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+--- Thread: How does an autobox fail when running too much power? (/showthread.php?tid=6991)
How does an autobox fail when running too much power? - m1tch - 01-15-2016
Hi all,
Still doing my project W210 E300 Turbodiesel estate project in stages, I am keeping the stock 722.6 box for a bit, will be running low boost on a big turbo soon plus water/meth injection before I swap out the pump at a later date. Will be looking to see the performance I can get out of the stockish setup without swapping out the pump for larger elements (8mm elements are planned).
Just wondering more about the Autobox though, this is the first and only autobox I have had in a car, just wondering what its like when it starts to fail with higher power levels. In a normal car with a manual box the clutch will slip, I know that the autobox does have various clutches but as there is no direct connection with the engine I don't know if the autobox 'slips'? I know you can get flaring, is this the equivalent as a slipping clutch in a normal gearbox? I will be getting the gearbox controller at some point to help with the line pressures (which should hold the clutch packs tighter etc).
If I feed too much power into the stock box is it just a case that the box simply flares with no additional power being put down rather than a large explosion of cogs and gears as it might be with a normal manual box?
Thanks in advance!
RE: How does an autobox fail when running too much power? - SurfRodder - 01-15-2016
Heat...as the power increases the tendency to slip increases and heats up your clutch packs and fluid...more slip and more heat...burnt clutch packs.
RE: How does an autobox fail when running too much power? - m1tch - 01-17-2016
(01-15-2016, 11:45 AM)SurfRodder Heat...as the power increases the tendency to slip increases and heats up your clutch packs and fluid...more slip and more heat...burnt clutch packs.
Ah, so if you run too much power into the gearbox all of the fluids heat up even more and then the clutch packs burn out? I guess that's the same with a slipping clutch! My car does have a transmission cooler so that should hopefully keep the temperatures down a bit, is there anything mechanical that could break within the gearbox or is it just a case of toasting the clutch packs?
RE: How does an autobox fail when running too much power? - charlysays - 02-22-2016
(01-17-2016, 08:03 AM)m1tch(01-15-2016, 11:45 AM)SurfRodder Heat...as the power increases the tendency to slip increases and heats up your clutch packs and fluid...more slip and more heat...burnt clutch packs.
Ah, so if you run too much power into the gearbox all of the fluids heat up even more and then the clutch packs burn out? I guess that's the same with a slipping clutch! My car does have a transmission cooler so that should hopefully keep the temperatures down a bit, is there anything mechanical that could break within the gearbox or is it just a case of toasting the clutch packs?
The clutches are not usually the weak point on the 722.6. There is a roller bearing in the K3 clutch which is somewhat prone to getting spat out and then destroying the planetry gears downstream. Also the planetry sets themselves have bronze bushings which are also a failure point.
That said, they are still a solid transmission and most failures will be due to the fact most of them do not get serviced anywhere near adequately.
Mercedes said they were sealed for life, which is not a very long life if they don't get fluid changes.
Your best bet is to drain the TC, transmission, drop the pan and see whats in there. A bit of sludge is normal but any significant bronze hues or chunks larger than a grain of sand indicate potential failure. I know this from running early 722.6s for the last 80,000 miles.
Change the fluid and filter every 30k miles for optimum transmission life. Use a fluid which atleast meets MB236.14.
While you're at it change the multi plug/ pilot bushing.
How to's on all this are to be found on MBclub UK or Mercedes owners forums stickies
If the transmission is healthy then it should be able to handle 250bhp for a good while. Pulling away is when the most stress is on the drivetrain.. once you're over 20mph the radial forces on the bearings decrease a lot.
RE: How does an autobox fail when running too much power? - erx - 02-22-2016
Automatic transmission slips like clutch with manual gearbox, mine slipped with 4th and 5th gear, engine rpm went up but speed stayed the same. 300td has weak box but with stock pump elements it should be fine, mine started to slip with hx35 and 7,5mm elements, it was fine with stock turbo and 2bar boost.
The newer the box the better, there are actually four generations of 722.6 boxes and from 2002-2003 they should be fine, bushes were replaced with bearings and some more improvements were made.