2003 IS300 Rear Diff Noise - Lexus IS Forum
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post #1 of 3 (permalink) Old 06-16-2012, 05:54 PM Thread Starter
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2003 IS300 Rear Diff Noise


I have a well-maintained 2003 IS300 with an LSD rear diff. Today I went to change the fluid since it's at 110k and, according to the dealer service records from the previous owner, it was last done about 55k miles ago. In any case, everything seemed to be fine, I used Lubro Moly 75w90 GL-5 synthetic gear lube, almost 1.3qts exactly. I went for a quick drive after closing everything up and all seems great, but I notice a very faint "voom" or whirling noise only when going very low speeds doing a circle in the middle of the street at full steering lock, and only if I give it a little bit of gas. I just got the car, and I'm not sure if it was doing it before now that I was hyper-sensitive to anything I felt out of the ordinary. It's silent at all other speeds and circumstances, and I stopped filling after fluid started to dribble out of the fill plug.

Is this normal for torsen style LSD diffs? I could only hear it with the windows down, climate control and radio off; any vent power, radio noise, or windows up and I can't hear it.

This is my first Lexus so I'm not sure how sensitive they are to things like this, I've used the same gear oil in my Mercedes for years with no problems, and I've done that service on my Benzes a dozen times, and it's nearly an identical procedure on those cars as it is on my Lexus. I did not add any LSD additive, but from what I gather we don't need it, and most synthetics already include it anyway.

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post #2 of 3 (permalink) Old 06-17-2012, 03:53 PM Thread Starter
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Bumping my own thread here, but I managed to quiet it down. I figured adding some limited slip additive couldn't hurt, as I later found out reading online that the particular gear oil I used does not include any LSD additive in their additive package. I just picked up 4oz of Kendall additive at the Toyota dealer and injected that into the diff today, now it's quiet as can be under all circumstances. I did read last night that friction modifier can be added to Torsen style LSD's in order to quiet down some harmless noise, in my case it solved the problem. I imagine guys using most synthetic gear oils notice no added noise after a fluid change becuase most have LSD additive included, at least that seems like a good theory.
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post #3 of 3 (permalink) Old 06-17-2012, 08:07 PM
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Glad you figured it out! Cheap and easy fix.

It depends on what kind of oil you use. I just got an LSD M98 with AMSoil 75W90 gear lube (500K mile service one) and its quiet as can be I'll try the Severe Gear oil next time.
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