Life and times of the DCT gearbox fitted to the E89 35i/35is

[B21]

Copy of article on DCT box and updates and issues I've had..

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.


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.

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.