I'm getting ready to change out the gear oil in my diffs - 1st time since I've had the truck. I'm mostly posting to confirm my research is correct after lots of searching around. I'm planning to go with 75-140 in the rear and 75-90 in the front. I have a 3.73/LSD rear, but it's my understanding no additive is needed - correct?

I'm thinking about using Valvoline synthetic lube. It runs about $10-13 a quart locally depending on weight. I also considered using Amsoil severe gear - they claim 50-100,000 mile drain intervals. I like not having to worry about stuff, but I also like the idea of changing out a bit more often in case of any kind of contamination or dilution. I do drive off-road a fair amount. I also tow 7-10,000 lbs regularly.

Any thoughts?

What would be a reasonable drain interval for the Valvoline synthetic? The specs seem pretty comparable to M1, which is $20 a quart anywhere around here.

Thanks!

 

I change every 30,000 miles with Amsoil severe gear, 75w90. I see no need for the 75w140.

 

Only use synthetic GL-5 and no additive is needed. I do as you are thinking of going with the weight of 75w-140 in the rear. Because I also tow heavy I change the rear at 15k and the front at 30k miles. The rear is always darker than the front when I change both. I have found that Mobil 1 is a little cheaper at AutoZone.

 

Personally, I run redline 75-90 front and 75-140 rear. The spec is for full synthetic GL5, so I don't extend the change schedule based on using synthetic.

I asked redline about using their gear oil that doesn't have Ls additive. One of their engineers wrote back that although AAM's Ls system does not require additive, it doesn't hurt anything and could actually reduce temps.

So anyway, I run the regular redline in my current truck and my last truck with good results.

 

Last change of Amsoil (not brand loyal, just using a good syn oil for extended drain intervals) with about 80k mi on it came out of both axles looking about the same and not alot different than the fresh oil poured back in, very clean, hardly any metal on the magnet.
In fact I didn't change the front. Sucked out a little sample, set it beside some new oil and decided to not waste the 30min and 2qts of oil....like new.
If you're just using it as a daily driver, occassional towing, 100k intervals with synthetic gear lube is fine, IMO.

 

Redline 75w90 up front and 75w140 rear for me.

 

Many will not agree but I absolutely do agree.

I changed my front at 30k miles and again at about 55k miles. I was actually upset that I didn't check the oil first at 55k and just cracked the fill plug and zipped the bolts out and saw what looked like NEW oil pouring out! I now have 116k miles and checked it maybe 10k ago and it still looks new. I talked to my brother who owns a shop that specializes in axles and gears and is very well known. He laughed and said to use a name brand full synthetic and do the front every 75k miles!! I trust him over anybody.
I do the rear more often but that is different.

 

Based on this and some other info I've found, I'm thinking about running the Amsoil severe gear for around 50k or so (I'll keep an eye on how it's looking).

Does anyone notice a drop in MPG using 75w-140 vs 75w-90 in the rear? I'm trying to decide if my towing is severe enough to need it. What about 75w-110 in the rear as a compromise. I tow maybe 20% of my overall miles at 15-20k miles a year. My trailer is about 9000 lbs loaded. A lot of the driving is over mountain passes etc. so I don't want to under do it, but I don't want to effect my mileage too much for unloaded highway driving!

 

No change in MPG at all for me. I tow quite a bit heavier at times, and have towed up long grades in 110+ temps occasionally, so I like the bit of extra protection.

 

I did not notice any change but I changed it at 15k miles and that was more than 9 years ago.

 

If this holds true, then why do semis go 750,000+ miles on synthetic 75/90 with zero bearing, hub, or gear failures?

 

Exactly. I'll admit, I OCD, overkill some things when it comes to maintenance, but after you see enough vehicles driving around with a bazillion miles on them and never checked or changed the gear lube I gotta think that our trucks are ok for more than 30k mi on gear lube.
Of course, mine is mostly empty driving and almost zero heavy towing. Should get the opinion of a couple of the guys on here that hotshot for a living. If they're putting on 100k mi a year on their trucks, I bet they aren't changing gear oil every 4 months.

 

I've seen semi rear ends fail, but it does seem very rare, and that one had more than 750,000.

It would be interesting to see a comparison of gear contact area and oil capacity vs h.p. between pickups and class 8 trucks.

 

I used Amsoil 75-110 severe gear oil in the rear diff and did not change the front as I have Dynatrac free spin hubs and the front diff hardly ever turns. I run the back diff 60,000 Miles or 100,000 kilometers and I change the front every third or forth rear diff changes or earlier if I suspect it might have gotten drowned.
Jim O

 

LOLOL!!! Good one,,,,IVe changed both Axles lube on mine once at owners interval,,, it was so clean, I was amazed only a trace of metal on the rear magnet, went with royal purple 75-90W w/additve. was towing 16K heavy sprint car trailer quite alot,, Sold the race car, trailer and all,,

Now just tow my boat and stock trailer with a few cattle or my Stump grinder/tractor/loader and firewood,,, not sure if the book interval makes much sense after reading this thread