It actually makes sense that a freer flowing exhaust system would change how the engine performs therefore it would change how the transmission shifts. I've always seen this difference is all the vehicles where I modified the exhaust system, the whole vehicle dynamics are changed. In your case, it sounds like for the better.

 

AA80E with Lock up torque converter is the same trans in the IS F, RC F, GS F and LS 460 SPORT/F SPORT. First appeared in the 4th Gen LS in 2007-2017, 3rd Gen GS 460 (2008-2011)…not to be confused with AA81E only used with the 2GR applications.

With that said, have you been experiencing this before or after you modified your wheels/tires and etc.

 

This happens to a lot of cars. Whether it's modified or not does not impact this behavior. Mine is bone stock and has done it since new.

 

So, I've modified my driving habits a bit since getting IS 500. I typically start braking pretty early, but that seems to set of the clunk rather reliably. What I been noticing is that the car likes more brake pressure. Hence, lately I've been braking a bit later and harder than I normally would prior. Nothing too crazy, maybe 10-20% difference. That seems to work a lot better. Still get an odd lurch once in a while, but nowhere near what I used to get in the past.

This reminds of the first gen DSG (dual clutch gearbox) I got in my Mk5 GTI. For a while I was driving on the defective mechatronics unit that they recalled eventually and gave everyone affected 10 year DSG warranties. One of its issues was this exact behavior. It would slam into gear while slowing down to a stop.

Ugh... Now thanks to IS 500, I can add PTSD from resurfaced old trauma to my list of issues.

 

got my transmission replaced because of this exact same issue it's been going on, unfortunately it made no difference so the dealer had to convince me that it's normal, clearly it is NOT!!! today i went to test drive another is500 just to compare and that IS500 transmission was buttery smooth, i will schedule an appointment and take it back, i dont care if they gonna have to put another 10 new transmissions to get this fix but i am not going to deal with it, it is stopping me from loving this car, hste to drive it around my neighborhood, it should not this be this way

 

Is your issue the downshift when coming to a stop? Particularly it shifts from 5th to 3rd. Skipping 4th seems to make a harsh jerk. Seems like the trans is programmed to make the skip. It’s much more pronounced when cold but is present when warmed as well.

 

You must have the nicest dealership on the planet!

 

yes!!! What i also noticed, the tach doesnt align with the actual gearing, because i feel the downshift but the tach remain showing i am on the 5th gear for a second or two then it drops to 3rd.

 

I'm pretty sure that the TCM thinks you're going to hit the gas again so it hangs on 3rd. When I drove my car like a Camry for the first few thousand miles it started shifting like a Camry (also fully warmed up). I've been driving spiritedly lately, and when I do, it likes to hold that third gear when coming to a stop. But if I start acting like I'm in the Camry again it seems to adjust quicker. Just my observation, could be wrong.

 

Do not forget that our cars have a torque converter. The RPM will not always be an absolute function of wheel speed and gear ratio of the current gear. If you leave the car in Normal mode and automatic shifting mode while cruising at moderate speeds, you would see the Gear Position displaying 8th gear, but the RPM will vary itself up and down in certain conditions. I believe it locks the torque converter while cruising in auto mode, but it also unlocks from time to time depending on what you want the car to do. For instance, if you want to simply add a little speed to make a casual pass, it may rather unlock the torque converter to allow a little more torque rather than downshifting to 6th, or whatever.

This brings me to the reason for the clunk, at least in my experience - I think it is the torque converter unlocking while we decelerate. This is just a hypothesis, but... read on, if you will. The torque converter locks above certain speeds in 2nd gear or above, and, conversely, it unlocks at certain low speeds. I observe the clunking noise/feeling when I am in manual mode if I keep the car in second gear if I decelerate gradually (i.e., just foot off the gas or gentle braking) in addition to while decelerating in Normal mode with the gear selector in Drive. I can also feel it locking up in manual mode - happens in second gear at about 23 MPH. It feels like the car hesitates for a second when it hits this speed unless I give it a lot of throttle. Regardless of how warmed-up the car is, it will always happen. Maybe the reason I only notice it in second gear in manual mode is just due to how gearing works. Second gear has a higher ratio than 3rd, 4th, etc., so any changes in torque to it will be more easily felt than those higher gears. And, as mentioned before, the torque converter only locks in second gear or higher, so I wouldn't have felt it in first gear. This may also explain why downshifting into first gear can be quite rough at low speeds. If you perform it at higher speeds, i.e., above 25 MPH or so, the car performs a rev-matched downshift into first, though there's still a bit of roughness to it. Either way, I don't experience any other weirdness with the transmission outside of these low-speed deceleration scenarios, which is exactly where we expect the torque converter locking and unlocking to be done.

By the way, I will say that I noticed some similar behaviors in my prior car, my IS 350, though not as pronounced as in the IS 500.

 

It's normal.......one of the quirks of an old school trans and engine. I don't love it, but I deal with it. Somewhere there is a video of a guy dissecting the transmission. I believe @arentz07 is correct.

 

I noticed that if I just leave the car in sport plus, I almost never have these rough downshift when approaching to a stop.

 

i will tell you why, it only happens if you reached the 6th gear and then start slowing down, if you slow down right after after 5th gear it’s not going to do that, and sport plus usually keeps in low gears.

 

Makes a lot of sense! Sport Plus all the way!