Would it be overkill to change the differential fluid once a year. I have front and rear Lockers. I also never put more than 9000 miles a year on my 90 Bronco!

 

I wouldn't call it overkill. I would call it preventative maintenance. You never know when you are going to ingest water into the vent tubes.

 

Once a year is a great idea- definitely not overkill.
I change gear oil in my differentials about every month or two. Water gets in the rear even when it hasn't gotten close to the breather hoses. I have yet to find evidence that water ever found it's way in the front though. Gallons of Coastal 85W-90 are only like 6 bucks at Discount anyway.

 

According to the specs we had at the lube rack ford recommends it only every 100,000 miles but chevy recommends it once every 15,000 and dodge every 12,000. Definitely not overkill.

 

Overkill? Maybe. Doesn't hurt. All depends on how you drive and what load is on it.

If you go through deep water, change everytime and you should also check your hubs.

If you tow, I think the recommended is something like 12,000(I am not sure, might be 36K). Normal service is I think 100K but that makes me really nervous. I would say 50K max, 30K is a good compromise.

Yearly is not so much as to be a bother and like I said definitely won't hurt. Be sure to check the magnets and flip out the oil at the bottom of the case with your finger. I also like to wipe things down with a clean rag. If you have limited slip, be sure to get the additive required.

I tow and use synthetic, so I plan on something around 20-30K. Since I have own my F250, I have changed it 3 times in 36K miles, once because of a leaky gasket and once to put in new seals. When I did the first change at about 40K? the oil was like slighty dark honey. When I did the next change due to a leak using the gasketless sealer, the oil had maybe 10K and was like new. Now I have a good old fashioned gasket and will probably go another 10 before changing.

Just my opinions,

Jim Henderson