On my 2000 truck owners manual it states that the rear differential comes with synthetic oil and there is no need to change it. Are they right about this one? Thanks.
change synthetic rear diff?
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The OEMs will change suppliers for 9 cents a gallon difference in price. My guess would be that they don't have the very best in there.
Were it mine, I'd certainly change it.
Were it mine, I'd certainly change it.
well, Doug Hillery , a board member ...owns a fllet of long hual trucks in Austraila ..he changes his trucks over to synthetic at a certain point and then never touches the differential fluid again! Run a search on him ...good reading
Here in Atlanta, word on the street is "fear the OEM synthetic gear lubes". Several rearend shops report much higher failure rates with synthetic dope than conventional. Many refuse to use any brand of synthetic to avoid the extra risk of falure.
My source on this is a guy who has been doing gear sets and total rebuilds of RWD axles for many years. He does 200-300 of them a year. From 50's Chevys, including early Vette rears to monster 4x4's to classic musclecar 12 bolt conversions and even regular late model trucks, suv's and vans.
His personal failure rate is 3 rearends gone bad out of over 1,000 that he has at least put a new crush sleeve in, where most are either gear replacements and/or new bearings. He's good and many gear changes he has success with are used gear swaps from a different rearend. You have to be good to have zero failures from using used gears you know.
While no explaination exists for why there are so many failures associated with synthetic gear lubes, whether real or not, there is apparantly enough rumors going around where many who rebuild rearends for a living, at least in this area, are refusing to use any sythetic.
My friend recommends 20k changes of the dope with convetional fluids for 3.55 ratio's or higher. He likes Valvoline but is fine with any major brand. But for lower gears like 4.10, he recommends more frequent changes if you ant to see 300,000 miles of service.
My source on this is a guy who has been doing gear sets and total rebuilds of RWD axles for many years. He does 200-300 of them a year. From 50's Chevys, including early Vette rears to monster 4x4's to classic musclecar 12 bolt conversions and even regular late model trucks, suv's and vans.
His personal failure rate is 3 rearends gone bad out of over 1,000 that he has at least put a new crush sleeve in, where most are either gear replacements and/or new bearings. He's good and many gear changes he has success with are used gear swaps from a different rearend. You have to be good to have zero failures from using used gears you know.
While no explaination exists for why there are so many failures associated with synthetic gear lubes, whether real or not, there is apparantly enough rumors going around where many who rebuild rearends for a living, at least in this area, are refusing to use any sythetic.
My friend recommends 20k changes of the dope with convetional fluids for 3.55 ratio's or higher. He likes Valvoline but is fine with any major brand. But for lower gears like 4.10, he recommends more frequent changes if you ant to see 300,000 miles of service.
What is the history of probelms on the vehicle model and axle ? If there don't seem to be problems I wouldn't worry too much about it, but I have found that Mobil 1 gear oil looks kind of new when I change my axles (I'm supposed to do either no change or a 15k mile change for severe duty), compared to the OEM fuid that looked like black snot. Synthetic is spec'd for the rear axle but I use it front and rear.
The lower the gear ratio (higher numerically) the hotter the diff will run. Unless you significantly increase the tire size, a lower gear's pinion will spin faster at any given speed than a higher gear. Overdrive does NOTHING to slow the pinion rpms, NOTHING. Overdrive lowers engine rpms for a given transmission output shaft speed. On RWD, the transmission output shaft speed equalls the pinion speed in rpms.
If you tow a heavy load for any distance, say a car on a trailer for 200 miles and you have lower than a 3.55 gear... you should probably change the dope when you get home. It is heat that turns the dope black, not milage. The more work you do, the more heat you make.
Me? I wish someone would make diff covers with a clear window so you could see the color and level of the dope without having to put a wrench on it! This would be handy if you drive off road because you could check for water ingestion in the dope by the color change in the dope.
Ahhhh... if I only had Bill Gates' fortune to play with...
If you tow a heavy load for any distance, say a car on a trailer for 200 miles and you have lower than a 3.55 gear... you should probably change the dope when you get home. It is heat that turns the dope black, not milage. The more work you do, the more heat you make.
Me? I wish someone would make diff covers with a clear window so you could see the color and level of the dope without having to put a wrench on it! This would be handy if you drive off road because you could check for water ingestion in the dope by the color change in the dope.
Ahhhh... if I only had Bill Gates' fortune to play with...
Change the gear lube. It's like $20. A rebuilt rearend is close to a grand. No gear lube is lifetime.
www.jegs.com has those clear covers.
www.jegs.com has those clear covers.
Been using synthetic gear lubes on various vehicles with stock and racing gear sets with NO problems for years..he should blame/check his set-up when doing gears and not the equipment he uses for failures.Almost all the major manufacturers specify 75W-140 SYN. out back for towing. A Jeep Rubicon I service has tagged on both front& rear Dana 44 axles "75W-140 SYN " go figure
and I still change out the fluid at regular intervals,synthetic or dino.Lets go back to leaded gas too
In OD a driveshaft is spinning faster than it would be in 1:1.
Krull is right, an overdrive will not change the rear end speed at all, how does '99' figure the gearbox ratio changes the driveshaft speed? Differential overdrive?...maybe, on a Mac truck.
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Ok you win. I'll gas up my Cessna 172 with unleaded and you come fly with me.quote:
Originally posted by Greaser:
Lets go back to leaded gas too
I will need someone to hold the yoke steady so I can bail out when the engine siezes up from using the wrong fuel. Me?
I always burn leaded AV gas... and I pack my own chute too...
Thanks! I guess I don't get out much anymore.quote:
Originally posted by Dominic:
kruL they do make clear differential covers. Look them up on google! Theyre high impact resistant acrylic and do allow you to see the fluid
Very popular on show trucks.
I see them for teeny tiny weak 10 bolts and puny 14 bolt corporate 6 lugs.
But I need them for *REAL* rearends... a couple for Dana 60's and about a dozen for Corporate 14 bolt 8 lugs.
If you see any, please link me!
MolaKule
Staff member
Change the differential lube first at 5-10 k and then 30,000 k thereafter unless you use a Used Oil Analysis regime.
The diffy shops and racers I work with use synthetics. The bearings and gearsets last longer and run cooler.
If you're racing under NCRA rules and swapping gear sets for each track, then one can use a mid-viscosity lube (such as SF's HDS-R) or a 75W140 dino with a Ford 9".
I changed out Amsoil 75w90 from my toyota rear and transfer case after about 100k of miles and it came out slightly darker than it went in. No metal particles or such in the used oil or on the magnetic drain plug. This was with an open diff on a 4x4 1992 pickup truck.
I have a friend who never changed out the diff fluid on his 2x4 excursion diesel or his tranny fluid both did not last 80k miles. Rear clutches locked solid and chewed up the rear tires before he noticed what was going on.
Change out the fluid quickly on the factory stuff and periodically on clutch type posi units. I don't think the detroit locker type rears are all that hard on rear gear oil although the truetrack type or auburn type might be harsher.
My driving was all desert with no river crossings.
I have a friend who never changed out the diff fluid on his 2x4 excursion diesel or his tranny fluid both did not last 80k miles. Rear clutches locked solid and chewed up the rear tires before he noticed what was going on.
Change out the fluid quickly on the factory stuff and periodically on clutch type posi units. I don't think the detroit locker type rears are all that hard on rear gear oil although the truetrack type or auburn type might be harsher.
My driving was all desert with no river crossings.
No one has even asked spellbound what type of truck he has, and what type of driving condition either.
I'm guessing its a Chevy.
I'm guessing its a Chevy.
14 bolt 6 lug maybe?
I ran Mobil 1 in the front and rear diff of my 98 Z71 from 20,000 miles until 77,000 miles when the rearend had to have new pinion and carrier bearings. The fluid had also been changed twice during those miles. I wasn't hard on this rearend and only towed a 5x10 utility trailer on an infrequent basis.
I may have just had a bad rearend but I don't trust synthetics in it now. I'll just use conventional and change it more often.
Wayne
I may have just had a bad rearend but I don't trust synthetics in it now. I'll just use conventional and change it more often.
Wayne
I just replaced Mobil 1 75-90 with Amsoil 75-90 SVO in a 99 Crown Vic 8.8 non-locker. I just got the car with 40K miles. What was probably the original lube was dirty. I only ran the Mobil 1 for about 2K miles and it looked very dirty. It also looked airated. I used the within half inch of fill plug method to determine how much to install which ended up being 2 Qts. I installed the factory spec'd 3.75 pints when I filled with Amsoil. Too much lube is not a good thing...
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