Hello everyone,
Recently I have noticed that my 2012 RX 350 (115k miles, automatic, 3.5 L V6 FWD) clunks when shifting to Drive or Reverse (from Park or between those two, but NOT to/from Neutral). This sound is also noticeable when accelerating from a stop and when letting off of the accelerator. From what I can tell it is largely localized to the passenger front wheel well.
lexusclunk1.mov
(In the video, I am shifting between Drive and Reverse to reproduce the sound.)

I have done some research but have found many different answers and was hoping to get some input from people who are more knowledgeable. Common answers included worn motor/trans mounts, low/dirty transmission fluid, and a bad CV joint

Information I think may be helpful:

• While replacing the serpentine belt the other day, I noticed that the front passenger CV boot was leaking just a little. Strut was dry.
  
• To my knowledge, the transmission/fluid has never been serviced/replaced. Shifts are smooth and do not jolt. No slipping that I have noticed.
  
• The top, passenger side motor mount is pretty worn and the rubber hat is partially separated.
  

Thank you very much for your help and let me know if any other information would be helpful!

 

Does it clunk on bumps and speed bumps? If yes, I would suspect a suspension component, like ball joint, control arm bushing, or struts. If not, I suspect motor and/or transaxle mount(s). The torn upper mount, commonly referred as the dog bone strut, will likely not cause the noise if it still has rubber but should be replaced before the rubber insert pops out or wears down further. I wouldn't rule out the CV shafts, but if they clunk that loudly, they would have excessive clearance, causing noticeable vibrations when accelerating.

 

I appreciate your reply! Just tested and I cannot hear the sound when going over speed bumps. I do not feel any vibrations when accelerating (but I could just be unfamiliar with what it might feel like).

 

In your video, it looks like that transaxle mount is moving too much. If it makes the same noise with the front end up in the air, try to feel the mount when it makes the noise. If that is the culprit, you will feel the clicking in your hand. You have two mounts, at either end, and a center mount at the front. The front one is the expensive one.

 

I assume you can hear the nose with the RX not moving. If so, have an assistant observe the top support. You mentioned the rubber is torn. This member provide bracing as the engine experiences shift in torque [loading].

Also, share with us your idle P/N rpm and D or R rpm [foot on the brake].

Salim

 

Hello again, sorry for the late reply!

I took some new videos of all the visible mounts (could not get a clear angle of the front mount):
Dogbone: https://youtube.com/shorts/KecxX9sX4Zw?feature=share
Passenger side bottom: https://www.youtube.com/shorts/CH8l_vJBUEs
Driver side bottom: https://youtube.com/shorts/S6RnfbJ9Ekg?feature=share
This looks like an excessive amount of engine movement to my untrained eye, but I am curious to know what you think!

As for the RPMs: They sit normally around 900-1000 in D or R, but during the shift they would spike up to about 1300 and then return back to normal.

Thanks again!

 

There seems to be movement at the dogbone. Do you see a tear/rip. if so replace it.

Engine rpm seems a tad bit high but they are not under user control unless some one did some tampering.

Salim

 

Hello again!

I just took these photos of the mount. From what I can see, there is some cracking in the rubber, but I cannot tell if it is fully separated.




Probably irrelevant, but I had a question about what the box at the top of the mount was? I found the part number 123630P120 (likely going to order through rockauto)

Also regarding the RPM, I don't think I let them settle fully before reporting the numbers. I checked again after the engine had reached operating temp and they were around 750 on all gear selections with the same perturbations when shifting.

Thanks again!

 

Also, does anyone know the torque specs for the dogbone mount?

Thanks in advance!

 

750 rpm is a good number. If it is higher then the engine is producing more torque+hp and the shifts become harsher.

Box on top of what? For the lower mount, the electrical pulses are used to counter the engine force to reduce vibration ... almost like sound cancelling noise.

Salim

 

I think it was around 59-70. I just changed mine out recently and that was the range.