Sequentronic Gearbox - Drops out of gear - HELP??!!!

[RegBarton]

Hi all!
I've got a 2001 (Y) C200K Sport Coupe Evolution Panorama with the Sequentronic Manual Sequential Gearbox. Lovely car (Jasper Blue), EXCEPT:-
The gearbox keeps dropping drive in 6th gear.
The usual condition is:- you're happily driving along in 6th (manual or auto mode), take your foot off the accelerator to slow down a bit, but when you go to accelerate up again, it's as if the car is in neutral. The gear indicator stays showing 6th. You can engage 5th, drive picks up, and then carry on as before.
I've taken the car to a local Merc specialist who says it's logging an error code for "rear axle ratio incorrect". The rear wheels and tyres are the same size as each other, and the same as the front ones.
Merc suggest replacing the rear wheel speed sensors (around £200), but the specialist thinks that if these were the fault then the ABS/BAS lights would also come on. Alternatively, Merc suggest the gearbox control unit, but that sounds horribly expensive, and they don't seem confident that it will solve the problem.
Anyone any ideas, or can anyone recommend someone with specialist knowledge of this gearbox and its control units?
Thanks,
Reg

 

[television]

Hello Reg, I dont think anyone here can help with your repair,its too new and individual,you can have a read up on it here.

http://www.mercedestechstore.com/pdfs/286_722.9/286 HO 722.9 062504.pdf

http://www.mercedestechstore.com/pdfs/286_722.9/286 Mod 1.1 722.9 Trans D-A 050504.pdf


http://www.mercedestechstore.com/pdfs/286_722.9/286 Mod 1.2 FLASHING ETC 050504.pdf

http://www.mercedestechstore.com/pdfs/286_722.9/286 Poster cutaway.pdf

http://www.mercedestechstore.com/pdfs/286_722.9/286color hydraulic diagram.pdf


Malcolm

 

[Sprint'n'Go]

Malcolm, I think you are mistaken about this gearboxes identity. If I understand correctly it is not the latest 7G box, but the 6 speed automated manual type box as used in my sprinter with sprintshift. Designated 716.6 it does have a history of being problematic. I can't think of any obvious reason for it to drift out of gear but as an educated guess I would think it could be one of the hydraulic selector solenoids that is weak or losing pressure for some reason and allowing the gears to deselect without the computer noticing.
This is not a million miles from the reason my gearbox was replaced under warranty, it suddenly began violentley jumping out of first gear under acceleration but was fine in the other 5 forward gears. I had to creep away from standstill until I could select second gear then drive as normal until I next came to a standstill. This was put down to a faulty selector solenoid.
see item 120 here -

http://www.detali.ru/cat/oem_mb2.as...M=716.627&CT=GM&cat=69Q&SID=26&SGR=600&SGN=05

Just been on merc parts online site and this part is around £500, If I remember correctly from when my box was changed it was suggested the complete box was less than £1000 inluding the selectors and this comes set up from the factory.

 

[television]

Thank you Steve for pointing out the error of my ways I do miss things sometimes, and as for this box I know nothing about it.

so sorry for the miss posting. Malcolm

 

[Sprint'n'Go]

Thank you Steve for pointing out the error of my ways I do miss things sometimes, and as for this box I know nothing about it.

so sorry for the miss posting. Malcolm

Malcolm, you have forgotten far more than I know so I will let you off...... this time

 

[type49]

Not many of these sold at all. Very rare. Probably not many people around who know this set up with confidence, that includes MB dealers.

 

[psmart]

We own one but so far touch wood no problems. At 28K, I would hope for no problems though.

A slightly different issue on the Ducato I own, it has a known problem of the 5th Gear wearing very early due to the high loads it carries and jumps out of 5th gear. Being manual, as per the sequentronic, perhaps this could be an area? ie. faulty 6th gear?

 

[television]

We own one but so far touch wood no problems. At 28K, I would hope for no problems though.

A slightly different issue on the Ducato I own, it has a known problem of the 5th Gear wearing very early due to the high loads it carries and jumps out of 5th gear. Being manual, as per the sequentronic, perhaps this could be an area? ie. faulty 6th gear?

I will check on the wear issue,this was the fault with the 722.5 box where the 5th gear faces of the gears wore,pushing the gear out under light no load conditions.

Malcolm

 

[television]

I have had a look today,nothing for this fault,it would seem that the fault could be electronic rather than mechanical.

The fault will be coded,best to get them red out,other than that nothing else.

Malcolm

 

[stumpy]

One of our works Sprinters did a similar thing to me. The Auto mode dropped out leaving me with manual only. But only gears 1,2,3. Top speed of 40 revving the goolies off it. But turned it off, swore, and restarted - all fine again. Sounds like an electrical glitch to me.

 

[RegBarton]

Hi All - Thanks Steve H for your suggestion about the Hydraulic Selector Solenoid. I had an Alfa 147 Selespeed (Sequential Manual) previously, and the hydraulic selectors were prone to failure on these too (although fortunately, I avoided that problem!).
You say the part is £500 - are these fittable by any competent mechanic, or would it need Merc to change it?
Also - anyone any ideas how the fault can be correctly diagnosed, other than by Mercedes, who want to charge me £200 just to tell me what's wrong with it.....
Thanks!!

 

[RegBarton]

I have had a look today,nothing for this fault,it would seem that the fault could be electronic rather than mechanical.

The fault will be coded,best to get them red out,other than that nothing else.

Malcolm

Hi Malcolm - thanks for your thoughts and comments too!
The fault readout says "Incorrect Rear Axle ratio" - but no-one seems to be able to suggest what fault conditions would give rise to that message (other than someone having fitted an incorrect back axle - which seems most unlikely!). Other suggestions have been to check that the rear wheels were the same size as each other, and the same size as the fronts (which they are), and are equally worn (which they are). Other than that, a bit of a blank. Any other ideas?
Can anyone suggest a good independant specialist with experience of these boxes?

 

[panason1c]

Hi Malcolm - thanks for your thoughts and comments too!
The fault readout says "Incorrect Rear Axle ratio" - but no-one seems to be able to suggest what fault conditions would give rise to that message (other than someone having fitted an incorrect back axle - which seems most unlikely!). Other suggestions have been to check that the rear wheels were the same size as each other, and the same size as the fronts (which they are), and are equally worn (which they are). Other than that, a bit of a blank. Any other ideas?
Can anyone suggest a good independant specialist with experience of these boxes?

Did you check that the tyre pressures are equal?........un-equal tyre pressures would alter the rolling radious of the wheel(s) which the abs sensors would detect and throw up a fault/code

 

[Sprint'n'Go]

You say the part is £500 - are these fittable by any competent mechanic, or would it need Merc to change it?
Also - anyone any ideas how the fault can be correctly diagnosed, other than by Mercedes, who want to charge me £200 just to tell me what's wrong with it.....
Thanks!!

Unfortunately, with this system I don't think even mercedes know how it works (apart from the guys that designed it, maybe). Mine was jumping out of first but the computer didn't notice. I suspect this is what generates the incorrect axle ratio fault as the engine revs dont tally with what the wheels are supposed to be doing. Most gearbox specialists wont be able to help you as it is such a specific design and software package that you are stuck with Mercedes or an exceptionaly clued-up independant merc specialist.

The impression I got when mine was done was that a full gearbox was fitted to avoid the hassle of setting up the shifters as any savings would have quickly been negated if they had struggled to get it right.

 

[RegBarton]

Thanks guys.
Thanks Panason1c - yep, checked the tyre pressures too!
Thanks Sprint n'go - and you're probably right about it being too much of a pain to try and diagnose......
But your thought about the Hydraulic selectors got me thinking..... and I've now proved that it drops the gear FIRST, and THEN the warning message comes up on the dashboard a couple of seconds later. I thought it was dropping drive because it thought the back axle ratio was wrong - but now I think it's dropping drive first, thinks it's still in gear, can;t reconcile the speed of the gearbox to the speed of the back wheels, and pops up the fault code.
Anyway - car is going in tomorrow to have whatever fluid the box uses changed for a measured quantity, in case it's just lost fluid - which would cause the hydraulic selectors to drop out.
I'll let you know..... BUT if anyone can shed any light on what fluid it takes, or where the heck it goes - that would be helpful!!!

 

[Sprint'n'Go]

Thanks guys.
Thanks Panason1c - yep, checked the tyre pressures too!
Thanks Sprint n'go - and you're probably right about it being too much of a pain to try and diagnose......
But your thought about the Hydraulic selectors got me thinking..... and I've now proved that it drops the gear FIRST, and THEN the warning message comes up on the dashboard a couple of seconds later. I thought it was dropping drive because it thought the back axle ratio was wrong - but now I think it's dropping drive first, thinks it's still in gear, can;t reconcile the speed of the gearbox to the speed of the back wheels, and pops up the fault code.
Anyway - car is going in tomorrow to have whatever fluid the box uses changed for a measured quantity, in case it's just lost fluid - which would cause the hydraulic selectors to drop out.
I'll let you know..... BUT if anyone can shed any light on what fluid it takes, or where the heck it goes - that would be helpful!!!

As far as I know there are 2 oil systems. The main one is the traditional gearbox oil to lubricate the gears. In the vans, the same oil is used in the manual and the sprintshift boxes (the internals of the sprintshift unit is basicaly a manual box) and oil level shouldn't be critical unlike a traditional auto box. The other oil system is just used by the hydraulic selectors and clutch slave cylinder and includes a reservoir that appearsto sit under the gearbox see item 170 here - http://www.detali.ru/cat/oem_mb2.as...09730.413&CT=GM&cat=65Z&SID=26&SGR=600&SGN=05

God knows what oil this should be or how you get it into the system! possibly some sort of brake/clutch fluid? Only mercedes can tell you this.

Whatever you do make sure your mechanics are scrupulously clean when doing this top up. I had a new pressure pump fitted about 10k before my selectors packed up and I always suspected that some muck got in during the pump change which caused this fault.

 

[television]

Steve,sorry to put this here,any idea's
http://forums.mercedesclub.org.uk/showthread.php?t=25462

malcolm

 

[RegBarton]

Hi Sprint'ngo - thanks for another helpful response - really appreciated.
I've been talking to Mercedes. Initially, they told me that the box uses standard Auto Transmission Fluid..... then, when I pointed out that it wasn;t an auto box, they then asked me if I was going to drain the torque convertor out too.....!!! Who ARE they employing these days??
In the end, they advised that the only oil reservoir in the gearbox does the gears themselves and the hydraulic clutch action too. Everything else is electronic.
It takes a "Mercedes Gear Oil", there's no dipstick, it's simply a drain and refill. Takes about 1.2 litres apparently. Helpfully (not!) Mercedes supply it in 1 litre bottles..... at about £15 each. So - £30-quids worth is being delivered tomorrow and we'll see what difference (if any) it makes!
REg

 

[Sprint'n'Go]

Hi Sprint'ngo - thanks for another helpful response - really appreciated.
I've been talking to Mercedes. Initially, they told me that the box uses standard Auto Transmission Fluid..... then, when I pointed out that it wasn;t an auto box, they then asked me if I was going to drain the torque convertor out too.....!!! Who ARE they employing these days??
In the end, they advised that the only oil reservoir in the gearbox does the gears themselves and the hydraulic clutch action too. Everything else is electronic.
It takes a "Mercedes Gear Oil", there's no dipstick, it's simply a drain and refill. Takes about 1.2 litres apparently. Helpfully (not!) Mercedes supply it in 1 litre bottles..... at about £15 each. So - £30-quids worth is being delivered tomorrow and we'll see what difference (if any) it makes!
REg

This doesn't sound right, try talking to a commercial dealer and ask about the Sprintshift gearbox. there seems to have been more of these boxes fitted to vans than cars so you might get more sense out of them??????

 

[stumpy]

Rossetts are the guys who look after our vans and having over 500 sprinters with this 'box, they ought to know whats what.