Your specialist subject..the life and times of the DCT gearbox fitted to the E89 35i/35is

[B21]

I thought a brief primer of this box for all 35i /35is owners...

The Getrag 7DCI600 aka BMW GS7D36SG is a 7 speed dual clutch transmission (DCT) aka DSG gearbox which came in four versions. They were essentially the same except for gear ratio and bell-housing combinations. They all feature the same input spline, filters, oil pan and weigh about 85 kilos For reference.

The first version of the GS7D36SG came in the 2009-2013 135i, 2008-2013 E9X, and 2008-2016 Z4 E89. It was rated to handle 520NM torque.

A second phycially identical version was used for the S55 powerered M cars rated at 700NM.

Two other versions that were related but physically different to the E89/S55 were used on V8 powered M cars.

It came with a mechatronics unit which provided a very high level of oversight and control and offered multiple driiver modes.

Although the look and feel of the unit from a drivers side is very similar to the later automatic box the ZF8HP45 found in the 18i/20i/28i it was a completely different affair.

The 'cleverness' at the time was the intrinsic ablity to pre-select the next gear going up or down the box ahead of its use and then releasing the clutch that was driving the current gear whilst simultaneously engaging the next gear resulting a shift speed of 60 m/s without reducing power transfer to the prop shaft..making for about a 0-5 to 1 sec improvement in power to accelerate the car compared to a manual shift.

Viewed in history the DCT box was a stop gap pending the arrival of the ZF8HP which in the end could do almost everything better than the DCT box.

 

[B21]

Based anecdotally on user group reports it seems that the DCT box is pretty reliable.

Almost all reports of issues are either related to leakage from one or more of four places on the box, in some cases having leaked enough oil then the box malfunctions usually with an overheat issue or occasionally broken / trapped / damaged wires going into the top of the unit.

The OE plastic sump pan is prone to leakage and it’s usually seen as an opportunity to do an oil / filter change at the same time.

Folks often change the pan for an alloy pan. These range in price from £400 ish to over £800..OE pan is about £140.

Unfortunately the sump pan is the only leakage area that can be addressed with the gearbox in situ..the other areas which leak require a full or partial removal.

The filter changes are straightforward…a snap in filter under the box accessed by removing the sump pan and a circular filter in the side of the box held in place by a big circlip.

The fluid is a bit trickier.

It’s important to get the Getrag specific fluid…I used Fuchs version..around £20 a litre.

Total capacity is about 7 litres.

The fill procedure is not straight forward.

First stage is to insert about 4 litres into the level / fill point up the side of the box right next to the exhausts..there is a heat shield which BMW says you need to remove.

At this point the procedure is to put the plug back in…start the car, run the car till the gearbox temp is around 40c, in part by running the engine at 2,000 rpm for 1 minute..using ISTA or Bimmergeeks Protool select 1 st gear …not by doing it manually…then back..

Then while the engine is running remove the plug and top up until it dribbles out..this takes another 2 ish litres of fluid..when I did my change 6.5 litres was required to complete the process.then while engine running insert plug again.

The reason for this process is that when engine is not running the clutch activation systems are not pressurised so without this two stage process there is not enough fluid in or circulation.

As regards mods the only one common used in the E89 world is to remap the box using xHP via an iOS or Android app.

The cost is around £300.

The developers have made many improvements to the shift logic mostly by refinement.

The product uprates clutch pressures to cope with tuned engines ..at least 19 Bar up from 17 Bar..

You can program your drive, sport and manual modes to suit your tune / preferences plus many other options for hard core tuners.

For a stock car along with MHD probably one of the best improvements after removing runflats.

 

[B21]

This is my personal struggle with my DCT box…

All was well until I decided to change the fluid and at the same time use a trendy alloy pan to look cool and carry a bit more capacity..

After my local low tech garage had fitted it, there was some very light oil seepage from the pan..maybe a drop or two of fluid if that per night.

I tried two or three times to subsequently get a garage to see to the leak without anybody taking me up on it..I wonder why..

I then got a ‘BMW service centre’ to change the o ring and refill it..after much drama with torque settings and having to get a fresh o ring airlifted in from the states.

However I noticed when driving along the odd puff of a burnt oil smell occasionally..when I got home the next day I could see a good patch of fluid on the ground.

I thought with 7 litres of fluid no big deal..

A couple of weeks later when trying to fo a full power 3rd gear test run for a new ECU tune it firstly prematurely shifted into 4th..on another run I then got ‘the bong’ with car going into limp mode.

Switching off and repeating the attempted run resulted in same situation.

My Protool code reader said..

5A44 clutch 1 incorrect pressure
5A41 Pressure sensor, clutch 1, total failure.

I pooed myself

Slowly drive home, rechecked the box..no errors.

Booked an appointment with same said garage..they then cancelled my appointment saying they were busy and they’d get back to me the next morning.

I went through the ‘if you need to get it done sometimes you just have to do it yourself.’

It looked like after cleaning everything thoroughly around the gearbox that the leak (when stationary ..no engine running ) iwas just from my after market alloy oil pan seal..

Side seal seems dry..couldn’t see the top seals / wire seal but was hoping it was just the bottom seal

Here’s are some photos plus the amount dripped out in 15 hours onto my wooden platform I usedfor crawling under the car..

I’ve bought a pressure filler and decided to fit my back up Polish alloy pan to see if the leaks stop..

Fair amount of damage to under tray plastics so got some alloy and pop rivets to repair some of the cracks ..

I dropped the ‘seems leggit’ alloy pan…

The sealing o ring had popped out from its groove so it wasn’t possible to see if it was seated properly..

However the fitter had used some grease to try and retain it prior to fitting..

When I inspected the o ring it came apart indicating that maybe it had been pinched..

More worrying was damage to the mating face in the same area..was he poking the o ring back in ?

You can see compared to the new Polish version that the Polish version has a thicker more positively located o ring..

3 litres of fluid came out…I think it should be at least 5 litres ..

Frustratingly the Polish pan uses the OE pan drain plug which was thrown away when the US pan was fitted..

My £16 new plastic drain plug arrived so I could start the reassembly can begin..

After loading 4.5 litres up then I had to use Bimmergeeks Protool as my ISTA for reasons I’ve yet to work out wouldn’t talk to the DCT as well as a couple of other ECUs..

Followed the same procedure with a couple of commanded shifts into 1st and 2nd for good measure..another 2 litres went in…

So 3.5 litres came out and 6.5 litres of Fuchs finest went in..

The dribbling out of fluid on the two fills felt like I was swimming in a sea of fluid.

I’ll take the car out for a 100 mile run on Sunday and see what gives.

 

[simnew]

Interestingly I was comparing how the Getrag box behaves compared to the ZF in my 440iGC. Certainly on my z4 35i 2009 and 89k miles, it selects gears from P to R to D much more slowly. You really have to wait fir it to engage. It’s probably less than 2 seconds but it does seem strange at times. Also it seems to slip more especially when cold and pulling away for the first time. When it’s warm it’s fine which is pretty quick. Also at a stand still in drive, it seems to disengage somehow but it still has creep when releasing the brake. I even get the odd little judder when cold but not afterwards.

In operation, it’s smooth and works perfectly but the programming of the box is much less likely to drop its gears than the ZF. In a sense it uses tge torque of the engine more in a way which the ZF seems much more keen to change down and make the engine rev.

The gearbox oil has been changed and it seems as though it’s working fine, but I do find myself being more gentle onto the throttle than the ZF requires. Is this other people’s experience ?

 

[smorris_12]

Very interesting info. I know everyone raves about the 8 speed, but I'm surprised a TC auto beats a DCT (tho I have no experience of either.)

 

[B21]

Technology moves on..the DCT was the only solution to handle the N54 torque at the time..the then ZF6HP was only good for about 300nm of torque against the 500 nm of the 35is.

However once the ZF8HP moved beyond its initial 450 nm limit the DCT days ere numbered.

Apart from a 60 ms delay in certain circumstances compared to the DCT on single shifts eg 3 to 4 , 5 to 5 the ZF box out points the DCT in every way.

 

[Pondy]

Technology moves on..the DCT was the only solution to handle the N54 torque at the time..the then ZF6HP was only good for about 300nm of torque against the 500 nm of the 35is.

My Alpina B3 had a factory tuned N54 (360bhp and 550nm) and a 6 speed ZF slushbox. The gearbox was fine....same couldn't be said for the N54!

 

[pvr]

I have the ZF8HP in my X5M, despite my hatred for auto boxes it is pretty good and find it so much better than the DCT that was always in the wrong gear to me at roundabouts.

 

[B21]

Technology moves on..the DCT was the only solution to handle the N54 torque at the time..the then ZF6HP was only good for about 300nm of torque against the 500 nm of the 35is.

My Alpina B3 had a factory tuned N54 (360bhp and 550nm) and a 6 speed ZF slushbox. The gearbox was fine....same couldn't be said for the N54!

I was incorrect on the ZF6HP…there was a 600nm option which as you say was fitted to your Alpina and derail 7 series BMWs.

That box did have a relatively slow 600ms shift and although the basis of the ZF8HP did lack quite a few of the extra subtleties of the ZF8HP..but was pretty good for a first attempt at a new technical direction…I’m sure if we could have all gone to a B58 engine in a Zed we’d be much happier..

 

[B21]

I have the ZF8HP in my X5M, despite my hatred for auto boxes it is pretty good and find it so much better than the DCT that was always in the wrong gear to me at roundabouts.

My experience was very similar apart from the fact that I love auto boxes..

However using xHP to update the logic of the DCT it’s now almost as good from a drivers viewpoint compared to the ZF8HP in my 20i E89

 

[mr wilks]

I have had both boxes multiple times in various Bmw cars , the simple facts are the DCT is flawed & has failings , the ZF8 does not ( or i have yet to discover them )
Speaks volumes when the more recent M5 & M4 no longer use the DCT , seems Bmw have resorted to offloading the surplus stocks of them in the later X1 where they hope the new owners won't notice

 

[Pondy]

I remember reading a really good article on twin clutch autos a few years ago. It was specifically about the VAG group boxes, but I presume they are all very similar in the way they actually work.

The bullet points were that you have to use them to how they need to work and not expect them to work how you want them to (as they won't or can't). TBH the article put me off wanting a DCT (as I did before).

The ZF8 in my B58 was as good and quick as anybody could ever realistically need IMO. Just too many gears! I hear Ford have a 10 speed auto now.

Luckily we will all be electric soon, so gearboxes as we know them will be a thing of the past!

 

[ronk]

The bullet points were that you have to use them to how they need to work and not expect them to work how you want them to (as they won't or can't). TBH the article put me off wanting a DCT (as I did before).

How are supposed to use them?

I tend to stick in D and let it sort itself out! If there’s a more sympathetic way then i will alter my method

 

[B21]

The BMW DCT is not ‘adaptive’ in the true sense but it tends to mirror your behaviour …so if you drive like an old woman in Drive it tends to get sloppier with its shift logic..if you put it in Sports mode (push the comfort / sports button) it will tend to hang onto gears but if you are still driving like an old woman it will tend to relax…als
o throttle response and steering feel changes in sports mode

Best option is to move the DCT lever across into manual select mode but not touch it..it then engages another shift program that spins the engine more and is sharper in its behaviour.

With xHP you can improve a lot the behaviour in all modes..

 

[ronk]

 

[Christopher72]

A lot of great detail here --- it would do well in the 'How To' section with your latest experience and steps.

 

[Pondy]

The BMW DCT is not ‘adaptive’ in the true sense but it tends to mirror your behaviour …so if you drive like an old woman in Drive it tends to get sloppier with its shift logic..if you put it in Sports mode (push the comfort / sports button) it will tend to hang onto gears but if you are still driving like an old woman it will tend to relax…als
o throttle response and steering feel changes in sports mode

Best option is to move the DCT lever across into manual select mode but not touch it..it then engages another shift program that spins the engine more and is sharper in its behaviour.

With xHP you can improve a lot the behaviour in all modes..

That's all very well and I have no reason to disagree (cos I don't know), but that is a 'software' or 'programming' thing.
I was talking about the fundamental way a twin clutch gearbox operates mechanically; IE with two 'rows' of gears, one odd and one even, with a clutch for each.
From what I read, they are fundamentally designed to pre-select the next higher gear when going faster, then only start to select those in reverse order when you are slowing.

So if you are in 4th gear and accelerating, the gearbox will have 5th ready. If you decide you want 3rd, it can't do it without having to think seriously about it, which takes a while.

All from what I understand without any actual experience of them of course!

 

[B21]

You are correct in what you say you are in 4th …you’re accelerating, it preselects 5th..if you move up it swaps to 5th in 60 ms..

You are in 4th, you’re accelerating, it’s preselected 5th, you lift your foot off and you coast ..it stays in 4th with 5th preselected…

You are in 4th , you’re accelerating , it’s preselected 5th, you lift your foot off and you touch the brakes, it preselects 3rd, then downshifts when speed range and driving mode are compatible…

Similar on a hill, it downshifts even with braking to accommodate predicted requirement….

Simples

 

[B21]

A lot of great detail here --- it would do well in the 'How To' section with your latest experience and steps.

Wilco

 

[ronk]

But amend the Headline before you do!
Ie the E899 bit