Jmax3

Had this issue noticeably start over a year ago, since then I have had all 4 new tires put on, wheel bearings, recently both front axles which i thought could help but didnt. The hum starts softly at 30mph then gets louder with speed til about 65 on the highway then it's a constant pitch or tone that doesn't get any louder. Then its a loud road noise, not much if any vibration associated with it. My mechanic said it was hum coming from the upper differential which in this model is tied in with transmission. Sealed transmission at that so I changed the fluid, didn't help. Anyone experience this? Such an annoying noise, 180k on it now had it since 70k have taken great care of it. Is it a warning sign transmission is on its way? Any advice or feedback is greatly appreciated!

604GSE21

is it awd? did u change fluids on front, center and rear diff? and was it top up properly?

Jmax3

Yes is awd, the front differential shares fluid with sealed transmission that fluid was changed, I wasn't aware of a center diff and it having its own fluid? The rear differential fluid was not changed. I didn't know they had independent reservoirs. Drove it today now feeling a vibration with the hum. Even on deceleration in between 25-60 mph.

primavera

That's the first time I ever heard of differential sharing fluid with transmission. They are two separate units and both use different fluids to operate, WS fluid for transmission and 75W90 gear oil for differential. If someone put the same fluid in tranny and diff you're in trouble.
Might wanna find out exactly what went into your transmission and how much fluid was pumped in as this is critical in those vehicles.
Lots of info covered on the subject, use search window.

2013FSport

iTrader: (2)

It's the first time we've heard of it as it's incorrect information!
The front and rear diff's are hypoid gears that take GL-5 (GL-4?) gear oil. The transfer case takes ATF as does the transmission.

I'd suggest OP find a new a new mechanic and get all the fluids changed ASAP with synthetic.

Too bad all that money was spent.

s3v3n

iTrader: (3)

I had this hum issue and turned out to be the tires. After replacing with another brand, the hum monster went away.

Edit: the tires were Michelin AS/3+ .... I replaced them with AS 4.

2013FSport

iTrader: (2)

I bought used diff to keep the 350 RWD on the road while the original diff gets a dose of LSD.
The used diff sings under light load making a 'whirrrrrrrrrrrrr' sound at steady state cruise.
Light or hard acceleration, it's quiet. Minimal or maximum engine braking, it's quiet.

It had 93k on when pulled from the donor. It also runs about 60° hotter than mine before I pulled it (162°F vs 102).

I'm just saying, even a Lexus diff can go awry. Thankfully this is temporary use only.

s3v3n

iTrader: (3)

I'd really lean into replacing the tires but that's me. I had the same process done (fluid changes for front/rear diff and transmission) , and also went to several Lexus shops and had them thoroughly check the wheel bearings - the last shop called it and told me it's my tires since they clearly checked all the possible parts that would cause it.

2013FSport

iTrader: (2)

I hear ya. As the tread gets low, many tires transmit more noise. I'm living it now. The whirrrrrrr came with the diff. No other changes were made.
No suspension was taken apart.

s3v3n

iTrader: (3)

I think this 08IS350 is also having this hum issue but not sure if it's the diff or the f-sport-like exhaust that it came with. Sometimes I can't differentiate between a hum or a mild-drone. Hopefully it's the latter.

Are you having the LSD built by a third-party shop?

2013FSport

iTrader: (2)

No, I'll be doing it myself. Likely post it in my build thread with a write up. I've never done Yoda, but about 50 others. Only had one whine which was a used gear set to a different case. I bought off craigs list for drag strip use, and I'm guesting its prior life hosed it up.

Your saying your own rig makes noise?

s3v3n

iTrader: (3)

Yes and I don't know if it's also coming from the diff or just the exhaust drone.

2013FSport

iTrader: (2)

I've got the F-Sport axleback and intake. The sound is easily discernable at cruise, not in the drone power band of the exhaust. Adding to that, barely changing the load applied changes the noise. That's not to say the noise gets louder, more to say the noise from the boneyard diff is binary. Either there or not there based on load. Which is somewhat typical of gear mesh being off.

That said, straight cut gears like in a motorcycle transmission do get louder and louder as the load increases. Well, to a point.

MikeFig82

iTrader: (13)

Here's the information on the front differential.

https://www.clublexus.com/forums/is-...l#post10282976


Also the information on the transfer case combined with the AWD transmission.

https://www.clublexus.com/forums/is-...ase-fluid.html

Paul4949

Was your tires worn on the inside only and not even wear across the tire? My tires look good but are worn on the inside and I am experiencing a sound like the OP is describing. I went to Discount Tire and let the sales rep ride in my IS250 AWD and he too said it was the tires making the sound. I also changed diff fluid and installed a wheel bearing hub assembly and the sound is still there. But I did notice that when I played with rotating the tires the sound would change.