Point of interest synthetic oil in front axle

chuckp · January 22, 2004

Have herd that some 2500 seires truck in very cold weather dont have synthetic oil in the front axle and it is causing failers with no parts avalable ,i guess you can tell by the color of the vent tube either black or white i think is synthetic and black is non synthetic.

(not 100% sure on the color synthetic or non)

2002

2003

2004

Check it out for your self.......................................

chuck

chevroletmb · January 22, 2004

the vent plug color only tells you if the vent plug is compatable with synthetic

white is, the black one will leak if exposed to synthetic fluid

as i understand it none of the 2500's have synthetic front axle fluid from the factory

my dealership put synthetic into every new truck before it's sold but only because it's cold up here in canada. the regular gear oil won't lubricate properly at lower temperatures causing the failures.

chuckp · January 22, 2004

What i am saying if you dont have synthetic you will cause damage to your front bearings and your ring and pinion.Thats all i am saying ,have a friend at a dealership with eight of the trucks with broken front ends....no parts

chuck

JayMan · January 22, 2004

Yeah I doubt they factory fill the front axle with a good GL-5 synthetic 75W-90 gear lube. Heck, that might add $1.25 to invoice. Ok, I'm being silly.

There is a TSB that explains this in detail, and you've heard right. See, factory fill is a regular GL-5 gear oil 80W-90. According to SAE/API specs, that stuff is frozen solid at -12 F and is borderline at around 2 F.

Cold temp gear lube viscosity - the Brookfield Viscosity - is measured in Poise. It has been determined through empirical testing that a gear lube with a cold viscosity +1,500 Poise will cause excessive wear/failure in most axle designs. This is due to "channeling" where the Ring gear cuts a hole or "channel" in the lube. Certain large skidders and mining trucks may tolerate +3,000 Poise.

At a viscosity of 1,500 Poise, gear lube looks like taffy. If you poured it out a beaker at that viscosity, it would almost jiggle like Jello. Not only will the Ring gear run dry and suffer scoring and abrasive tooth wear from the pinion gear, the pinion bearing ball bearings will also cut a hole in the gear lube.

The pinion bearing in the rear axle will fail before the Ring gear, as the pinion bearings must absorb all the rotational torque. Running dry it will overheat, score/check, and finally the cage will come apart. Pretty messy when that happens.

The front axle is a different situation. First of all, even when you poke the 2HI button, the front axle is still partially engaged. There is no "free" position like the old 4WD trucks.

The front wheels still turn the CV joints and halfshafts. Where the halfshafts go into the front axle case they're supported by the case bearings. Those bearings are in motion whenever the truck is in motion, even when in 2HI. So if the gear oil viscosity is +1,500 Poise, those poor case bearings are running dry and they'll croak.

The front axle is "engaged" by a DC motor electrical actuator. The DC motor drives a worm gear that pushes or pulls a pawl: at the end of the pawl is a fork. You know, like a shift fork in a tranny.

There is a splined collar on a splined shaft at the R&P and spider gears. The fork fits into the collar. When the pawl pulls the fork/collar one way, it disengages the R&P from the halfshafts. Pushed the other way, the halfshafts are engaged to the R&P.

So you can imagine when the gear oil has the consistency of taffy. I'm sure chevroletmb is familiar with -42 F weather, as I am where I live. At -42 F (No windchill, that's ambient temp folks brrrrrrr) an 80W-90 has a consistency more like a brick. You'd need a hammer and chisle to move it.

Imagine starting up a nice new GM truck at that temp, taking off, and pressing 4HI: the case bearings are running dry as the ball bearings have cut a channel through the frozen gear lube, so they won't last long. The DC motor strains to move the pawl and collar, but can't as the collar is froze solid.

CRUNCH CRUNCH CRUNCH CRUNCH CRUNCH BANG OH F***!

This is NOT a GM problem, all the other makes have it. My 1990 Toyota 4Runner had a similar front axle, called the ADD, and Toyota was VERY specific to recommend a 75W-90, preferably synthetic, in the front axle for Canadian and Cold Climate use.

I run a commercial synthetic GL-5 in my front axle: Mobil MobilLube SHC 75W-90, which is Brookfield rated at 980 Poise at -40 F. This is quite a bit below 1,500 Poise, so a good safety margin, with an operating limit of -54 F.

I think GM might have avoided most of this problem if they had factory-filled with a regular 75W-90. It's not as good as a synthetic, with a much poorer high temp rating compared to an 80W-90, but its low temp is good to -40 F.

XTOAK · February 1, 2004

This is something that shouldn't be ignored especially with the temps some of you have been having this winter in the lower 48 states. Seems to be alot more severe for you all than you've had in recent years.

I have a coworked who just picked up his brand spanking new 2004 2500HD and had less than 700 miles on it Tuesday, when the front diff froze up on him and I mean burned the bearing and internals a pretty blue. The dealer admitted they "forgot" to drain the dino oil and install the synthetic per the TSB. Ends up GM gave him a free 7-year powertrain warranty for the hassle of having a new truck crater on the frozen highway and to help rebuild his confidence in GM quality. Hey, mistakes can happen but at least they made it good.

I immediately called my dealer whom I purchased from and they were able to look it up on the phone and confirm they had completed the TSB on my truck. Might be something worth checking if you're having extended cold temps in the northern states....

JayMan · February 1, 2004

Well, if you have to operate in temps colder than -40, you have to take SPECIAL precautions. No vehicle as it leaves the factory is ready for that sort of environment.

What does that entail? Winter front, synthetics all around, block heater, battery warmer, oil pan heater if available, survival kit, etc.

The extra "cost" to at least run synthetics is really not extra at all. When you figure that a regular off-the-shelf 5W-30 is frozen solid at -35 F, or a regular cheap 80W-90 gear oil is hard as a brick at -30 F, the extra wear and even failure costs you way more than the extra "cost" of synthetics.

Ditto for the automatic trans. Regular Dexron III ATF exceeds 100 Poise Brookfield viscosity at around -35 F, while Mobil 1 ATF is rated 51.5 Poise Brookfield at -40. I can't believe they don't recommend a synthetic ATF in Alaska of all places.

You know, GM could have avoided most of this problem by just filling the front axle with a regular non-synthetic 75W-90. That stuff is good to almost -40. The "extra" high-temp protection from a 80W-90 is minor, and most synthetic 75W-90's have superior high temp properties compared to even a regular 85W-140.

It wouldn't hurt to drain and refill the front axle again with a synthetic 75W-90, just to play it safe. I've always had good results with Mobil MobilLube SHC 75W-90 in cold temps, at least in my commercial equipment.

RossT · February 3, 2004

You really do need to check that it's been done. Both dealers in my town do it to every truck that comes in. I purchased my silverado in a town 300 miles away. I had my local dealer check, and it hadn't been done. They did it for me free of charge!!

YZRider · February 3, 2004

I took mine to the dealer as the front end seemed "stiff" and we were experiencing -35C temps. I had checked and I had the black vent. They changed the oil to synthetic, but left the black vent in? The TSB I had said to change the vent for the white one. I guess they figure they will pocket the $30 from GM for the new part?? I may have to go back.

bigdogs · February 4, 2004

I got mine changed to synthetic with that TSB too but never did check to see if they changed it to the white cap, it was not listed on the invoice, just the oil.. Where is the vent cap located on the front? On a COLD concrete floor I want to spend as least time as possible on it

JayMan · February 4, 2004

I got mine changed to synthetic with that TSB too but never did check to see if they changed it to the white cap, it was not listed on the invoice, just the oil.. Where is the vent cap located on the front? On a COLD concrete floor I want to spend as least time as possible on it

Depending on how tight the engine bay is, you might have an easier time determining the vent from above:

Look along the frame rail near the left front wheel: you should see a black vent hose attached somewhere along the side or top of the frame rail. You should also be able to shine a bright Maglite or similar flashlight and actually see part of the top of the front axle.

If the engine bay is too tight, then you have to get on the cold concrete.

Look above and somewhat behind the axle fill plug, which should be on the driver side of the axle. There will be a plastic grommet about an inch or so wide, and the vent tube should be hooked up to that. The vent system is at the top of the axle.

Hope you can accomplish this task quickly while laying on the cold cement. Otherwise if your vertebrae are as gimpy as mine, they'll pull the Pretzel Trick on you and you'll have to wait until July before they calm down.

I switched my front axle to a commercial synthetic 75W-90 at 600 initial miles, and still have the black plastic vent grommet. No leaks yet.

ranch43 · February 4, 2004

I just took my truck in today after I told them the 4 wheel was going in hard. They said they put 90 weight in at the factory, and with our cold it is way too much. They flushed and filled it with synthetic and are "pretty sure" no permanent damage was done. We'll see.

bigdogs · February 4, 2004

Thanks Jerry, I'll see if I can see what color it is w/o lying on the concrete.

XTOAK · February 4, 2004

I spoke with a fella yesterday who is an inspector for the State of Alaska Oil & Gas Commission, and he was on his way to Anchorage last week in his 2002 2500HD Ext. Cab 4x4, and the front end went out on him just as he was going into Anchorage. He said he slowed down to get off an exit ramp and the thing went...sounded like heck he said. He said he was able to put it in 2 wheel drive and took it to Alaska Sales and Service.

The tech took one look at it and said it was because the front end didn't have the synthetic oil in it, so under warranty they replaced the front diff and filled it with syn.

That makes two guys I know personally here in Alaska...might be worth a check even if you live in the lower 48.

JayMan · February 4, 2004

Look, I know a lot of folks don't want to think about servicing their front axle:

It's dirty, it's messy, a pain in the a**, and you stink of gear oil after all is done. When you consider the huge pain in the a** of a possible front axle failure, it suddenly becomes a minor chore.

I'm still not sure why GM chose a heavy 80W-90 to a 75W-90. According to my Esso Lubricant Products Handbook, and the Mobil Commercial Lubricants Products Handbook, here are some typical specs:

Kinematic Viscosity 100 C :

Esso Gear Oil GX 80W-90 15.8 cSt

Esso Gear Oil GX 75W-90 15.8 cSt

Mobil MobilLube SHC 75W-90 15.9 cSt

Flash Point :

Esso Gear Oil GX 80W-90 165 C /329 F

Esso Gear Oil GX 75W-90 150 C / 302 F

Mobil MobilLube SHC 75W-90 205 C / 401 F

Pour Point:

Esso Gear Oil GX 80W-90 -27 C / -17 F

Esso Gear Oil GX 75W-90 -45 C /-49 F

Mobil MobilLube SHC 75W-90 -48 C / -55 F

Brookfield Viscosity at -40 C:

Esso Gear Oil GX 80W-90 Failed test +1,500 Poise

Esso Gear Oil GX 75W-90 1,300 Poise

Mobil MobilLube SHC 75W-90 980 Poise

The Brookfield cold temp test is very important, as a viscosity >1,500 Poise will usually cause the axle to fail. Since regular GL-5 80W-90 and 75W-90 appear to be priced the same even by the 5 g pail, I honestly can't see why GM chose the 80W-90. The increased high temp flash point is very minimal, only a difference of 27 F.

The commercial Mobil synthetic product has a high temp rating almost 100 F higher than a regular 75W-90, and 72 F higher than the 80W-90. At -40 the commercial synthetic is still quite safe to use.

I would say, if in doubt, change to a synthetic. You will have better low temp protection AND better high temp protection. About the only thing you have to watch out for is leaks from the vent grommet. I did my initial service at 600 miles, then every fall, no leaks yet.

JimWilson · February 5, 2004

I took mine to the dealer as the front end seemed "stiff" and we were experiencing -35C temps. I had checked and I had the black vent. They changed the oil to synthetic, but left the black vent in? The TSB I had said to change the vent for the white one. I guess they figure they will pocket the $30 from GM for the new part?? I may have to go back.

May? You might want to increase that priority to "will". GM certainly didn't make a change to a different breather cover for no reason, and my guess is that it no hablo synthetic. You should really consider getting that taken care of.