Bradster

Bradsters suggestion shouldn't apply to your 92. The part he's talking about is a one piece butterfly bracket that bolts onto each of the front cats and mounts to the bottom of the transmission with four bolts. The four bolt mounts have rubber bushings in them where it bolts to the tranny. Up until mid 91 I believe, there were two separate brackets, then it was changed to a single bracket to help minimize exhaust vibration

JBrady

I am also not for throwing parts at a problem BUT... yours is one of those mystery deals.

I wonder if something in the ABS system, traction control or something in the CPU is malfunctioning. May be worth swapping computers just to rule out that. Maybe a member would swap computers for a test?

EastWind

what year is your car? lol, don't go broke or waste too much money chasing it if it is not so major. cars age, take it as a little feature. my car vibrates like hell right now, and I see that I need engine mounts, steering yoke, rear control arms and rear struts. but seeing that the car is old, am going minimal and pushing it. going to do just the engine mounts and steering yoke for now. i can live with a 1990 old car riding a little bit rough.

JimsGX

I thought about the ABS kicking in for some reason as a possibility. I don't know about the ECM, but maybe if it was working in conjunction with the ABS, I guess it's a possibility.

I know what you mean Eastwind. Other's on here have either accepted a few bugs with their cars or ended up selling them and sometimes buying a newer LS because they couldn't tolerate some type of vibration that they couldn't figure out.

I started to take the right front apart today to put in LBJ's, and inner and outer tie rods. I got the inner and outer tie rod off, then had to quit for the day, but I'll finish it up tomorrow. I think both the old inner and outer on the passenger side are pretty sloppy. Who know's, maybe I'm onto something. I had to take a 1 1/4" open end wrench and grind the end of it down to create a SST for the inner tie rod. I got it off the vehicle okay. Tomorrow I have to get the old tie rod out of the bracket that one end of the steering damper bolts to. That has a 2" aluminum nut on it that surrounds the old tie rod.

JimsGX

Wanted to give an update to this and ask another question...

I replaced the inner and outer tie rods, the lower ball joints and the steering rack grommets/bushings. The car is running like new but I still have a vibration between 25~30mph. I think I'm getting closer to figuring it out though... This just keeps getting more wierd!

When I put both the front windows all the way down, the vibration goes away. If I put only one of the front windows down (either one), the vibration is still there. So, I've tried taping off the doors where they mate to the body and taking it for a spin, but that didn't have any effect. I tried opening the tilt on the sunroof and opening the sunroof all the way, but that doesn't have any effect. I also tried turning off the climate system completely and also tried changing the air flow to recirculate. I haven't tried taping off the front windows around where they seal, but I plan to try that tomorrow. I also plan to take off the two plastic wheel well covers on the two front wheels to see if anything is going on in or around there since the vibration is felt through the wheel to some degree. The car is super quiet inside when all the windows are up. I don't have any wind noise / air leaks around the doors or windows when everything is closed up at any speed.

Does the 1st Gen have any exhaust vents inside the car that work to refresh the air inside the cabin? I know many cars have these and they're typically located towards the rear of the vehicle. Not power operated, but they allow the air in the cabin to flow through and exhaust out. I wanted to check these if they exist to see if they were possibly blocked or faulty in some way.

I've searched the forum extensively with little results except one thread a few years back that talked about a "dead window or door gasket seal". Any ideas or similar experience along this vein would be appreciated.

Thanks!

Jim

Amskeptic

Weird indeed. The phrase most-often used by manufacturers regarding the issue you bring up here is "drumming". There are many aerodynamic effects that can initiate drumming, but most of the time, a small-to-moderate opening of a rear window will cancel its effects in the interior.

The interior air exhaust technology has evolved quickly since 1971 when flow-through-ventilation became the norm. With your unusually persistent symptoms, I would start with the Lexus air-door check in the climate control diagnostics, you may have dampers stuck open/closed. I do not know the Lexus method for interior air exits, my old BMW E34 brought air from below the package shelf to the inside rear pillars into the trunk and exhausted beneath the side bumper cladding through one-way valves.
Colin

skperformance

iTrader: (6)

Is the plastic cover under the engine still there?

JimsGX

Yes it is. I've tried running with it off and on but it doesn't have an affect.

I'm starting to wonder if I misdiagnosed the fact that the sound goes away when both front windows are down. It may just be much less noticeable under those circumstances. I'm going to closely scrutinize everything under the car from the tranny forward again to try and find something out of whack. Definitely running out of components to replace at this point. Only thing left under there that hasn't been replaced are the steering rack, sway bar links, wheel bearings and the shocks. It seems rotational though so I don't think it could be any of those. I'm going to check the runout on the hubs and make sure that the brackets that hold the calipers in place are true. The brakes, including the rotors and three of the calipers are brand new. The left front caliper didn't need replacement because it had been replaced around 15k miles prior because it was frozen. The vibration was there prior to everything being replaced. I'm missing something that is very subtle. Neither Lexus or my Indy have a clue what it is at this point.

Is it possible for a wheel bearing to cause something like this, yet over 12k miles or more not show any other signs of being bad? It doesn't seem likely to me but...

Thanks

suprafantx

Do you replace the steering rack grommets/bushings with OEM ones or after market ones? If you use OEM ones, I would suggest the Daizen steering rack bushings. The 62 MPH vibration of my 2nd GS400 is gone when I replace the stock bushings with the Daizen bushings.

JimsGX

Hi,
I used the OEM ones from Sewell Lexus. They had a slight design change to them that was made back in 91 to prevent the rack from moving inside the bushings. The ones I replaced were the old design.

Thanks

skperformance

iTrader: (6)

Just for fun try it with the trunk open.

JimsGX

LOL! Maybe I should take all the doors, hood, and trunk off then add them back one by one until the vibration returns...

skperformance

iTrader: (6)

No , just to allow air to escape with a different path and change the aerodynamics so slightly with the windows still closed so you can concentrate on that and not the air from an open window.

JimsGX

I'll give it a shot SK... Out of town for a few days but I'll try it when I get back.

Thanks

JimsGX

Update to my vibration problem... My local Lexus dealer had the car for six days but they weren't able to find the cause of the vibration... They checked the angle of the driveshaft and shimmed the differential down about 1/16th of an inch with a shim but it didn't fix the problem.

I've ordered three 70 gram and three 71 gram prop shaft bolts to try and fine tune the balance of the shaft. They should arrive later this week. I believe the standard bolts on the shaft are either 68 or 69 grams.

Using some hose clamps around the shaft, I've been able to minimize the vibration between 25 & 30mph but it created other vibrations when accelerating above that speed.

Jim