How often should I be changing Rear Diff fluid?

If you don't use 4WD often that could be condensation. Back when trucks still had manual locking hubs you could lock them to let the front end spin if it had been a while since you used 4WD. That would warm up the diff, circulate fluid and evaporate any condensation. Since trucks now have electric shifting transfer cases and automatic differential disconnects it's not possible to do that unless you trick the system.

The better solution to of course to go 4 wheeling every month...

I tend to change fluid a lot, usually at least once a year, but it's mostly because of contamination from trails and water crossings. I like synthetic, especially in the rear diff, since it does run cooler in my experience. But for the most part I use plain dinosaur Castrol, Valvoline or something similar. Any decent fresh fluid changed more often is better than expensive fluid left in too long.

 

I think the most important thing is that it's being done at all from time to time....as opposed to never being done. Pick any flavor of 75/90 juice...be it synthetic or conventional and roll with it.

That said...I tend to be a little more fanatical about maintenance. I do the 30k diff service with M1...which is probably more than needed. But that's me. Advanced Auto stocks it and I snag 4 quarts using a coupon.



Pick up a couple of these too.

 

My 96 Tacoma with 408K and 05 4Runner with 295K the diff fluid has never been changed and haven't had any issues. For the most part they stay on the pavement. Just stating my experience.

 

So......what's the favorite choice for 75-90 full synthetic gear oil ?

 

I use Castrol full synthetic 75w90. Mainly because that's the only synthetic choice I have at the stores I have visited.

 

I bought my truck at 70K, had 150K before I changed the diff. Fluid was still golden and there wasn’t any metal shavings on the magnet. Every 30K is overkill IMO

 

Bought my truck new; Changed the fluid out quite early, about 10-15k miles(can't remember) I was shorted 1 quart in the rear diff from the factory_ fluid was nasty dark and full of metallic flakes. - Changed it again at around 50k miles_ Rear fluid and Front fluid was slightly dark; going to do it again here soon since I'm at 111k miles now =[

 

I would read up on what actually is rec'd also when it is changed. Not just rec'd by Toyota.
Fer instance, one of the larger diff. rebuilders does not rec'd Royal Purple by name. In fact they rec'd dino. overall. *I may be remembering wrong, read up*
I believe they're going by an average on failures they've warrantied.

 

I don't know why or if they'd recommend for or against Royal Purple specifically but could you perhaps be thinking of the oil recommended for brand new rebuilt differentials? When you re-gear, for example, you need to break-in the gears and you'd want to use plain lube to do that. For one the oil will need to be changed almost immediately to flush all the metal shavings created during break-in and that would be a waste to use expensive lube after a couple of hundred miles. Also synthetic is generally not ideal for anything newly rebuilt, engines, diffs, etc., since it can prevent a proper break-in from happening.

 

Every 100k with Redline 75W90 since it's a POA group V synthetic.

 

https://eastcoastgearsupply.com/ft-2536-ecgs-gear-oil-recommendation.html

It's just another opinion as they say. I had RP when I read it but am going to heed them next change....which I should do this spring as we had flooding last fall.

 

One important detail in that FAQ is this statement, "ECGS recommends Dino (Non-Synthetic) 85w140 Lucas oil with a Ford or Dana limited slip additive for clutch style posi's."

For clutch type limited slips that would be a very critical point. They rely on friction to work and synthetic vs traditional would make a big difference.

The rest of the page doesn't really say if they mean for all diffs, like open diffs and mechanical lockers. The factory electric lockers on Tacomas don't need any special additives to work or increase protection, for example. It sounds like ECGS means what they say as general recommendations and if so it's fine advice (e.g. watching temperatures) although I'd disagree with using 85W140 personally.

 

Not to side track, but those Ford straight 6 300cu were work horses!

 

Before that the engine was a 240, it's an ancient design. I wish we could go back and just forget CAFE for trucks. Worst I could ever do was bend pushrods redlining through mud with my '70. Can't say a 302 was any worse in an area though.

 

I just had 5.29 gears installed in mine. They used 85/140. I asked what they recommended using after first drain and they said they would stick with the 85/140. Said they have done tons of these and always use the same non synthetic oil. Don't know if I should go to the

$30 Mobil 1 75w90 Mobil 1 104361 75W-90 Synthetic Gear Lube - 1 Quart (Pack of 2)

Mobil 1 75w90 or keep the same?

 

I’m not sure either, my gut always tells me to stick with what Toyota uses and recommends. They obviously know their stuff. I also believe whatever oil the truck starts with it is best to stay with, but your case is a little different. Might be worth starting another thread

 

Honestly the only failures I've ever seen is from either water getting in or a leak letting the level get to low to do any good.

OR..a shop not setting it up correctly on a change.

I have never seen a rear FAILURE from old fluid.

 

Anywhere from 30k to 50k should be fine.

Preventative maintenance on Fluids, filters, and belts will go a long way towards warding off any future issues.

I know, I know, everyone has a story of their 500k mile diff or transmission, but maintenance is inexpensive and easy. Why NOT? One of the key reasons many people point to for their Toyota purchase is “reliability.” This assumes that someone wants to keep a vehicle long term and maximize an investment - otherwise people should start finding new buzzwords to justify their Toyota purchases, because just about everything on the road will go 100k+ without issue these days.

 

I agree.. “Why NOT?” Is exactly how I feel. Surely can’t hurt to give it fresh fluid. Although I’m weird and do believe in giving it the exact same fluid it already had.