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4EAT paddle shifters?


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32 replies to this topic

#1 presslab

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Posted 21 March 2008 - 10:37 AM

The 4EAT is an electronically controlled transmission. This opens up the door for electronic modifications. :lol:

I'm toying with the idea of a paddle shifter. Anyone know why this won't work? The transaxle has two solenoids to select 1-4 gear. I'm guessing that reverse is a hydraulic thing that is physically selected by the gear shift lever?

I plan on using the stock computer to control the AWD clutch, and of course to keep the stock automatic driving mode. Maybe eventually mod the AWD clutch for adjustable torque bias. :banana:

How about line pressure control? Should I just modulate that based on the throttle position? Maybe back it off for downshifts? I plan to just leave the torque converter unlocked when in paddle shift mode.

Anyway just a hair brained idea, thought I'd throw it out there.

#2 Gloyale

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Posted 21 March 2008 - 11:12 AM

The 4EAT is an electronically controlled transmission. This opens up the door for electronic modifications. :lol:

I'm toying with the idea of a paddle shifter. Anyone know why this won't work? The transaxle has two solenoids to select 1-4 gear. I'm guessing that reverse is a hydraulic thing that is physically selected by the gear shift lever?

I plan on using the stock computer to control the AWD clutch, and of course to keep the stock automatic driving mode. Maybe eventually mod the AWD clutch for adjustable torque bias. :banana:

How about line pressure control? Should I just modulate that based on the throttle position? Maybe back it off for downshifts? I plan to just leave the torque converter unlocked when in paddle shift mode.

Anyway just a hair brained idea, thought I'd throw it out there.



The shifting is not determined solely by electronics. I don't think it would work. I could not get my Legacy 4eat to hold first gear solely by electronics(like the old GL TURBO with 1st hold) Would not grab 1st and hold it until I modified the shifter to actually pull the cable down to 1st.

I think the valve body could be modified to the point were all shifting is done elctronically, but not stock. As it is stock it requires hydraulic passages to be physically switched via the gear selector valve. If it didn't, it would be *drive by wire* with an electronic shifter, no cable required.

Also, having an unlocked TQ would completely defeat the reason for selecting the gear manually, Engine Braking. The trans does a fine job of downhifting on it's own to accelerate. It's deceleration that requires the driver to select the gear, and with an unlocked TQ you would not have any engine braking at all. Dangerous

#3 grossgary

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Posted 21 March 2008 - 11:43 AM

Anyone know why this won't work?

it's already been done, so that answers that question. i'd imagine there's even companies out there that would do it for you. the person that i know that's done it has no intention of publicizing any details.

reverse is purely hydraulic/mechanical in nature and works even if you run the trans without a TCU at all. so a paddle shifter could be triggered to work but have it "disengaged" when the shifter is put into R - and then you'd have reverse.

#4 presslab

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Posted 21 March 2008 - 05:01 PM

Thanks for the info guys.

I don't think the torque converter is a problem as the TCU unlocks it whenever the brakes are applied.

Gloyale, how did you try to lock it in first? Did you drive the solenoids directly? Below it shows how 1st gear is used even in the "D" mode.

Here is a good document on the operation of the 4EAT:
http://www.endwrench...004pdf/4EAT.pdf
and
http://www.northursa...ission/4eat.pdf

#5 Gloyale

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Posted 21 March 2008 - 05:30 PM

Thanks for the info guys.

I don't think the torque converter is a problem as the TCU unlocks it whenever the brakes are applied.



I don't think that's true at all. In fact I've specifically read about how and when the TCU uses the TQ lock up enabling engine braking.

I don't think the TCU even has a way of knowing that the brake are applied. The older ones I am sure have know way of telling the brake are applied.

Try this, drive 45mph in *D*, then drop the shifter into second. You'll feel the engine braking as the TQ locks and engine brakes the car. Not until vehichle speed and rpms lower will the TQ unlock.

Gloyale, how did you try to lock it in first? Did you drive the solenoids directly? Below it shows how 1st gear is used even in the "D" mode.



If you're familiar with the Original GL/XT 4eat, you know that it has D,3,and 2 range on the selector. 1st was selected via a switch. When the lever is in 2, and the switch activated, the TCU electronically activates and hold 1st gear(with locked TQ for engine braking)

I installed a Legacy 4eat as a replacement. Wired in and controlled by the GLs TCU, it could not select *1st hold* simply by the switch. I had to modify the shifter to make the lever physically pull the selector valve to *1st*

I think the problem is that certain hydraullic passage are inactive depending on the selector valve position.

It is possible, Gary says it's been done. But to me it seems that the valve body needs to be set up so that it can facilitate soley electronic gear selection.

#6 nipper

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Posted 21 March 2008 - 05:45 PM

http://www.endwrench...e/sysdrive.html

Do your research there.

1-2-3 are mechanical selections. D is all computer controlled. The ECU depening upon generation can lock up the TC whenever it sees fit. There is a rather complicated method for shifting. The dance is between the solenoids, selay valves, and the reduction of power by the ECU to help reduce shift shock.

I dont think it can be done, unless you have the paddles control the shift linkage itself.


nipper

#7 presslab

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Posted 21 March 2008 - 07:48 PM

I don't think that's true at all. In fact I've specifically read about how and when the TCU uses the TQ lock up enabling engine braking.


Well, mine does for sure. Lightly touch the brake pedal and the RPMs drop. Let up and the RPMs go up again after a second. I'm sure it uses it sometimes for engine braking, but touch the brake pedal and it unlocks it.

I don't think the TCU even has a way of knowing that the brake are applied. The older ones I am sure have know way of telling the brake are applied.


It must. Otherwise it'd be pretty much impossible to lock the brakes up without stalling the engine completely. I lock up my brakes all the time, no stalled engine. :grin: I'm still looking for a TCU schematic for my 88 GL-10...

Try this, drive 45mph in *D*, then drop the shifter into second. You'll feel the engine braking as the TQ locks and engine brakes the car. Not until vehichle speed and rpms lower will the TQ unlock.


If I drop the shifter into second, it will shift into second. When cruising at 45MPH my 4EAT is in 4th gear. I'm not sure how that test shows the torque converter locking up...

If you're familiar with the Original GL/XT 4eat, you know that it has D,3,and 2 range on the selector. 1st was selected via a switch. When the lever is in 2, and the switch activated, the TCU electronically activates and hold 1st gear(with locked TQ for engine braking)


Yeah that's the one I have, the 1st hold switch. It works fine, but it will shift to 2nd, 3rd, etc if I approach redline.

I installed a Legacy 4eat as a replacement. Wired in and controlled by the GLs TCU, it could not select *1st hold* simply by the switch. I had to modify the shifter to make the lever physically pull the selector valve to *1st*

I think the problem is that certain hydraullic passage are inactive depending on the selector valve position.

It is possible, Gary says it's been done. But to me it seems that the valve body needs to be set up so that it can facilitate soley electronic gear selection.


Hmm that's interesting. Do you know if the TCU was energizing the right solenoid for 1st gear? In those PDF documents I linked, it shows how the "D" mode can select gear 1, 2, 3, 4 with the solenoid. Should work fine I think.

#8 grossgary

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Posted 21 March 2008 - 08:38 PM

It is possible, Gary says it's been done. But to me it seems that the valve body needs to be set up so that it can facilitate soley electronic gear selection.

well i may have misled a bit - let me put it this way. his latest goal was to build his own car...and i don't mean like any typical mechanic - but starting with building his own foundry to cast parts. body panels all designed and built by him (carbon fiber). his resources and skills are a bit off the charts.

#9 crazyhorse001

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Posted 21 March 2008 - 08:40 PM

I'd think you'd have to piggyback an electronic controller onto the TCU. It wouldn't be as simple as that, but it's definately doable.

#10 Gloyale

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Posted 22 March 2008 - 12:26 AM

Well, mine does for sure. Lightly touch the brake pedal and the RPMs drop. Let up and the RPMs go up again after a second. I'm sure it uses it sometimes for engine braking, but touch the brake pedal and it unlocks it.


No. Not if you're already off the gas and coasting. And if it does drop it's because the speed is droppping.

The TCU does however know when throttle is fully closed. Throttle fully closed, at lower speed will force Lock-up non-opertaion. So when you go from on the gas to off, lock up is released.

It must. Otherwise it'd be pretty much impossible to lock the brakes up without stalling the engine completely. I lock up my brakes all the time, no stalled engine. :grin: I'm still looking for a TCU schematic for my 88 GL-10...


I have those schematics, the whole FM actually for every year of EA82. There is no signal sent from the brake to the TCU, at all.TCU on you're car has no connection to the brake what so ever. Only the force of decelleration from them indirectly is *felt* by the trans.

Besides, auto transmissions have been working for years without any sensors, switches, or computer.

Yeah that's the one I have, the 1st hold switch. ..........


.......
Hmm that's interesting. Do you know if the TCU was energizing the right solenoid for 1st gear? In those PDF documents I linked, it shows how the "D" mode can select gear 1, 2, 3, 4 with the solenoid. Should work fine I think.


Yeah, it's wired in like stock, and all solenoids function.

You may be right that in *D*, the TCU can select any gear it wants.

But in my case, I'm not driving the solenoid directly. I'm asking the TCU to do it, and it's electronics want the shifter in second. Which doesn't allow the TCU to select, since the Legacy trans needs to physically be in first for the correct hydraulic passages to have pressure. Additionally, *1st hold* is different than simple first gear. It increases transfer pressure, and I believe holds the Lock-up for engine braking, although all the literature say in 1st range lock-up is inoperative. However *1st hold* is different, I can feel the TQ locked when crawling down steep muddy hills offroad.

But I guess the more I read and study the diagrahms, I think it is doable. The key is that the selector needs to be in *D*.

#11 presslab

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Posted 22 March 2008 - 01:48 AM

No. Not if you're already off the gas and coasting. And if it does drop it's because the speed is droppping.

Well I guess we'll have to disagree. :dead: So why does my engine speed raise back up when I let off the brake pedal? I don't touch the throttle.

I have those schematics, the whole FM actually for every year of EA82. There is no signal sent from the brake to the TCU, at all.TCU on you're car has no connection to the brake what so ever. Only the force of decelleration from them indirectly is *felt* by the trans.


Maybe you can scan them and upload them for me? 88 GL-10 Turbo w/ 4EAT. ;) I only have a '90 Legacy diagram and it has a brake connection.

Besides, auto transmissions have been working for years without any sensors, switches, or computer.


Sure nuff but the old ones didn't lock up the torque converter.

#12 nipper

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Posted 22 March 2008 - 09:32 AM

Older transmissions also had a govenor in the rear, new ones use a VSS sensor. Older ones had far more complicated valve bodies, and many many more parts. Thats why they last so long now, the computers help control engine power to reduce shift shock and stress on the clutches. They also have much better internal pressure control then older transmissions.

Comparing a computer controlled transmission with an older style one just is not valid anymore. Its like trying to diagnose a modern fuel injected engine using the methods set up for a carberator. I dare you to show my the float bowl on a FI engine.


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#13 Gloyale

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Posted 22 March 2008 - 10:14 AM

Well I guess we'll have to disagree. :dead: So why does my engine speed raise back up when I let off the brake pedal? I don't touch the throttle.

I want to see video of this.

#14 nipper

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Posted 22 March 2008 - 10:29 AM

I want to see video of this.


so do i

nipper

#15 presslab

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Posted 22 March 2008 - 11:25 AM

I want to see video of this.


Sorry, it's really crappy. But here it is:
http://presslab.us/g...&g2_itemId=4822

and another
http://presslab.us/g...&g2_itemId=4825

#16 nipper

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Posted 22 March 2008 - 01:19 PM

I'm not really seeing anything shocking here. you take your foot off the gas, the rpm drops. As the speed keeps dropping the engine rpm picks up a bit.

This is not a transmission issue, this is an issue with something in the engine When was the last time this car had a tune up, and when was the last time the idle air control motor was cleaned, and the EGR checked?


nipper

#17 Gloyale

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Posted 22 March 2008 - 01:42 PM

I think you have a vacuum issue. Hitting you're brakes is causing you're engine to stumble slightly.

Anyway. Good luck with the paddle shifters

#18 presslab

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Posted 22 March 2008 - 01:53 PM

I'm not really seeing anything shocking here. you take your foot off the gas, the rpm drops. As the speed keeps dropping the engine rpm picks up a bit.

This is not a transmission issue, this is an issue with something in the engine When was the last time this car had a tune up, and when was the last time the idle air control motor was cleaned, and the EGR checked?


nipper


It runs pretty good. I am having a hesitation problem at 10+ PSI boost but not sure why, otherwise it runs fine. I do have bigger injectors and a modified MAF, WRX intercooler. New plugs the other day actually, IAC is good (checked and adjusted it a month ago), doesn't have EGR (CA model Turbo.)

The thing is if I don't touch the brakes the RPMs don't come back up. I'd really like to see the TCU diagram, if anyone could scan it for me I'd appreciate it.

Anyway I think this tangent of the torque converter locking up and brakes doesn't really matter in the grand scheme of my paddle shifter plan. I really do think just leaving it unlocked will totally be fine. It seems like in the "3" gear selection the torque converter doesn't lock up either, and there is plenty of engine braking.

#19 nipper

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Posted 22 March 2008 - 01:56 PM

Im betting you have a leak in the power brake booster.


nipper

#20 nipper

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Posted 22 March 2008 - 01:57 PM

PS leaving it unlocked is going to kill your gas milage. Spend a tank driving around in d3 and see how quickly you burn up that 3.30 a gallon gasoline.


nipper

#21 presslab

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Posted 22 March 2008 - 10:24 PM

PS leaving it unlocked is going to kill your gas milage. Spend a tank driving around in d3 and see how quickly you burn up that 3.30 a gallon gasoline.


nipper


I'll check the brake booster, that's a good idea.

Yeah good point, although I plan to use the paddle shifter only on windy roads and for normal driving just use the stock TCU. I'd bet the mileage on windy roads will be the same, except the tranny won't be shifting all over the place. :lol:

Try 3.80 (premium for the turbo) here in N. CA!

#22 Psyko

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Posted 10 April 2008 - 11:03 AM

So, it seems nobody really knows anything about how the 4EAT works. I'm game for making my own custom TCU, but I first need to know the "what for and when" behind the overrunning clutch, line pressure and lock-up that are controlled by SS 3, DS A and DS B (if you don't know what SS and DS are, you probably don't know what I'm asking about anyway ;)). Otherwise it will run wastefully and shift painfully. I've got partial answers from the '88 XT FSM I've got, but not enough.

If anybody knows anything about the transmission or knows of a good USB based oscilloscope for the Mac that has a good trigger and record feature, it'd be awesome to pick your brain. I'm not holding my breath though.

#23 nipper

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Posted 10 April 2008 - 11:18 AM

So, it seems nobody really knows anything about how the 4EAT works. I'm game for making my own custom TCU, but I first need to know the "what for and when" behind the overrunning clutch, line pressure and lock-up that are controlled by SS 3, DS A and DS B (if you don't know what SS and DS are, you probably don't know what I'm asking about anyway ;)). Otherwise it will run wastefully and shift painfully. I've got partial answers from the '88 XT FSM I've got, but not enough.

If anybody knows anything about the transmission or knows of a good USB based oscilloscope for the Mac that has a good trigger and record feature, it'd be awesome to pick your brain. I'm not holding my breath though.


I thought i explained how things worked.... but a long thread who knows. What i will tell you is expect that the tranny wont last for the life of the car with just home grown paddles. Youll be bypassing everything that gives the tranny long life.

google endwrench transmissions and read up on it there.

good luck

nipper

#24 presslab

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Posted 10 April 2008 - 11:34 AM

So, it seems nobody really knows anything about how the 4EAT works. I'm game for making my own custom TCU, but I first need to know the "what for and when" behind the overrunning clutch, line pressure and lock-up that are controlled by SS 3, DS A and DS B (if you don't know what SS and DS are, you probably don't know what I'm asking about anyway ;)). Otherwise it will run wastefully and shift painfully. I've got partial answers from the '88 XT FSM I've got, but not enough.

If anybody knows anything about the transmission or knows of a good USB based oscilloscope for the Mac that has a good trigger and record feature, it'd be awesome to pick your brain. I'm not holding my breath though.


These are my thoughts based on what I read.

The overrunning clutch is for engine braking. If SS-3 fails Subaru says there will always be engine braking but does not mention any other bad effects, so for paddle shifter I think the overrunning clutch should always be engaged.

I have seen aftermarket controllers simply control line pressure DS-A using throttle position.

For lock up DS-B I have also seen aftermarket controllers create a "5 speed" where "5th" gear is 4th with the torque converter locked up. Otherwise the torque converter is not locked. When locking up DS-B should be modulated for a smooth transition.


For PC they have soundcard oscilloscope software, maybe this is good enough for your needs, and not sure if Mac has that option. I'm using a HP 54600B I picked up for $75. :lol:

#25 Psyko

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Posted 10 April 2008 - 11:45 AM

Move along. Nothing to see here.




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