Umbo

IMHO the biggest shortcoming of the SC is the slow downshifting. If I'm coming out of a corner and try to accelerate hard, there is an obnoxious delay before the tranny can downshift and the car starts to move. It almost feels like the car is about to stall. Admittedly this is my first car with an automatic tranny so maybe this is normal auto tranny behavior. Has anyone else noticed this? Is there a way to fix it? Can you downshift manually with an automatic tranny? If so then where in process of cornering should the manual downshift be performed?

tfischer

At about the half-way point, just before you hit the apex.

I will add that I used to enjoy trying to accelerate hard as I would come out of every corner, but the high price of tires soon broke me of that habit.

JCtx

That behavior SHOULDN'T be normal buddy, but ALL Lexii cars I've had (4 of them, all V8s and new), behaved that way, including my present '04 SC. It's because of the 'intelligence' crap Lexus still insists is a 'good feature', but they should at least bypass it on the 'power' setting.
All my previous automatic cars (Hondas, Acuras, BMWs), all downshifted immediately.

I learned to live with it, but it $ucks. And yes, you can safely downshift manually. I do it quite often, especially at today's gas prices (it takes almost WOT to invoke a downshift otherwise). And yes again, before the tranny kicks in, it momentarily feels like the engine died . I sold my first Lexus (SC400) for that reason, but since the cars are fantastic, I learned to live with that 'idiosyncrasy'.

Cheers.

dmizock

I've found that turning off the VSC seems to eliminate or at least reduce the "stalling" when accelerating through corners. I never had this experience with my GS430 even though it too had VSC.

rominl

iTrader: (4)

well if you guys want, just put in the aftermarket tq converter and that would solve the problem. throttle should be much better and downshift would be a lot faster too.

though probably there will be the CEL (check engine light) problem. not a problem, it just says that the tranny is having something funny (higher stall speed)

1NICESC430

I always use my automatic transmission as a manual.

I use second gear in town, third at road speeds of 40-50 mph, fourth at short distances above 50 mph, and fifth at sustained highway driving. I always downshift when slowing down and occasionally I downshift to first. Generally speaking, I tend to keep my RPMs at around 3000 unless I'm on the highway in fifth..

I'm older now and no longer crazy, so I tend to drive slower than 80 mph, but NEVER below the speed limit, so don't complain when you get behind me.

Incidentally, there's a nice throaty exhaust sound when I downshift to second or first. Wish I had that sound all the time.

Umbo

I've read very positive things about the Dragon Torque Converter on other threads. People who have installed one think that it was the best mod they've ever done. Pardon my ignorance but does anyone know basically how they work? Are there downsides besides the cost?

rominl

iTrader: (4)

tq converter take and amplifies the tq and power from the engine and put it on the wheels. the PI tq converter with 2800 stall speed, which a lot of people with v8 engines here have, will raise the stall speed from the stock 1800rpm (??) to 2800, so the car could get its power much quicker.

i have driven car with it before. the throttle is so much quicker, and the car pulls A LOT harder.. and i mean it

the only downside for 430 engine is that it has more sensors, and you will very likely get CEL coz' the sensors see some different stall speed on the tq converter. but it has nothing bad for the car at all

another bad thing is your gas mileage might decrease a tiny bit

Umbo

I had a chance to learn all about torque converters from Howstuffworks.com and NHRA.com. Here's the readers digest version.

Basically a torque converter is the automatic transmission's equivalent of a clutch. It is actually a hydraulic clutch filled with transmission fluid. It's main purpose is to allow the engine to idle when the car is not moving. When the rpms of the engine increase, fluid forces are transmitted from a propeller like Turbine attached to engine, to a another propeller like Stator attached to the transmission. Aftermarket TC's like the Dragon allow the engine rpm's to increase to a higher level before the Stator starts to strongly engage the transmission. Since most engines tend to have more Torque (rotational force) at higher rpms, the car becomes faster off the line.

Stall Speed is measured by locking the transmission in a fixed position and then rev the engine until is stalls. Stall speed is the engine rpm at the time of the stall. It is dependent on both the engine and the TC. Aftermarket TC's have higher Stall Speeds than stock TC's.

When a car with an auto tranny reaches about 40 mph the speed of the Turbine and that of the Stator are almost matched. There is still some slippage however since they aren't mechanically linked. That slippage accounts for most of the decreased gas mileage of an automatic vs a manuel transmission. I'm not sure if I have this part correct but I think that the high performance TC's have more slippage and therefore get worse gas mileage.

More info at:
http://www.howstuffworks.com/torque-converter.htm

JCtx

Hey Umbo, most modern auto trannies have 'lock up' converters, which mechanically lock up either top gear, or the 2 highest. I don't know how it's done to be honest, but I remember having that feature since my 1997 Ford F150: it had a 4-sp tranny, but you 'felt' 5 gear changes. The '5th' was the converter locking up, and you could see a small drop on the rpms as well. I don't feel that on the SC, but I'm sure it's there; that's why it takes forever to invoke a downshift (right... experts?).

I'm curious as how the lockup is achieved (sliding pins?), so if somebody has the answer please post.
My immediate next question is if aftermarket TQ have the lockup feature as well. Without the lockup feature, there's more slip, therefore more wear, and a sooner rebuild.

Umbo

ELP, I don't know if the stock Lexus TC has a lockup mechanism but the Performance Industries web sit doesn't make a mention of it on their Dragon TC. I would doubt that a TC without a lockup mechanism would wear out faster since all the slippage is transmitted through transmission fluid resistance. There is no metal on metal slippage.

Is there anyone out there with an after market TC on an SC 430?

JCtx

Umbo, the little I know is if there's slippage, there's wear buddy. Not much, but some. The TC is similar to a wet clutch on most motorcycles: plates operate under fluid, which reduces wear, but there's still wear when you slip the clutch.
Most auto trannies reach 100K miles without needing the TC rebuilt. When the plates wear beyond their service limits, you'd have similar symptoms of a worn clutch, or if you were low in fluid: rpm increase without forward motion. And it'd eventually get to a point where the car just won't move when in 'D', regardless of engine speed.

I'd like to see a complete cross-section of a tranny like ours. I'm curious about the 'lock-up' mechanism.

rominl

iTrader: (4)

the PI TC has the lockup mechanism. i forgot either someone called them and asked them or it's on their site. probably someone called thogh

honestly i don't know of any, people got scared by the CEL i guess, though it's actually no problem

if i were to get the sc430, i would put in TC for sure. the thing i "hate" about the sc430 is the very poor throttle response. my gs400 is a lot better

Umbo

Rominl, what does "CEL" mean?

I've been manually shifting the tranny for the last few days. It makes a tremendous difference. Downshift to 2nd gear going into corners and 3rd gear just before passing on the highway. No more annoying lag waiting for the downshift to occur automatically. Much more responsive and sporty this way. Boy, Lexus really needs to work on this lame *** stock auto tranny. Thanks for all the advice. I'm probably going to get the Dragon as my next mod.

JCtx

Must be 'Check Engine Light'.
Have a great weekend.