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Dreaded Diff Whine

1759 Views 13 Replies 7 Participants Last post by  NRNG759
Im getting a whirring/whining noise when I get to 40 mph and it gets louder with speed, no clunking that I’ve noticed. It’s only when I hit the gas but with any amount of acceleration it howls, even light taps. I know it’s coming from the diff but I don’t know the serviceability of the specific issue I have. I’ve read about how much of a pain these things are to not only get apart but aquire parts for as well, if at all. I swapped royal purple 75w-140 gear oil with lsd additive included about 150 miles ago but to no avail (maybe I need to wait longer). I don’t want to spend 12-1500 dollars if I don’t absolutely have to. My question is, does this sound like something that can be repaired or am I looking at a new diff soon? I’d like to as much use out of it as I can but I’m sure when I go on vacation in a month it will give out the first day lol. Any recommendations help.
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I will be replacing my rear fluid soon, I also use royal purple 75w-140 gear oil. When using the RP is the additive still necessary? I am concerned because mixing additives with fluids not specifically approved may have some adverse effect. ty
I will be replacing my rear fluid soon, I also use royal purple 75w-140 gear oil. When using the RP is the additive still necessary? I am concerned because mixing additives with fluids not specifically approved may have some adverse effect. ty
I’d bet either the RP comes with an additive or they have their own. I wouldn’t mix the gm stuff with it.
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I’d bet either the RP comes with an additive or they have their own. I wouldn’t mix the gm stuff with it.
As far as I know it's a stand alone. I'll call RP in the morning, based on experience, RP is good to take calls and answer questions. ;)
RP has its own additive called “Synerlec” as of right now it has helped none but who knows. Doubt I’ll be lucky enough for my issue to just be an oil change. :D
RP has its own additive called “Synerlec” as of right now it has helped none but who knows. Doubt I’ll be lucky enough for my issue to just be an oil change. :D
It's been a good product for me so far, probably one of the best you can buy. I suggest you drain it, take a good look with a very bright light and see if there is anything concerning to start off with. Hope all is well, keep us posted!
Yea OP I can guarantee the whine is going nowhere with a fluid change. Been there and done that. You are hearing gear wear likely as a result of bearing wear.

That said…it will run fine most likely. Mine howled the whole time I owned it and it’s still in one piece. Granted it’s going to have a 427 and twins in front very soon so we will see how the new owners luck is.
Yeah everyone I talk to on here, Facebook, etc. are giving me the same advice. I found a new diff for $800 but I feel that a high mileage diff is going put me right back where I started along with being out 800 bucks. It baffles me that not a single person on the Internet has rebuilt one of these things successfully, at least that I know of (thanks GM). Guess I’ll have to blare Music everywhere I go, it’s already catless with Long tubes so maybe I’ll stick a pair of corsas on it in place of the stock mufflers so the sound will magically disappear :)

Yea OP I can guarantee the whine is going nowhere with a fluid change. Been there and done that. You are hearing gear wear likely as a result of bearing wear.

That said…it will run fine most likely. Mine howled the whole time I owned it and it’s still in one piece. Granted it’s going to have a 427 and twins in front very soon so we will see how the new owners luck is.
I’d love to hear an update after everything gets put in, if he’s not blowing his to pieces putting that much power through it then I’m not going to worry about it for a while lol.
People HAVE put new bearings and seals in them and and have had some reduction is noise; but you'll not likely get the noise completely gone without buying a new diff, simply because there are NO replacement gearsets on the market. A scored up gearset is going to be noisy. The good news is that these diff are beastly strong and they don't blow apart like the Gen1 diffs famously could.
The problem with the design (IMHO) is that the diff case is too compact for an IRS unit and has no cooling provision and insufficient fluid capacity, meaning that it can't shed heat. Remember that old school live axles used fluid movement within the axle tubes to lube the axle bearings and this movement also COOLED the fluid. The fluid has a very short lifespan due to being cooked. Cooked lube doesn't lube... shear strength is lost and the bearings overheat leading to bearing wear which in turn leads to carrier misalignment which leads to gear tooth damage and eventually it gets so loud it gets replaced.
(but they don't break, which is notable).
Get a new diff and replace the diff fluid every 30,000 miles and you'll likely avoid the issue completely.
However, with all that being said.... i bought a brand new GM diff last year and it had a slight bit of whine, brand new.
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People HAVE put new bearings and seals in them and and have had some reduction is noise; but you'll not likely get the noise completely gone without buying a new diff, simply because there are NO replacement gearsets on the market. A scored up gearset is going to be noisy. The good news is that these diff are beastly strong and they don't blow apart like the Gen1 diffs famously could.
The problem with the design (IMHO) is that the diff case is too compact for an IRS unit and has no cooling provision and insufficient fluid capacity, meaning that it can't shed heat. Remember that old school live axles used fluid movement within the axle tubes to lube the axle bearings and this movement ALSO cooled the fluid. The fluid has a very short lifespan due to being cooked. Cooked lube doesn't lube... shear strength is lost and the bearings overheat leading to bearing wear which in turn leads to carrier misalignment which leads to gear tooth damage and eventually it gets so loud it gets replaced.
(but they don't break, which is notable).
Get a new diff and replace the diff fluid every 30,000 miles and you'll likely avoid te issue the next time.
However, with all that being said.... i bought a brand new GM diff last year and it had a slight bit of whine, brand new.
This is great info and I would bet you nailed the chain of events that lead to failure/crazy loud whine.
Mine has 46k miles on it and I’ve had it the last 20k miles and I just replaced the fluid. Mine looked pretty decent and there was very little on the magnetic drain plug luckily.
There is no whine that I can hear and I feel lucky.

When I first bought the car I flew up to Indiana and drove it back to Atlanta and I brought an IR temp gun and at one of the fuel stops checked the diff temp and it was over 300 degrees If I recall correctly…just driving at an easy constant 80mph!
I was shocked how hot it was at almost no load, fluid def won’t like that for long.


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Based on my diff cooler thermostat turning the pump on at 210 and that only taking 30 minutes of driving 80 MPH in 80* ambient I'm not at all surprised by your temp observation. That's also the first time I've seen anyone post any data point between my observation on how easy it is to activate the pump and people getting the over temp warning on track, which I have been told happens at a temp well beyond the fluid already being cooked. Everyone should be putting diff coolers on these things.
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Based on my diff cooler thermostat turning the pump on at 210 and that only taking 30 minutes of driving 80 MPH in 80* ambient I'm not at all surprised by your temp observation. That's also the first time I've seen anyone post any data point between my observation on how easy it is to activate the pump and people getting the over temp warning on track, which I have been told happens at a temp well beyond the fluid already being cooked. Everyone should be putting diff coolers on these things.
I assembled a diff cooler of my design a while back but haven't yet made it electrically complete; I have been waiting until my current build process and I'm planning to have it up and running once the car is back on the road.
I drew my conclusions about diff heating from multiple observations, the most illuminating of which was the condition of my old diff. I bought the car from its original owner, a school teacher who DDed the car for years and then gave it to her daughter to DD to college. Every indication is that the car was never beat on or hooned and it was 100% stock at 120K.
The diff whined, but it was not awful. I didn't truly need to change it but I did. Inspection of the original diff upon strip down revealed horribly burnt fluid, caked in places, discolored iron and steel, bad bearing wear, lots of clearance and misalignment. The fluid was only a little bit low. The gear teeth are scored, but not destroyed. I intend to have this diff around as a spare and I'm very curious how noisy it will be, now that I've refreshed the bearings.
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Curious y'all what mileage are we looking at on these?
I assembled a diff cooler of my design a while back but haven't yet made it electrically complete; I have been waiting until my current build process and I'm planning to have it up and running once the car is back on the road.
I drew my conclusions about diff heating from multiple observations, the most illuminating of which was the condition of my old diff. I bought the car from its original owner, a school teacher who DDed the car for years and then gave it to her daughter to DD to college. Every indication is that the car was never beat on or hooned and it was 100% stock at 120K.
The diff whined, but it was not awful. I didn't truly need to change it but I did. Inspection of the original diff upon strip down revealed horribly burnt fluid, caked in places, discolored iron and steel, bad bearing wear, lots of clearance and misalignment. The fluid was only a little bit low. The gear teeth are scored, but not destroyed. I intend to have this diff around as a spare and I'm very curious how noisy it will be, now that I've refreshed the bearings.
Amazing 120K ......I'm on #4 and they really haven't gone more than 25-30K before it's unbearable.....
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