DB9 transmission

[V12Ray]

Hi all, hopefully some of you can help me with a transmission problem on my 2005 AM DB9 automatic

When car stood still, foot on brake but still in drive, a lumpy vibration coming from underneath, there's still power to the wheels when foot on brake, I was under the impression that the mechatronic gearbox, via the solenoid, dumps the hydraulic fluid so there's no power to the wheels....maybe I'm wrong, I cannot find a definitive answer....apart from that it drives well with no problem moving up or down the box, again, no problem with tiptronics

Fingers crossed someone can help diagnose my problem

[paulrog1]

Whilst in D there will always be drive to the wheels.

As the gearbox is at the rear the driveshaft inside the torque tube will rotate with the exact rpm of the engine.

The ZF gearbox is normally very reliable in these cars, the drive train also.

A lumpy vibration could be a misfire, normally when the ignition coils start to fail, the misfire problem is a common fault on the DB9.

Keep us updated.

[V12Ray]

Thanks for that mate.....had all 12 coil packs changed 3k miles ago (mileage now 46k)

Searched some of the material available ie possible causes...from flywheel problems through to drive shaft bearings and into torque converter...but all these possible faults come with inherent gear change problems, which there is none...started to think it was the gearbox itself, which I believe is a
6-speed Touchtronic II Mechatronic ZF 6HP26....still I'll soldier on.....cheers

[V12Ray]

V12Ray said:

Thanks for that mate.....had all 12 coil packs changed 3k miles ago (mileage now 46k)

Searched some of the material available ie possible causes...from flywheel problems through to drive shaft bearings and into torque converter...but all these possible faults come with inherent gear change problems, which there is none...started to think it was the gearbox itself, which I believe is a
6-speed Touchtronic II Mechatronic ZF 6HP26....still I'll soldier on.....cheers

Also...I have a 2021 Audi SQ5 auto....when foot on brake & car in drive, there is no power to the wheels, ie I can attempt to rev the car but it won't move from tick over (750rpm).....I thought the Aston & indeed most automatics did this...

[pschlute]

V12Ray said:

I was under the impression that the mechatronic gearbox, via the solenoid, dumps the hydraulic fluid so there's no power to the wheels.

Had a 2005 DB9 for 10 years. This did not happen

Edited by pschlute on Friday 4th November 19:53

[pschlute]

V12Ray said:

Also...I have a 2021 Audi SQ5 auto....when foot on brake & car in drive, there is no power to the wheels, ie I can attempt to rev the car but it won't move from tick over (750rpm).....I thought the Aston & indeed most automatics did this...

Are you assuming that when foot is on brake the transmission disengages ? That may be the way a 2021 Audi works, It is certainly not how a 2005 auto car works, of any make.

Also, why do you think the Audi is disengaging ? If your revs are limited it would suggest it is the brakes/torque converter that are preventing increased revs.

Edited by pschlute on Friday 4th November 19:56

[BGB autosport]

At low rpm the torque converter effectively slips allowing you to hold it on the brakes. Has it ever had a gearbox oil change? That's where I would start, new filter, tube seals, bridge seal and some fresh ZF oil.

Edited by BGB autosport on Friday 4th November 19:59

[V12Ray]

Nice one..as I've said, it's been quite difficult to get clear concise answers, so thanks for that.....and yes I did presume, although not fully committed to, that the transmission disengages when the brake is applied.....much appreciated,cheers

Edited by V12Ray on Friday 4th November 20:10

[V12Ray]

BGB autosport said:

At low rpm the torque converter effectively slips allowing you to hold it on the brakes. Has it ever had a gearbox oil change? That's where I would start, new filter, tube seals, bridge seal and some fresh ZF oil.

Edited by BGB autosport on Friday 4th November 19:59

Transmission fluid changed at 38k, new filter fitted, would have to look through my invoices to see if seals were also changed....

Edited by V12Ray on Friday 4th November 20:11

[pschlute]

V12Ray said:

Nice one..as I've said, it's been quite difficult to get clear concise answers, so thanks for that.....and yes I did presume, although not fully committed to, that the transmission disengages when the brake is applied.....much appreciated Paul, cheers

At low engine revs the impeller in a torque converter puts out between none and a very small amount of power to the rest of the assembly. The tech has not changed for about 70 years.

[V12Ray]

The 2021 Audi SQ5 diesel has a ZF eight-speed Tiptronic transmission.....so the method I used for testing if the transmission disengages when the brakes are applied is obviously wrong/flawed, I shall have to test again...it did seem that the Audi didn't want to increase the rpm...no feeling of needing to depress brake pedal further to keep the power in check.....with the Aston though, I could put full pressure on the brakes & it still tried to spin the wheels

I've just been reading that by far and away the weak link is the torque converter...so further investigative work is needed.....cheers

[Simpo Two]

V12Ray said:

I've just been reading that by far and away the weak link is the torque converter...so further investigative work is needed.....cheers

Yet when my 2007 DB9 was diagnosed as needing a new TC, nobody had ever head of a TC failing before - which suggests they're very reliable.

I would hazard a guess at a lumpy idle for some reason (as in engine).

[Sebastian Tombs]

V12Ray said:

Also...I have a 2021 Audi SQ5 auto....when foot on brake & car in drive, there is no power to the wheels, ie I can attempt to rev the car but it won't move from tick over (750rpm).....I thought the Aston & indeed most automatics did this...

I’ve never heard of any automatics doing this.
Why would you want it to do that? Wouldn’t you lose the ability to creep in traffic, or hold the car on a hill?

[V12Ray]

I realise this now, just trying to get to the bottom of my problem....cheers...


It was explained to me, by an
hydraulics engineer, although not automotive, that in some cases, when the brakes are applied, the flow of hydraulic fluid into the torque converter decreases, until the car comes to a complete stop, in which case, via a mechatronic solenoid, the hydraulic flow ceases altogether and the engine settles to tickover....when the brakes are released the mechatronic solenoid opens and introduces fluid into the TC....this then allows 'creep'
https://www.quora.com/For-an-automatic-car-in-driv...

Edited by V12Ray on Saturday 5th November 12:48

Edited by V12Ray on Saturday 5th November 12:49

Edited by V12Ray on Saturday 5th November 13:11

[BGB autosport]

V12Ray said:

I realise this now, just trying to get to the bottom of my problem....cheers...


It was explained to me, by an
hydraulics engineer, although not automotive, that in some cases, when the brakes are applied, the flow of hydraulic fluid into the torque converter decreases, until the car comes to a complete stop, in which case, via a mechatronic solenoid, the hydraulic flow ceases altogether and the engine settles to tickover....when the brakes are released the mechatronic solenoid opens and introduces fluid into the TC....this then allows 'creep'
https://www.quora.com/For-an-automatic-car-in-driv...

I had an A5 with a CVT that did this.

Are you confident that whomever changed the oil followed the correct fill procedure? Any leaks? A low oil situation can cause a surge, however I would have expected other issues worth shifting, loss of drive etc

[LTP]

As far as I know there is no connection between the brakes and the transmission in a conventional auto box with a torque converter. When the car is stationary then the torque converter is “stalled” and is trying to put drive through to the wheels but the car is stopped from moving by the brakes. This is why a conventional auto will “creep”. To get a rapid getaway off the line some people will apply throttle to increase the torque being transmitted to the wheels while the brakes are on, so the engine doesn’t have to build torque as the brakes are released and throttle opened. Doing this is not a good idea, by the way.

A twin-plate clutch transmission, like a DSG or PDK, actually has two conventional clutches and so, when stationary, both clutches will be fully disengaged to avoid wear, otherwise the clutch linings won’t last long. Opening the throttle will tell the transmission ECU to start to let out the clutch and away you go - a bit like the AML Sportshift in the Vantage, but as we know that is a single clutch system

A CVT is the spawn of a corrupted mind that didn’t enjoy cars or driving and, while I know how they work in principle, I have no idea how the neutral works and am not particularly interested.