Swapped Tranny issues

[benebob]

So we've narrowed down exactly what the race car (and Marlettpat's) tranny are doing. They both have Impreza 1.8 FWDers in 'em at the moment. It seems that at full throttle it shifts into second then doesn't go anywhere until you take your foot off the gas. Both are doing it in 1st (redline autoshift) or D. We are running the SVX torque convertor, Pat the Impreza. Both have the SVX awd TCU in 'em. We're thinking that a TCU swap is in order but don't wanna go to something we can't leave in 1st and have it redline shift for us. Any ideas on a TCU or other issues that might be causing it. Both shift better than any awd Subie tranny I've been in provided you're not at full throttle.

[SVXRide]

Cosmic rays? Lack of adequate sacrificial offerings at the 4HEAT altar?

Seriously, your trans is acting like the Powerglide in my parent's Camaro - let up on the gas to bump the engine vacuum up and make the trans shift earlier.

Have you changed the ATF? Any chance that this version of the 4HEAT has a different fluid capacity?

Since both 4HEATs are FWD versions, I'm wondering if there is something going on regarding the signal going from the TCU (from an AWD-equipped SVX) to the trans telling it to shift. What does the TCU do when the car is in "limp home" mode?

Have you tried putting the FWD fuse in and seeing if it still behaves in the same way?

-Bill

[benebob]

Originally Posted by SVXRide

Cosmic rays? Lack of adequate sacrificial offerings at the 4HEAT altar?

Seriously, your trans is acting like the Powerglide in my parent's Camaro - let up on the gas to bump the engine vacuum up and make the trans shift earlier.

Have you changed the ATF? Any chance that this version of the 4HEAT has a different fluid capacity?

Since both 4HEATs are FWD versions, I'm wondering if there is something going on regarding the signal going from the TCU (from an AWD-equipped SVX) to the trans telling it to shift. What does the TCU do when the car is in "limp home" mode?

Have you tried putting the FWD fuse in and seeing if it still behaves in the same way?

-Bill

Now why would I wanna let up on the gas? You don't get there as quickly then although I'd say we lost about a second per lap the last time out which would put us up there about .5 sec slower than the Elise with the national caliper driver.

Fluid is right about mid level in ours. We did change the sludge when we dropped the pan. I highly recommend it for most of the higher mileage subarus. This lowely FWD with 80k on the odo had about a 1/2 inch of thick crud down there. Rest of the fluid was fine though.

Didn't even think about the FWD fuse. I'll have Pat give it a shot.

Limp mode I think drives it in 3rd only or something like that. We're getting plenty of power. Just that bogging which on an autox course is tough to pinpoint when you're doing everything else.

[oab_au]

I think it needs the FWD TCU. In the AWD box, it uses the rear speed sensor to provide the shift speeds. As the FWD box only has the front speed sensor, it needs the FWD TCU to signal the changes.

Harvey.

[benebob]

Originally Posted by oab_au

I think it needs the FWD TCU. In the AWD box, it uses the rear speed sensor to provide the shift speeds. As the FWD box only has the front speed sensor, it needs the FWD TCU to signal the changes.

Harvey.

So this speed sensor is it in the tranny? If I put the FWD fuse in would that do the trick if it isn't?

[oab_au]

Originally Posted by benebob

So this speed sensor is it in the tranny? If I put the FWD fuse in would that do the trick if it isn't?

No Bene, that will only turn off the C solenoid line, does nothing. It is still looking for a signal from the rear sensor to time the change, that is not going to come. Not to mention the problem the AWD TCU is having, trying to work out why the front wheels are spinning while the rear are not turning.
The FWD TCU uses the front speed sensor to do the changes.

Give it a go, either FWD TCU will do the job.
Harvey.

[benebob]

Originally Posted by oab_au

No Bene, that will only turn off the C solenoid line, does nothing. It is still looking for a signal from the rear sensor to time the change, that is not going to come. Not to mention the problem the AWD TCU is having, trying to work out why the front wheels are spinning while the rear are not turning.
The FWD TCU uses the front speed sensor to do the changes.

Give it a go, either FWD TCU will do the job.
Harvey.

Gotcha but why does it not seem to have issue except at full throttle? I would think it would have issue elsewhere too. Only code it shots back is sol. C which was kinda shocking to me as I thought it might have more issues as well. Any idea if the Impreza TCU shifts automatically at redline? I'm guessing we'd want a FWD SVX tcu as it will shift at a higher RPM. I think the Impreza 22 and 18 are both 6k redlines.

[SVXRide]

Ben,
Harvey had this comment in SVXHunter's 5 speed, "my brakes are locking up" thread:

"The only electrical connection is from the ABS to the TCU, that causes it to change to 3rd gear. Dont think it would be a problem."

Maybe Harvey can shed some light on this comment as it might relate to the issue at hand?

-Bill

[Bobb]

Hi Ben, If you have the owners manual take a look. It says if you put the transmission in first gear it will stay in first gear. If you put it in second gear it will shift between first and second. If you put it in third it will shift between first, second and third dependent on were you have the accelerator. If you have the manual mode engaged. In third gear it will shift between second and third. If in second gear it will stay in second, even starting in second. As pointed out before, selecting first, it stays in first. What year is the Loyale transmission from? Maybe that has something to do with it. Take care, BOBB

P/S How is Yogi? "B"

[benebob]

Yeah Bobb, 1st keeps it in 1st until it hits redline then it shifts to 2nd until speed slows enough to go back to 1st. Some Subies just hit a rev limiter (which is what we don't want). We want it to shift only when necessary. It's a 93 Impreza tranny.

ABS??? There isn't any ABS on our car

[SVXRide]

Originally Posted by benebob

*snip*

ABS??? There isn't any ABS on our car

Ben,
My point exactly...in removing the ABS have you eliminated a signal that the TCU is expecting? There might be a wire floating around now that needs a resistor hooked up to it to "fool" the TCU - thus my comment about Harvey enlightening us.
-Bill

[oab_au]

Originally Posted by SVXRide

Ben,
My point exactly...in removing the ABS have you eliminated a signal that the TCU is expecting? There might be a wire floating around now that needs a resistor hooked up to it to "fool" the TCU - thus my comment about Harvey enlightening us.
-Bill

Thats a signal that the ABS pulls a low on, to tell the TCU, what its operating, and to go back to 3rd. The wire thats been disconnected from the ABS, would stay at a high, so it should not be causing the problem.

I am pretty sure that all 4eat will change at peak rpms to save the engine. That change point is probable different for the different engines.

I remember saying a long time ago, that the shift pattern in the TCU of the smaller engines may have a better shift timing than the SVX. Because they don't have as much power to waste, the TCU would do a faster, harder change to maintain velocity.

Harvey.

[SVXRide]

Harvey,
There you go! So, it would appear that the focus shifts (pun indended) back to the TCU being used (and the speed sensor input).
-Bill

[benebob]

That makes more sense. Pat's car still has ABS and his is doing it as well. Bill BTW, I had to stay home so I'm not in DC. We'll hook up at some point. Sorry, I completely forgot!

[TomsSVX]

I do not believe you can swap a tcu from any other model subaru without changing the wiring. You would need to change all the pins on the pinout to match with those in the new tcu. I tried to swap the tcu from the car i got my trans out of in my FWD and it would never leave 1st gear. So i left the svx tcu in the car.

Tom