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Want better low end performance, try this! It's free!

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Old 09-18-08, 10:31 PM   #1
KC95SC400
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Default Want better low end performance, try this! It's free!

Long read here. Info applies to my 95 SC400 but likely applies to other years and to the SC300.

So I've been on a quest to make the transmission shift better. The main problem I have been trying to fix is bouncing off the rev limiter during the 1-2 shift. I have so far upped the line pressure and shimmed the accumulators. Still bounces at WOT. Link to more info.. http://www.clublexus.com/forums/performance-and-maintenance/378241-going-to-mod-my-sc400-auto-box-a340e.html

But....I've been studying trans info on TIS (Toyota Information System) during down time at work and have learned quite a few interesting things. First off, the trans is electronically controlled but line pressure IS NOT. Appears that the line pressure is controlled by the throttle valve cable. There is also an adjustment on the valve body of the transmission. I have upped my pressure using the valve body adjustment already.

I have also learned that there are 4 solenoids in the trans. Solenoid 1 and 2 control shifting. Solenoid 3 is for lockup and Solenoid 4 is for "accumulator back pressure modulation". The ECU uses information from the no 2 speed sensor and the overdrive direct clutch speed sensor to determine and control shift speed for a "smooth shift". I decided that in my application, a smooth shift isn't ideal so I decided to try unplugging the overdrive clutch speed sensor. I noticed the car would squat harder during acceloration but I decided it was just my imagination. Having the sensor unplugged did not fix my rev bounce problem so I plugged it back in. I then decided to cut the wire, at the ECU, for the no 4 solenoid. Still bounces away but again, the car felt like it was squatting like crazy during acceloration both from a stop and on a downshift.

Did some more reading a found a document that says "The electronic control system for the A341E, A342E automatic transmissions provides extremely precise control of the gear shift timing and lock-up timing in response to driving conditions as sensed by various sensors located throughout the vehicle and in response to the engine’s running condition. At the same time, the ECU control reduces vehicle squat when the vehicle starts out and gear shift shock".

Now, keep in mind that my car has double the stock power but, I definately do notice a difference with the solenoid wire cut. Basically, with everything connected as it is supposed to be, the ECU makes the trans slip a bit to lower power enough to prevent the car from squatting. I imagine that the difference would be noticed on a stock SC. I have also noticed a slight difference in normal shift feel. Shifts a bit harder and faster.

If anyone is willing to try doing this, let me know, I'm curious to see what happens. It's a very easy mod and hasn't even thrown any codes on my car. I'll explain what to do if someone wants to try it.

KC
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Supercharged 96 Lexus SC400. Water / meth injection. Ross pistons. The "thick" factory rods.Gasket matched intake and heads. ARP head studs. Cometic head gaskets. ACL rod bearings. Flipped intake. Supra LSD. Built transmission. PI converter. Supra Tokico shocks with swift lowering springs. IMF headers. X-pipe. 2.5 inch exhaust. Adaptronic. Suprastick. Much more.

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Old 09-18-08, 10:34 PM   #2
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Oh, almost forgot, meant to post the info from TIS. Go to the last page to read the paragraph of interest.

KC
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Old 09-18-08, 11:43 PM   #3
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ill give it a shot on my supra if theres a way to do it w/o cutting the harness.

im still waiting on accumulator o-rings and the deep tranny pan though
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Old 09-19-08, 06:37 AM   #4
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50+ views and only 1 respone? Come on guys, we are talking more low end performance here for free. A possible free / easy fix to that horrible off the line performance that everyone is always complaining about. Most people, including myself, spend big money on torque convertors for this. Don't get me wrong, a higher stall still has benefits, but this could be done free.

93MSB, I'm not 100% sure your tranny is the same but you can try. I will look into it for you to make sure the solenoids are the same.

There are two methods to do this.

1. Unplug the overdrive clutch speed sensor. The only reason this sensor is on the transmission is so that the ECM can compare its signal to that of the no 2 speed sensor. Using this comparison, the ECM controls shift smoothness. There is one con with uplugging this sensor though, it will make the overdrive light on your dash flash after a trip or two.

2. Cut or unplug the no 4 solenoid wire. Does the same thing but, it won't set a code. At least it hasn't on my car after several days of driving and a few passes at the track.

For anyone who wants to try this but is unsure about cutting the harness, try unplugging the od speed sensor first. Does the same thing. If you decide it's doing something for you, then you could move to the solenoid. The only real advantage to cutting or unplugging the actual solenoid is that the light won't come on.

The od speed sensor is on the driver's side of the transmission. It is on the case right behind where trans case is bolted to the bell housing. Should take anyone about 5 minutes to find and unplug it. Then if you don't like the change, simply plug it back in. If you do like the change but are annoyed by the od light blinking at you, move on to cutting the solenoids power.

KC
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Old 09-19-08, 07:39 AM   #5
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doesn't apply to me, but I really like how you did your research.
Got it down, and then posted your findings for the members.

kudos
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Old 09-19-08, 10:57 AM   #6
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Great info KC
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Old 09-19-08, 11:04 AM   #7
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Where on the tranny is the sensor located. Im thinking about trying it.
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Old 09-19-08, 11:20 AM   #8
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KC, good find.. i'll probably give it a shot when i get my car back.
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Old 09-19-08, 11:28 AM   #9
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Now, i've got a question? Is it possible to wire a switch to the solenoid so you can swith between a smooth shift and a harder shift?

Maybe even wire into the ECT/PWR switch?
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Old 09-19-08, 06:10 PM   #10
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KC95SC400,

I did a bit of skimming through the 95 supra manual. I found that the a340e (2jzge version) only has 3 solenoids solenoid1, solenoid2, and a lock up solenoid. It also does not have the overdrive clutch speed sensor. So the particular method you described will not work for the sc300.

I also took a look at the 2jzgte version of the a340e found in the supra turbos. It has 5 solenoids, 1-4 have the same operations as the 1uzfe and the 5th one is to control line pressure

im going to read more in depth about the 2jzge version of the a340e to see what i can find.

ill be happy to email you the .pdf's for the a340e if you want to have a look at it

Last edited by 93MSB; 09-19-08 at 06:38 PM..
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Old 09-19-08, 06:12 PM   #11
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Quote:
Originally Posted by IS_250 View Post
Now, i've got a question? Is it possible to wire a switch to the solenoid so you can swith between a smooth shift and a harder shift?

Maybe even wire into the ECT/PWR switch?
i dont see why not, if im not mistaken all you would need to have is an on/off toggle switch to complete the circuit to the ecu
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Old 09-19-08, 06:45 PM   #12
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Quote:
Originally Posted by RedPhoenix View Post
Where on the tranny is the sensor located. Im thinking about trying it.
Same here. Can anyone post a diagram showing it's location?
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Old 09-19-08, 07:31 PM   #13
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this is the best i could find guys, its not real clear and i dont have a sc4 to take a pic.

It looks to me like its on the passenger side of the tranny about halfway down. maybe drivers side? i cant tell from the diagram.




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Old 09-19-08, 07:31 PM   #14
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so will overdrive/od button still work?
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Old 09-19-08, 07:33 PM   #15
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my buddy did a similar thing on his altima. the transmission didnt like it and started to shift like crap. we had to do a full fluid flush about 3 times to bring it back to stock. maybe our trans is different but the saying is "you cant have the cake and eat it too" there are always downfalls with all positives.

i dont have to worry about this problem though
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Old 09-19-08, 07:33 PM
 
 
 
 
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1995, 94, a340e, a342e, automatic, downshift, es300, flashing, lexus, light, od, p0715, ranger, sensor, speed, toyota, transmission

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