Ok - my first post at Club Lexus but been lurking for a few months now: I have a 2007 LS460 Base 2wd with about 180k miles. I bought it from my best friend (since we were 4 yo). I bought it back in October for near to nothing. He owned it since 2009, but he is not mechanically inclined. I enjoy turning my own wrenchs. I like to remind him he's paying other men to be a man for him.

I have a strange rumble at times. It almost sounds like driving over a rumble strip. It usually happens at low RPM (2k-ish) between 40mph and 50mph but I've heard it as low as 20mph. The vibration needs some torque (it never makes it going downhill - it usually happens going up a slight inclice but the steaper the inclide the lower the speed to make the sound). The flex couplers look ok. The transmission mount looked ok but I didn't really know what to look for there. It started happening suddenly two weeks ago.

But I just noticed that the diff is slightly wet (oil). It appears to be from the differential input seal at the propeller shaft (input pinion of the differential.) It doesn't appear to the be a bad leak. Could low diff fluid level cause this sound? Or could there be a bigger issue at the input pinion that needs addressing which is causing the vibration? Or could the sounds be something totally different (like engine mounts)?

I have Toyota OEM diff fluid on the shelf but I'm waiting for replacement diff plugs to come in bc the curent plugs look rough. I tried removing the fill plug but I think it's going to take heat to get off. I have searched CL forums for two weeks but not found anything matching my vibration sound or a differential leak. I apologize if i missed something. But I have found many very helpful posts, so I'm glad I've found this site. TIA.

 

It is a good starting point to check the fluid level. Have you tried rocking the propeller shaft to check if there is excessive movement?

 

Yeah - I tried a little but didn't give it too much attention. If you think it's a possibility, I'll give it another go. Actually, another symptom I forgot to mention, I noticed a bit of a clunk between shifts at this higher gears under load, especially in the higher gears. It's not much, but this car is otherwise so smooth.

I'll tug on the shaft first thing in the morning... wait...

 

I believe motor mounts gone bad gives odd shift between 3-4 or 4-5. While your rear has a leak. the motor and transmission mounts could be shot. You have enough miles. Have someone rev the engine in park while you watch engine. If the engine twists from torque revs, mounts are bad. Maybe multiple issues. Check for codes too.

 

No codes except for TPMS. I am working on my techtstream setup to get more in there. But no CELs.

I had previously discounted the motor end of things because the sound was all from the rear. But most of the sound is from the rear deck vibrating. Certainly worth a look. And honestly, I drive it a lot harder than my buddy did. I'll give it a look. Thanks.

 

Failed transmission mounts can cause misalignment of the drive shaft resulting in vibration. As I stated before, see if there is too much play where the shafts goes into the differential.You will need to replace the leaky diff seal regardless.

 

Check the drive shaft carrier bearing, that's the first thing that comes to mind with what you describe

 

Thanks guys. I got the diff fluid changed. Had to pull the dremel out to cut a notch in the fill bolt then drive it loose with a brass drift - PITA.

I put the car in neutral and played with the driveshaft. There is movement but it didn't seem to be excessive and it seemed to be not at the flex coupler. Rather it was between the diff input flange and the differential ring then there is a little more play in the output shafts. I don't really have anything to base the amount of play (IE - what is excessive). I'm about to drive it down to Costco to get some new tires. We'll see if the new fluid made any difference. If the noise isn't different, I'll give the driveshaft more attention. I'm only on ramps right now, so it's tight under there. And man they love their heat shields / panels. It's quite different than my Land Cruiser.

 

I wounder if the differential pinion bearing is failing.

https://parts.lexus.com/p/Lexus_2010...036634010.html

 

Also I would suspect imbalanced main prop shaft. Sounds implausible but I did replace at least two bad shafts, with zero visual damage, in my time. First symptom was vibration thru center armrest around 40-50mph.

 

My drive to get new tires took a few hours, so I was able to define the circumstances better. Of course, the new diff fluid did nothing - neither did the new tires.

The rumble strip vibration starts almost exactly at 1200RPMs every time (1100RPMs - 1300RPMs). It's a pretty narrow RPM band. That's why I don't see it over 50mph - above 50 the rpms are above 1500. Doesn't happen in the really low gears either. The condition started suddenly a few weeks ago and has not changed. I'll start investigating the possibilities you guys have offered. And I really appreciate the help. If anyone has any other ideas, I appreciate it.

 

With that info I would say prop shaft

 

Yes looking more likely. There is a surefire way but it involves downloading an app and some basic maths.
Basically you need to dl an app that does vibration analysis. There's plenty on ios/andoid but hit and miss. You need it to be able to display HZ spectrum of vibration picked up by phone's sensors.
You lay phone down flat on the armrest/seat/anywhere with big vibration, set app to 'flat' setting if present, drive up to affected speed, start charting. You will get a chart, spectrum of all oscillations detected. Some will be wheels etc, but the biggest one will be your thing.
Then it's time for math. You will have to calculate in sequence: rpm of wheel(s) at affected speed (google), then using a known rear differential and main differential ratios (I bet my boys striker. swfla, anfanger and all other of course will chime in with ratios. mine was 3.77:1 or something !NOT ACTUAL VALUE!), by that you calculate main pror shaft RPMs in affected range. Then just convert rpm to Hz. If it matches - 'well, there's yar prablem'. This procedure is pro level prop shaft diag and only one document on the internet describes it. Helped me a lot. I remember gunning parts.

 

3.08 rear diff, 4.60 1st, 2.72 2nd, 1.86 3rd, 1.46 4th, 1.23 5th, 6 is 1:1 and you can easily get it manually into each gear to test a certain shaft RPM vs the HZ app. Check your tires to figure out size/diameters based on what is actually on the car

 

I think the vibration is around 38hz and it mostly does it in overdrive (7th or 8th) - it MIGHT do it in 6th. Tires are 27.3" diameter. I still need to pinpoint the gear, but it's definitely in a taller gear.

But if it were the driveshaft, wouldn't it most likely be at a particular speed not related to engine RPM / torque? I can make the car make the noise if I can get a slight hill and it drops down to a high enough gear (overdrive), but it can be at anywhere from 25mph to 50mph. It's always right near 1100 - 1300 engine RPMs with the same amount of torque from the engine. I'll try it this evening, but I'm not sure if it will make the sound is under-drive (<=6th) or drive. Car drives great outside of the 1100 - 1300 RPM range in any gear or speed. I drive 500 miles a week up up into Boykie-land. It's great on the interstate doing 60+.

I'm willing to try anything but I just want to make sure the issue is understood. You guys are great for trying to help me out here. Been a contributor for 16 years on the land cruiser forums (ih8mud). I hope I can become a contributor here as well.