Differential Gear Oil Analysis

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Staff member
Jun 5, 2002
Iowegia - USA
Used Gear Lube Analysis for 1992 Suburban's Rear Differential. Differential had 254,763 miles and 73,687 miles on Gear Lube. This is a synthetic Gear Lube, 75W90. Physical Properties: Viscosity 14.5 [Still in SAE 90 grade]. % Solids TR Oil Degradation: % Oxidation 96.4% out of 100% %NOx 57.3% of 100% TAN 3.6 SpectroAnalysis: Fe - 231 Cu - 1 Sn - 1 Al - 2 Ni - 1 Mn - 3 Si - 109 Na - 2 P - 1152 OAI Comments: Oxidation elevated - No Kidding! TAN Elevated - No Kidding! Analyze Operating Conditions - This means "open-er-up" and see what's going on. Change OIL, Resample at Next Regular Interval. All other elements zero. Analysis didn't include sulphur. Would have liked to have seen the Sulphur content. In my view, they should include this for gear oils. When the metallurgical analysis comes in I will reveal the rest of the story. In the mean time, consider what oxidation means in this context and why the Total Acid Number "TAN" was high.
No Sprintman, it was not Redline, but I am considering putting Redline in all of my diffy's! We had been having problems keeping rear U-joints in this vehicle. A noise developed in the 10-bolt, 8.75" ring gear differential and we had one last U-joint replaced. I pulled the cover off and found all kinds of sheared metal, plus some pieces of gear tooth adhering to the magnet. Thank goodness for magnets! Upon further inspection, I found two teeth of the ring gear (teeth next to each other) had sheared off on the outer edges. The Drive pinion gear was still engaging the ring gear on the inner section of the ring gear where there is still enough tooth material for engagement. I cleaned the diffy out and installed new GL-2-4 gear lube and promptly took it to my Dyno shop for repair. Took photographs for repair shop and for any upcoming claims. The metallurgical analysis showed normal alloy content for Rings and Pinions, but found particles of metal (embedded in the roller bearing asseblies) indicative of the type used in the shim pack. They also found the broken ring gear teeth did not have the Rockwell hardness it should have had. They theorized the following scenario: Comments in [] are my injections. "Shim pack material finally wore [shucks, it only had 254,000+ miles on it] and broke apart causing brinelling in the drive pinion inner bearing and race, which then caused extreme heating of the GL, causing it to oxidize. The oxidation and extreme heating, along with the large metallic particles floating around, reduced the lubricant's ability to provide a surface film of organometallic sulphur and phosphorus compounds. The lubricant further became acidic over time, thus reducing the ability to reduce acid attack on teeth surfaces. The weaker teeth on the Ring gear were then left unprotected, and since softer than normal, sheared apart under the forces of the drive pinion. Most likely, one tooth broke and being adjacent to the second tooth, caused its failure as well. The teeth that sheared either had low induction heating (heat treating) at manufacturere or were annealed by the hot spots, causing them to soften over time. The lubricant performed well beyond what could be expected in this failure scenario; the viscosity being at the median end of the SAE 90 grade even after bearing failure. Recommendation: On large and heavy vehicles with the smaller differentials, especially significant for GMC vehicles, change oil every 17,500 - 30,000 miles for normal use, and every 12,500 miles if pulling any loads over 1.5 tons axle weight, and over 500 pounds Tongue weight." " BTW, There was also a blunted tooth on the drive pinion. I examined all bearings and races (even the wheel bearings) when returned from the metallurgical lab, and saw that only the inner drive Pinion bearing and race had been damaged. All other bearings appeared to be in good shape considering their mileage and the adjacent failure.
Another problem with GM 10 bolt 8.5" differentials from 91-2000 (on many GM light duty trucks and rear drive cars)is a faulty factory gasket which prevents lube from getting to the axle bearings.
Why would a gear lube suffer oxidation and nitration? Does the differential really get that hot? Why would it have a TAN? Did it start out with a TBN that degraded to a TAN, and if so how?
Differentials normally run pretty hot, but with the extra metal Molakule had in this one, it ran really hot. When doing measurements on other lubricants than motor oil, i.e., gear oil, hydraulic oil, etc., you use the measurement of TAN (total acid number) vs TBN (total base number) used in motor oil. That's as for as I can take it. Molakule, Terry, Bob, or George. Care to explain all this. [ August 22, 2002, 07:39 PM: Message edited by: Johnny ]
Far be it for me to dissuade someone here from using Red Line's gear oils but I once talked to a Toyota Atlantic racer who had better luck with Synergen's Syngear II racing gear lubricant. http://www.synergynracing.com/products/syngearll.html The application where he saw the difference was the Staffs gearbox in his Ralt formula racer. I forgot the wear examples he cited but I remember he was mightily impressed with the results. --- Bror Jace
Molakule Is that 10 bolt known as a Salisbury diff? If so I had one in my 1971 Holden Monaro 350 Chev and nothing but trouble. Broke 3 left and 2 RH axles and then 'split the hemisphere' or something they told me and required a new housing. The Ford stuff eg. 9" is so much better no wonder most GM race cars use it.
You know gear lubes have not been covered like motor oils and I thought this would be interesting to point out. When gears have sit, especially heavy equipment, gear oils have had plenty of time settle back to the bottom of the unit. This type of lube system for such a unit is a slash system where the oil is splashed up on the gears and no oil pump is used. Now the interesting point is that most all gear oils have no climbing ability. Redline, Amsoil, Mobil, and I'm not sure just how many more doesn't climb when cold. Thats why so many have put the lucas additive in so that when the gear starts to pull, the lubricant has a tendency to stick and pull up, where most will fall back off until the splashing effect starts at a higher speed. This is just one little problem that most lubricant manufactures fail to address in my opinion. Schaeffers, and a small other handfull of specialized lubricant companies actually have the gear oil creep up even with the gear barely moving. Now look at the picture of a rear end pinion and ring gear,  - As you can see, oil can settle down off the gears and the ring is used to pull the oil up. In some of these specialized oils like schaeffers for example, the gear oil will climb up until it reaches about 130 degs, and by then it thins out and reacts like any other gear oils with less resistance. The other aspect of a gear oil, EP,EP,EP. This is where most fuel mileage is lost due to the sliding action of these gears creating heavy amounts of friction therefore drag and ultimatly fuel mileage. Alot of gear oils are heavy on the ph, to such a point of smelling like a rotten egg. From the way I understand it, this type of additive chemistry in heavy amounts can cause the pitting on yellow metals and such in a lot of older gear systems. The ep levels of this type of additive is adequate and works well but with the use of Mo, you will experience a much higher level of protection, lower levels of friction and ultimatly better fuel mileage. here is a picture of how moly works in a gear system.  -
Bror, Absolete difference in shifting a Miata trans with the Syngear vs another brand synthetic gear oil in the Miata here we own. This one was supposed to have been fixed under warranty" second gear hub and slider tolerances too close" makes for hard shift to 2nd when cold. Not now!
Just wanted to add some info about the splashing effect. Red Line performs differently than other oils. It will splash nearly instantly.
Cold weather can be just as damaging to differentials and transmissions as sustained high-temperature use. Rapid oil flow to the bearings and adequate lubricant splashed to the gear teeth is critical to prevent component fatigue and premature failure. At -15°F an SAE 90 gear oil will take more than 5 minutes to flow to the bearings while Red Line 75W90 requires only a second.
And Bror if I remember right I thought their complaint was inadquate clinging? In such a case they should be using the Shockproof gear oil. Did they ever try it? I suspect not:
ShockProofTM Gear Oil - a unique lubricant containing a suspension of solid microscopic particles as an extreme pressure agent. The viscosity characteristics allow the lubricant to resist throwoff and provide a film thickness greater than an SAE 250 grade, with the same low fluid friction as with our 80W140. Recommended for offroad racing and problem gearboxes.
Originally posted by Jason Troxell: Just wanted to add some info about the splashing effect. Red Line performs differently than other oils. It will splash nearly instantly.
Sorry Jason, but that's an impossibility. No oil can SPLASH unless there is something to agitate it, So, when a big truck or heavy piece of equipment, in low range, starts to SLOWLY move, that lubricant is NOT being agitated enough to splash. A ring gear is moving through the lubricant and if the lubricant has a clinging or creeping effect, then it can supply enough lubrication from these types of starts by sticking too the ring gear instead of relying solely on splashing. Even your car, when you first drive out of your driveway, which most back out, that isn't enough speed to agitate the lubricant into a splash. Try this little experiment, get two bowls, and two manual egg beaters. fill both bowls half way one with your redline or what ever gear oil you like, the other with either Schaeffers, I think Mystic is another, Hydrotex? and from what I have read, this syngear to name a few.(if you can't get one of those get a bottle of lucas additive and add to the 2nd gear oil)The latter I advise against for normal use but for this experiment will demonstrate the creep characteristics. Now, take your egg beaters, stand it straight up in the middle of the bowl, spin the handles, then do that with the other one with the creep additive. This will demonstrate how the clinging effect is on a gear oil. What happens in Schaeffers case is, that oil will climb all the way up to the handles depending on how fast you turn the beater. The other will push away and will not climb. I don't even include Amsoil in this as I had a dealer the other day come by with his 80w90 marine gear lube and it did exactly the same as all the rest. It pushed away. Another thing to look for in a gear lube, especially if in a boat or high moisture area, Take two little jars(a mason or baby food jar) fill 1/4 of water, 1/4 gear oil(50/50 of each) (this also works with hydraulic fluids) shake both vigorously in the same hand, both at the same time for a minimum of half a min or better. When done, put on to a flat surface, and examine the speed of separation of the gear oil from the water. Also take note of the air bubbles from the agitation that has foamed. Again, with the amsoil dealer his did a pretty decent job separating, took approx 1.5 mins to completely separate. Schaeffers, less than 20secs when set down to completely separate. Also, found good amount of bubbles in the fluid, the argument he had was schaeffers was dark couldn't see it, I gave him that, but then we examined the top where the bubbles where sitting on the top, again, no comparison. Now the amsoil did a whole lot better than some stuff terry gave me awhile back on my trip, I think was syn something don't remember. It didn't do well at all like most I had seen. I never have tried that with mobil or pennz but a lot of chevron as that is popular around here. Again, no comparison. Of course, lastly, our dreaded timken machine. Again, the moly held out over and above as the picture shows above how it affects the basic metal over a 3.5 yr stretch on a gear box which I suspect doesn't have a pump either and rely's on the climbing properties of a lubricant. Yeah, I know, me and my back yard experiments, but I think it shows some interesting characteristics which are very important when it comes to cooling.
No, never have seen a redline lubricant in these parts. I think you'd find the creep comes more into play especially in cars as they usually start out from a dead stop and take off with some torque. yes, standard gear oils will leave a minor amount on the gears but with the creep, it provides an awsome hydrodyamic coat before the ring turns halfway. This is another reason to take any ordinary car/truck, and drive it slow for a short time, allowing the ring and pinion to get some basic lubrication applied prior to acceleration. Interesting thing about the creep additive is, it is thick when first starting out, but once it gets to around 130degs, it has thin back out like ordinary gear oil. Also it will not creep at that temp but by this time, it has already coated the gears. Now add the Mo to the mix, got an excellent boundary lube in an area that really shears hydrodyamic properties since there is so much pressure applied between the two gears trying to push that vehicle from a stop to what ever speed.
Actually Phillips petroleum recognizes the Timken test ! I as looking at their gears oils and they showed a value of some type load number.
Our LE oil Tech rep has a machine with meshed gears in plexi-glass. Its run with an electric motor. The LE gear oil is sucked up and on the gears in a string like ribbon. It realy stays on the gears and will not sling off. Its realy crazy how well it will ride up and will keep the gears in a constant bath of lube. We have had great luck with it in our Faulk speed reducers and a local river dredging company had to rebuild there crain gear box every year. With LE no problems for over five years.
Yep, forgot about LE. Just keep in mind, like motor oils, there is many sides to a quality gear oil as well. Climbing is getting it there, Water separation, aeration, ep properties, and more.
Bob, This is probably a good time to ask ...what is your opinion of the LE product? It looks like a high quality petroleum basestock with a robust additive chemistry - similiar in that sense to the Schaeffers approach .... [ August 23, 2002, 07:55 PM: Message edited by: BOBISTHEOILGUY ]
Excellent company. Has some great stuff. I'm not all that impressed with their special Ep additive (monolec?) and such, but they are no dummies in the lubrication industry. We went up against them head to head at a iceplant a year ago. Guy wanted some food grade grease. On the surface, both looked good. Both showed promise to do the job no problem. The thing that won us out over them was 1-, theirs didn't hold up to the timken machine. The customer wanted both of us there, and both to be put on the timken. So, we did. The two reps themselves was there, they put on the grease, and pushed the lever. We were so suprised as we expected better from them as they also did, but it wasn't the case. We even done it a 2nd and 3rd time, each time the results were the same. The 2nd thing that the customer like about ours over theirs, Price. The interesting thing is, there is many companies that have great stuff but they also demand a higher price. I've seen one company that produces grease with the same exact quality as schaeffers and they charge for that same tube of grease we have, 7.00 per tube. ours, under 3.00. So with that in mind, I have seen many that we come up against, and compare equaly except in price. I thought their gear lube demo was good. gear oil demo
Gee, Bob, can you shrink those pictures down some? They thoroughly wrecked this thread. [freaknout] Jason, you might be right about the Shockproof gear oil. Stan said he didn't experiment with different weights of Red Line ... and I bet he didn't try the Shockproof gear oils, either. [Frown] Do you remember my conversation with Stan on Use.net? It was several months ago. [Confused] He was whining at an unrelated vintage race and someone tipped him off to the Syngear II. He tried it, noticed a difference and was happy. That's about it. [I dont know] --- Bror Jace
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