5 speed auto gearbox issue

[Eska]

Hi,

My car has thrown up some error OB2 error codes to do with the transmission, specifically P0740, P2761 and P0741 which I’m told may suggest the torque converter may be at fault. There are no warning lights and if I clear the fault codes they do not always reappear immediately and the car drives without any noticeable fault, the gearbox works as it should and I’m experiencing no gear selector issues when selecting drive referees or park etc.

Any experiences / feedback as to what to do would be appreciated.

 

[bigwinn]

All seems to point as you have said to the torque converter

What’s the condition and age of the gearbox oil as I’d check that first?

 

[Eska]

I’ve had the car for 4 months but looking at the base of the gearbox the car has a fluid leak around the gasket and I’m pretty sure it’s never had a gearbox service. So original filter and fluid and a fluid leak but not so that it drops under the car. I’ve booked it in for a gearbox service hoping that may work. Here’s a picture of the base of the gearbox.

 

[bigwinn]

The risk here- and many will repeat it

You now have codes pinging up on an auto box, the logical thing to do is change the fluid

Some say that will make things much worse as you have issues inherent in the box

But- and I caveat this saying it’s your car and your decisions, seeing that fluid leakage I would drain the old fluid, slap a new filter and gasket on and pop new oil in- and I’m a gambling man!

 

[Rockhopper]

Chap on the Facebook group ended up scrapping his Z4 after a fluid change went horribly wrong. An auto trans specialist and two BMW independent workshops said not to risk it unless you are chasing a problem and doubly so if its never been changed before.
There are lots on here and on the Facebook group who have changed theirs and had no problems.
Mines on 110k and I've not changed it yet!
If you hadn't read the codes would you have thought there was anything wrong?
My inclination if its driving fine would be to leave it till if fails then chuck in a second hand box.
Oil leak might be an MOT issue? Not sure how they treat gearbox leaks though.

 

[Spriteracer]

It would be worth checking the level and topping up as you don't know how long the leak has been going on. Could have lost quite a bit over many months / years which may have blown away when the car was driven - hence little evidence of leak on the floor. May need to renew the seal though which will need a fluid change anyway.

For what its worth I have had fluid changes done on E34, E39, E61 and Volvo XC70 all at roughly 150k miles +. No issues at all.

 

[smorris_12]

I've never been convinced by the "oil change killed my gearbox" argument. I suspect it's a case of the post hoc ergo propter hoc fallacy[1] and the autobox was about to die any which way. Possibly old oil full of gack is thicker and takes up the gaps between excessively worn clutch plates better than new thin oil and leaving it in there is just postponing the inevitable a little.


[1] After this, therefore because of this

 

[deltasierra]

I suggest taking it to an auto gearbox specialist, mine has got niggles and have asked for an oil and filter change which involves a new sump plate, quoted at £200. The experts have all the kit to do the job properly, electronic as well as mechanical.

 

[bigwinn]

I've never been convinced by the "oil change killed my gearbox" argument. I suspect it's a case of the post hoc ergo propter hoc fallacy[1] and the autobox was about to die any which way. Possibly old oil full of gack is thicker and takes up the gaps between excessively worn clutch plates better than new thin oil and leaving it in there is just postponing the inevitable a little.


[1] After this, therefore because of this

I like that term- I'm going to use that daily

 

[Rossi1001]

Chap on the Facebook group ended up scrapping his Z4 after a fluid change went horribly wrong. An auto trans specialist and two BMW independent workshops said not to risk it unless you are chasing a problem and doubly so if its never been changed before.
There are lots on here and on the Facebook group who have changed theirs and had no problems.
Mines on 110k and I've not changed it yet!
If you hadn't read the codes would you have thought there was anything wrong?
My inclination if its driving fine would be to leave it till if fails then chuck in a second hand box.
Oil leak might be an MOT issue? Not sure how they treat gearbox leaks though.

On the flip side I've got the 5 speed auto (wish it was 6!) and I was having a major intermittent issue where the engine wouldn't turn over or start because it wasn't engaging park correctly. Changes were laboured and going up an incline it wasn't changing down a gear anywhere near early enough. Mine had 94k and was on the original oil. Got a local BMW specialist to do it at £300 all in (I'm South Essex). He showed me the oil that came out of it and it was somewhere between marmite and treacle in consistency. Horrendous!

He explained that you can't drain the torque converter part so he recommended a second round of oil a few weeks after the first one. I changed the pan cover too as it was very rusty and possibly nearly porous. That was £125 new from BMW. Used ones on ebay were not much cheaper so not worth it.

Touch wood it's been a significant improvement with no further issues and I'm glad I did it. Have faith!

 

[Eska]

Thanks Rossi1001! I will be getting the fluid changed and I will see how things go thereafter. I’m aware that you can’t fully drain the fluid but that held up in the torque converter and I’ve been told that that fluid mixing with the new fluid is beneficial. I did a change on my old E36 at 180k miles and there were no after effects. Good point about the pan cover I may order one from BMW.

Thanks to all too who have responded - much appreciated!

 

[smorris_12]

Talk of the torque converter reminded me of something. I've done a couple of autobox oil changes and dropping the valve body releases quite a lot more oil from higher up in the box than just dropping the pan. On one of them we reckoned that we put back nearly the full rated capacity of the box - the amount left in the torque converter must have been very little. Can't remember if that was a GM or ZF box tho.

 

[Rockhopper]

When I've watched autobox disassembly videos it looks like there is a good couple of litres in the torque converter. In fact Google suggests that roughly half the total fluid capacity of the box is in the torque converter.

 

[bigwinn]

In the past where I’ve drained the sump but not the torque converter it’s taken 6 litres to fill again

I think the total capacity is around 8 litres

 

[smorris_12]

I'm probably over exaggerating on how much was left in, it's a while since I've done one. I just have this vague memory that we got far more back in than we expected to based on reading beforehand. I rather think it was that we'd dropped the valve body where received wisdom was just dropping the pan.