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Impreza 4EAT question.


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13 replies to this topic

#1 SUBARU3

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Posted 17 February 2006 - 05:20 AM

Hey Guys and gals:

What would cause a 4EAT trans. (95 Impreza AWD), to shift 2nd to 4th for a moment and then back to 3rd?

The trans has 82 K, no problems at all otherwise and good clean fluid.

Basically, under 'normal' acceleration it shifts fine from 1st -2nd, but then from 2nd to 3rd, it feels like it goes to 4th and then downshifts back to 3rd and then as speed climbs, it shifts correctly to 4th. The torque converter lockup happens correctly too. No downshifts difficulties either.

Now if you do a HARD acceleration, it seems to shift 2nd to 3rd to 4th OK.

Again no slippage, touque bind or any other issues with the tranmission.

When cold ity shifts perfectly!

Your thoughts?

Thanks, Todd

#2 grossgary

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Posted 17 February 2006 - 06:44 AM

i know the earlier versions have a subtle shifting issue between 2nd and 3rd that's normal, they all do it. 2nd to 3rd kind of takes awhile, that's the best way i can describe it. hard to put in words, it's "soft" so to speak and takes longer than it should. i always disconnect the shift resistor on the passenger side strut tower (could be located differently depending on model) to help it shift a little firmer. the trans shifts all around better that way, a little harder than most are used to but i say it's better. still has the same lag or whatever you want to call it, but it's better. if it's that, then it's normal for the 4EAT. it's bad enough that someone on this board had the transmission valve bodies modified to try and alleviate it and it STILL did it, better but was still there.

if it's something else then pardon my rambling.

#3 OB99W

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Posted 17 February 2006 - 07:29 AM

[...]Basically, under 'normal' acceleration it shifts fine from 1st -2nd, but then from 2nd to 3rd, it feels like it goes to 4th and then downshifts back to 3rd and then as speed climbs, it shifts correctly to 4th.[...]

Two questions:
1) Does it do this when the engine/trans are cold?
2) Does it do it when warm with the shift lever in "3", not "D"?

Both of those conditions should inhibit operation in 4th unless engine speed is excessive. I'm wondering if somehow the TCU is getting a wrong signal (or misinterpreting something) so that it temporarily "thinks" there is an over-rev situation, forces an upshift, and then corrects.

Bad ground connections have been known to cause strange trans problems, so they might be worth looking into.

#4 2X2KOB

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Posted 17 February 2006 - 07:41 AM

What's the deal with this disconnecting of the shift resistor on the passenger side strut tower? Never heard of that one before. Is this something I might see on a 2000 OB? Is this documented somewhere? Thanks,

#5 grossgary

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Posted 17 February 2006 - 09:35 AM

there is a company that sells a device to splice in-line with the shift resistor. they market it for the SVX i believe, but it'll work with a wide range of 4EAT's. i think the idea is that it bypasses the resistor at certain times. basically it's a marketing tool that makes money off the option of disconnecting the shift resistor entirely. that device seems more than needed to me. better option is to disconnect the shift resistor and if you don't like the way it shifts, reconnect it and leave it stock. mine are always disconnected, shifts much better. it's harder and firmer shifting but feels much more solid to me. there's even been discussion a long time ago that it's better for the trans because the clutches engage quicker without it. doesn't feel as cushy, but it's quicer and firmer, leaving less time for the clutches to wear. but that effect is certainly minimal whatever it may be. i haven't payed much attention to the newer models though. i don't think my impreza does it as bad as the XT6, i'll try it on my impreza if i remember.

we've discussed, posted pictures and stuff at www.xt6.net before, i'm guessing there's info on it at usmb as well?

this probably isn't the cause of his problems, but something to look at if it is a 2-3 shift issue. if the resistor is bad you can isolate the problem by disconnecting it.

#6 SUBARU3

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Posted 17 February 2006 - 03:20 PM

Thanks all for responding.

Hmm.... I have noticed that when the engine is cold, like on a COLD morning, (I live in TX), the shift from 2nd to 3rd seems better and it doesn't seem to hit 4th from 2nd. Now after I'm warmed up, it behaves like I stated in the 1st post. I guess thats the 4th inhibition from the temp. I'll try the gearshift in "3rd" and see. I think it will do the same thing.

Todd

#7 SUBARU3

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Posted 17 February 2006 - 07:22 PM

Well, it seems to do it during normal acceleration with the selector in "3rd" too. Not quite at much as when it's in drive though.

Now if I'm real gentle on acceleration, it shifts through to 2nd, 3rd, 4th fine. But I have to be real light on the gas.

Todd

#8 OB99W

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Posted 17 February 2006 - 09:09 PM

Well, it seems to do it during normal acceleration with the selector in "3rd" too. Not quite at much as when it's in drive though.

Under "normal" conditions, I wouldn't expect any shifting into 4th when the selector is in 3rd; it should be inhibited unless revs are so high that the shift is forced.

Now if I'm real gentle on acceleration, it shifts through to 2nd, 3rd, 4th fine. But I have to be real light on the gas.

This is again sounding as if the TCU (at least momentarily) thinks there's a higher engine speed than there really is, or something like that. Does the tach do anything unusual when the symptom occurs?

#9 SUBARU3

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Posted 17 February 2006 - 10:41 PM

The tach is fine. I just see the revs go down and then back up abit as it shifts from 2nd to 4th to third. (Selector in Drive)

Could it be the torque coverter locks up for a second in third and then unlocks? It seems like just a few hundred rpm below what it should be in third.

Todd

#10 OB99W

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Posted 18 February 2006 - 07:57 AM

The tach is fine. I just see the revs go down and then back up abit as it shifts from 2nd to 4th to third. (Selector in Drive)

Okay, this is now sounding like the band servo is momentarily keeping the band applied as it would for 2nd (and 4th), rather than immediately releasing the band for 3rd. Take a look at http://endwrench.com...s/pdfs/4EAT.pdf . Scroll down a few pages to the section "Band Servo Operation". Read that and look at the diagrams to the right. It would seem that if either the servo is a bit sticky or the 3R accumulator is sluggish, that might explain the behavior you're experiencing; gentle acceleration might give sluggish things enough time to actuate, and hard acceleration might raise pressures a bit and force something sticking to move.

I know you said the trans has "good clean fluid", but if it's not really fresh, maybe a flush would help. If there's a bit of "varnish", new fluid sometimes will break it down. That's about all the insight I can offer for now; hope it leads to something good.

#11 SUBARU3

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Posted 18 February 2006 - 04:46 PM

Okay, this is now sounding like the band servo is momentarily keeping the band applied as it would for 2nd (and 4th), rather than immediately releasing the band for 3rd. Take a look at http://endwrench.com...s/pdfs/4EAT.pdf . Scroll down a few pages to the section "Band Servo Operation". Read that and look at the diagrams to the right. It would seem that if either the servo is a bit sticky or the 3R accumulator is sluggish, that might explain the behavior you're experiencing; gentle acceleration might give sluggish things enough time to actuate, and hard acceleration might raise pressures a bit and force something sticking to move.

I know you said the trans has "good clean fluid", but if it's not really fresh, maybe a flush would help. If there's a bit of "varnish", new fluid sometimes will break it down. That's about all the insight I can offer for now; hope it leads to something good.


Very interesting.....I will do a change of the fluid again...maybe a flush??
This sounds like what may be happening! I'll report back.

Thanks much!

Todd

#12 friendly_jacek

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Posted 20 February 2006 - 12:02 PM

there is a company that sells a device to splice in-line with the shift resistor. they market it for the SVX i believe, but it'll work with a wide range of 4EAT's. i think the idea is that it bypasses the resistor at certain times. basically it's a marketing tool that makes money off the option of disconnecting the shift resistor entirely. that device seems more than needed to me. better option is to disconnect the shift resistor and if you don't like the way it shifts, reconnect it and leave it stock. mine are always disconnected, shifts much better. it's harder and firmer shifting but feels much more solid to me. there's even been discussion a long time ago that it's better for the trans because the clutches engage quicker without it. doesn't feel as cushy, but it's quicer and firmer, leaving less time for the clutches to wear. but that effect is certainly minimal whatever it may be. i haven't payed much attention to the newer models though. i don't think my impreza does it as bad as the XT6, i'll try it on my impreza if i remember.

we've discussed, posted pictures and stuff at www.xt6.net before, i'm guessing there's info on it at usmb as well?

this probably isn't the cause of his problems, but something to look at if it is a 2-3 shift issue. if the resistor is bad you can isolate the problem by disconnecting it.


Based on this I did some searches that uncovered a few discussions on this couple of years ago. It sounds like the disconnect could be beneficial for the fragile SVX' tranny but it messed up Legacy777's subaru transmission as well as somebody's nissan maxima.
Legacy777, do you care to add to this?
Also, Grossgary, what is the year of your subaru?

#13 OB99W

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Posted 25 February 2006 - 10:43 AM

Todd, I just came across this:
http://www.scoobymods.com/forums/showthread.php?t=2213

I thought it might be interesting, although the symptom seems to be an increase ("flare") of a couple hundred RPM, rather than the momentary decrease you mentioned (assuming I understood you correctly) during the shift.

#14 SUBARU3

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Posted 25 February 2006 - 06:23 PM

Ob99...thanks for the link. Very interesting reading. I printed it for reference.

Todd




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