Rear differential oil analysis

[Lund1990]

Had an analysis run on my rear diff oil when I changed it.  Everything seemed just fine from what I could tell when I had it apart. But my analysis seems to tell a different story. What are the clutches in the LSD made out of?

reardiff.pdf

Edited April 7 by Lund1990
Forgot to upload oil analysis

[Mopar1973Man]

Limited Slip Differentials require 80w-140 synthetic not 75w-90 which is too thin and might be the cause of damage.

Just for fun... check out the conversion between engine oil and gear oil.

 

 

 

[Doubletrouble]

 Is there also a friction modifier that needs to be added to the diff oil? 

 This is something I need to do this year as well. 

[Mopar1973Man]

Not to ...

 

This is exactly why I'm telling people with manual transmission quit using the stock fluids which are to thin for high HP usage. When your putting down more HP and more TQ the thin fluids can't protect metal parts when the lube oil has thin way out at 200°F during operation. Same holds true on rear axles you need to be thicker.

[Lund1990]

The only extra power I'm getting is from my little edge tuner that stays on three because I can't turn the piece of junk down without taking it apart. I did put 140 in the rear differential; it's the first time it's been apart since I've owned it. Mind you, I've only put on 20k miles at most. I plan to put SAE 50 in the transmission here within a month. The transfer case just got split, fixed, and filled with fresh ATF. I figure with all this, I may as well change the front differential fluid too.

 

Edited April 9 by Lund1990

[Lund1990]

Most gear oils encountered in the market are designed for Limited Slip Differentials (LSDs) and do not necessitate the addition of a friction modifier. However, if chattering occurs after an oil change, a measured amount of friction modifier may be introduced. It is crucial to note that excessive amounts of friction modifier can also lead to adverse effects.

[Mopar1973Man]

This is why if you use the proper 80w-140 gear lube like I get from NAPA is already properly mixed friction modifier and GL-5 lubricant. I'm still pretty sure as the test showed 75w-90 just being the wrong fluid. You can download the FSM book from the download area and fluid specs are listed in the first little bit of the book.

[Lund1990]

The test doesn't check for the original viscosity, that's what I wrote down because that's what it calls for, so I figured that is probably what was in there. I'll be able to get a good idea going forward since I'll have changed everything myself. 

[Lund1990]

NAPA, I don't even step foot in there anymore unless they are they only ones that have something I need today.  Or to have my Stihl equipment serviced. Napa is almost always the most expensive place in town. Plus not having to keep track of receipts for warranties is a great service of O'Reilly auto for a guy that loses everything

[Doubletrouble]

 I can't speak to O'riley's but I used to be a loyal autozone customer. I have noticed in the past several years their quality has dropped dramatically.  Their "lifetime" parts are cheap Chinese made garbage which allows them to keep handing you a new replacement every year or two. 

 I have a local Napa store near me and I have to say the quality of the parts there is much better than AZ. I will pay a bit more to save on doing the labor involved all over again. In general though, replacement part quality I believe has suffered everywhere to some degree or another. Just my $.02

[Mopar1973Man]

Same here. AZ and O are cheap China parts that tend to fail often and have lots of lifetime warranty like my Clutch Hydraulics. My problem is AZ and O are 250 mile round trip where NAPA is 75 mile round trip I might pay more for the parts but I don't have to change them as much. Like a NAPA 375-190 thermostat will out live AZ or O or Cummins. Better products for slightly more money. Oh yeah Napa thermostats have been upgraded 6 times since 2002 when I bought my truck. Just for fun I'll never buy a Cummins head gasket being Cummins don't manufacture the gasket but a company called BLK out China does. Quality? I've had a Cummins gasket delaminate and blow out in less than 1k miles.

[Tim Waldo]

On 4/8/2024 at 4:35 PM, Mopar1973Man said:

Limited Slip Differentials require 80w-140 synthetic not 75w-90 which is too thin and might be the cause of damage.

Just for fun... check out the conversion between engine oil and gear oil.

 

So the book calls for SAE 80W-90 not 75w-90.... 

The only 80W-90 I can find is NOT synthetic, thus would need modifier, the only modifier I can find comes in 4 oz bottles, book says to add 10 oz, I'm guessing just to the rear differential.

Should I not go with what the book says? rather than the 80w-140 synthetic?

 

On 4/8/2024 at 4:35 PM, Mopar1973Man said:

 

 

 

Edited April 26 by Tim Waldo
add info