Differential - 1991 Chevy Caprice 5.0l Automatic

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No .

The car gas 46,000 + original miles on it . Was my Mom & Dad's car before they passed away . Been parked most of the time , the last 20 years or so .

Only work I have done on the differential is replace the pinion seal 2 - 3 years ago . Guessing it went bad , from going dry , while setting .

Best I remember , I used 75W-90 dino lube oil . Probably O'Reilly house brand . That is where I purchased the seal & the lube oil .

Thanks , :)
Wyr
God bless
 
With use of mineral 75W90, your 1991 Chevy Caprice differential is encountering impending trouble , whether or not you'd by mistake over-tightened pinion lock nut.

Other than the messy re-work on disasembling the pinion assembly as suggested by several posters above , which I believe may not be necessary for now, you have the easier option of measuring differential operating temperatures after 30 miles drive of high speed at 70-80 mph , either by way of IR gun or by way of sticking your index AND middle fingers on the 3 points on differential housing I described earlier, and start counting numbers of seconds your fingers can hold on to it.

In the unlikely event of your fingers able to hold on to the housing for 15-20 seconds,the differential is good.
If your fingers can't hold on for 2 seconds, trouble is coming ...... of course this isn't providing you actual temperatures in *F or *C.

The choice of options is with you, really.
 
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Originally Posted By: zeng
With use of mineral 75W90, your 1991 Chevy Caprice differential is encountering impending trouble , whether or not you'd by mistake over-tightened pinion lock nut.

Other than the messy re-work on disasembling the pinion assembly as suggested by several posters above , which I believe may not be necessary for now, you have the easier option of measuring differential operating temperatures after 30 miles drive of high speed at 70-80 mph , either by way of IR gun or by way of sticking your index AND middle fingers on the 3 points on differential housing I described earlier, and start counting numbers of seconds your fingers can hold on to it.

In the unlikely event of your fingers able to hold on to the housing for 15-20 seconds,the differential is good.
If your fingers can't hold on for 2 seconds, trouble is coming ...... of course this isn't providing you actual temperatures in *F or *C.

The choice of options is with you, really.

The silliest method I have heard. I might buy it only if your nose itched while performing the above procedure.
 
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Originally Posted By: zeng
With use of mineral 75W90, your 1991 Chevy Caprice differential is encountering impending trouble , whether or not you'd by mistake over-tightened pinion lock nut.

Other than the messy re-work on disasembling the pinion assembly as suggested by several posters above , which I believe may not be necessary for now, you have the easier option of measuring differential operating temperatures after 30 miles drive of high speed at 70-80 mph , either by way of IR gun or by way of sticking your index AND middle fingers on the 3 points on differential housing I described earlier, and start counting numbers of seconds your fingers can hold on to it.

In the unlikely event of your fingers able to hold on to the housing for 15-20 seconds,the differential is good.
If your fingers can't hold on for 2 seconds, trouble is coming ...... of course this isn't providing you actual temperatures in *F or *C.

The choice of options is with you, really.


I guess I need to look it up . I was thinking the factory fill was some sort of 90W dino oil ? Chevrolet was certainly not using synthetic oil in 1991 .

It sounds like you are advising against 75W-90 oil .

Am I mistaking what you said ? Am I all wet ? :)

I hope the weather will be warmer , this weekend & I can pursue some of the kind suggestions which have been made . Including taking the temperature test .

The Caprice is not a daily driver . I can take as much time as necessary , investigating this .

Thanks , :)
Wyr
God bless
 
Originally Posted By: zeng
With use of mineral 75W90, your 1991 Chevy Caprice differential is encountering impending trouble , whether or not you'd by mistake over-tightened pinion lock nut.

Other than the messy re-work on disasembling the pinion assembly as suggested by several posters above , which I believe may not be necessary for now, you have the easier option of measuring differential operating temperatures after 30 miles drive of high speed at 70-80 mph , either by way of IR gun or by way of sticking your index AND middle fingers on the 3 points on differential housing I described earlier, and start counting numbers of seconds your fingers can hold on to it.

In the unlikely event of your fingers able to hold on to the housing for 15-20 seconds,the differential is good.
If your fingers can't hold on for 2 seconds, trouble is coming ...... of course this isn't providing you actual temperatures in *F or *C.

The choice of options is with you, really.


I think I am hearing , you are suggesting , monitoring the temperature of the left and right carrier bearings and the pinion bearings ?

Thanks , :)
Wyr
God bless
 
A 90wt GL5 in year 1991 is essentially an AGMA 5EP (Equivalent to ISO 220) Extreme Pressure gear oil with a KV@40*C of 198 - 242 cSt.



whereas current 75W90 gear oils typically has a KV@40*C of 90 - 110ish cSt, i.e 2 grades thinner at AGMA 3EP (Equivalent to ISO 100) extreme pressure gear oils.

Hence , it's inadequacy in worn-out gears and whining noise in use, if push comes to shove.
 
Originally Posted By: WyrTwister
I think I am hearing , you are suggesting , monitoring the temperature of the left and right carrier bearings and the pinion bearings ?

Thanks , :)
Wyr
God bless


Yep, to establish whether all the 3 temperatures are above say, 80*C(176*F).
If yes, check if lock-nut end pinion bearing temperature is higher than carrier bearing temperatures.
If yes, and the delta is as high as say, 10*C(20*F) difference .......
then, excessive over-tightening of lock-nut as suggested by several posters above IS your immediate problem/defect that requires remedial action without further delay, by another rework.

In the unlikely event (because of 75W90 being in use) that after 30 miles of high speed 70-80 mph drive, all 3 temperatures records say, 50*C(122*F) and below, then the mechanical condition of the so-called 'over-tightening' of pinion lock nut is indeed, well and good and a non-issue.

After sorting out 'over-tightening' issue, if any, we may subsequently deal with the original question on 'whining' noise in the opening post.
 
Last edited:
Originally Posted By: zeng
A 90wt GL5 in year 1991 is essentially an AGMA 5EP (Equivalent to ISO 220) Extreme Pressure gear oil with a KV@40*C of 198 - 242 cSt.



whereas current 75W90 gear oils typically has a KV@40*C of 90 - 110ish cSt, i.e 2 grades thinner at AGMA 3EP (Equivalent to ISO 100) extreme pressure gear oils.

Hence , it's inadequacy in worn-out gears and whining noise in use, if push comes to shove.



Most of what you kindly posted went clean over my head ! :-(

But what I think I got as the bottom line is the 75W-90 is too " thin " ?

This has been suggested , would it be " thicker " / more appropriate ?

https://shop.advanceautoparts.com/p/valvoline-synpower-full-synthetic-75w140-gear-oil-vv982/7070058-P?navigationPath=L1*14924%7CL2*15038%7CL3*16157

Thanks , :)
 
Originally Posted By: WyrTwister
Most of what you kindly posted went clean over my head ! :-(
But what I think I got as the bottom line is the 75W-90 is too " thin " ?

I'm sorry. Yes, 75W90 is too thin, as evidenced from the whining noise reported for now.

Quote:
This has been suggested , would it be " thicker " / more appropriate ?
https://shop.advanceautoparts.com/p/valvoline-synpower-full-synthetic-75w140-gear-oil-vv982/7070058-P?navigationPath=L1*14924%7CL2*15038%7CL3*16157

Depending on your impending measured temperature readings, you may want to consider Valvoline's 80W140's and 2 other 85W140 as well for shear stability and its higher KV40*C.
The above 75W140 is highly shear-unstable .
https://www.valvoline.com/our-products/grease-gear-oil
 
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Try Amsoil Severe Gear in SAE75W110. A good all around viscosity.

I assume you had the correct shimming for proper loading?
 
Originally Posted By: MolaKule
Try Amsoil Severe Gear in SAE75W110. A good all around viscosity.

I assume you had the correct shimming for proper loading?


I did not " go into " the differential . Only changed the pinion seal .

If you mean , by shimming , messing with the crush sleeve , no , I did not mess with it .

Thanks , :)
 
I am guessing , too " thick " of gear oil will have few downsides , as long as you are not in an extremely cold climate ?

Thanks , :)
Wyr
God bless
 
Originally Posted By: zeng
Originally Posted By: WyrTwister
Most of what you kindly posted went clean over my head ! :-(
But what I think I got as the bottom line is the 75W-90 is too " thin " ?

I'm sorry. Yes, 75W90 is too thin, as evidenced from the whining noise reported for now.

Quote:
This has been suggested , would it be " thicker " / more appropriate ?
https://shop.advanceautoparts.com/p/valvoline-synpower-full-synthetic-75w140-gear-oil-vv982/7070058-P?navigationPath=L1*14924%7CL2*15038%7CL3*16157

Depending on your impending measured temperature readings, you may want to consider Valvoline's 80W140's and 2 other 85W140 as well for shear stability and its higher KV40*C.
The above 75W140 is highly shear-unstable .
https://www.valvoline.com/our-products/grease-gear-oil



So , you are suggesting something like this ? This seems to be dino oil , not synthetic .

https://shop.advanceautoparts.com/p/valvoline-high-performance-85w140-gear-oil-vv825/7070005-P

Thanks , :)
 
Originally Posted By: WyrTwister
Originally Posted By: zeng
Depending on your impending measured temperature readings, you may want to consider Valvoline's 80W140's and 2 other 85W140 as well for shear stability and its higher KV40*C.
The above 75W140 is highly shear-unstable .
https://www.valvoline.com/our-products/grease-gear-oil

So , you are suggesting something like this ? This seems to be dino oil , not synthetic .
https://shop.advanceautoparts.com/p/valvoline-high-performance-85w140-gear-oil-vv825/7070005-P
Thanks , :)
Yep, this Valvoline High Performance Gear Oil 85W140 is a dino, with KV@40*C 394 cSt, VI 98.Highly shear stable.
You may also consider Valvoline :
a)DureBlend Gear Oil 85W140 with KV@40*C 331 cSt, VI 117; or
b)Heavy Duty Synthetic Gear Lubricant 80W140 with KV@40*C 284 cSt, VI 146 ;or
c)Synpower full synthetic Gear Oil LS 75W140, as suggested earlier on, comes with KV@40*C 171 cSt, VI 183 which would be most highly sheared with the lowest KV@40*C of 171 cSt to start with, offering the least oil film protection among the 4 oils here.
Not knowing your differential operating temperature today, I would speculate options a) or b) are likely at the sweet spot.
With proper preload sorted out, a thicker gear oil generally is in a better position to possibly deal with whining noise in its initial phase.
 
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Take the cover off anyway and make sure your diff gasket has the two holes or slots to send lubes out to the axles. I've seen a lot of those 8.5 axles with the wrong gasket and very ugly axles in the wheel bearing area as a result.
 
Originally Posted By: DoubleWasp
Take the cover off anyway and make sure your diff gasket has the two holes or slots to send lubes out to the axles. I've seen a lot of those 8.5 axles with the wrong gasket and very ugly axles in the wheel bearing area as a result.

If you do this, why not just pop off the drums, disconnect the drive shaft and measure your bearing pre load properly using an inch pound torque wrench on the pinion nut and check the required torque needed to rotate and compare to specs? Gear oil, use what is specified in your manual, no guess work.
 
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From what I could find in the owner's manual , it specified GL-5 . Could not find a chart for viscosity .

Thanks ,
Wyr
God bless
 
Weather permitting , hope to do some of the " test " that have been suggested . This weekend .

I did nor realize it was necessary to remove the drums to check pre-load with an inch pound torque wrench .

Drove the Caprice last night at about 11:30 PM to give our daughter a lift home from work . About 20 blocks through residential streets with pronounced dips at some of the intersections . Drove 20 -v 25 MPH & did not hear any whining .

Then headed across town to drop her off at her place , heard the whining again ( some streets 40 MPH speed limit ) . My theory is when I started out , the gear lube was cold / thicker . As it warmed up / thinned out some , the whining started .

Criticism ? Suggestions ?

Thanks , :)
 
75-90 is the spec according to the manual for my 1992 Wagon. I use Amsoil 75-110. No complaints, and ive replaced my seal as well. That thing just went downhill really fast one day. I also changed my diff yokes to a 1350 yoke so I could run an aluminum Chevy SSR driveshaft. That worked wonders in removing vibes from the drivetrain, especially at high speed. Having a factory 3.27 rear, it matters.
 
I did not realize it was necessary to remove the drums to check pre-load with an inch pound torque wrench .

Thanks , :)
 
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