legacycentral bbs

hey guys,

I have a 1992 Legacy L FWD auto. In the morning I always warm up the car. When I get out on the beltway and hit around 60mph, I notice that my rmp's are at 2350rpm. After driving for about 8 miles my automatic transmission feels like it shifts up a gear, almost like it shifts into overdrive and my rpm's drop to about 2000rpm @60mph. Can someone explain what is happening since I know that our cars are just 4 speed autos. without overdrive and why this happens after the car or auto warms up.

Thanks!!!

What you're describing sounds like the torque converter locking up. But at highway speeds it should always be locked up, so I don't know...

Also, technically, I think 4th gear is an overdrive on the 4EAT.

It's your torque converter locking up. The TCU varies the amount of lockup that occours.

I thought the TCU could only cause lockup, not prevent it, and that lockup was supposed to only be possible in 1st and reverse.

To answer this question, one must first understand the concept of a torque converter, as well as the concept of lockup.
A torque converter has four main parts; the pump, the turbine, the stator, and the lockup clutch. It works much like two fans blowing against each other. Fan 1 is the pump, fan 2 is the turbine, the stator is a set of blades fixed in between them with the blades at a sharp angle relative to fan 1, and the lockup mechanism... well, we'll get to that.
Basically when your engine turns, it causes fan 1 to blow. Fan 1 blows across the stator. The stator forces the fluid to curve at a sharp angle and directs it on fan 2. This causes fan 2 to spin. Fan 2 is conected to the pump inside your transmission and to the input shaft. It turns the input shaft which is engaged to the output shaft by a series of gears and clutch packs. The clutch packs are engaged through the valve body by the fluid that is pressurized by the pump. Have I lost anyone yet?
Anyway- lockup occurs at highway speed. Of course there are lots of losses between the fans. Energy is lost when the fluid from the pump hits the stator, then more energy is lost at the turbine because every little bit of energy that crosses the blades isn't turned into rotation. Some sneaks by without doing anything. (This is quantified by "turbine efficiency") This is also why you lose so much hp through an automatic transmission. Not only are the components inside heavier, but energy is lost in the torque converter before it ever gets inside to the gears.
Now- back to lockup. At highway speed the lockup solenoid engages lockup- hence locking the pump and turbine together via a lockup clutch. This prevents any loss within the converter, so the engine and transmission are effectively connected together as if you had a clutch and pressure plate setup instead of a torque converter. If your solenoid or lockup converter goes bad, it will oftentimes cause the engine to stall when you come to a stop (just like when you forget to push in the clutch on a manual car) because the engine is connected to the tranny via the lockup clutch. Less often lockup will not engage, causing gas mileage to suffer slightly. An intermediate symptom is converter shudder, where the solenoid cannot hold pressure or will not let enough fluid by quickly enough, and the converter clutch shudders either all the time or just right when it applies. Either way it's annoying and a pain in the ass.
As for the TCU- it decides WHEN the transmission should go into lockup. It takes readings (throttle position, engine speed, vehicle speed, coolant temp, transmission oil temp) to determine whether the car needs to use lockup yet or not. The reason on a cold day (despite "warming up" the car) you drive 5 or 6 or however many miles before lockup finally engages is because the TCU determines that instead of gas mileage, what you really need is more drivetrain temperature. With this in mind, it keeps the unit out of lockup, and instead allows the torque converter to thrash the fluid about between the pump and turbine which warms it up. Not using lockup also makes the engine run higher RPM, which warms it up faster as well.

Forgive me if i'm mistaken, but it sounds like you're explaining the theory of how these systems work generally, as opposed to specifically on our Legacies.

I reviewed the factory service manuals before and this is what I got out of it:

Torque converter lockup is not directly controlled by a solenoid. There is a lockup control valve which prevents lockup when hydraulic pressure is applied to it. When that pressure disappears, the converter locks up.

The hydraulic valve control unit dealie in the transmission (the purely mechanical part) produces pressure to drive the lockup valve only in 1st and reverse. The hydraulic line going to the torque converter lockup valve also has duty solenoid B attached to it. When duty solenoid B is energized, it drains pressure away from the lockup control valve.

So, if the TCU doesn't do anything, then the torque converter is unlocked in 1st and reverse, and locked up in 2nd, 3rd, and 4th. But the TCU can also choose to lock up in 1st or reverse by actuating duty solenoid B.

When the ATF is cold, I thought the TCU tried to speed warmup by preventing upshifting into 4th gear.

What am I missing here? Is any part of this incorrect?

The 4EAT does prevent shifting into 4th before the fluid has warmed up. Even if you are lettign the car warm up, the fluid in the tranny may not be up to temp.

I had really never noticed this in ym car until after i had a full flush and fill of the transmission fluid.

MK

thanks a lot for the prompt respnse guys. the car has been doing this ever since it was new. i'm just wondering why in our cars and not in others. i know that in many cars this might go on for less than half a mile and then the auto shifts up a gear or goes into O/D. is anyone else experiencing this problem. usually when the transmission doesn't shift up i go 70mph b/c at if i go any faster the rpm's will be at 3k. once it shifts i can take it up to 80-85 mph with below 3k rpm's on the tech. does anyone else find this annoying?

MK makes a good point -- if you're warming the car up by letting it idle, it won't warm the ATF up well. So maybe your car is avoiding 4th gear because ATF is still cold.

In my opinion the best way to warm a car up is to drive it gently. That way you warm up the transmission and differential fluids as well as the coolant and oil.

I first discovered this "feature" on my 1990 Dodge Dakota (one of the only times Dodge has been ahead of it's time). Since my dad owns an automatic transmission shop I had almost endless resources to find the answer (that I don't have at my disposal right now because I'm living in WI and my dad's still in VA- so don't drown me with 4EAT questions because I'm new to Subaru). Anyway I'm going to try to get all the 4EAT information from ATRA that I can get, and we'll go from there.

Brandon

nice, keep us updated

The TC definitely locks up in 3rd and 4th. At least on mine, theres a very noticeable difference in part throttle acceleration when the TC is locked and unlocked, and the TC locking is very obvious when it occurs...

91White-T wrote:The TC definitely locks up in 3rd and 4th. At least on mine, theres a very noticeable difference in part throttle acceleration when the TC is locked and unlocked, and the TC locking is very obvious when it occurs...

Are you saying the TC also can be unlocked in 3rd and 4th?

That's what I've noticed... Yes. Maybe MY tranny's all messed up too, who knows?

yes, it can be unlocked in 3rd & 4th. It's never really fully locked, and I do think I have some issues with mine locking up......but it definitely varies the amount of lock based upon other inputs, tps, load, etc.

I think my problem is that lockup is not happening smoothly, so I have to give it more throttle, and then it finally un locks....and it's annoying.......I want the auto box gone anyway......

Josh, you could swap in pretty much any FWD 5MT right? Are you considering doing that swap in the future?

I would like to convert my car to AWD.....couple reasons....better traction, plus I can run the AGX's. Also, if I decide to do a turbo swap, it'd be better at handling the power.

Plus the kicker.....I want 3.9 gearing! I want to find a beater 91 legacy with motor problems, but good drivetrain. Do the drivetrain swap, and then build the ej22t motor up in my free time.

I however need another daily driver car in addtion to the currently legacy, and the donor legacy.....

You might consider doing a FWD 5MT swap in the meantime. It'd be pretty cheap (I know of some junkyards that occasionally have specials where transmissions go for as little as $30), and the experience would set you up well for the AWD swap.

yeah.....I guess you're right.....but i'd want to have all the hardware, like pedals, etc.

other thing too....I'm pretty sure all the FWD trannies are cable clutches so that would be one less thing to do on the first time around.

decisions.....decisions......

The pedals and stuff are the same, I think.

You're right that the FWD trannies use cable clutches while the EJ22T ones are hydraulic, but I think you can convert cable clutches to hydraulic using stock parts. It will be push-type instead of pull-type, though, so you'd need a little new hardware the second time around anyway.

I've read somewhere that the reason the transmission locks up when it warms up is for the simple reason that when you release the throttle, the rpm's stay at where they were and gradually come down. This allows for instant power in case if the need be arises. When the transmission isn't locked up the rpm's instantly drop when you let go of the throttle and therefore not having the instant power if the need arises. You can try this on your cars and see.

When my car is cold the RPMs hang, and I've got a 5-speed. My old 5-speed Impreza did that too. I thought it was just because when the throttle plate was cold the lubricating grease was a little more viscous or something.

Spartus, my 93 AWD AT does the same as yours. After the engine, tranny, whatever warms up, I've noticed an rpm drop in the "D" range, something like going into 5th gear. I just always viewed my tranny as an automatic 4-speed with an automatic 5th O/D gear. In fact, when it's in "5th" gear on a level road, if I depress the accelerator just ever so slightly, it will downshift into 4th gear. It's not in third gear because if I manually shift to "3" then the tranny downshifts noticeably and rpms go up.

And I appreciated both Beastar's and vrg3's explanantion of the trans because I don't quite understand how automatic transmissions work so both explanantions gave me a better idea.

You do not have a 5th gear. What you are feeling is the torque converter unlocking, that's why it feels like it "kick's down" and RPM's raise.