Observation & possible solution (LSD)

[Tbonem3]

Been thinking this for a while, figured I'd make a thread and see what people think.

In my direct and indirect experience, our LSDs start to die around 120k or so.

The SB to come in and get the 75w140 diff lube WITH FM booster occurred years ago when few of these cars were above 100k miles. This was to quell the clutch's noise to satisfy owners' feelings afaik, not related to performance or operation at all.

My take: Your diff probably has close to or more than 100k by now. If you have a diff that isn't inherently noisy or you're willing to live with a little groaning, it'd say it's best NOT to ADD any extra FM (friction modifier) beyond what's already added to a LSD specific diff lube.

Not sure people are aware, but the available GL5 75w140 lubes are mostly already LSD specific (they'll say so) and contain some amount of FM. The FM booster is EXTRA FM in order to silence the LSD further. There are a few 75w140 GL5 lubes out there with no FM fyi.

IMO, I'd rather hear the LSD a little, knowing that it's locking, than have a quiet LSD that's slipping too much.

You can feel if your LSD is dead, as you accel out of a turn. It'll be really noticeable if you drive a car with a working LSD, then drive yours and try to feel it. I can best describe it by saying it's not as "dynamic." Like driving a non-M (open diff aka pegleg) through a corner versus an M.

In my case (only 72k mile diff though), I used an LSD specific lube (Amsoil), but added a tiny amount of extra FM (lubegard) to the point where I have just a little groaning on slow, tight turns. Enough to know it's locking, but not so loud it's embarrassing.

[lemoose]

Are you saying that around 120k owners should expect to no longer hear the diff bind up- therefore indicating the diff is past its service life? My diff is still noisy taking tight turns around the parking garage. Car mileage is at 177k now (no reason to believe my diff was ever replaced) but I flushed end replaced with just plain LM 75w140 (no FM) oil around 120k.

[loudspeaker69]

I noticed when I gunned it from a roll the rear felt like it was shimmying to the left or right when it was completely sticking to the tarmac and my buddy said “that might be the diff on the way out”

Every bushing is changed.

Sigh…

I’m on 144k

[Thoglan]

Sounds a little bit more likely to be rear steer from RTA bushing deflection.

The rear walks a bit similarly on mine at 100k, but I'm pretty sure it's the lack of monoball RTA bushes, not the diff.

[jet_dogg]

I never had a problem with mine before it went into storage other than the clunk, able to control slides and such no problem.

Since I'm redoing everything decided to just replace the diff since it's probably time.

[Mattn1192]

I have 161k miles and have zero noise back there. Also changed my diff fluid about 2 weeks ago with the oem diff fluid (has FM in it already) & it’s still going strong. No noise after changed fluid. Pretty happy about that, because I was a bit worried from reading other peoples posted on here about groaning noises after diff fluid change.

[loudspeaker69]

Sounds a little bit more likely to be rear steer from RTA bushing deflection.

The rear walks a bit similarly on mine at 100k, but I'm pretty sure it's the lack of monoball RTA bushes, not the diff.

I have Rogue Engineering Rear Trailing Arm Bushings, which are 95A Poly Bushings.

Everything is changed in the rear suspension and it is mostly poly.

[Tbonem3]

Are you saying that around 120k owners should expect to no longer hear the diff bind up- therefore indicating the diff is past its service life? My diff is still noisy taking tight turns around the parking garage. Car mileage is at 177k now (no reason to believe my diff was ever replaced) but I flushed end replaced with just plain LM 75w140 (no FM) oil around 120k.

No, just that, in my experience and time spent talking and reading about others', the LSD starts to slip more. So, is extra FM needed? I think, if someone's LSD is quiet, it could possibly be slipping too much where, perhaps, only putting in regular gl5 75w140 (not fm booster) might extend the "lock life".

This thread isn't about the diff, just about the LSD. Seems to be going off topic already.

Was looking for further discussion. I also don't know a ton about our lsd. I think it has it's own oil in the unit, but it seems like the lube, with fm, gets in there and affects operation? The lube is chiefly for the gears (ep).

[lemoose]

No, just that, in my experience and time spent talking and reading about others', the LSD starts to slip more. So, is extra FM needed? I think, if someone's LSD is quiet, it could possibly be slipping too much where, perhaps, only putting in regular gl5 75w140 (not fm booster) might extend the "lock life".

This thread isn't about the diff, just about the LSD. Seems to be going off topic already.

Was looking for further discussion. I also don't know a ton about our lsd. I think it has it's own oil in the unit, but it seems like the lube, with fm, gets in there and affects operation? The lube is chiefly for the gears (ep).

I guess I should have said something along the lines of "begins to act more like an open diff" to be clear. The FM is to allow more slippage, so if its beginning to slip, that is probably the opposite of what you'd want to do.

[SandeepM3]

Thats exactly what I have been doing for years now. The service bulletin is purely to take care of customer complaint of noise and not the diff actually having an issue. Even says if customer comes back add more. So if the diff was originally meant for a certain amount of fm(what's in the original 75w140) I would imagine adding more would change the lock characteristics. I want it to lock as aggressively as it was meant to.

[Tbonem3]

Ya makes sense, I'm surprised it's been discussed so little over the years. The amount of slip/lock you'd want vs. Noise concerns.

From memory, all the diff lube threads focused on silencing the diff, with no regard to slip esp with mileage/age in mind. I'm trying to change that.

Unless someone has something that nullifies the idea that we can slightly increase the lifespan of our LSDs by using lubes with less and less fm?

[Tbonem3]

I have 161k miles and have zero noise back there. Also changed my diff fluid about 2 weeks ago with the oem diff fluid (has FM in it already) & it’s still going strong. No noise after changed fluid. Pretty happy about that, because I was a bit worried from reading other peoples posted on here about groaning noises after diff fluid change.

So this is aimed at someone like yourself. High mileage, no noise, using, I assume, the oe saf-xj +fm that is in clear bottle with red cap or grey bottle with green cap.

Your LSD is probably dead at this point, or close to (no offense, I had a 170k diff at one point too). Try, if you can afford/want to, the oem castrol fluid in gold bottles (syntrax iirc) -1L on amzn was $16 now up to $25 but still cheap, plus half liter bottle exist as well (need 1.2L). And see if there's any noise. Someone like you should want less slip, is my point.

A sunday fair weather vert for a 50 year old and his wife to cruise to the beach? Nah don't sweat it. You'd want the silence, I imagine.

[Tbonem3]

Or maybe noise isn't the best gauge? (but what others are there besides feel?) Maybe to some degree, they will all make noise with a lube sans fm, and that, alone, isn't evidence that it's still locking adequately?

Maybe peeling out is the only way to be sure 😄

[oceansize]

Maybe peeling out is the only way to be sure 😄

That is my go to move.

[Flat-Six]

So this is aimed at someone like yourself. High mileage, no noise, using, I assume, the oe saf-xj +fm that is in clear bottle with red cap or grey bottle with green cap.

Your LSD is probably dead at this point, or close to (no offense, I had a 170k diff at one point too). Try, if you can afford/want to, the oem castrol fluid in gold bottles (syntrax iirc) -1L on amzn was $16 now up to $25 but still cheap, plus half liter bottle exist as well (need 1.2L). And see if there's any noise. Someone like you should want less slip, is my point.

A sunday fair weather vert for a 50 year old and his wife to cruise to the beach? Nah don't sweat it. You'd want the silence, I imagine.

This is very good and interesting. I have 121K, LSD is dead quiet. I will definitely try the fluid that you recommend. Can you send a link, just so I get the right stuff? I am headed to track on 10/29 and will try to get it in before.