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  1. #11

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    Hmmm. Time to search for more detailed and long term tests to compare , me thinks. good arguments on both sides just not sure which I will follow at this time.
    2010 Chevy Silverado Z71 ext cab.4x4
    72 Monte Carlo 350-415 hp- sold (June 2011) to pay medical bills
    79 Impala 350 4bbl 375 hp- sold (June 2011)to pay medical bills
    oldfart2413@gmail.com

    "If He asks you to go a mile go two"

  2. #12

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    I'm a bit skeptical, so I'll stay neutral on the truth of this claim, but I'll personally stick with GMs spec of using synthetic oil in my rear axle. As far as the front diff goes on my 03 Avalanche, the original GM spec was for non-synthetic gear oil, but I'll use synthetic on my next change because GM put out a bulletin saying that using synthetic would help reduce the damage it will do to itself, especially in the cold winter climate we have here.

    I'm really just a fan of synthetic oil overall though.

    2001 Silverado Reg. Cab Not-So-Base -- SOLD
    2003 Avalanche Z71. No Cladding. Check out my Mod thread.
    1974 Triumph Spitfire 1500 - Work in Progress
    2003 Sierra 3500 Duramax. The Newer, Better Work Truck


  3. #13

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    I see both sides of this issue and wonder am I on the right side, the fence or the left side. Currently on the fence but PM is coming due so I need to make a decision
    2010 Chevy Silverado Z71 ext cab.4x4
    72 Monte Carlo 350-415 hp- sold (June 2011) to pay medical bills
    79 Impala 350 4bbl 375 hp- sold (June 2011)to pay medical bills
    oldfart2413@gmail.com

    "If He asks you to go a mile go two"

  4. #14

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    Quote Originally Posted by pmf608 View Post
    I'm a bit skeptical, so I'll stay neutral on the truth of this claim, but I'll personally stick with GMs spec of using synthetic oil in my rear axle. As far as the front diff goes on my 03 Avalanche, the original GM spec was for non-synthetic gear oil, but I'll use synthetic on my next change because GM put out a bulletin saying that using synthetic would help reduce the damage it will do to itself, especially in the cold winter climate we have here.

    I'm really just a fan of synthetic oil overall though.
    With the cold temps you regularly see in your part of the country Synthetic lubes are probably the best, oil sludges and will even freeze at a certain temp (depends on the grade your using) the viscocity changes drastically when you get near 0deg, you wont have these issues with synthetic as its formulated to with stand colder temps.

  5. #15

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    Quote Originally Posted by the phantom View Post
    I was talking to a guy that rebuilds front and rear differentials for the past 30 years and he told me that synthetic oils are great. But not for the differentials. He said the reason why you shouldnt use it is because conventional gear oils push the contaminates to the side walls of the diff cases and it sticks there not allowing it to be continually ran through the gears and bearings. He said that he has seen bearings shot after about 50-60k miles because of this. He said that synthetic oils are the best for any system that is filtered but diffs are not. And the properties of the synthetic blends do not allow any wear contaminates to stick to the sides like the conventional oils. I guess if you continually change the oils maybe this statement may not apply. But then at what interval would be acceptable to not allow any of the contaminates to wear on the bearings ect. Just thought I would share an opinion.
    The logic here from your mechanic is slightly flawed. Given that the gear oil suspends particles, and particles will cling to any material surface they come in contact with, if you follow your mechanics logic that the contaminants are "pushed" out of suspension, they'll also be pushed onto the gear surfaces, which would be worse than being simply suspended.

    I can completely see a logic trail that would lead a mechanic to conclude if crap is stuck to the sides of a gearbox, it must be better than having it float in the oil... That would only hold true if the crap wasn't actually the oil. Conventional oils breakdown far faster under sheer pressure than synthetics. When I've cleaned differentials, I've noted the same crap on the sidewalls of the insides that your mechanic notes. I've also seen synthetic oils not produce nearly as much of that junk.

    It's important to not that this is a sealed system with NO blow-by (such as in an engine), the only contaminants in gear-box oil are produced by the gearing, the oil, and any water that finds its way in (usually from a submerged axle, requiring a swap of fluids anyway).

    Because conventional oils breakdown faster than synthetics under massive sheer pressures, when your oil breaks down during the gear contact, the by-product is that your gearbox will wear faster. This means you have contamination from broken down oil AND particles from the metal wear. It may not even be visible to the eye 40K miles, but minute particles worn from the metals will be higher in convention over synthetic.

    I'm with dpeter on this one. Quality synthetics will result in less wear over time, and do a better job protecting your diff from both sheer and heat damage. Increased friction increases the heat output... conventional oils will simply NOT be as cool as synthetics over the whole life of the oil.

    I find your mechanics comment that he has seen bearings fail "Because of this" an interesting postulation. Concluding causation in an environment with a myriad of parameters is difficult at best. For example, how does your mechanic KNOW it was the synthetics that caused it? Could it have been because the synthetics replaced the crappy conventional oils and resulted in so much crap being dislodged from the sidewalls that the oil couldn't do it's job (meaning if conventions had never been used it'd be better?) Or what if there were minute fluctuations in the bearing fabrication process that were simply exposed during normal wear and tear. Was it simply a defect part?

    Basically, having a few events (over 30 years!) where synthetics were used and bearings failed does NOT make a conclusion. In fact, he may simply be LOOKING for synthetics during early part failure that is actually a result of a failed PART, not fluid!

    When folks are looking for evidence to support their already forgone conclusions, it's been my experience they'll usually find it.

    That being said, I believe the minimum expected serviceable life of your differential and gear box will be just fine using either quality conventional or quality synthetics. I believe high quality synthetics may make it last longer, run cooler, and have less friction total resulting ever-so-slightly better MPG, but the minimum lifespan will be met either way!

    If your mechanic won't warranty his work because he believes synthetics are poor substitutes, I personally would stick conventional fluid in there. You'll save a few bucks at the changes, and it becomes his problem to deal with if there is premature failure.

    Cheers,

    -Skippy
    2006 Vortec Max 1500
    Performance:
    -Custom Tune (389HP 440 Ft/lbs Trq - Dyno'd) | Volant CAI | Magnaflow Dual-in/out Exhaust w/3" stainless pipe tips | Fully Built Transmission w/ Red Eagle Clutches & Kolene Steels w/ Corvette Servos and Stage2 Shift Kit | 35K Tranny Cooler | Mobil 1 | Royal Purple Rear Diff
    Other:
    -Spray-in Bed Liner
    -Premium Sound w/lifetime Satellite Radio | Leather | Sunroof | Heated Seats
    -Limbstriping from USING the truck (those are badges of honor)

  6. #16
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    Reading, PA
    Posts
    291

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    Quote Originally Posted by the phantom View Post
    I was talking to a guy that rebuilds front and rear differentials for the past 30 years and he told me that synthetic oils are great. But not for the differentials. He said the reason why you shouldnt use it is because conventional gear oils push the contaminates to the side walls of the diff cases and it sticks there not allowing it to be continually ran through the gears and bearings. He said that he has seen bearings shot after about 50-60k miles because of this. He said that synthetic oils are the best for any system that is filtered but diffs are not. And the properties of the synthetic blends do not allow any wear contaminates to stick to the sides like the conventional oils. I guess if you continually change the oils maybe this statement may not apply. But then at what interval would be acceptable to not allow any of the contaminates to wear on the bearings ect. Just thought I would share an opinion.

    Wow, based on this logic I wonder how my last truck (450HP+, 800TQ+, manual trans, towed regularly) made it to 270k with synthetic fluids in the differentials. Does this guy realize that almost all new cars come with some grade of synthetic in the differentials from the factory? How many of them ever actually get changed and they live a lot longer life than 50k?

    It is more likely his experience comes from a failing differential that someone put synthetic in as a band aid, and because it failed with the synthetic fill, it must have been the result of using the synthetic fluid...not that the differential was on its last leg to begin with.

    On edit: another thing to keep in mind is that not all synthetics are equal...there are good ones, there are bad ones. But no different than the conventional oil choices.

  7. #17

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    Im leaning towards putting synthetics in my diffs when I have my mechanic put my new 4.56 gears that I should be receiving monday in my truck. This guy I was talking to claiming this was NOT my mechanic and had a booth setup for selling gears and was just giving me his recommendation. Needless to say he did not impress me enough to buy the gears from him and I ended buying the same ones he was selling from a different vendor. Although with the test info that RayVoy had linked and some of the other opinions here I feel I learned from this thread. THANKS GUYS AND GMTC!!!!




    2011 Silverado CrewCab 5.3L*Ram Air Look Cowl Induction Reflexxion Hood*6" Pro Comp Lift*Flowmaster Dual exhaust*Perfect Launch Rear Diff. Cover*Led Smoke Taillights*L.E.D.Smoke 3rd Brakelight*60" L.E.D. Tailgate Bar*Rearview Mirror Reverse Camera and Sensors*Smoke Headlight Covers*Front Bumper Grill Insert*Deezee Black Alum. Diamond Rail covers*20" Ultra Motorsports Rims wrapped with 35.5"B.F. Goodrich Tires*Inchannel Raingaurds*CAI*Bullydog GT Tuner*Alpine Amp*Boss 6x9's*Boston Acoustic Subs*Terrantula Tweeters*Custom Sub box*Red Led Interior Accents*5% Ultimacool duo tint rear window and doors, 20% front doors*Custom Vinyl Graphics*Demolded*Debadged*Painted drums and calipers*
    Future Mods Include: Custom Interior Hydrographics, Electronic Rollup Toneau Cover, 4.56 Gears, Painted rear bumper

  8. #18

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    I will always run synthetic oil in my diffs...i use Mobil 1 Fully Sythetic 75w-90 in my rear end and cant remember what i put in the front of the last truck...when my new truck comes due for rear diff and front diff change,TRUST ME i will us sythetic oil...and i run Mobil 1 FS 5W-30 in the motor...you cant tell that i love Mobil 1 right?!

    2009 Chevrolet Silverado 1500 LT Z71 Crew Cab "All-Star Edition"

    Line-X'd Bed
    Line-X'd Custom Brush Guard(Heavy Duty)
    5.3L Flex Fuel
    Factory Black Running Boards
    BF Goodrich All-Terrain KO's(265/65R18)
    2" Rough Country Leveling Kit
    EGR In-Channel Vent Visors
    Exterior PLUS Package
    Interior PLUS Package
    K&N Drop-In Air Filter
    Bowtie Mud Flaps
    Cat-Back Dual Exhaust
    Black Bowties
    DeeZee Toolbox(Debadged)
    Diablo Sport Predator(AFM Disabled)
    ProFlaps
    Towing Mirrors
    Next Planned Mods
    Bigger Tires
    Aftermarket Rims

  9. #19

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    Quote Originally Posted by ChevyBoy2009 View Post
    I will always run synthetic oil in my diffs...i use Mobil 1 Fully Sythetic 75w-90 in my rear end and cant remember what i put in the front of the last truck...when my new truck comes due for rear diff and front diff change,TRUST ME i will us sythetic oil...and i run Mobil 1 FS 5W-30 in the motor...you cant tell that i love Mobil 1 right?!
    I'm a fan, too. Though, I get a kick out of the various arguments about which high end products are that Nth degree better. Seriously... If you use synthetics and follow the standard change schedule, you'll never come close to getting to the point where it'll make a difference. I love Mobil1, because it's a GREAT product without the insane prices of the other guys... Though.. >i do run Royal Purple in my rear diff... only because Mobil1 never seems to be in stock when I do my rear diffs!

    Skippy.
    2006 Vortec Max 1500
    Performance:
    -Custom Tune (389HP 440 Ft/lbs Trq - Dyno'd) | Volant CAI | Magnaflow Dual-in/out Exhaust w/3" stainless pipe tips | Fully Built Transmission w/ Red Eagle Clutches & Kolene Steels w/ Corvette Servos and Stage2 Shift Kit | 35K Tranny Cooler | Mobil 1 | Royal Purple Rear Diff
    Other:
    -Spray-in Bed Liner
    -Premium Sound w/lifetime Satellite Radio | Leather | Sunroof | Heated Seats
    -Limbstriping from USING the truck (those are badges of honor)

  10. #20

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    Quote Originally Posted by Skippy View Post
    .. >i do run Royal Purple in my rear diff... only because Mobil1 never seems to be in stock when I do my rear diffs!

    Skippy.
    I've got RP in both of my diffs as well, but after reading the comparison testing, in that article I found for post #2, I might have 2nd thoughts about continuing to use it. The article did say all products tested met the industry requirements, so it is probably a good product to use, just that some of the others tested so much higher.
    Ray

    '09 Avalanche LTZ - Black
    '05 Envoy XL (sold)

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