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Has anyone had any dealings with or any knowledge of the Merc 722.6 5 speed auto box thats fitted to jeep grand cherokees and pretty much every merc from about 98 to 06?
got a slight issue with the one in the jeep. and being a porridge box virgin i dont really know what to be looking at
Main problem is two fold - and one of them being kinda important.
1 - when cold it feels very slow to engage drive and when setting off it just kinda draaaags. maybe 30 seconds later and its fine.
2 - when it fully up to temp and working hard - eg dragging the caravan down the motorway or high speed motorway driving - when you get off the motorway and start doing normal stop start driving, you frequently get the engine management light pop up and it will go into limp mode and stick in 1st or 2nd gear. You cruise to a stop and and the MIL light goes out and pop it out of drive and back in and everything is fine for a bit, then it will do it again. Other times the MIL light comes on and goes away with no other symptoms. Once or twice during very high speed runs (only 70mph, honestly), the MIL light will go on the revs will jump from 2500rpm to 2750, light will go out and it goes back down to 2500....Only seems to do this after doing 'hard work' as well.
These boxes dont display error codes on the dash either - when you get the codes from the obd11 it just gives a generic "the gearbox has told me it had a problem" number 0702 and thats it. To get the proper codes you need to plug it in to a merc or jeep bit of kit and get raped a million quid for the privilege of reading the gearbox ecu directly.
Before i go for the dealership trouser down route - does anyone have any idea what might be causing this?
In my own mind I'm thinking oil level wrong, giving bad cold gearbox response and possibly overheating after working hard? Also true to form there is no dipstick on these merc boxes, just a cover saying dealership only so i have had to buy an aftermarket dipstick for it. Should be here next week.
they also only accept atf4+, would the wrong oil cause these problems?
cheers for any help,
Another bloody dent...
The wrong oil will certainly cause problems. A lot of modern autos don't have dipsticks as they are way too confusing for "joe public" to use leading to over and under filling so having a dip stick is just asking for trouble. None of the current Land Rover autos have dipsticks either as far as I know. The theory is that you would only attempt to put oil in it if you know the correct way to fill the box and measure the level. It's also a bloody good way of getting warm ATF all down your arm if you get it wrong !
Gut feeling suggests you're probably right about it getting over hot when you're pushing it hard and you'd certainly expect it to throw some sort of warning. Might be worth checking the gearbox oil cooler isn't disintegrating (or full of mud if Sara has been taking it off road !)
On the 1st point, do you mean it seems to hold a low gear for longer than you'd expect when it's cold ? Are the shifts crisp when it does change ? If the answers yes to both of those then that's probably normal behaviour, nearly all electronic boxes do it.
I'd have thought you'd be able to find an independent that can interrogate the box ECU, the one I use at Thirsk seems to have a unit that can speak "natively" to most vehicles including all GM models as far as I know. Might be worth asking around your local area at any medium size car servicing/repair places. You could try Station Autos at Thirsk if you're out that way on your travels.
1st line of attack is usually to change oil and filter as if it's been cooked it could be sludging up a bit when cold and then breaking down when hot , have you sniffed the dipstick hole ? If it smells burnt then that could be the cause but then you have to ask why it's burnt, usually caused by A and or B clutch pack wearing out. i.e loads o dosh .
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