My 2001 LS430 with 110k miles rides very well, but has a low frequency oscillation that "shakes" a few times after crossing uneven joints in the pavement, a distant "jolt" that you feel through your seat. It's most noticeable over 55mph. Kind of like bad damping, but shock rebound is perfect when tested sitting still.

Can engine or transmission mounts cause this symptom? If not, any ideas?

Thanks in advance!

 

Motor mounts are mostly felt during shifting. The engine itself will actually move around a bit. When they are bad they can transfer additional vibrations to the driver. I would look at your front lower control arm bushes as well. Usually this is the cause of noises / clunks when driving over uneven pavement but motor mounts are a common wearable item. Really need to inspect them for play to determine their condition.

 

It's tough to tell because some types of road can unsettle a car in different ways. Even when everything is working correctly, you can have that happen.

I will say though that the "bounce" test for struts is not a great way to really know if the struts are ready to be replaced. I had a rear strut that had a ridiculous amount of oil coming out of it and was obviously blown, yet the car wasn't really bouncing. If you can bounce a corner and it keeps going, the struts probably needed replacing a long time ago.

I would say at nearly 15 years old, they probably aren't dampening the way they should at this point. It doesn't mean you need to go out and replace, but it's likely part of the problem. You're probably getting some up and down momentum and the struts have a hard time slowing it down.

When you replace the struts, it really becomes apparent how sloppy the old ones are. I like a smooth ride, so razor sharp handling is not a priority, but the car definitely feels more connected to the road when the struts are doing their job.

 

Any recommendations on replacement struts? OEM or aftermarket?

 

I have a 2001 LS with 259K miles - never replaced the struts. No suspension issues. Like you, I live in northern climate. Before you replace the struts, I'd be very sure that's the problem. Have the lower control arm bushings ever been replaced? Lower ball joints? Front sway bar bushings? These are typical at your mileage. It's not to say though it's not the struts. I would do a thorough diagnosis before doing anything, especially the struts, but your description does sound like worn lower suspension parts.