OK, so: a bit of a tune-up on the 300TE has awoken the 4matic, just in time to earn it's keep during London's only snowy week this year.
The behaviour of the 4matic is clearly not right: when sitting at idle, in drive with the brake on, a medium-frequency vibration goes through the whole car. Go into neutral and it stops; move the 4matic cutout in the engine bay, and it stops. The vibration is harsher in reverse than in drive.
I think this is the 4matic unit slipping; it has less friction than the brakes or the torque converter, so when sitting still with the driveshafts held by the brake, the gearbox is rotating the driveshaft to the transfer case, against the grip of the clutch inside the 4matic.
Now, the $5000 question is: is the 4matic clutch pushed closed by pressure of the hydraulic oil in the system, and could this symptom therefore be fixed by changing the hydraulic oil? I haven't seen any instructions on lifetime of the oil in the system and therefore I suspect mine has been around since 1988. If so, I'm gonna drain it and refill it. If on the other hand the 4Matic is "normally closed", and oil pressure in the hydraulics opens the clutch, then it has to be the friction surface that's dead, and I'm just looking at a recon transfer case ($$$$$$!).
I have some hope that it's about the oil, because the behaviour gets worse as the car warms up, which I wouldn't associate with a friction surface problem.
Or have I misunderstood the way 4matic works?
__________________
Steve
London, right in the middle
98 E55
99 E300 TD
97 SLK
1996 Subaru Legacy Twin-Turbo Estate
i"m not sure about the vibration, however i just changed the gearbox filter and transmission fluid on my 4matic and the difference is amazing!the changes up and down are now almost un-noticeable, i am sure no one has changed them before, so you could not do any harm by changing the oil and it has to be the first thing to eleminate as it will be the cheapest, good luck and let us know if it cures it.
Hmm; interesting point. I had the gearbox rebuilt when I got the car last year, and as you say, the change was a revelation - I think this is something a bit different.
Once it's not about minus ten degrees outside, I'm going to have a brave poke around the hydraulic systems...
i have a warning light in the middle of the speedo, a triangle with ! in it, it is comeing on at 75mph, and goes of when i drop back to 74mph, have you any idea what this may be caused by, i have changed one of the drive shafts and the other looks to be in good order.
thanks for that, can i ask if you know why it is only coming at 75mph, i would have thought that if a sensor was damaged it would be on all the time.as it is as soon as i drop back to 74 it goes off.
not sure about this car but its common function for abs wheel sensors to operate at certain driving speeds, for example my volvo the wheel sensor unit consists of a sensor for 0-10mph, and 40mph, when one goes bad you get the light, so good chance one of your wheel sensors has gone bad.
The automatic locking differtial is activated at a front-to-rear axle speed difference of 2km/h. The yellow function indicator lamp in the speedometer comes on.
The system will not be engaged at speeds over 35km/h.
Shutoff is at a vechicle speed above 38km/h at the latest. The function indicator lights up also at higher speeds, if a drive wheel starts spining (Warning against slippery road service). But the automatic locking differential will not engage.
Mine also comes on at around over 70mph and then goes off again when speed is reduced. So does that mean the 4 wheel drive will only work upto 35km/h and then disengage. Any idea's???
Linear Mode
