IS2000

I have a stock GS430 with 18's. Everytime I power out of a corner, I manage to break loose my rear tires and the VSC immediately cuts off the power and applies the brakes to get the rears in place. Obviously, I need to upgrade to a LSD.

My search yielded the following from Mean Gene:

"Q - IMHO, it depends on how U drive your GS. If ya do alot of highway driving or like to autocross, then the TRD differential ( utilizing the 3.23 gears ) probably would be better for ya. The engine will turn lower cruising rpms & give the same economy as the stock ( open ) diff. For myself ( former drag racer ), I willingly gave up some mpg ( about 1 mpg when cruising at 80 mph or so ) for the deeper holeshot & subsequent lower 0-60 & quartermile times ( it knocked of .2-.3 depending on traction ) offered by the steeper 3.76 gearing."

I gather Mean Gene is saying that for off-the-line performance, RMM LSD 3.76 is the way to go and I'm totally in favor of this even at the cost of a few MPGs.

Now here is the part that confuses me:

"As far as hitting the rev limiter, it happens occasionally but I've learned to E-shift at about 5700-5800 rpms & I'm hitting 6k by the time the tranny actually shifts. As a reference ( because I don't know where Mike hid the original Lexus Q&A data from the old website :eek: ), the T/C dropped my quarter mile times by about .3 - .4 while the RMM LSD knocked off an additional .2."

I do not understand why Mean Gene hits the rev limiter "occasionally" when he leaves the car to shift by itself. Isn't the beauty of an automatic tranny its "consistency" in shifting? I do not have the E-shift feature, therefore, does this mean the RMM LSD isn't for me?

Lastly, I have no plans on upgrading to a T/C or valve body. Is it possible that these mods are the ones that are affecting the occasional hitting of the rev limiter by Mean Gene? Or is the higher gearing of the RMM LSD solely to blame for the "rev limiter problem" and thus, is not for me.

Will I be better off with the TRD LSD instead? But from my search, I gather that it will slow me down a bit because of the lower gearing but improve my top speed. I don't really give a whit about top end since speeds beyond 120mph is suicide in my opinion.

DaveGS4

iTrader: (2)

The TRD LSD gearing is exactly the same as stock, so you will not slow you down any , only improves traction.

Most guys with the RMM (aka Supra TT) LSD don't claim to have experienced hitting the rev limiter. However, for those that it does happen to - it's got to be the different gearing that causes the supposed rev limiter problem. TC and valve body shouuldn't impact it at all.

If you don't plan to heavily mod your GS, IMO go with the Supra LSD for the extra punch off the line. I went with the TRD variety because I may eventially put FI on my GS.

skier1

I just put a Supra TT auto differential in my GS4. I had problems with spinning the right rear tire when turning right with heavy throttle. The Supra differential with it's Torsen LSD and higher gear ratio (3.76:1) is a great choice. I have noticed a little bit better accelleration and NO tire spin. If I try real hard turning right, I can get both tires to spin, but just a little. The LSD works great! AS of yet, I have not hit the rev limiter. For $325, it's probably one of the best mods you can do. It takes a few hours to install. Next mod hopefully will be the PI Dragon Torque Converter.

BananaGS

-getting the Supra TT LSD is like getting an LSD with a free SRT intake
vs
-the TRD LSD is just a LSD

but TRD LSD can with stand alot of HP, so if you want to get your car in the 500-600HP range, your only choise is the TRD.

-if you gona stay 400 HP or under, the supra TT will do just fine.

Supra TT is gear driven LSD, never have to rebuilt-> should last forever.

TRD is clutch type, so you will need to be rebuilt, depend on how much the LSD is used. since the clutch wear oout.



Anh.

Mean Gene

I was told that the deeper gears MIGHT cause a problem with the electronically controlled transmission because it is programmed for use with the stock 3.23 gears. Because the 3.76's make the engine rev faster, the tranny can't react fast enough ( at least w/o a valve body upgrade or SRT's "rumored" tranny ECU ) so it tags the rev limiter. It happens most often when it's cool or if I've just recently reset the ECU. This just seems to make sense to me as cooler weather brings out a few extra horsepower & it's been long debated about resetting the ECU ( works for me ). Maybe one of these days Mo or Marken will give us an update on the ECU project?

IS2000

Skier1,

I take it from your post that you are very happy with the Supra TT LSD "auto." I assume there is a manual version of this and I should NOT get that. Furthermore, you mentioned about being able to break loose the rear tires on a hard acceleration while cornering. At this instance, does the VSC intervene by cutting off power? Or does the VSC take a back seat and allow the LSD to do its job? Any adverse effects of having the LSD in conjunction with the pre-programmed VSC? I say pre-programmed because I seriously doubt Lexus had parameters in place for a LSD upgrade? Or are they one step ahead and VSC works in harmony with the LSD? Is your GS the 400 or 430 model? Was it a direct bolt-on or was some welding involved? I just want a back-to-stock escape route if something goes wrong.

Sorry for all the questions but I kinda want to get this right the very first time.

BananaGS,

You stated that if I keep my HP below 400 horses, the Supra LSD will work just fine. Are you referring to crank HP or wheel HP? I'm really praying for some divine intervention that Toyota builds a supercharger for the 430 engines since so many of its models are using that engine from the LS, SC to the GS. And with all the horsepower war going on with MB, BMW and Audi, I'm thinking Toyota might have to step up a notch.

skier1

IS2000, Good questions. When I leave the VSC on, it still works just like it did before I swapped the rearends. I have noticed no difference. If the wheels begin to spin, it activates very quickly. Now since this new gear has a higher gear ratio, the engine does rev quicker and the car accelerates faster. I believe that Mean Gene is correct about hitting the rev-limiter, I just haven't done that yet. The weather here in Florida is much warmer that it was in January and I just put the gear in a week or so ago. I could hit the rev-limiter if it were colder. But that wouldn't bother me. I don't floor it every time I take off (Oh how I love it though!). Now for the fit, it is an EXACT replacement. The only noticeable differences is that the Supra TT diff has cooling fins cast into the top and bottom ot the housing. This does not interfere with the installation. Now for HP handling, The friend that helped me put mine in has a '94 TT supra auto(I wanted to steal his gear!). His car is putting down 375+HP at the rear tires. No problems with his gear. I can't speak for if his hits 400+HP at the rears. Now the 6SP Supra differential's have a taller gear ratio, something like 3.1xx:1. I have also heard that the ring gear inside is a larger diameter. I think that this will fit into a GS but with this taller gear ratio, I wouldn't do it. The GS would be a bit slower off of the line but have a bit more top end. It is an LSD unit, but you would need more HP to spin the tires.

The thought of a supercharger has entered my mind a few times. I just sold my '93 supercharged Thunderbird. With 4:10 gears and 17lbs of boost, it was a monster off of the line. Lots of torque. My question is TRD makes a Supercharger for the 4.7L Tundra. Are the engine blocks the same between the Tundra and the GS4? If so, and they are and the Tundra block is just a bored out GS4 motor, why wouldn't a TRD SC fit on a GS4? If so, that is the way I would like to go. Cheaper that the SRT aftermarket kit.

BananaGS, I'm still lookin for a Supra TT auto differential for ya! I'll PM you when I find something.

IS2000

The TRD website has identical part numbers for the Supra / GS400 LSD.

ARISTO
LEXUS GS400/300

Part Number: 41301-JS401

I seriously doubt any rev limiter problems will occur with this unit since it is TRD certified. I assume this LSD has the 3.76 gearing?

http://www.toyota-trd.com./en/strt/d_lsd.html

BananaGS

IS2000,
i think you stil confuse, LSD and 3.76gear are 2 different things. The part you are seeing in TRD website is just the LSD. The new suppra differential is $2200, not $800 (new price) Go to RMM website, and look at the RMM/Supra diff unit if you don't know what the diff look like. www.rodmillen.com, what you are seeing on TRD website is just the LSD part

(400RWHP, but this is what people with Supra TT auto is running, but I don't know the exact HP that this thing gonna fall apart, but is was proven that the gear will break with high horse power Supra)

hey, skier1, thanks. let me know if you find anything.

Also, from what i've seen so far, the folks with 18" rims don't have the rev hitting problem. The folks that has stock wheels (17) some had seen this under heavy accelelation from stop. Note, you don't hit the rev limit everytime, just during WOT from stop. hopefully, Mean Gene can confirm this....

IS2000

I'm so clueless

BananaGS,
Is the 3.76 gear like the 5th gear ratio? Like 1.0 -1st gear, 1.5 - 2nd gear, 2.0 -3rd gear and so on?

"The part you are seeing in TRD website is just the LSD. The new suppra differential is $2200, not $800 (new price) Go to RMM website, and look at the RMM/Supra diff unit if you don't know what the diff look like. www.rodmillen.com, what you are seeing on TRD website is just the LSD part"

What am I buying with the TRD LSD? I saw pictures of small gears in the TRD site.

What is this supra differential? Is this not a LSD as well? Is this the unit?

http://www.rodmillenstore.com/gs_400/diff.htm

The picture seems to include the entire LSD housing. I suppose the TRD LSD merely uses the old stock housing and simply replaces the gears inside?

Am I making sense?

BananaGS

Ok, I just typed the whole page of info, but losted, oh well,
just look at the picture then, the picture showed the inside of a torsen diff, but I hightlighted where the LSD part, so if you get the TRD, that where it would go in.


the ring 3.76 effect your transmission rotation in EVERY gear tranmission gear, not just in 1st,2nd....

skier1

IS2000, the 3.76:1 it the ratio of the pinion gear to axle ratio. This means that the pinion gear, which the driveshaft connects to, will spin 3.76 revolutions for every axle revolution. So, the higher the ratio(i.e. 3.27 stock or 3.76 Supra TT auto) the driveshaft spins more for every rear axle revolution. If the ratio was 1 to 1, for every turn(revolution of the driveshaft) the rear tires would spin 1 turn. If the ratio was 2:1 then the driveshaft would spin 2 times for every 1 turn of the rear tires. 3 to 1, driveshaft spins 3 times to the tires 1 spin. So, going from a 3.27:1 ratio of the stock gear ratio to the Supra TT auto 3.76:1, the driveshaft will spin 3.76 times for every turn of the rear wheels. This allows the engine to rev faster because there is a bit less load on it. It's just like changing gears on a 10-speed bike. First gear is very easy to pedal, because the ratio of you pedaling is high. If you switched to 5th gear, it's harder to pedal, but you can travel faster. Now for the TRD LSD. This is only the center unit that BananaGS pictured. The Ring gear bolts to the LSD. Th pinion gear(and it's bearings) are pressed into the front side of the housing. Some say it is easy to do with no adjustments(backlash). I have not done that myself. I opted to buy the Supra TT auto differential because it has both 1) Torsen LSD and 2) higher gear ratio (3.76) compared to the stock GS (3.27). This will accomplish 2 things for you, prevents only one wheel from spinning when you are hard on the throttle and allows the engine to rev quicker due to the 3.76 gear ratio which makes the car accelerate faster. The TRD LSD I think is a Clutch type differential while the stock Supra TT is a Torsen. The TRD clutch differential can handle more horsepower, but may need to be rebuilt, due to clutch wear with high horsepower cars. The Torsen unit is just gears arrayed in such a way to deliver even torque to each side(wheel) when more power is applied. Light throttle around a corner and the wheels turn at different rates, floor it around a corner and the increased torque causes the unit to apply the power evenly to both sides and keeps one wheel from spinning. I don't know the details on this, but if you search for Torsen LSD on google.com, you will find a lot of info about it.

Hope that this helps.....

BananaGS

yeah, what skier1 said.

IS2000

So to simplify things, I should just buy the picture below so that I need not open up the guts of the stock differential in order to put in the TRD LSD, right?



Inside this differential, is the 3.76 ring gear and the Torsen gears and whatchamacallits, right?

skier1

IS2000, Yup! That's exactally what I bought and put in my GS4. Mine was used and came out of a Supra TT with an automatic transmission. I believe that the Rod Millen unit is actually the same thing. Rod Millen buys the Supra TT auto unit to sell it as theirs. I don't know if it has the Torsen LSD or the clutch style LSD (like the TRD). It depends on what you are doing to your car. If you are going with big horsepower, then I would look for a TRD clutch style. I, on the other hand, probably won't be making over 400HP at the rear wheels, decided to buy the used Supra TT unit. Much cheaper and works very well. What are your plans with your car? Do you have a GS3 or GS4? If you have the GS3 and plan on putting on a big WHOMPING turbo, then plan ahead and look for the clutch style unit, like the TRD. I believe that TRD makes just the LSD that goes inside the differential housing, like BananaGS pictured.