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  #16  
Old 04-23-2014, 12:55 PM
NiftySVX NiftySVX is offline
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Re: 4eat be made to handle more?

Messing with the resistor only changes line pressure under certain conditions, mainly low speed. If you really want to make a difference it has to be done with software or by modding the pump. It's a tradeoff though, I had a pump that boosted base line across the board by quite a lot but it bogged the motor down and the car got 16 MPG. What's more, it creates binding in the rear under certain conditions. Not really a problem but an annoyance.

Ditched that trans, went with a low mileage tested good pump (cleaned it up of course) and did a few things here and there in the valve body and got a setup that is pretty slick.

This trans has a nasty tendency to bang into 2 and 3 under light throttle conditions if you aren't careful. When I put a different resistor in mine and had the big daddy pump, it would shift so hard into 2 that it tore the little rubber domahicker that goes in the crossmember to secure the mount. It also destroyed my rear bushings.

IMHO and in my experience with these transmissions, messing with the dropping resistor isn't much good. The only real good mod like this a product made by one of our long time members, but if you build yourself a valve body you may not need it.

Even more, simply changing the accum springs will liven up the 4EAT quite a bit. I have a stock spring in my 1-2, a middle of the road spring in the one for 3rd shift, and a stiff spring in my band accumulator. This, along with a stock (ish) valve body and my trans shifts great. It is actually my favorite one I have ever done or had.

Totally a different boat than you though, as I don't plan to mod the engine for serious power.

I still have my level 10 high stall converter that I liked fairly well but it churned the fluid pretty seriously and required a substantial cooler to keep cool in aggressive driving. I am not using it in my current setup.

Somewhere I have the scope patterns and line pressure records for the dropping resistor delete, I will look them up and try and get them in this thread as they may be of interest to you.

We lost the guy who really knew about this stuff, but he is around. The other guys who were the guru's of the electronics side of the auto box are "retired".

Dig through some of the stuff on the forum and check it out, but honestly, the best way to learn about these is to fiddle with them and then put it in a car and see how you like it. It's not hard to drop the valve body and add some washers or springs, nor is it to actually rebuild the trans. Getting it out of the car and cleaning it is the worst part. Used/bad ones are basically free to anyone who pays shipping.

Many moons ago, I learned about these things by building and tinkering with one made of spare parts that I would pull in and out of a 94 Legacy FWD.

The number one most important thing about these transmissions is that you use the correct bearing in the high clutch and the correct shim at the pump. If you don't, it will seize the high clutch in short order.
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  #17  
Old 04-25-2014, 08:25 PM
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david_12121 david_12121 is offline
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Re: 4eat be made to handle more?

Thanks for the info, again.
I'll keep all of that in mind and will post on this thread when the turbo is done.
Hopefully in 2 months
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  #18  
Old 04-26-2014, 04:27 AM
Chucksta Chucksta is offline
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Re: 4eat be made to handle more?

Hey.. Nifty makes some great points about what affects the hydraulics of shifting a 4EAT transmission. I think that what you're looking for, however, is keeping it in one piece, as you increase net horsepower. Unless I mis understood your intentions, It's gonna be a five speed sooner or later, you'd just like "later" to be on your terms.

Let me start with a bit about the dropping resistor. To preface my comments and observations, there have been some epic threads and they contain some personal battles that have resulted in people being banned and people leaving the site. Seriously. Some of the stuff I've read ( and I've read threads well over 100 pages.. every word!), contained the blood and soul of some damn smart people who devoted countless hours, extensive time and energy, and their own money into getting inside the engineering of our SVXs'.

Here's how "SmallCars" approach the dropping resistor, to modify the shifting line pressure. In parallel to the factory 13 OHM ( approx) resistor, the kit wires in a 4,000 Ohm resistor. There's a tap into the manifold vaccuum line, and an adjustable ( spring based) controller in the vaccuum line. Under light load ( high vaccuum ) it does nothing.. the TCU simply sees the factory dropping resistor in the circuit. When you get a bit heavier footed, the engine vaccuum drops, the switch goes "click", and the 4K resistor kicks in. That effectively signals solenoid "A" to send out full line pressure. As such, it is either on, or off... no in between. It keeps the factory resistor in the circuit to stop the TCU from throwing a CEL light. You can adjust it's tip in threshold with the set screw, which adjusts at what vaccuum level the system is actuated. It's a very simple device. It works. I had one. It functioned exactly as it was designed to.

I had an issue with how it functioned though. In their infinite wisdom, Subaru engineers, to accomplish their goal of unobtrusive shifts, designed the ECU / TCU / TPS interface to do something at WOT that, well, I personally didn't care for. On WOT shifts, the TCU reduces line pressure, and the ECU cuts injector band with to "soften" the shifts.. WTF? I got my foot mashed to the floor for a reason!.. Pull power? Shift "soft" ? I don't think so.. I didn't want to get into the transmission ( As you can see from NiftySVX's posts, there's more than one way to skin the cat!)

So I bought a different shift kit. Yup, more money than the small car one, but it's effect on firming up the line pressure to shift harder is progressive and linear to throttle input, not on or off. It wires into the TCU and eliminates the pressure cut and injector bandwith drop at WOT. With an ( I'm assuming ) stock valve body, light throttle shifts are noticeable, but smooth. WOT gives hard, but not, in my opinion, damaging shifts. It shifts like it's on a mission, not like it's trying to be polite.

As far as modding the dropping resistor is concerned, I'd play with it, just because it's cheap and easy. As NiftySVX noted, it'll have less effect at higher throttle inputs, and won't address the injector bandwith and line pressure cut at WOT. But, for around $5.00 for a resistor and pig tail, it's cheap McGuyvering. It won't hurt anything any worse than pushing the stock configuration and getting slippage on every shift. Use your "butt dyno" to determine the balance between functionality and futility.

I wasn't kidding about just disconnecting the resistor and going for a quick boot.. A couple of miles will show you just how hard one ( a 4EAT in stock configuration) can shift. That's with no mods. It'll "bang" through the gears, but, stuff your foot into it and you'll see how fast it slams the revs down on a WOT shift. Yup, you'll get a CEL light, and the ATF temp light will flash 16 times very time you start it until you hook it back up again. Once you hook it back up, the CEL light and the flashing ATF temp light will stop flashing after four restarts, as the A solenoid is no longer throwing code at the TCU.

Variable resistor? Yeah, I thought about that too, just don't forget that it needs to be rated for at least 25 watts. It doesn't matter what the OHM rating is, the watt rating represents the resistors ability to shed heat. There's a reason that the resistor is in that metal holder under the hood, and not in the TCU, or under the dash. You could always put in a triple pole switch, and just leave the third one with no resistor in it. You could label them "cruise", "pushing her a bit hard", and the third one "Yee ha, Billy"

Hopefully, you've been able to glean some good info from this thread. If your objective was to make a 4EAT, hold together under the extra load of forced induction, until you get a five speed, you've definitely been given some options..

As far as the drifting thing goes.. Umm.. I've never given any thought to the VTD, or any method of wheel / axle power transfer.. My WRX is viscous coupling and the transition between front and all four loose is seamless and undetectable. Get to the limit of traction, push the gas pedal and all four come loose at the same time. My SVX acts the same way, I've never experienced an issue with power transfer and all four not coming loose at the same time. I use the throttle to extend the arc of the corner, or usually , back the throttle off to let it reel itself back in.. It was a bit of a learning curve to go from the dead even 50 / 50 balance of the WRX to the "slight understeer" of the SVX.. If I pushed it and the front just washed, I'd be looking at it being an issue with the transmission. But, that being said, I've never pushed at it like that, I usually am pretty close to the edge of traction when I add enough throttle to get into the sphincter pucker zone.
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  #19  
Old 04-26-2014, 12:09 PM
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david_12121 david_12121 is offline
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Re: 4eat be made to handle more?

oh you get me, man...you definitely get me

I have a feeling that in my case, the softer the shift, the less chance of it grenading. Yeah, it'll slip more and have a shorter life span but I won't break it the first shift. And that's the thing with shift kits...to my knowledge, they're designed for stock or slightly modded cars.

And the injector band reduction seems like a nice feature in my case but I'll be running megasquirt so that won't be happening. (still haven't fully figured it out but icingdeath's half tutorial helped a lot)

Also why a 25w rating? If I go with a 20ohm one, with the car running at 14v, it'll be using 15w. The 30ohm will use even less! Though I'm pretty sure they sell potentiometers with heatsink hookups. I'll look into that.
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DIY FTW!
1993 SVX 25th Anniversary Edition @+142k
-Rebuilt Tranny @135k
-Regasketed Engine @140k
-Enkei Raijin 18x8.5, with 255/35/18's @140k
-BC racing Coilovers (From STI's) @142k
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  #20  
Old 04-26-2014, 10:06 PM
Chucksta Chucksta is offline
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Re: 4eat be made to handle more?

Lol... the elusive tightrope between "grab the next gear and go" and "go bang"..

If you want to see what a TCU control unit shifts like, let me know. I'm pretty sure my kid can get a video from my phone to upload to YouTube Any excuse to engage warp drive is a good one. It's what it does to the 2 / 3 shift that was the most dramatic change. The 2 / 3 shift is a combination shift, for lack of a better technical term. One band releases and another one ( the brake band ) engages, hence the mechanical adjustment on the outside of the trans. Full line pressure against full engine output was a good balance.

The wattage rating on the dropping resistor is just for it's ability to dissipate heat. Capacity in excess of the mathematically calculated load is just a safety buffer. Kinda like oversizing your trans cooler.

Hmmm... so... you've got just a few miles on a fresh rebuild autobox.. I've got 90% of a 5MT conversion. Monday, I'm going to find out definitively if my '94 has a bad trans, or if the PO didn't know to adjust the brake band. If the trans turns out to be good, I'll just be servicing her and selling her ( It's definitely a "keeper", but I just don't have room for another one). If the trans is bad, I'll either have to find a 4EAT and sell all the 5MT conversion bits, or go 4.44, or finish the swap. Might be time to play "Let's make a deal"..

I'll post back Monday night.
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