Going to mod my SC400 auto box A340e
#1
Going to mod my SC400 auto box A340e
Many of you probably know about this mod, but there doesn't seem to be too many people on this forum that have done it.
I originally found the thread on Supraforums but here is a very good writeup on how to do it. http://www.lexusclub.co.uk/lsocautoboxmod.pdf
I'm hoping to do this within the next couple of weeks. Seems like a no brainer to me. Shim the 1-2 and 2-3 accumulators to quicken the shifts and turn the adjustment screw on the valve body to up the line pressure. Should take a few tenths off on the track AND actually make the auto last a bit longer.
I have not had any real problems with my trans, even at 320++ rwhp (have installed headers, full 2.5 inch exhaust and a smaller pulley on the Vortech since I was on the dyno last). The biggest problem I do have is that the trans doesn't shift fast enough at WOT causing the engine to bounce off the rev limiter, not good for going fast and probably not good for the engine or the transmission. I have the throttle cable that goes to the transmission about maxed out, this does help but it still bounces. Also, the engine retards timing during shifts to make them smoother, it is said on Supraforums that the quicker shift eliminates this, since it shifts too fast for the ECU to respond.
I do not intend to go too aggresive on the shims, likely about a 1/4 inch, seems to be what the Supra guys like. I already have traction problems when downshifting so I don't want to go crazy. I just want a tight 1-2 and 2-3 shift. I SHOULD be (based on 1/8 mile times) in the high 12's in the 1/4, a few tenths saved on shifting might get me into the mid-high 12's.
Let me know what you guys think. If anyone has done this, please share.
KC
I originally found the thread on Supraforums but here is a very good writeup on how to do it. http://www.lexusclub.co.uk/lsocautoboxmod.pdf
I'm hoping to do this within the next couple of weeks. Seems like a no brainer to me. Shim the 1-2 and 2-3 accumulators to quicken the shifts and turn the adjustment screw on the valve body to up the line pressure. Should take a few tenths off on the track AND actually make the auto last a bit longer.
I have not had any real problems with my trans, even at 320++ rwhp (have installed headers, full 2.5 inch exhaust and a smaller pulley on the Vortech since I was on the dyno last). The biggest problem I do have is that the trans doesn't shift fast enough at WOT causing the engine to bounce off the rev limiter, not good for going fast and probably not good for the engine or the transmission. I have the throttle cable that goes to the transmission about maxed out, this does help but it still bounces. Also, the engine retards timing during shifts to make them smoother, it is said on Supraforums that the quicker shift eliminates this, since it shifts too fast for the ECU to respond.
I do not intend to go too aggresive on the shims, likely about a 1/4 inch, seems to be what the Supra guys like. I already have traction problems when downshifting so I don't want to go crazy. I just want a tight 1-2 and 2-3 shift. I SHOULD be (based on 1/8 mile times) in the high 12's in the 1/4, a few tenths saved on shifting might get me into the mid-high 12's.
Let me know what you guys think. If anyone has done this, please share.
KC
#2
Lead Lap
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Sounds like it will work well. Getting a modded 1uz into 12's would be so great to see, as most people just swap. When I get more done to my 1uz I am thinking about this mod too. Would be happy to hear your results
#4
Bedlam lives down the road from me. Ive been in his car with modded auto and it shifts alot faster.
The shims are basically made from ally and can be made up easy enough. Jobs messy but not difficult. If you've got access to a ramp/pit, it will be alot easier.
goodluck bud
The shims are basically made from ally and can be made up easy enough. Jobs messy but not difficult. If you've got access to a ramp/pit, it will be alot easier.
goodluck bud
#6
Originally Posted by Ian300D
Where do you plan on getting the shims. I've been eyeballing this for a while, as it's one of my only complaints on the SC400. That and the no aftermarket DIN.
Originally Posted by Teflon Don
Bedlam lives down the road from me. Ive been in his car with modded auto and it shifts alot faster.
The shims are basically made from ally and can be made up easy enough. Jobs messy but not difficult. If you've got access to a ramp/pit, it will be alot easier.
goodluck bud
The shims are basically made from ally and can be made up easy enough. Jobs messy but not difficult. If you've got access to a ramp/pit, it will be alot easier.
goodluck bud
I have had a couple of valve bodies off in the past to replace solenoids and such, mostly on Camry's. The worst part is usually the mess, chances are I'll end up with trans fluid in my armpit at some point. LOL.
Originally Posted by SC400TT
Looking forward to seeing your results on this mod KC. I am curious how this will perform, hold up and compare overall to the BL built tranny I paid for.
Keep us posted...
Keep us posted...
I imagine your power levels are WAY higher than mine though, the BL tranny should be a good investment for you. I'm surprised you haven't decided to go 5 or 6 speed yet.
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So I should be doing this soon, within the next week or two. I would have been able to do it today (slow at work) but I had to order the filter. I'll keep you all posted.
KC
#7
Instructor
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I started this project last night, the pipes were a little stubborn coming out. Im in the process of attempting to find a solid shim, otherwise ill probably just stack washers.
Im also going to order the deep trans pan and hopefully they can get me the o-rings for the accumulators.
ill post my results when i finish which will likely be next week sometime
Im also going to order the deep trans pan and hopefully they can get me the o-rings for the accumulators.
ill post my results when i finish which will likely be next week sometime
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#8
So, I actually did it yesterday. So far I'm not impressed. I stacked washers (20mm width) 4 high which came out to 7.62mm for each accumulator (1-2 and 2-3). Everything seems to be working as it should. Very slight increase in shift speed and firmness part throtte, still bounces of the rev limiter (the problem I was hoping to fix) between 1 and 2 shift.
The adjustment screw looks a bit different on my valve body, it only actually has two spots for adjustment. I turned it in anyway past where the adjustment stops are, pushing the valve into the valve body more. Should be doing the same thing.
I've read the unplugging the no 1 speed sensor will stop the rev bounce, I'm trying a little expirement, I'll post with more info later.
I will likely end up adding a few more shims later. When I have the valve body back down I'll double check that I didn't damage the gasket the first time although I'm pretty sure it's fine. Probably wouldn't be a bad idea to replace the accumulator orings.
KC
The adjustment screw looks a bit different on my valve body, it only actually has two spots for adjustment. I turned it in anyway past where the adjustment stops are, pushing the valve into the valve body more. Should be doing the same thing.
I've read the unplugging the no 1 speed sensor will stop the rev bounce, I'm trying a little expirement, I'll post with more info later.
I will likely end up adding a few more shims later. When I have the valve body back down I'll double check that I didn't damage the gasket the first time although I'm pretty sure it's fine. Probably wouldn't be a bad idea to replace the accumulator orings.
KC
#10
Ok, noticed a change I didn't notice right away. Seems to shift down through the gears quite a bit faster. Say your going 30mph in forth and you slam it, it goes third then to second (or first) faster than it was.
The other expirement I mentioned. I've read that disconnecting the no 1 speed sensor wire improves the rev bounce from 1-2. Problem with not having a number 1 speed sensor is that you'd then have an inoperative speedometer. Also possible issues with trac, abs and who knows what else. Well, I was looking at the wiring diagram and noticed that the signal wire for the no 1 speed sensor goes through the combination meter and THEN to the ECU. So, rather than disconnecting the sensor I cut the wire from the combination meter to the ECU. I still have a speedo and so far no problems with anything else, no blinking lights, nothing.
And...it seems to have very much helped the bounce problem. It's wet out and nearing rush hour traffic time so I didn't get to thrash as much as I would like but there definately seems to be less bounce and delay on the 1-2 upshift. Gonna leave it cut for now until I can drive around a bit more.
Will still likely throw in a couple more shims next week. I wonder if the Lexus accumulators are bigger / hold more fluid than the Supra ones, could be why the difference isn't very dramatic.
KC
The other expirement I mentioned. I've read that disconnecting the no 1 speed sensor wire improves the rev bounce from 1-2. Problem with not having a number 1 speed sensor is that you'd then have an inoperative speedometer. Also possible issues with trac, abs and who knows what else. Well, I was looking at the wiring diagram and noticed that the signal wire for the no 1 speed sensor goes through the combination meter and THEN to the ECU. So, rather than disconnecting the sensor I cut the wire from the combination meter to the ECU. I still have a speedo and so far no problems with anything else, no blinking lights, nothing.
And...it seems to have very much helped the bounce problem. It's wet out and nearing rush hour traffic time so I didn't get to thrash as much as I would like but there definately seems to be less bounce and delay on the 1-2 upshift. Gonna leave it cut for now until I can drive around a bit more.
Will still likely throw in a couple more shims next week. I wonder if the Lexus accumulators are bigger / hold more fluid than the Supra ones, could be why the difference isn't very dramatic.
KC
#13
Lexus Test Driver
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The SC400 and Supra TT are the same transmission minus the longer 1st gear in the SC.
http://www.clubna-t.com/forums/showthread.php?t=2932
http://www.clubna-t.com/forums/showthread.php?t=4145
http://www.clubna-t.com/forums/showthread.php?t=2932
http://www.clubna-t.com/forums/showthread.php?t=4145
#14
Pole Position
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The SC400 and Supra TT are the same transmission minus the longer 1st gear in the SC.
http://www.clubna-t.com/forums/showthread.php?t=2932
http://www.clubna-t.com/forums/showthread.php?t=4145
http://www.clubna-t.com/forums/showthread.php?t=2932
http://www.clubna-t.com/forums/showthread.php?t=4145
sorry for gettting off the topic.
#15
Lexus Test Driver
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All the info is there about the bellhousings and output shaft. But to answer your question, no. The SC400 is electronically controlled where as the 1jz auto is more like the 2jz-ge auto which is line pressure controlled with the clutch packs of the SC400 auto.