was so I cleaned it up a bit and put several coats of paint on it to slow it down.

 

Saga continues. Discovered significant rust on the frame rails. Side of the boxed frame has a hole large enough to get my 4 fingers in. Like that on both sides. I know they make support pieces to weld on but scraping all that crap is more than I want to do. I thought it wouldn't be too bad just doing the sections where the coating lifted but when I scraped a section that looked pretty good and wouldn't have to be scraped, I found rust. I drove this truck from the dealers to the ziebart shop. Brand new non-rusted metal and brought in for renewal treatments. Friggin unbelievable.

What's an '05 XLT with 48,000 miles, nice black paint, excellent running gear that needs frame replaced or repaired worth in this market? I couldn't peddle it and not inform a buyer. Maybe someone with a decent frame or somebody that needs a good parts truck???
Any thoughts on how you would handle this?
Thanks for the help

 

That says all you need to know about Ziebart. Coatings will cause corrosion underneath it. i think a better way is to spray the bottom with fluid flow every year.
If you plan to keep the truck perhaps it's worth it to get another frame. Toyota replaced a lot of rusty frames on their trucks a few years ago. I have no idea what it would cost.