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  1. #1

    Default Gear head said not to use synthetic in diffs and this is why!!

    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.




    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

  2. #2

    Default

    Maybe, I'm not buying into it though, synthetics are so much better than conventional grease, there is just no comparison.

    Some reading: http://www.sinwal.com/data/The%20Stu...ar%20Lubes.pdf

    The Amsoil Severe Service lub toped the tests, followed closely by GM's brand.

    http://www.amsoil.com/storefront/svg.aspx
    Ray

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

  3. #3

    Default

    That is a lot of testing that is for sure. I guess my only thought on the tests are that it really doesnt put any of the oils through its real life scenario such as the time factor involved. If these tests could be conducted over a period of 4 and 5 years including the temperature changes in that amount of time I may lean more to agreeing that the synthetics do what they say. I think I would lean more to using synthetics in my diffs when I change my gears soon and just change the oil out often. Afterall I did buy a rear diff cover that has a drain plug in it.




    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

  4. #4

    Default

    GM diffs (especially the front one), have a habit of picking up water, changing the fluid more often than the recommended interval is not a bad idea (unless you get it done at a GM shop).
    Ray

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

  5. #5
    Sr. Engineer
    Join Date
    Oct 2010
    Location
    Indianapolis, In
    Posts
    487

    Default

    They push contaminates to the side walls of the diff case!!?? WTF and OMG. You know my dad had a car that only took a key to run. I know this for a FACT because I never saw him change oil or put gas in it so it had to be the key. I wonder what ever happened to that car. I think I was about four or five when it went away and then he got this truck that he was always putting gas in. How is it that old saying goes--- Believe half of what you see and none of what you hear.
    2000 GMC YUKON SLT, 5.3L tow pkg, G80 rear/w 3.73 gear

  6. #6

    Default

    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.
    My gear guy said the exact same thing when I had the front and rear diffs redone on my 03 yukon xl. He runs conventional oil with a friction modifier. He refuses to put synthetic in a diff. I said "I will buy the synthetic oil to put in the diffs when you are done" He responded, "You can buy it, but there is no way in hell I will put it in, you are welcome to drain my oil out and put it in yourself, but I will not honor my warranty".
    Last edited by Pikey; 11-30-2012 at 07:10 PM.

    1995 Silverado 4x4
    6" BDS Suspension Lift-3" Body Lift-Add A Leaf in rear -Trailmaster SSV Shocks-Duel Steering Stabilizer Kit -AirAid Cold air intake-
    4.56 Gears with Detroit Auburn Locker-Pro-Comp Traction Bars with duel shocks-Aluminum Skid Plate Kit-38.5" x 16.5" Mickey Thompson Baja Claws-Constant Dropping fuel gauge

    2005 Yukon XL Jet Power Programmer, Bilstein Shocks, Bilstein rear springs, Helwig Anti-sway bars, EGR Window Visors, EGR Hood Shield, Denali Headlights, Headlight harness upgrade, GE NightHawk Bulbs, White Night Rear lighting system, Russell Braided SS brake lines, PowerStop Brake pads, PowerStop cross drilled and Slotted Rotors, http://www.gmtruckclub.com/forum/sho...5-GMC-Yukon-XL
    2002 Silverado ext cab 2wd (Sold)
    2003 Yukon XL (Totaled)

  7. #7

    Default

    Quote Originally Posted by Pikey View Post
    My gear guy said the exact same thing when I had the front and rear diffs redone on my 03 yukon xl. He runs conventional oil with a friction modifier. He refuses to put synthetic in a diff. I said "I will by the synthetic oil to put in the diffs when you are done" He responded, "You can buy it, but there is no way in hell I will put it in, you are welcome to drain my oil out and put it in yourself, but I will not honor my warranty".
    Well, there are still guys who insist on changing engine oil every 3,000 miles..........................



    .........hmmm, what did I just start
    Ray

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

  8. #8

    Default

    So if you drain the oil out, then pull the diff cover, obviously all of the contaminates will not be suspended in air. So how do you find out how true this is. Remove the entire rearend out of the vehicle, put it on a bench and pull the cover off facing up and look inside with the oil still in it??? suck the oil out and see if the contaminates are against the walls of the housing? what prevents the contaminates from sticking to any of the other parts inside that dont move. I dont know. It sounds like a possibility that it may be true. But we could also argue that synthetics are so good that there are no wear contaminates to worry about.




    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

  9. #9
    Sr. Engineer
    Join Date
    Oct 2010
    Location
    Indianapolis, In
    Posts
    487

    Default

    "But we could also argue that synthetics are so good that there are no wear contaminates to worry about."
    I'm going with this one
    2000 GMC YUKON SLT, 5.3L tow pkg, G80 rear/w 3.73 gear

  10. #10

    Default

    Quote Originally Posted by the phantom View Post
    So if you drain the oil out, then pull the diff cover, obviously all of the contaminates will not be suspended in air. So how do you find out how true this is. Remove the entire rearend out of the vehicle, put it on a bench and pull the cover off facing up and look inside with the oil still in it??? suck the oil out and see if the contaminates are against the walls of the housing? what prevents the contaminates from sticking to any of the other parts inside that dont move. I dont know. It sounds like a possibility that it may be true. But we could also argue that synthetics are so good that there are no wear contaminates to worry about.
    When you drain the oil out if you strain it you'll find your contaminants, right in the oil, just like conventional oil.
    If this mechanics theory were true you wouldnt need a filter on your engine, all the contaminants would be stuck to the sides of the oil galleries, I've broken open quite a few engines, gear box's, and axles running Synthetics and none of them had anymore contaminants sticking to the sides than there was on parts using conventional dino oil.
    When I used to work on Jets we had huge oil pots for the main induction gearbox's that unbolted from the bottom of the gearbox that you dropped straight down then tilted to drain the oil into a bowser, we used synthetic oil for all the engine lube and after dropping over at least a 100 oil pots in a 20 year career I've never seen what that mechanic describes happen, the contaminants were always mixed in the lube.

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