VS Auto Trans - not engaging final gear?

[Jaymz]

Hi all,

Bit of a strange one, but I think there is a simple answer (well hoping anyway) to it.

I will try to explain the best I can:

The car:
1996 VS Series 2 Executive
3.8L engine - stock
Auto trans - stock
220,000kms on the clock - serviced every 10,000 at Holden service centre

The problem:
When accelerating to 100kmph when leaving town the trans changes gears correctly and once it gets to 80kmph there is a final change into what I would call Overdrive. This results in the rev counter dropping to below 2000rpm and stays around there - gives great fuel economy.
Once the car has warmed up/driven for awhile the trans no longer does the above.
It is almost like the car is in Power mode (small button next to the shifter).
This results in the rev counter sitting above 2000rpm when at 100kmph and drains my fuel!!
The car changes the lower gears fine, plenty of grunt and pull!

What I have tried:
Took it to a trans shop who ran a service on it. No problems found - issue still remained
Replaced the thermostat to lower the running temp of the engine - issue still remained
Tried changing gears with the shifter when problem occurs - does not resolve it
Tried changing between Economy and Power (button next to shifter) - does not resolve it
Ran computer error code checks - all OK (code 12 back each time)

I know that it might be that the trans has come to the end of its life (and I am planning to move to a manual and V8 soon) but I want to enjoy it more before I take if off the road.

Gut feeling is there is a sensor or something that is not reporting properly - but I don't know

Has anyone seen anything like this before?
Can anyone suggest something I can try?

[IBLOWN]

When you're at 100kays with the engine warm in Drive if you pull the shifter into 3rd does it drop down a gear?

If it does drop down then its your torque converter not locking up.

[Jaymz]

Yup it does drop down gears when i move the shifter. It will also drop gears if I floor it.

What would cause the torque converter lock up sometimes, and other times not?
I guess it will require replacing? (sorry I am not a trans expert so excuse the dumb questions)

[IBLOWN]

Neither am i lol but i'd say its got to do with heat or the controller.

Im very suprised the auto trans place didnt pick the torque convertor as a problem.

[astormsau]

What you are talking about is the transmission locking up the torque converter to give you best fuel economy and reduce the heat out of the transmission.
There is a solenoid and a valve required to lockup the converter (TC). This is a very rough explanation, the same valve used for locking up 4th also enagages the TC. The valve opens to different levels, say half open for 4th and fully open for TC lockup. That valve becomes faulty and causes the TC to either lock and unlock as you drive, only sometimes lock or never lock... Often this results in a worn out TC as it is getting locked and unlocked all the time when you cruise on the highway.

The solution to fix the lock/unlock issue is for a transmission place to replace the valve. Usually they put a slightly bigger one in there. Expect to pay about $300-$400 for it in Australia. They can do the job without removing the transmission. In my case the TC was also damaged so although it would always engage once the valve was replaced, with the TC engaged the car would shudder and when it unlocked the TC on hills,etc you would get a grinding/thump noise for a second... once the TC was replaced ($650 job) the whole thing now works perfectly. A slipping TC can bring up the check engine light, in my case it wasn't quite bad enough to turn on the engine light but it did come out of lockup sometimes due to slipping.

Drew

[Jaymz]

@IBLOWN, So am I. Maybe they missed it or something, I dont know.

@Drew, Thanks for that explaination. I have had a read of a couple of sites about the torque converter to get an understanding of it, but your explanation helped loads. The engine light definately has not come on while driving which is a good thing. Hopefully it is just a valve. NZ money might be a bit more (hopefully not though)!
I will look at booking it in to get it looked at over the next week or so and let you all know how it turns out.

Thanks again guys, you have been more than helpfull!!

[The1]

check for error codes for a start Checking error codes VR/VS (Revised)

It could be TCC not locking up, could just be a solenoid to, best check for errors first.

[Jaymz]

Error codes showed up as 12 last time I checked. But I will check again tonight to be doubly sure.

[shauny83]

buy some nulon tranny treatment and give it a crack then, i had the same problem, got the fluid, went for a drive and it hasnt done it since, sure something might be on its way out, ( solenoid, TC ) but i'll prolong it as much as possible when it comes to trannys, they equal money i dont have.

[Jaymz]

Thanks, I will give it a go. I have a feeling that it might need a replacment part though!

[shauny83]

lets us know how you get on!

[Jaymz]

Sorry for the delay, it has been a busy week!

Right, some developments in the whole saga.

I haven't had time to get the car in for service (it is only my weekend runner - not the daily car)

I took it out for a spin Tuesday night and noticed some worrying symptoms that I want to check with you guys:

At about 86km per hour (when the torque converter is locking) there is a noticable vibration when accelerating (only for a moment though) and the lock isnt locking up.
The vibrations are similar to driving over the rumble strips on the side of the road (here in NZ anyway) but just not as violent.

Is the diagnosis a stuffed torque converter then? or just a symptom of a dodgy valve?

Again, not too worried at this stage, the Senator is almost mine! See here: James' '96 VS Exec