Differential fluid the magazines are recommending

[femtnmax]

Just thought I'd share this info with everyone:

The lastest copy of Mopar Action, in the tech tips, says to use 75W-140 synthetic.

In Chevy High Performance, Insider Tech Special, Jeff Strange of Strange Engineering says don't be pursuaded by the market hype. "We get to see the burned bearings and burned ring and pinion sets that are a consequence of many of the special rearend fluids used these days".   "We recommend regular petroleum-based oil 85/145W... we have been very happy with Lucas rearend oil".   "As far as fluid that reduces a measurable parasitic drag, we are not privy to any meaningful data".

The choice is yours.  For myself, I think I'll stick with Jeff's recommendation. 

[quagmire]

I personally run Mobil full synthetic, no issues yet.  But I do remember in the late 90's when Ford started using full synthetic in their diffs as factory fill I started to see quite a few rear end problems.  I can't count how many diffs I rebuilt on 97 up F150's and their other trucks that had bearing failures.  Same thing also happened with the Jeep Grand Cherokees around that time too.  I probably did a couple dozen of them because of howling and other noise complaints.  It may just be have been coincidence, but it seemed to become a problem when they started recommending synthetic gear oil.  I know the Jeeps had defects and design flaws, dunno about the Fords.  Tons of other manufacturers don't have any problems though.

[vinb]

I was using Amsoil synthetic 75-90W in the street car and didn't like the way it looked after a couple thousand miles (BLACK/DIRTY/VERY THIN like water)..
Went back to basic 80-90w gear oil with the additive. I say the bearings will probably last longer..

Race car's ,  synthetic is great but street cars I don't think so... Just My

[73EStroker]

The black synthetic oil reminds me to say my previous 03 Dodge 3500 1 ton diesel had the same coloured oil in the diff as what was in the engine after 5000miles - black. I had lots of trouble with that diff as it was the first of those un-Dana's made by the ex-GM plant. So that reminds me to change the oil in my newer 07 diesel.

[BoughtItNew]

After installing a brand spanky new prototype TruTrac in my 8.750 I dutifully filled it with Mobil 1 gear lube.  After 6 trips down the strip at Byron and 8 down the track in Belle Rose, LA the TruTrac turned into a spool.

Detroit Locker rep (a former colleague and good friend) told me to use a petroleum based lube.  They fixed it for me and it's been run on Valvoline Dura Blend ever since.  Have seen no measurable difference in ET, either.

[Changin Gears]

Chrysler been recommending synthetic for years in trucks and Jeeps when trailer towing.  In fact, if you got the trailer tow package you got synthetic.  I really can't believe either conventional or synth would cause a failure.

I've been using Shell Spirox 80w-140 for years in everything including my truck, jeep, and even my race cars 'crash box'.  I by it in 5 gallon buckets from the distributer.  The last one a bought a couple year ago cost $80, that works out to $4 a qt.  On the bucket it states that it meets Rockwell, Eaton and Mack's 500,000 mile change interval.  You do need the additive with Sure Grip though.

[femtnmax]

Here's an update to my own post.  I work on a ranchers trucks to help out an old vet.
he grew up in the depression, so he drives his rigs carefully, not wanting to break down or have to spend money.   He lives in a small house with wood stove, candlelight and a fresh water spring outside.  Said it was all they had when he was a kid, and its all he needs now.
Back to the auto discussion:  he runs mobile1 synthetic gear lube.  So he calls me just the other day.  He checking the fluid in one of his trucks.  There's metal in the rear axle fluid.  He pulls the cover, the ring and pinion are scuffed and damaged, and one of the spider gear thrust washers is showing damage.  Must have a lot of damage if you can see it from the outside.
So what does this tell me about using synthetic gear lube???   Makes me think even more that Jeff Strange is correct.  I'm going to stay away from it.

[71chally416]

I had my only ring gear failure on the street EVER using the synthetic stuff, and it was with probably the weakest motor I ever had. Never again. Bottom line is it has no benefit so why use it?

[duodec]

Sucks not having access to all my old mags and documentation.  There was an article years ago about using Mobil-1 synthetic gear oil in manual transmissions and rear axles that absolutely did not recommend it.  The reason I remember them giving is that the synthetics are made up of very complex "long chain" molecules, quite different from 'real' petroleum.  These long molecules did not handle the type of forces created by very high pressure gear tooth contact and the molecules would start breaking down.  Real petroleum holds up much better under that type of pressure.

Perhaps that explanation has changed over time, but that is what I remember.  I happily use synthetic engine oil but its dino lube in the rear axle for me. 

[haroldbrown2]

Geez, ya'll have me paranoid now.  I have over 152K on my 00 F150 daily driver with the stock synthetic rear lube changed once (around 80K) with fresh synthetic.  I think since it's about time to mess with it again, I'll go petroleum now after reading this!

[Changin Gears]

Geez, ya'll have me paranoid now.  I have over 152K on my 00 F150 daily driver with the stock synthetic rear lube changed once (around 80K) with fresh synthetic.  I think since it's about time to mess with it again, I'll go petroleum now after reading this!

I hope your joking.

I do only get about 100 passes per ring/pinion in my race car with synthetic, but its more of a broken teeth issue though.

[haroldbrown2]

Heck no I'm not joking!  The factory recommendation was to change the synthetic differential fluid every 75,000.  First time it was changed around 75000 or 80000.  I'm about to roll 153,000 and time to change it again.  Guess I'll go w/dino since synthetic isn't supposed to hold up.  I guess this was one area I wasn't taught as a kid (changing rear lube), as my Dad never changed any diff lube in any of his vehicles, and always got at least 100,000 miles before he sold one off.  Never had a rear end break either.  He drove a '68 Chevy truck from new until 1986 daily only replacing the cam/lifters sold it for nearly what he paid for it (unrusted SWB).  He was fanatical about oil changes every 3K miles, and I've only recently backed off from that in the last few years on newer vehicles to about every 5,000 miles.

[Changin Gears]

I thought your were happy with the 150k miles?

[haroldbrown2]

I might be stating it wrong, I'm tickled to get 153,000 out of anything.  Just had never heard synthetic diff fluid was a no-no and intend next time I change (either this weekend or next), I'll use regular gear lube.  I'm glad I read this. 

[quagmire]

If the car is still under any warranty, only use what they recommend.  They can and will find out if you used the wrong type of fluid and will deny any warranty claim if they catch it.  I don't know, there are literally thousands and thousands of vehicles out there that use synthetic and NEVER have a problem.  In fact, I don't think any manufacturer specs dino oil in there diffs anymore.  I question whether the failures are in fact from syn lube or merely coincidental.  I've seen quite a few failures on certain makes and models, but that leads me to believe it is a design flaw rather than a lube failure.  I currently work as a district service manager for a big OEM, and I almost never see warranty issues with diffs and none are lube related failures.  Any warranty failure part is sent to a lab where a team of engineers pick it apart and determine the cause of death, so there'd be concrete evidence if it was a problem or not for that very small few that do fail for whatever reason.  I will continue to run syn oil until I have real evidence that it is detrimental.