Gear noise at hwy speeds, rebuilt 400,000 mile differential

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We did this with the marking compound. It checked out per the Factory Service Manual.

Mind sharing gear backlash and pinion preload installed in thousandths of an inch ?
Images/photos of gear contact patterns achieved may be hard to come by , I suppose ? .
 
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Let me help you out here on what “most likely” is happening from one who has done a lot of work in gear design and servicing. What you have is a helical bevel gear set (90° transfer) regardless of the application and/or specifics such as hypoid, miter etc. Very basic design.

I am assuming your backlash and contact patch is within factory limits and the pinion is toleranced properly per your comments. This is also assuming the original gear set was manufactured as a MATED PAIR. (they were run in together)

(“most likely” is based on the assumption that your information as related is accurate with the understanding that different people have different hearing and interpretations of sounds and different conversational definitions- this is where I would use accelerometers, UT and thermal to make the determination but we go with what we have)

Those assumptions are critical to what I’m about to post because if they are not correct then the following could still be correct but there would be no way to know without a tear down and assessment. Pictures of the contact patch around the set with dye and clear pictures of the profile and finish would help assess the condition.

Based on the information provided, you are almost certain to be experiencing “singing” (gear jargon) due to a combination of finish changes and probable geometry change along the face/flank.

It is a condition well known for all gears but prevalent on helical designs and most prevalent on helical bevel due to the geometry. It is very common on gear sets that are rebuilt that don’t follow some simple rules. (which are seldom in anyone’s IOM manual because nobody seems to think about it)

The helical bevel transfers power in a wiping motion rather that a full push so it’s on a pressure gradient (virtually identical to a worm gear in mechanical principal). This also brings surface finish/asperities into a more critical role than other arrangements. That wiping motion is also relative to the applied load and the engaging/retreating tooth geometry has t hold the gear still during the transfer.

When a gear set is run in, the gears are loaded to force some deflection and mating above design (to test the gear/machining/geometry/finish) and basically allowed to “mold” into each other. (sometimes compounds are used to alter the finish a bit too)

Once installed this pattern continues over the service life and "wears in".

What then happens over the normal course of a gear is the typical polishing and normal surface pitting along the contact path and there can be some load-initiated deflection. This “indexes” gears.( to each other)

So, during a rebuild, it is customary to mark the gear set so the mating patterns are put back and its customary to glass bead the teeth to remove the polished finish and create a textured surface that will hold oil allowing for a “field lap”. (this often eliminates the “singing” because the polished surfaces tend to sling oil off which is why a textbook sign of under lubrication is polishing so when it holds oil and re laps itself this starts a new mating).

Its not the “kiss of death” if those actions are not taken but it traditionally creates both conditions you describe and because it is a more polished face than designed, it will run hotter due to a change in the tribological regime it was designed for.

Thicker lubricants can dampen the effect but not for long usually because the mechanical wiping will overheat then in the contact patch so even when they may return to design viscosity in the pumpkin- they have less film strength in the engagement area.

What leads me to believe you are probably OK ( just inconvenienced) is your statement that you don’t hear or feel grinding or shuddering from 0 to that 60 odd MPH because if there was severe deformity there, the gear would want to try to back drive and you would know that instantly and there’s no hiding that.

All things equal, eventually they will wear in on their own but as you stated, the vehicle will probably be long gone by then.

If the temp runs abnormally high during normal driving then I do suggest a rebuild with checking the entire gear geometry and blasting the teeth.
 
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I am concerned about the Amsoil Severe Gear 80W-90 in my 1992 Previa N/A RWD's differential.

When driving on the freeway at 80+ mph the differential gets up to 235 degrees F in ambient temperatures of 90+ degrees F. (IR Thermometer shooting rear of differential) ........

There ,you have it . Thinner oil runs hotter vs thicker oil runs cooler in real life .
A thinner Amsoil SG 80W90 has a much higher operating temperature of 235 F (113 C) , at a very low operating viscosity of 11.7 cSt , hence providing substantial lower oil film thickness MOFT for components protection with metal shavings at low'ish 15000 miles intervals .


This afternoon when I drained the Amsoil Severe Gear 80W-90 it had some metal debris on the magnet.

Mo.......you said that running 85W-140 will likely increase my operating temperatures, ................
No . It is exact opposite .
85W140 reduces your operating temperatures
as demonstrated below , by as much as 5F -35F .

I am using an IR thermometer gun and I register between 200 - 230 degrees F. Depending on the ambient temperature. ..............
85W140 at 200F (93.3 deg C) delivers an operating viscosity of 35 cSt, i.e 3 times that of 11.7 cSt ( from thinner 80W90) . Alternatively,
85W140 at 230F (110 deg C) delivers an operating viscosity of 21 cSt , i.e 1.8 times that of 11.7 cSt (of thinner 80W90) .

Hence, factoring in higher pressure-viscosity coefficient of mineral 85W140 than that of synthetic 80W90 , you easily more than double ,if not triple the differential operating oil film thickness MOFT , by extension, very substantial components longevity derived from thicker 85W140 .
 
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apham8

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Mind sharing gear backlash and pinion preload installed in thousandths of an inch ?
Images/photos of gear contact patterns achieved may be hard to come by , I suppose ? .

I don't have actual photos, but everything was done as per the Factory Service Manual. All tolerances were correct and within range. And the contact pattern was as pictured.
 

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apham8

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Its not the “kiss of death” if those actions are not taken but it traditionally creates both conditions you describe and because it is a more polished face than designed, it will run hotter due to a change in the tribological regime it was designed for.

Thicker lubricants can dampen the effect but not for long usually because the mechanical wiping will overheat then in the contact patch so even when they may return to design viscosity in the pumpkin- they have less film strength in the engagement area.


ABN_CBT_ENGR, thank you for your input, highly appreciated and valued.

This is precisely the answer I was expecting. I figured that something was off because of the process that we went through in the rebuild. And just like you mentioned it is not necessarily something that a manual, even a Factory Service Manual, would suggest.

I did go ahead and go with the Schaeffer's 293 75W-90. Sure enough the "singing" was still there at 60 - 70 mph. Same drive as last night with the Lucas 85W-140 with similar ambient temperatures of 79 degrees F, versus 81 degrees F. Rear differential read 220 degrees F, versus 222 degrees F with 85W-140.

I'm satisfied for the time being with the Schaeffer's 293. I will continue to run it, but after taxes the price is virtually identical to having Amsoil Severe Gear delivered to my house. So it may be a toss up between Schaeffer's and Amsoil Severe Gear.

All things equal, eventually they will wear in on their own but as you stated, the vehicle will probably be long gone by then.

If the temp runs abnormally high during normal driving then I do suggest a rebuild with checking the entire gear geometry and blasting the teeth.

ABN_CBT_ENGR, I would rebuild the rear end if I were planning to keep this vehicle much longer. And if I do end up keeping it as a back up vehicle I will likely throw in a LSD into it. The swap has already been done by someone else with the same vehicle. From the gauging their cost, swapping in a LSD would likely be just bit more expensive than an entire rebuild.
 
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apham8

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There ,you have it . Thinner oil runs hotter vs thicker oil runs cooler in real life .
A thinner Amsoil SG 80W90 has a much higher operating temperature of 235 F (113 C) , at a very low operating viscosity of 11.7 cSt , hence providing substantial lower oil film thickness MOFT for components protection with metal shavings at low'ish 15000 miles intervals .



No . It is exact opposite .
85W140 reduces your operating temperatures
as demonstrated below , by as much as 5F -35F .


85W140
at 200F (93.3 deg C) delivers an operating viscosity of 35 cSt, i.e 3 times that of 11.7 cSt ( from thinner 80W90) . Alternatively,
85W140 at 230F (110 deg C) delivers an operating viscosity of 21 cSt , i.e 1.8 times that of 11.7 cSt (of thinner 80W90) .

Hence, factoring in higher pressure-viscosity coefficient of mineral 85W140 than that of synthetic 80W90 , you easily more than double ,if not triple the differential operating oil film thickness MOFT , by extension, very substantial components longevity derived from thicker 85W140 .

What you're saying may be true, but I don't think my data necessarily supports the temperature claims regarding gear oil weights.

Amsoil Severe Gear 80W-90 @ 235 degrees F was with driving 80+ mph in 90+ degrees F ambient.

Lucas Conventional 85W-140 @ 222 degrees F was with driving 80+ mph in 81 degrees F ambient.

The ambient temperature differences likely account for some of the differences in temperature readings.

The logic you're presenting very well may be the case. But my numbers are abnormal to say the least. My differential is running at elevated temperatures from the norm. With virtually no additional load nor towing, I'm reading numbers that are expected of heavy loaded conditions.
 

MolaKule

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Thanks MoleKule for the response. We did this with the marking compound. It checked out per the Factory Service Manual.

I have a suspicion that the pinion and ring have been worn in some kind of way that is causing the noise. Mind you, the differential had 400k miles on it! That’s when the bearings were replaced. So it is a worn out unit.

I just did a run this evening at 80+ mph with ambient temperature of 81 degrees F. I registered 220 degrees F on the back of the differential. I’m concerned if conventional fluid is ok at that temperature? I drive like this, 80+ mph, daily and ambient temperature is 90+ degrees F.

I am likely going to keep running this differential just as it is until it gives up, which I hope it doesn’t. Honestly, I cannot invest more into it. I’d be better off getting into another vehicle.

Right now, I’m leaning towards Schaeffer’s 293 75W-90, which is about $10-$11 locally per quart and changing twice per year.

I think that Schaeffer's Blend is a good choice.
 
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I did go ahead and go with the Schaeffer's 293 75W-90. Sure enough the "singing" was still there at 60 - 70 mph. Same drive as last night with the Lucas 85W-140 with similar ambient temperatures of 79 degrees F, versus 81 degrees F. Rear differential read 220 degrees F, versus 222 degrees F with 85W-140.

I'm satisfied for the time being with the Schaeffer's 293. ......................... So it may be a toss up between Schaeffer's and Amsoil Severe Gear.
The improved performance of Schaeffer 293 achieving lower operating temperature of 220 deg F (against 235 deg F of Amsoil 80W90) assuming identical operating conditions, has positively increased operating viscosity to 13 cSt (against 11.7 cSt operating of Amsoil) .

Meanwhile the Lucas 85W140 has had no real advantage at quite similar temperature of 222 deg F vs 293's temperature-wise , however it delivers a higher operating viscosity of 24 cSt, which is 1.85 times that of 13 cSt of 'improved' Schaeffer 293 .

Now, Lucas 85W140 in this scenario still deliver far more superior component protection and longevity with nearly 1.85 times thicker oil film thickness/strength , all other things being equal .

Feeling satisfied with Schaeffers 293 (at 13 cSt operating viscosity ) vis-a-vis Lucas 85W140 (at 24 cSt) , IMHO runs contrary to basic conventional wisdom of striving for components protection in lubricants selection or adoption .

Further more it is not in compliance with your stated statement at post #1 :

I have seen UOAs of Amsoil SVG and have heard testimonials on BITOG and want to have the ultimate protection for my daily beater vehicle.

It is a grave misconception common in this thread that thicker lubricants (in Lucas 85W140) merely (or solely) dampen whirring noise/whine , and .... random ?

My recommending (Lucas) 85W140 in your application is solely for components protection in the 'off target' differential operating behaviour divergent from intended performance parameters by increasing system operating viscosity ,operating MOFT, improved hydrodynamic vs reduced boundary lubrication regimes , etc etc .

Btw, Strange and East Coast Gear are also recommending Lucas 85W140 for their rebuilds ,as evidenced from several threads in this forum .

The noise dampening effect arising out of thicker lubricants is not the end, but an unintended by-product of this process of targeting/chasing after/achieving improved component protection and longevity .

I don't think you will ever need or require a rebuild with prolonged use of thicker lubricants (SAE 140 is preferred to 85W140 ,if it matters ) with potential elimination of whirring noise as experienced currently as time goes .
 
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It is a grave misconception common in this thread that thicker lubricants (in Lucas 85W140) merely (or solely) dampen whirring noise/whine , and .... random ?

My recommending (Lucas) 85W140 in your application is solely for components protection in the 'off target' differential operating behaviour divergent from intended performance parameters by increasing system operating viscosity ,operating MOFT, improved hydrodynamic vs reduced boundary lubrication regimes , etc etc .

Btw, Strange and East Coast Gear are also recommending Lucas 85W140 for their rebuilds ,as evidenced from several threads in this forum .

The noise dampening effect arising out of thicker lubricants is not the end, but an unintended by-product of this process of targeting/chasing after/achieving improved component protection and longevity .

I don't think you will ever need or require a rebuild with prolonged use of thicker lubricants (SAE 140 is preferred to 85W140 ,if it matters ) with potential elimination of whirring noise as experienced currently as time goes .

Zeng,

Respectfully, that’s not entirely correct. Let me explain why it isn’t and then show what is and why. I do lubrication assessments for a profession and there is a set and recognized methodology for this.

This is specifically on gearing and precisely on helical bevel sets (and you could include worms) because they are at the most extreme, but this applies universally for all gearing ( and most bearings) just in different percentages.

The “rule of thumb” in gear design is a ratio of RPM: Load. The higher the RPM, the lower viscosity- the higher the load the higher the viscosity.

The reason for that is the force to load profile of a gear through the transmission cycle. Gears are by definition boundary lubrication in nature and helical designs are the most extreme because they wipe and transfer energy not just an impact like the typical spurs and involutes.

The first duty of the oil is to literally fill up the tooth cavity and serve as an impact cushion for the incoming tooth, so the first function is in fact to buffer and initiate a severe decrease in velocities (under poisons model) that acts like a shock absorber. ( also addresses backlash and any potential back driving)

This is not as prevalent on helical designs but still present.

The reason is that on the gears line of force, the pitches hit and they “pivot” top and bottom of the flank and face so it’s more of a see saw than a slap.

By the time energy is being transferred there is virtually no film there to have strength so the MOFT argument doesn’t apply to a gear set. This is why gear lubes have EP additives that “microscopically explode” (a descriptive term) to lessen that metal to metal contact and other additives that put a sacrificial coating on them. It starts there yes but is quickly squeezed out preceding the tooth contact in helical sets.

This is the purpose of setting the contact patch relative to the design load relative to the transfer cycle relative to the flank/face geometry. If that is incorrect- no lubricant can overcome that eventual stress and wear. Even when correct, the lubricant will be squeezed out (plowed) during the cycle.

This is also why gears are expected to have surface pitting as part of normal service because there will be an element of surface fatigue that will cause pocking. They “pit” because of metal-to-metal surface hardening leading to surface fatigue (because of virtually no film during the contact cycle)

Thicker lubricants also tend to keep heat in the gears and thinner ones remove it better- the gear designer will make that determination when they decide the lubrication schema for that design because there is more than one correct way to build it but once built its difficult to change without modification.

( this is why we used to cringe on Falk boxes when people put Lucas or STP in them and said “yeah they cooled right down” until we tore them down and showed them that heat that WAS being released from convection of the case was now concentrated on the gear making it wear faster. It gave the ILLUSION of cooling when in reality was a damage enabler)

Regarding the damping of noise- get someone with a CSI 2140 or EU gun and let them demonstrate how various oils (with different bases and viscosities) adjust various noises. That’s done everywhere and is a common remedy in the field.

As far as ECG’s “recommendation”- their recommendations in their brochure are nothing more than highly opinionated garbage regardless of the quality of their product.

Any “recommended gear oil” has to be specified against the actual running and loading conditions of the gear set- not the properties of the oil in a “brand versus brand” contest.

I point this out because properties of any given oil (regardless of the property in question or the manufacturer) that do not directly address the requirements of a specific gear set simply don’t matter one way or the other regardless of they are “good, better or worse” than any other oil.

The gear set and its duty cycle combined with designed cooling, sump size etc. determines what properties and bases it needs for a lubricant- not reading a brochure.
 

MolaKule

Staff member
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...however it delivers a higher operating viscosity of 24 cSt, which is 1.85 times that of 13 cSt of 'improved' Schaeffer 293 .

Now, Lucas 85W140 in this scenario still deliver far more superior component protection and longevity with nearly 1.85 times thicker oil film thickness/strength , all other things being equal...

Show me proof where increasing the viscosity results in a LINEAR MOFT vs viscosity.

is a grave misconception common in this thread that thicker lubricants (in Lucas 85W140) merely (or solely) dampen whirring noise/whine , and .... random ?....The noise dampening effect arising out of thicker lubricants is not the end, but an unintended by-product of this process of targeting/chasing after/achieving improved component protection and longevity .

Another outright contradiction. You need to study up on the physics of the mechanical damping effects of viscous materials.


.

...Btw, Strange and East Coast Gear are also recommending Lucas 85W140 for their rebuilds ,as evidenced from several threads in this forum...

And that means what? One possible explanation is that Lucas is giving these firms a discount for specifying their gear lubes.
 

apham8

Thread starter
Messages
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Location
Duluth, GA
Thanks for all the replies everyone, I sincerely appreciate the inputs and opinions everyone has brought to the table.

Spoke with my mechanic today and I am looking to replace this differential and likely wheel bearings as well. The discussion about viscosities and gear oil (conventional vs. synthetic) is intriguing, but only meaningful within the context of a properly functioning differential, which I do not have.

Personally, I will get the rebuild sometime in the future and then run Amsoil Severe Gear 75W-90.
 
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2,879
Location
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Zeng,

Respectfully, that’s not entirely correct. Let me explain why it isn’t and then show what is and why. I do lubrication assessments for a profession and there is a set and recognized methodology for this.

This is specifically on gearing and precisely on helical bevel sets (and you could include worms) because they are at the most extreme, but this applies universally for all gearing ( and most bearings) just in different percentages.

The “rule of thumb” in gear design is a ratio of RPM: Load. The higher the RPM, the lower viscosity- the higher the load the higher the viscosity.

The reason for that is the force to load profile of a gear through the transmission cycle. Gears are by definition boundary lubrication in nature and helical designs are the most extreme because they wipe and transfer energy not just an impact like the typical spurs and involutes.

The first duty of the oil is to literally fill up the tooth cavity and serve as an impact cushion for the incoming tooth, so the first function is in fact to buffer and initiate a severe decrease in velocities (under poisons model) that acts like a shock absorber. ( also addresses backlash and any potential back driving)

This is not as prevalent on helical designs but still present.

The reason is that on the gears line of force, the pitches hit and they “pivot” top and bottom of the flank and face so it’s more of a see saw than a slap.

By the time energy is being transferred there is virtually no film there to have strength so the MOFT argument doesn’t apply to a gear set. This is why gear lubes have EP additives that “microscopically explode” (a descriptive term) to lessen that metal to metal contact and other additives that put a sacrificial coating on them. It starts there yes but is quickly squeezed out preceding the tooth contact in helical sets.

This is the purpose of setting the contact patch relative to the design load relative to the transfer cycle relative to the flank/face geometry. If that is incorrect- no lubricant can overcome that eventual stress and wear. Even when correct, the lubricant will be squeezed out (plowed) during the cycle.

This is also why gears are expected to have surface pitting as part of normal service because there will be an element of surface fatigue that will cause pocking. They “pit” because of metal-to-metal surface hardening leading to surface fatigue (because of virtually no film during the contact cycle)

Thicker lubricants also tend to keep heat in the gears and thinner ones remove it better- the gear designer will make that determination when they decide the lubrication schema for that design because there is more than one correct way to build it but once built its difficult to change without modification.

( this is why we used to cringe on Falk boxes when people put Lucas or STP in them and said “yeah they cooled right down” until we tore them down and showed them that heat that WAS being released from convection of the case was now concentrated on the gear making it wear faster. It gave the ILLUSION of cooling when in reality was a damage enabler)

Regarding the damping of noise- get someone with a CSI 2140 or EU gun and let them demonstrate how various oils (with different bases and viscosities) adjust various noises. That’s done everywhere and is a common remedy in the field.

As far as ECG’s “recommendation”- their recommendations in their brochure are nothing more than highly opinionated garbage regardless of the quality of their product.

Any “recommended gear oil” has to be specified against the actual running and loading conditions of the gear set- not the properties of the oil in a “brand versus brand” contest.

I point this out because properties of any given oil (regardless of the property in question or the manufacturer) that do not directly address the requirements of a specific gear set simply don’t matter one way or the other regardless of they are “good, better or worse” than any other oil.

The gear set and its duty cycle combined with designed cooling, sump size etc. determines what properties and bases it needs for a lubricant- not reading a brochure.

ACE ,
Thank you for your sincere and technical explanation on matters related to gears , and I need time to digest the contents here and I strongly believe there are things I definitely can pick up from your brain in this forum .
With mutual respect and friendly motivations, I wish to engage with you further in this forum , particulatly on matters/aspects I am weak at or ignorant of requiring exchanges .
Looking forward to further engagement in future , ACE .

As far as ECG’s “recommendation”- their recommendations in their brochure are nothing more than highly opinionated garbage regardless of the quality of their product.
I dutifully respect your opinion/position and let's respectfully agree to disagree on this note .
 
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Show me proof where increasing the viscosity results in a LINEAR MOFT vs viscosity.
Pleaseeee ............ don't put words (in bold) into my mouth , again .


Another outright contradiction. You need to study up on the physics of the mechanical damping effects of viscous materials.


.

Thank you . I have not rejected outright the phenomenon of damping and such .

And that means what? One possible explanation is that Lucas is giving these firms a discount for specifying their gear lubes.
Sorry , IDK.

Finally , please be respectful in exchanges Mr Staff Member Molakule .


Edit : I am coming out of 'retirement' from BITOG forum , after you locked threads we engaged in some several months ago .
I look forward to continue 'working' in this BITOG forum for a long time to come , with best of luck .
Please pray for me .
 
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MolaKule

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Pleaseeee ............ don't put words (in bold) into my mouth , again ....

If you make assertions you should be able to offer some technical proof of those assertions.

...however it delivers a higher operating viscosity of 24 cSt, which is 1.85 times that of 13 cSt of 'improved' Schaeffer 293 .

Now, Lucas 85W140 in this scenario still deliver far more superior component protection and longevity with nearly 1.85 times thicker oil film thickness/strength , all other things being equal...

Those were your exact words claiming that an oil with 1.8 times the viscosity of a reference oil has the same order of oil film thickness. That's considered a linear relationship.

You now have the opportunity to provide a sufficient fluid dynamics explanation as to why that would be so.
 
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.... which is 1.85 times that of 13 cSt of 'improved' Schaeffer 293 .

.....with nearly 1.85 times thicker oil film thickness/strength , all other things being equal .

is equals nearly by your understanding , and relating is as 'linear' (putting words into my mouth) ???????????????????????????????
Come onnnnnnnnnnn .

that an oil with 1.8 times the viscosity of a reference oil has the same order of oil film thickness.

1.85 times that of 13 cSt equals 1.8 times the viscosity of..

nearly 1.85 times thicker oil film thickness equals has the same order of oil film thickness.

Dear Mr Staff Member ,it is time for both of us to end this meaningless nonsense here right now , causing irritations to OP and general readers .

Edit: You may (ab)use your 'authourity?' to delete my post or remove my ability to post as a Mr Staff Member , but ...................................
pleaseeeeeeeeeeeeeeeeee , do not locked this thread of OP , all by your very ownself !

I'm done with you , OK ?
 
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Messages
2,879
Location
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Thanks for all the replies everyone, I sincerely appreciate the inputs and opinions everyone has brought to the table.

Spoke with my mechanic today and I am looking to replace this differential and likely wheel bearings as well. The discussion about viscosities and gear oil (conventional vs. synthetic) is intriguing, but only meaningful within the context of a properly functioning differential, which I do not have.

Personally, I will get the rebuild sometime in the future and then run Amsoil Severe Gear 75W-90.
OP , your as-is differential is indeed a functioning differential , albeit with some divergence from desired and is not 'fatal' ,with time .
JMHO.
 
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