Low Speed Shudder - Not Engine Start Up

[C5Bob]

I have an '07 Rx400h with 66,500 miles. I have noticed a 'shudder' or 'tire hop' at slow speeds that continues as long as I maintain the speed - 30-40 mph. At first I only noticed the shudder when the car and tires were cold, and I attributed the shake to flat spotted tires, because the shudder would go away. It must be noted that within 2 miles I am driving 50 mph or greater I recently installed new tires, and the problem is more pronounced, and lasts long after the tires are warm. At 40 mph the car feels like it is hopping on every tire rotation. Tires have been rebalanced, and are fine at other speeds. I can stop the shudder by accelerating to higher speed. It almost feels like clutch slip and grab. Is in possible that the electric motor is acting up?

All opinions are appreciated.

[RX400h]

Are you sure this is not happening on the same stretch of road? I feel the same thing on a certain stretch of road in our neighborhood. It dissappears 2 miles down the road.

[C5Bob]

I too have noticed 'washboard' black top that gives the same effect. Your question provides a very good description of what I am experiencing on a variety of roads. Thanks for the response.

[katzjamr]

there is a known problem in the software of the 2006 and 2007 400h at 40mph that causes the symptom you describe at 40mph in some vehicles. this came to light a few years ago, sorry i dont have the tsb, however lexus has a fix for it and your dealer should be able to go in and update the software. it feels like a torque converter grabbing and releasing at 40 mph and they should be able to get rid of that. the service manager told me yesterday while i was at the dealership that the same issue is popping up in some rx hybrids at a constant 70mph also, and they have a software update for that also. my dealership does not charge me for this work if i am there for another reason, i.e. lube, oil filter, or other service

[C5Bob]

Update:

Second re-balance at the tire store revealed 2 bad tires. Tires replaced today, and shudder is gone.

Thanks for the responses.

[Jim Clark]

Update:

Second re-balance at the tire store revealed 2 bad tires. Tires replaced today, and shudder is gone.

Thanks for the responses.

This is a perfect example of why Road Force Balancing is so important. Road Force Balancing would have identified the bad tires before they ever went on the car. It also measures the wheels to make sure they are not out-of-round. Regular balancing will not identify an out-of-round tire or out-of-round wheel, it will just compensate with wheel weights, only Road Force Balancing can identify out-of-round tires or wheels.

I'm guessing the tire store did a "regular" balance the first time and did a Road Force Balance when you brought it back.

Glad your outcome was good.

[RX400h]

Jim, do you know if any major tire stores have this equipment?

[hobbestank]

My experience with Road Force Balancing is from 6 years ago. FWIW, I had to call around to each shop and specifically request if they had the equipment. I think it cost $80-$100 to do my 33" tires, which is probably why it generally isn't offered unless someone has a problem (like out of round tires). IIRC, it even recommends which location to put each wheel/tire combo on the vehicle. It is the way to go though if you are very particular about your tire balancing.

[Jim Clark]

Jim, do you know if any major tire stores have this equipment?

I think most tire stores now have the Hunter RFB machine.

Most stores charge extra ($10-20 per tire), some don't. It takes the installer more time, especially if they have to rotate one or more tires on the rim which involves deflating the tire(s), breaking the bead seal, and rotating them on the rim to where the machine tells them. They only had to do that on one of the Paradas I put on the RX. The machine also tells them the best placement (tires that tested best go on the front). BUT, I'm not sure why because they're going to be rotated every 5k miles unless it's a staggered setup.

I had bought 4 Falken Ziex's for an Audi and 2 of the tires didn't pass the test. Tirerack immediately sent me 2 new ones and paid the shipping both ways. They said they would mount and test them on their RFB before sending the new ones, I assume they did, they passed. After the experience with the Falkens, I will always do RFB on all my cars.

On our RX's it's important, but not as important as on a Porsche 911 or other high performance sports car.