5 speed to 7 speed swap (722.6 to 722.9) - Mercedes-Benz Forum

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post #1 of 6 (permalink) Old 01-29-2016, 03:06 PM Thread Starter
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5 speed to 7 speed swap (722.6 to 722.9)

I've got a 2005 G55 AMG, with a 722.6 5 speed box.

The 7g tronic boxes are now cheap, and I could even justify buying a 2003-2004 car with all the electrics to use as a donor.

My question being is this swap even feasible? I've read the TCU is built into the gearbox and would need resetting in order to marry it to another car, but beyond this would a swap work complete with shift points that actually worked?

The added complication is that the G class is 4wd but as I see it the gearbox just has a single output to the center diff so the gearbox doesn't actually do any 4wd work unlike, for example, an impreza.

Anyone clever out there want to step in and tell me yes/no before I buy a salvaged 722.9 car?
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post #2 of 6 (permalink) Old 01-29-2016, 06:29 PM
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If you have that much spare money then just move up to a G63.
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post #3 of 6 (permalink) Old 01-29-2016, 07:05 PM
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I don't know why anyone would even consider replacing the rock solid 722.6 with a 722.9 which is much less reliable.
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2005 S430 4Matic 'Morton' W220.183 • 722.671 Rest in Peace

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post #4 of 6 (permalink) Old 01-30-2016, 02:54 AM Thread Starter
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To move to a G63 would be $75k for me (I live in the UK). A 2003-4 donor costs $6k and still has salvage value without a gearbox.

For me the 5 speed is really archaic. It's changes are jerky, it's not great at deciding what gear to be in. It's just a terrible box from a feel point of view.

Had the 722.6 in a supercharged jag. All the same issues with it.

Sure it's solid but it's a terrible gearbox from a drivers perspective.

Back to the question I asked, will the 722.9 actually hook up to the electronics?

Anyone with a Star / Das got an opinion on this?

The G55 is basically a C electronically and the C had the 7g in that era - what's it need to marry up the modules and sort the inputs out from the CAN?
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post #5 of 6 (permalink) Old 01-30-2016, 08:26 AM
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Originally Posted by cmitch View Post
I don't know why anyone would even consider replacing the rock solid 722.6 with a 722.9 which is much less reliable.
Maybe for the same reasons they replace comfortable and safe 16-17" wheels with low profile - tooth grinding 20's
The subject of swapping parts of drive-train on digital cars come pretty often.
Everything is doable if time and money is no object.
I know blog of Polish guy actually converting 603 mechanical diesel into digitally-controlled, turbo engine with matching 5-speed electronic transmission.
Reading the blog, the fact that W124 had reluctor rings with different number of knobs to work with 5-speed was his biggest surprise.
Coming to adopting one digitally controlled piece of equipment to different car.
I like to watch "Fast and Loud" - the program about top-end car restoring and converting shop. In one episode - (tried to find episode on youtube, but found promotional clip below) , they put racing engine from one car into classic hot-rod.
In the process they remove about 50 lb of wire harness, as they did not have electric mirrors and sunroof on the clasic.
So those top-end professional mechanic could not make the car computer talking to the "motor".
They call hyper-duper car technician and few hr later no dice.
Than come super-hyper-duper team of racing technicians who after several hr of work make the connection.
So if it took 3 levels of the best technicians in the country to make US engine to talk to its converted computer- imagine what DIY can face.
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Last edited by Kajtek1; 01-30-2016 at 09:04 AM.
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post #6 of 6 (permalink) Old 01-30-2016, 11:51 AM Thread Starter
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Guys I appreciate that DIY is a potential mine field. A freind of mine just put a viper v10 into a 1959 Chevy Apache - it runs just like it did in the ram - complete swap of the dodge electronics.

We're not dealing with that here. We're dealing with gearbox which is supplied by the same company and works with other cars with the same basic electronics as the G55. The difference is the 7g has the TCU built in which needs to be bonded to that specific car.

If no one has ever plugged in and done the adaptation for a 7g then thats the data point I'm looking for.

I'm asking on the off chance someone here has some experience of doing adaptations on the 7G and may know what inputs the ECU needs from the canbus.

It might be plug and play once Marry'd to the electronics, or it might work with a custom loom, or it might not be work trying.
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