1998 Ls 400 Drivetrain/chassis Issues

[LS 0181158]

Been awhile since I posted here! 1998 LS 400, now with 201K miles, drivetrain all original. Owned since 115K and maintained detailed records since then. Lately, I've observed the following irritations/concerns, and will attempt to break them into their own sections.

Potential failure of torque converter lockup clutch or related components:

The issue: At highway speeds, the mechanical linkage in the transmission--the one that is coupled when maintaining a constant speed--disengages on the slightest uphill grade or when even the smallest degree of acceleration is required. I know this is supposed to happen when sufficient additional power is delivered through the transmission, but I've owned the car for over 80K and definitely have a feel for what that threshold is. The lockup clutch refuses to stay engaged (disengagement is accompanied by a gentle driveline jolt and an increase of perhaps 150 rpm on the tach) unless the accelerator is absolutely feathered. It feels like the transmission is constantly "hunting" back and forth, in and out of the mechanical engagement--in top gear on the highway. The higher the speed, the more power is required, and the less likely the lockup clutch is to stay coupled.

Background: The car is a 1998, so remember it's the 5-speed transmission, not the 4-speed. The exact same symptoms described above manifested during March/April 2009 (this would have been around 155K miles) for approximately 3-4 weeks, then abruptly disappeared entirely until just this past Friday. Exactly a week prior, I had the Toyota dealer up the street flush the transmission and replace with 16 quarts of Type IV fluid as required. I was wary of the flush vs. a drain/fill, but the techs there seem quite competent and recommended the flush as a more effective way to replace the transmission fluid, which has always remained black even after prior drain/fill services. The transmission shifts great now--even smoother yet crisper gear changes than the ones before, which were just fine IMO. I'm on the fence whether the lockup clutch issue has anything to do with the flush, as this problem didn't occur until a week later and had manifested itself briefly almost two years ago. Is this mechanical, hydraulic [fluid issue] or electronic? Could this be the "torque converter lockup clutch solenoid" I've heard of? Other suggestions? Will I need a new transmission? And how bad is the impact of this continued behavior on the life of the current transmission?

Chassis vibration and steering wheel shimmy at highway speeds:

The issue: Also at highways speeds (particularly noticeable above 65-70 mph), I notice substantial vibrations coming through both the steering wheel and the chassis. It feels as if the car is running over lightly rippled pavement, but clearly has nothing to do with the road surface. The rapid pulsations of the steering wheel shimmy vary with road speed, but may also smooth our or reappear without apparent cause while maintaining the same speed. Likewise, the entire car can vibrate in line with road speed [sort of a rapid up/down shaking like might be felt on account of out-of-balance tires]. Also, releasing the accelerator to allow the car to coast down [from any speed] creates a sort of coarseness/subtle rumbling vibration that can be felt particularly up through the center console armrest. That glass-smooth highway ride I've experienced in even older, higher-mileage LS 400s and recall from my own car a few thousand miles ago? Pretty much gone.

Background: At my request, the aforementioned Toyota dealer inspected the following:

- Motor mounts [deemed fine condition despite the mileage]

- Transmission mounts [same as above]

- Wheel bearings [no issues there]

- Strut rod bushings [again, I was advised these are in fine condition]

To my knowledge, none of the above items have ever been replaced. I had brand new Sumitomo HTR A/S P01 V-rated tires mounted and balanced[on original rims] less than 2K miles ago. The car was aligned at that time as well. I'd been experiencing the steering wheel vibrations with the old Yokohama tires (the fronts were extremely worn), and to my chagrin there was little change with the new tires, aside from an obviously much quieter and smoother ride purely on account of the Sumitomos' deeper tread. Exactly 32 psi all the way around, no uneven tire pressures.

The only suggestion the Toyota dealer had regarding the chassis vibration was that the driveshaft and/or U-joints might require attention. For perhaps 10K miles I've noticed an odd 'binding' sensation transmitted through the drivetrain in top gear at exactly 76-78 mph--almost like this is some kind of odd harmonic frequency. Was never there before. So maybe it is something to do with the driveshaft. Of course, that explanation does not address the annoying steering wheel vibration/shimmy. I think I have to accept there are probably multiple issues at play here. Given the mileage, what are your suggestions, taking into account the items supposedly NOT worn enough to require replacement? On a side note, is it common for motor/transmission mounts, front strut rod bushings and wheel bearings to serve over 200K and remain entirely serviceable?

Within the next month or so, it appears I'll be moving halfway across the country, and I don't want to have to worry about (or be irritated by) my car either on the trip or in my new location! I'm prepared to spend a grand or more if the expense can be more or less assured to correct these issues.

Thank in advance for your suggestions!

[1990LS400]

The strut rod bushings usually don't last 115K miles let alone 201K miles. It's a well documented issue on the 98-00 LS and there have been many past threads about them. I forget the exact mileage but my strut rods/bushings were replaced at around 80,000 miles due to excessive wear and a bad come and go vibration at highway speeds. They needed replacing much earlier that that. I'll probably have them replaced for a second time before 150,000 miles.

I'm surprised that the transmission mount hasn't become overly compressed at 201K but I was told mine was fine at the 120,000 miles service.

[billydpowell]

one of my 99's had a little shimmy/vibration (very light, but there) @147k

replaced engine mounts, strut rod bushings (oem only) tranny mount....

now they are both smmmoooth..

by the way 32psi is too much, Lexus recommends 29psi.

[LS 0181158]

Thanks to both of you for your comments. I will take my car to a different mechanic up the street for an analysis of the driveshaft components/other drivetrain vibrations, since the Toyota dealer was standoffish in this department. I think I'll order the strut rod bushings beforehand and simply tell them to replace those parts at the same time. Having purchased the car with 115K, I am quite sure that at 201K, the car is still on its original bushings. I'll also have the mechanic take a second look at the motor and transmission mounts.

Where did you all order the strut rod bushings from? I will certainly go with OEM, but where is the best place to get them?

Hopefully this addresses at least the steering wheel shimmy.