JBrady

Two other things to think about.

Transmission output shaft.

Hood support.

Not sure what would be the best way to test the tranny output. Maybe on a lift and have someone hold the rotational speed at the vibration point while watching and feeling for vibration.

For the hood, thinking a large flat area that could start resonating to air flow at the given speed. In fact the above tranny test could eliminate or lend support to aerodynamic causation. Using a loop of something strong as a safety open the hood to the safety latch and take it for a drive. If a resonance is the issue the change in hood position should change or eliminate the vibration.

Either test is relatively easy and cheap and should generate some usable data if not locate the problem.

JimsGX

Hi jbrady,

With the vehicle stationary and the rear end on jack stands, the vibration can be felt when the speed is brought up to between 25 to 30mph. For this reason, it wouldn't be an air flow problem since the vehicle is sitting still. The dealer dropped the transmission pan and did a visual inspection and stated that the tranny looked brand new. The reason for dropping the pan was to check for any metal particles on the magnets and the filter. The filter screen was clean and there weren't any metal particles on the magnets. I would speculate that if the output shaft was having an issue due to a bearing that was bad, there would be transmission oil leaking from around the seal. Just a guess though...

Jim

spooze

iTrader: (2)

my car also has a slight vibration.

JimsGX

Vibration Update: I found the cause of my vibration!!

This past Friday I brought the car to a local tire shop that also does repair work. They agreed to let me work with the mechanic out in the shop to try and figure out what was causing the vibration. After adding weights and hose clamps to different areas on the front and rear of the driveshaft and taking test drives with some improvement, we took off the heat shield to take a look at the center carrier bearing. With the car up on the lift and the wheels turning at 28mph, we could see that the rear shaft was spinning out of round at the carrier bearing and the bearing was being forced towards the drivers side of the car within its rubber mount. We played around with raising and dropping the carrier bearing until we got it to a point where it vibrated the least. This ended up being about 1/8" down from its original location. From there, we used a couple of hose clamps around the rear shaft, right up next to the carrier bearing, to get rid of the rest of the wobble in the carrier bearing.

So the good news is that after chasing this for two years, I've found and eliminated the vibration. However, this is a brand new shaft and both the old shaft and new shaft had the same vibration... This leads me to believe that the true root cause of the vibration is that the rear differential isn't pointing straight forward (we're talking small amounts here) but is pointing slightly towards the left front as opposed to perfectly up the center. If this is true, it leads me to believe that the rear subframe of the vehicle is out of alignment and that the left rear side of the subframe needs to move slightly forward in order to correct the problem and eliminate the hose clamps and center bearing shim...

So now the next question is whether or not the rear subframe that is held in place by two or three bolts that bolt up to the underside of the car on either side of the vehicle, allow for the subframe to be adjusted forwards/backwards? Are the holes in the subframe that the bolts go through slotted?

One additional piece of info that leads me to believe that the left rear subframe might be too far back is that when I replaced the rear carrier arm bushings and strut rods back some time ago, getting the left rear strut rod back on was difficult. I had to use a 6' long pry bar and use significant force (my wife had to stand on the end of the bar and jump up and down on it) in order to get the left rear bolt back in on the strut rod. The right rear was really easy.

Jim

valex

Congrats on figuiring it out finally!

skperformance

iTrader: (6)

Nice, I am pretty sure that you can also get diff shims since it is just centering bolts .

JimsGX

I know the diff can be shimmed up or down in the front, is it possible to shim it from left to right as well without moving the whole rear subframe?

Garage7RP

iTrader: (1)

I do not think you can because the rear differential carrier bushings has no space to install shims to move the differential left to right.

As you mentioned earlier, you might have offset the subframe when you where changing the rear carrier bushings. Check for straightness of the subframe components comparing left versus right parts.

Congratulations on the discovery.

skperformance

iTrader: (6)

I think you might be right as i was thinking the normal axis with shims.
A good collision shop can rack it and pull it slightly to get it back . I have a bend on my right sub frame but it causes me no issues yet.

Amskeptic

Has the car been hit? Lexus/Toyota did not offer adjustment of the subframe, that would be exploding variable hell. A good optical alignment shop can measure your l/r wheelbase variation and that will tell you if the subframe is not square.
Colin

JimsGX

The car has never been hit. I knew the original owner. The vibration was there before I did the rear carriers and strut rods/bars. I think the attachment point up to the body of the car for the strut rod is fixed, and independent of the rear subframe. If this is the case, it may explain why it took so much leverage to move the left rear suspension forward when trying to install the bolt on the strut rod back up to the attachment point of the cars frame. I'm going to shoot a laser from up at the tranny end of the shaft, have the light shoot directly over the center of the carrier bearing, and see where it hits on the differential end of the shaft.

If I find an alignment issue from front to back, does anyone know if the rear subframe can be moved/adjusted at all? It might only take 1/16" or 1/8" of adjustment if my theory holds true... There could be that much play in the bolt holes of the subframe even if the holes aren't slotted. In this case, simply loosening the bolts, giving it a tap and retightening them may be enough to bring it back into alignment.

Any thoughts on this?

Jim

mpatrizio

That was my first thought as well.

Good luck with this Jim.

I can relate because I've spent the last 3 months chasing a vibration at 60MPH. It arose after putting NEW LS430 factory wheels on the car. I've since done engine mounts, tranny mount, and 5 road force balancings on the car and can't solve it.

My vibration seems to be coming from the right front, and I'm not sure what to change next. I might take it to the local Lexus independent guru master that has an LS and give him a shot at it first.

Good luck, these cars are sensitive as hell to the slightest imbalance, but they are fantastic when they're right.

skperformance

iTrader: (6)

Getting an alignment laser or photo will tell you nothing as it is measuring caster which is adjustable front and rear.
It is to show relation of all 4 wheels not the precise points each one needs to be at .

JimsGX

My plan is to attach a magnetic laser level onto the exact center of the driveshaft up near the tranny, have the light shoot over the exact center of the carrier bearing and see where it lands back at the shaft where it connects to the differential. I'm assuming it will be off center at the rear point by a small amount...

GABE_LS400

if i was you i would just take a hammer to the shocks and bend them, that will sure fix the vibration. Than spray some black spray paint to make them look new. Also dont forget to flush the motor with sugar. Open gas tank pour sugar in there run car for 20 mins and bam good as new bro.