I ran through the replacement parts for 10 bolt GM axles and found that the same bearings and carrier parts were common from 1972 until 2016 which would suggest there is no critical change in running clearances. I did find that the 12 bolt axle had a design change to reduce the ring and pinion thrust load several years ago but from the time that the factory changed its recommendation for rear end lubricants from 90W to synthetic multiviscosity there seems to be no change in tolerances. When the axle is torn down for repair there may be indication of the root cause of the problem but often thatâs not the case.
My experience with C-lock rear end failures is that operating without adequate oil will usually show up first with axles bearing failures and if the whining from those bearings is ignored long enough either the axle will cause the vehicle to drag to a stop or the outer pinion bearing will fail and the ring and pinion will grenade. But honestly rear axle failures other than axle bearing were a somewhat rare repair for me.
Friction modifiers were required for friction clutch posi-traction. Without the proper friction modifier the outer wheel would be drug in a turn until the clutch pack wore out prematurely resulting in non functioning of the posi-traction.
Were both these lubes GL-5 rated? I understand this has the extra anti-wear additives required for use in differentials.
I ran into this with a failed manual transmission once. The synchronizers were TOAST! GL-5 gear lube had been used. I did some research and the GL-5 gear lube has anti-wear additives that form a protective layer under stress. When on steel they are softer than the steel so sacrifice themselves in order to protect the steel.
The problem comes when these are used in synchronized manual transmissions with âyellow metalsâ. The protective layer is harder/stronger than the material it is between so ends up wearing the synchronizers instead. GL-5 gear oils which typically have that STINK we all know are great in diffs but not in synchronized transmissions with yellow metals like brass.
Do you have access to the container that was used? Was it a GL-5 gear lube or something else?
Many manual transmissions these days specify automatic transmission fluid which would not work in a diff. Obviously that wasnât used here but it could have been some other type of gear lube that wasnât GL-5 rated.
Is it possible the mechanic accidentally introduced some metal contaminants when refilling? But as others have said, those would take out bearings first.
less than one weekâs worth of driving . . . probably less than 300 miles, possibly far less than that
As I said, it had originally come in for a routine service, and the guy put in the wrong gear oil. it left under its own power, so to speak, and returned just a few short days later, on the hook
Tomorrow at work, Iâll compare the specs of the 75w90 synthetic gear oil, versus the 85w140 synthetic, which the guy incorrectly used
The 85w140 was from one of those mobile dispensers . . . the one in a drum, with casters and a pump handle. Iâll have to look on the label to determine if it was GL-5 or not
I donât have a background in chemistry or metallurgy and I canât speak with authority on the effects of GL5 on a differential of unknown age and use, but Iâm in the same business as you are, and have been all of my life. So my experience is purely anecdotal.
The only issues Iâve seen with GL5 have to do with synchros in older manual transmissions, and that wear happened over a significant length of time and use. And limited to synchros, not the actual gears and bearings.
GL4, GL5. 75W90, 80W140. Conventional, synthetic. I have a very hard time believing that a differential in what I assume is a domestic light or med duty truck, could go from perfect working order to trashed in 300 miles because of the fluid. I would think you could have put 10W40 in there and it would have lasted 300 miles. I just canât help but think there is a missing piece somewhere. Noise was there prior to service, driver got the truck stuck in the mud and rocked and revved it like crazy, who knows. Just my opinion.
Like I said in another post, if it were -30* or the truck went 300 miles doing launches at the 1/4 mile drags that would be one thing. But normal service, less than a week, just doesnât add up.
Even if it wasnât the cause of this failure, I would have canned him. Itâs one thing to make mistakes or be ignorant about something once. When someone points out the mistake and you do it anyway- good luck in your next jobâŠ
Seeing as how the deed may go unpunished, have him service another one in the fleet. If it fails in a week or two, you have your answer
I agree! I have come to realize certain people will not listen and just will find a way to mess things up over and over in my dealings with the general public. I am OK with this as long as they are willing to accept responsibility and pay for the repairs. I have problems when they try to blame someone else which seems to be all too common these days.
The guy was informed he was using the wrong fluid and did it anyway. I agree this might not be the complete cause of this failure as does everyone else but people like this WILL eventually be the root cause of some other issue. I donât even want to know what a diff in a heavy commercial truck costs but I am sure it isnât cheap.
Again, I have known people who basically run their diffs dry over and over and they didnât grenade like this. I would think that even with the wrong fluid or motor oil for that matter, this thing would have run farther than 300 miles as suggested.
You might look up online and see if there are other incidents of failure with this same type of differential. Sometimes you see certain parts with a defect that fail over and over again. It sounds like you have quite a few of these trucks with the same setup and none have failed like this. You might also research failures if the wrong fluid is used in that model.
A friend rebuilt a 12 bolt GM rear end and failed to fill it with lube and it began howling in less than 20 miles. The truck was brought back on a hook but never grenaded.
I know that with vintage cars, particularly vintage British cars. Itâs considered a big no-no to use modern GL-5 spec gear oil. GL-4 must be used. Apparently the GL5 eats bronze parts for lunch, and the older stuff doesnât.
What failures have you heard that were the result of improper lubricants in GM rear ends? And how improper were the lubricants that caused the failures?
Our warehouse department buys the fluids used in the shop
There are a few factors . . . such as what we request, whatâs already âin the systemâ in other shops, what the vendor(s) can easily locate and so forth
That last one is sometimes an issue, because we sometimes get a certain brand filter or fluid, because thatâs what the vendor can easily and quickly obtain, versus the specific brand we actually wanted
I had said the boss sublet the repair(s) out to an independent shop. Non-fleet, in other words. I donât know if it was a/the dealer or somebody else.
Anyways . . . the truck came back a few days ago, and I was told to make sure everything was fine.
I put it in the air and it was obvious that a complete axle assembly was installed. The only parts that were obviously reused were the brakes (rotors, pads, calipers and hoses). Maybe the axle shafts were also reused, but I didnât look into it any further, because I didnât even remove the tires to check.
I did check the fluid level and rubbed my finger on the fluid. Seemed to be the correct viscosity.
I drove the truck and all was back to normal. After the test drove, I did a final check on the fluid level.
I suspect the shop installed the complete axle assembly, rather than fix/overhaul the differential, because it was quicker. Less labor costs, but probably much higher parts costs. They also probably didnât want a truck eating up valuable space for a length of time. That last one may have been the deciding factor, for all I know
Thatâs what I did went the diff went out on my â72 Duster. Put it up on jack stands in in dorm parking lot, disconnected the brakes and driveshaft, swapped in a used rear axle assembly from the junkyard.
