I was checking an oil leak under my 4Runner the other day and I noticed that half of the outboard CV boot was gone. Is that a problem and how do I fix it?
What year is the 4Runner? 1993
Does it have ADD (Auto Differential Disconnect)? Yes
Does it have lock-out hubs? No
How many miles on it? Over 337K.
Was the axle, boot, and surrounding area messy greasy, or dry? It was dry.
Diagnosis by phone: This CV will need to be replaced. Since it was dry around the area all of the 
grease has been flung out of the CV joint. This is because with a 1993 4Runner with ADD the CV axles are always moving. The ADD only prevents the front driveshaft and transfer case innards from moving all the time. If lock-out hubs have been installed in place of the factory drive plates they can be set to free and the CV’s won’t turn.
Final diagnosis: Inspection shows that indeed the CV boot had torn in half. The inboard half of the outboard boot was completely missing. Not sure how that happened, but it was gone. The CV joint was running dry.
Solution: I pulled the old CV and replaced it. This isn’t a difficult swap and takes only about an hour and a half if you have all the right tools. Once it was replaced the owner now doesn’t have to worry about the outer CV seizing at highway speeds and causing unknown damage.