yet another tranny question

[lee]

OK, I'm gonna apologize in advance for the length. Not sure what's germane and what isn't, but want to get out as much info as I can to help garner potential solutions with my new problem. Also, keep in mind I live in flat-land. The only significant hills are the bridges high enough to let ocean running boats go under - somewhat steep, but not mountain grade, and not long - say 3/4 mile of climb at most.

I seem to have a transmission that slips only in 4th gear. Yes, 1, 2, & 3 currently work normally, no flare/slip. Here's the background up to this point (rebuilt tranny 22k miles ago):

a) about 15K miles ago I replaced the TPS as I always had a 2-3 flare under very light throttle - even though I never showed a trouble code on the power light. I also adjusted the bands and that didn't make the flare go away either.

b) On advice, external to a forum thread, for the 2-3 flare, about a week ago I tried moving the TPS up to a setting of as high as 0.685 volts. I have since moved it back to the original value at 0.500V (these figures are with a digital VOM). Coincidentally or not, that's the time my 4th gear slip started to appear.

The flare now seems to be gone, but I get a slip in 4th. I readjusted the bands, even tightened them enough to get the breaking effect in 1st & reverse (which should maximize 2nd & 4th band holding ability). That did NOT eliminate the slip, but in the interest of not burning up the band, I since backed it off some. OK, so here's the characteristics of the "slipping":

a) holding the car in 3 until I reach a stable, level ground speed of 45-50mph, then moving to D, results in a shift with about the right amount of feel. There is no flare in RPM, and the car continues normally.

b) going from a dead stop in D with moderate traffic flow, the car shifts fine at all appropriate points until it gets to 4th, then as it shifts, the RPMs climb to around 3K rpm whereas it would only have gone to around 2.5k rpm (with that amount of throttle) in the past.

c) trying to accelerate (at approx 1/3 throttle) in D/4th, at around 45mph, will result in a slipping of rpms up to nearly 4k rpm before the box kicks down to 3rd. Also happens when I try to maintain speed up a bridge/hill. If it slips enough to make it to ~4k rpm, there's a downshift to 3rd that "fixes" the problem for that moment.

d) I have not tried to maximize the amount of slip to see how bad it can get. Nor have I tried a stall speed test.

e) If I move off in D at a very moderate level, the system seems OK. I can gain speed on flat ground with light throttle with no slip (that I can perceive anyway). This would under conditions like when the traffic flow changed from about 50 to 55mph as the limit changed between towns.

f) when it is "slipping", I gain speed, it's just the rpm is higher than it's ever been and it "feels" like slipping is occurring - I'm basing this on to work & back conditions I've experienced since the rebuild some 22k miles ago.

g) there haven't been many opportunities, but if I give it a relatively heavy foot (just enough to avoid a downshift) the "slip" is there when it changes from 3rd to 4th - didn't really watch the speed, but I'm guessing around 50-55 mph for the 3-4 shift so you have an idea of how much throttle I'm talking about

Last point. The Power light now almost randomly gives me the 16 flashes on start-up (about every 4th time I start the car). The trouble code set is 31-TPS. I put back in my old TPS, one that never had set a code, and on the second startup, I got the flash again. Coincidence/TCU/??? There does not seem to be any other issues, i.e., with a manual downshift into 3rd I get engine breaking, etc.

[mile-hi-bri]

How long has it been since you changed/flushed the fluid? Is it natural or synthetic? Does it smell or discolored, etc.
Remember, the more it slips the worse it's getting, QUICKLY!
Did your first band adjustment seem like a lot of adjustment to achieve any difference? As I remember, the FSM says something like a 3/4 swing either way. Were you in this range, or more?
mile-hi-bri

[lee]

Originally posted by mile-hi-bri
How long has it been since you changed/flushed the fluid? Is it natural or synthetic? Does it smell or discolored, etc.
Remember, the more it slips the worse it's getting, QUICKLY!
Did your first band adjustment seem like a lot of adjustment to achieve any difference? As I remember, the FSM says something like a 3/4 swing either way. Were you in this range, or more?
mile-hi-bri

It's been Mobil 1 synthetic since the rebuild, with one 7-qt fluid change in the 22K miles since. It is not discolored or burnt. The first adjustment was made in a 3/4 clockwise turn, which made the bands to tight (slight dragging in 1st, reverse and slightly hesitant shift to 3rd), so I backed it off. BTW, I also use Mobil 1 synthetic differential fluid, with no sign of leakage between the two.

I also have an external Hayden plate & fin cooler and the Perma-Cool add-on external filter (with temp gauge). The fluid has never hit the 200 degrees F mark on the gauge (temp is measured on the output side of the transmission - before the coolers). Also checked for fluid flow by taking off the return line. With almost as fast as I could get the engine running, then turned off (about one second) I get about a quart of ATF that flows out on the return line into an old plastic milk jug "catch pan".

[subafan]

ok, i have a.... definitional!? question... what do we mean when we say the tranny 'flairs' or 'slips'?

[immortal_suby]

When my tranny died it had similar symptoms. I had the flare when I bought the car at 100k, disconnected the resistor and ran fine until about 160k when I got the dreaded 4th gear slip. I replaced the TPS, fluid, and tried a band adjustment to no avail.

I recall driving for a week or 2 with 4th slipping before 2nd started to slip too and it became undriveable.

Unfortunately I didn't have that tranny rebuilt - bought a used one instead, so it sits in my garage and I can't give you any autopsy report on what actually failed

I didn't have a TPS code at the time - at least I didn't know it if I did. Since I had the resistor unplugged I had ignored the blinking power light for a long time.

[immortal_suby]

The "flair' is referring to the tranny "over-revving" on the gear change.
The same feeling you'd have if you slipped the clutch too much in a manual tranny when shifting.

[lee]

Originally posted by subafan
ok, i have a.... definitional!? question... what do we mean when we say the tranny 'flairs' or 'slips'?

I'm certainly not in charge of definitions, but here's my take:

Flare: when changing gears transmission seems not to engage for a moment (or longer) and engine revs up with the feeling of no power transmission to the axles - almost like you hit a false neutral (that may be something only motorcycle riders experience, I've never felt it in a car).

Slip: when changing gears, or in a gear, engine revs and there is some feeling that power is being transmitted, just not normal amounts of it - some being used up in the slipping - if you've driven a manual and ever "slipped" the clutch you know the feeling I'm describing.

[lee]

Originally posted by immortal_suby
When my tranny died it had similar symptoms. I had the flare when I bought the car at 100k, disconnected the resistor and ran fine until about 160k when I got the dreaded 4th gear slip. I replaced the TPS, fluid, and tried a band adjustment to no avail.

I recall driving for a week or 2 with 4th slipping before 2nd started to slip too and it became undriveable.

Unfortunately I didn't have that tranny rebuilt - bought a used one instead, so it sits in my garage and I can't give you any autopsy report on what actually failed

I didn't have a TPS code at the time - at least I didn't know it if I did. Since I had the resistor unplugged I had ignored the blinking power light for a long time.

this sucks - couldn't you have lied to me (J/K).

and you beat me to the flare def, I must type to slow. however, seems like great (or perhaps twisted) minds think alike since we used the same feeling to describe the effect.

[Ron Mummert]

My solution would be for you to drive due west 'til you see water again, & make Randy II an offer on his "Rip my heart out, please" mechanic's special with a working tranny.
This is a marriage made in heaven. Remember those? I'll trust one of your cars is the opposite sex, as if it made a difference anymore.

Ron (rice is nice).

[subafan]

thanks guys... those were really good answers....
now i know that i did not have a flaring or slipping tranny....
my problem probably was the shop hooking up the cruise control, or the pedals wrong... because the rpm will go up, but so will the speed of the car...

ok, enough excursion... back to the thread

[huck369]

Lee,
It sounds like it could even be a Torque convertor going south, the slipping under load, might be the TC not locking up, and allowing excess slipping...which would show up worst in high gear (just like a bad clutch in a manual).

Just another avenue to check out.

[lee]

Originally posted by huck369
Lee,
It sounds like it could even be a Torque convertor going south, the slipping under load, might be the TC not locking up, and allowing excess slipping...which would show up worst in high gear (just like a bad clutch in a manual).

Just another avenue to check out.

Huck,

Do you know if the Subie transmissions can handle the typical stall speed test, i.e., stand on the brakes & gas & note engine rpm? That "should" tell me if it's a TC issue.

Also wondering about the servo that tightens the band for 4th - is that a different one from 2nd?

[huck369]

Lee,
I'm not even going to guess about the internal workings of an auto tranny....over my head.

I think power braking it to check the TQ, isn't going to hurt anything...if the tranny is going it might get it there a "little" bit quiker, but if its going bad, it's going bad, so it might be worth a try.
But you'll have to use you own judgement on it, I'd probably try it if it were mine, but I do things that some people wouldn't
Keep us posted as it unfolds,

[oab_au]

Gee Lee your questions are a lot better than mine. though I can answer yours.

I think it comes down to the Throttle Position Sensor. What is happening is the brake band is slipping, as it tries to hold the front sun gear. This is the different between 3rd and 4th. The high clutch is on in 3rd, all that has to happen to go to 4th, is to apply the brake band. This is where it is slipping, it grips = 4th gear, it slips = 3rd gear. The rpm rising is when the clutch slips and it goes back to 3rd.

The big question is why does it slip in 4th and not in 2nd? I think the Line Pressure is a lot lower as the band is applying for 4th, than it is when applying for 2nd because of the higher pump speed. The Line Pressure is the result of two pressures, one produced by the Transmission Control Unit based on road speed and a whole lot of modifiers. The other is the Throttle Pressure, this is the result of how far the throttle is opened. This the pressure we increase with the Shift Kit.

So where is the fault? it has to be either the Throttle Position Sensor (this really does need to show 0.5V at idle) or the resistors that you have on the ‘A’ solenoid. You could unplug the dropping resistor to see if the increase in Throttle Pressure stops the slip.

Happy hunting Lee.
Harvey.

[lee]

Thanks Harvey, Huck, et al,

I will try removing the dropping resistor.

Harvey, do you know if a failure in the 4A accumulator (I don't even know what their failure mode entails) can cause this sort of thing? I was under the impression the accumulator and servo were there to soften the shock in shift, and I'm wondering if it could be doing it's softening job just a bit too much.

It will probably be Monday before I get to try anything & report back progress. My "Honey do" list is long indeed this weekend.