TC Lockup too early???

[VSPantha]

Hi.
Over the last couple of weeks I've noticed I get TC lockup early. Like... under light to normal acceleration it'll shift normally from 1st, to 2nd to 3rd, then at around 80km's an hour it'll drop from 3rd into lockup pretty much bypassing 4th (rev's just drop to about 1500rpm). I originally thought it was slipping but if I give it a bit more throttle it'll unlock and accelerate then lock up again at about 100km/hr. I checked the transmission fluid last week, it was a bit low, so put topped it up to the checkered mark on the stick (fluid was hot, just driven 25k's), have just checked the codes (only getting 12's) so unsure what may be causing it. There does seem to be a bit of shuddering under normal acceleration. Seems to be coming from under the tranny hump (under floor of heater core/stereo area) can be felt by my left foot on the footrest.
Could these two things be linked? I've read on the forum that bad plugs/leads can cause similar symptoms to the above? Had new plugs 8000k's ago, could probably do with new leads. Unsure when the car had a tranny service last, fluid was a bit bubbly but didn't smell or look burnt.

[Brett_jjj]

Try changing the trans filter and some fresh fluid.

[VSPantha]

Would it need a flush? I asked a local mechanic about getting flush and filter change done and they said between $200-300 depending on how much needs to be flushed thru... Does that sound about right?

[Brett_jjj]

I do my own,about $30 for a filter and new pan gasket,and about $25 for 5 litres of fluid.The flush sounds a bit expensive to me.Someone on here should know what the cost is though.

[admir87]

i always thought the the tcc is meant to lockup at 80km/h :S

pretty sure mine does at the same speed

[VSPantha]

yeah, but what I'm getting at is that while it's still under power... it goes from 3rd then instead of changing into 4th then lockup, will go str8 to lockup. It has done it at 60k's an hour aswell... like it will randomly just bypass 4th and lockup straight out of 3rd gear?

[Brett_jjj]

If your going over 80 in 3rd gear it will lock up anyway.The Gregorys workshop manual says -The operation of the lockup torque converter is controlled by the ECU and a solenoid located inside the transmission.When the vehicle speed is above approx 85km/h and the transmission is in third gear or overdrive,the solenoid is energised by the control unit which allows pressure to lock up the torque converter,providing a direct drive between the engine and transmission.

[VSPantha]

but it shouldn't if you're still accelerating.... should shift into 4th until power/speed levels out. This is what I'm trying to get at... 4th gear should (and used to) hold for a while before it would lock up.

[Brett_jjj]

I dont think it matters if its under power or not.Mine locks up no matter if its under power or just cruising at around that speed.Mine is a V6 though.Im not sure if the V8 is different or not.

[woteva]

Mine locks up at 80kmph when in Econ, but behaves a bit differently when the Power switch is ON.

[Brett_jjj]

The power button changes the shift points.It should hold the gears longer when its out.

[VSPantha]

Well... I just went for a trip to the servo... in 3rd gear at 100km/hr is doing about 2800rpm... drop it into D with same amount of throttle dropped to about 1950rpm.
Coming back I left it in D and accelerated a bit faster than normal up to 100km/hr
Dropped into 4th doing 2200rpm at about 95km/hr, then locked a couple seconds later doing 1950rpm at 100km/hr.
Was in econ mode the whole time.
I know when I'm doing 80km/hr and hit the power button the revs jump up, it goes into 4th and it won't lock until it's doing 100km/hr.

[greenfoam]

The lockup is controlled by the computer at a set speed and load, unless it's locking and unlocking and being unstable with rapid locking and unlocking the change in lockup is all in your imagination I'm afraid . If it is wobbling around when trying to lock, see your tps sensor

[hako]

Check the fluid level as well - foaming indicates an overfull transmission which can cause all sorts of problems as air gets trapped in the valve body similar to having air in the brake lines.

[VSPantha]

Hey Greenfoam. Yeah I understand what it's supposed to be doing... just that recently it's not doing what it used to do... go into 4th... then lock up and drop about 300rpm when it locks. Will get the auto serviced and see if that changes anything!
BTW... I've been wanting to get hold of you to talk about getting a memcal done... can u plz pm me coz I got a couple of questions to ask ya

Hey Hako. The fluid was a bit low as stated in the original post... definitely not overfull

[Paiste402]

I dont really see why the trans would need a flush unless its running some seriously burnt fluid. Trans fluid is a natural cleaning agent anyway so a fluid change is like a small flush in itself.