OK - this is the situation. I am planning on trading in my '01 RX as soon as I can find a suitable CPO '05 RX. This could be two weeks or could be two months.

The four tires were pretty much worn out, and one had a leak so it had to be replaced. My tire guy had 3 tires that he had taken off an RX with about 60% wear left on each tire (40% gone). So, I put the spare tire on one wheel, and the used tires on the other three.

Now, I know I've screwed up the handling, braking, etc. BUT, I'm also hearing a weird noise (thump, thump) between 40km/hour and 60km/hour.

Given that (I believe) torque is distributed evenly amongst all four wheels under normal driving, is the difference in tread causing the differentials or the transfer case (sorry don't know the difference) to go haywire?

Thanks for any advice (other than stop being a cheap bas*ard and just buy four new tires!)......

 

You could put a worm in one of those tires and that can be done at any gas station.

40 to 60 km/h equates to about 24 to 36 mph us (have to do this conversion all the time in Mexico). Generally, if you have a problem with your differential or transfer case, the sound would be pronounced every few seconds at all speed ranges (broken grooves) or you wouldn't be able to move.

I don't know from where on your RX you are hearing this and if you hear it at any other point.

One thing is that if you are doing it while you are braking (and it would be more pronounced at the speed ranges you mentioned, that would a symptom of warped rotors and rather than replacing those, most auto service places (you don't need to do it at Lexus or Toyota) can machine those rotors.

I doubt it would be one of the gears in the tranny, but I won't rule that out since I don't know every detail here about your situation.

Also, how many km do you have on your RX?

 

A worm? Not sure what you mean by that. The old tires are gone. I'm now stuck with what I have.

I'm hearing it from underneath the front end of the car, and it is on acceleration and braking between the speed ranges I have mentioned.

I am hearing it during acceleration, plus I just had the brakes "done" a few months ago, so I don't think that it is the rotors. The noise only started once I put the "new" tires on.

It's more of a thump-thump noise than anything, so I don't think that it is the tranny.

I have 67,000 km on my car. All service has been done according to the owners manual.

 

If you happen to get a nail, for example, stuck in your tire, someone can pull it out and they put a small piece of flexible rubber that lookes like a little worm into the hole and the the sides of the hole expand as the air is put back into the tire. Old trick been used for decades. Any service station can do it. In Mexico, they have people who will actually take off the tire and patch it. Many people along the side of Mexican highways live off of this service.

I hope it is not one of the belts in the tires, though that would also be pronounced throughout the speed ranges.

I know of one piece that can make a similar sound and with acceleration there would be enough force to make it do a bump, bump, but at a stable speed range, it wouldn't move.

It is a joint piece, see this thread https://www.clublexus.com/forums/sho...d.php?t=202045 and I had to replace both sides on my RX given Mexico is not a happy place for suspensions. The way to check this is to jack it up a little enough that the front tires are clear of the ground and shake each of the front tires to see if they move. The picture is the second one down where the yellow piece of paint is seen in the picture and it is the piece just below the one with the yellow paint held to together by two bolts or known as the lower suspension arm. The other places I mention two can also make clunks if loose.

 

Another thing came to mind is to check your driver's side shock by going over a speed bump (take it like you normally would take a speed bump) though I think it would make a slight cling as I had a broken shock once going up the Nevado de Toluca extinct volcano (in record time I might add).