5th gear slip when cold

[octanepwr]

Hi

2002 Airtrek turbo 140km

My airtrek turbo will slip in 5th gear when cold. You put your foot down and it slips and gets on boost and accelerates.

Once it has warmed up it will not slip to raise the boost and accelerate - it will change down gear if you put foot down far enough, otherwise cruise at 100kph at less than 2000rpm.
When it does shift, unless you floor it to go down to 4th or 3rd, it still shows 5 gear in the indicator on the dash, even though it appears to have noticeably changed gear. I didn't know the gearbox had overdrive but it seems like it may be coming out of overdrive on 5th gear?
Note at this point if you put it into manual and shift down again it will go into 4, so it really does seem like it has overdrive on 5th gear. i.e. when it feels like it downshifts but still shows 5th, it is definitely not in 4th.

This makes me think that when it is cold it is simply not going into cruise overdrive on 5th gear.

Hot gearbox cruise at 100kph is just under 2000rpm.
When cold it will be between 2100 and 2500rpm depending on how flat it is.
All gears work perfectly fine when hot or cold and shift smoothly, I am just unsure why it will not sit at lower revs in 5th gear when it is cold.

My auto trans fluid is the correct level when hot on the dipstick (gearbox in N). When cold it does not register on the dipstick, so I added about 300ml more. Now it registers on the dipstick when cold. No difference made. It is clean and SP3 rated.

I hope someone can agree/describe what i feel like is overdrive on 5th gear?
Then it would make sense the gearbox does not go into overdrive unless it is hot.
This is normal like old 4spd auto gearboxes which does not go into 4th (4th is like overdrive) until they have warmed up.

Thanks

---------- Post added at 09:15 PM ---------- 6 hour anti-bump limit - Previous post was at 08:08 PM ----------

After reading a bit more about auto boxes in general, it sounds like the torque converter might just not be locking up until it is warm?
Anyone know better than me and if so is this normal (hopefully)?

Cheers

 

[dreggzy]

The issue you describe is in the torque converter or the valve body. The torque converter is like the clutch. It engages and disengages as needed, so when you are just cruising, it locks, which is the 'gear change' you experience. The valve body is the control module for the gearbox. If there is a fault in the valve body, it may not be sending a signal to the torque converter to lock. Best idea is to get it looked at by somebody who knows auto gearboxes. A torque converter is not expensive, however labour to change it may be expensive as the gearbox needs to be removed from the car.

 

[octanepwr]

Thanks for that.
I just read a bit more and it seems on many cars it won't let the torque converter lock up until the trans fluid has reached full temperature.
So seems normal.
Still like to hear from others with the same vehicle though.

---------- Post added at 10:47 PM ---------- 6 hour anti-bump limit - Previous post was at 10:44 PM ----------

It is also interesting how sometimes the transmission will seem to hold revs e.g. 3500rpm in 3rd gear, when you give it moderate throttle. Once your speed has risen more then it lets the revs rise up past 3500rpm.
Probably more torque converter stuff.

 

[vr2turbo]

I agree with bro. dreggzy that it could be the valves or the solenoid that controls it. Cold and warm the oil viscosity differs. I have heard of other cases then the auto box would not even run when cold in the morning and after some warm up only it will run.....