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Discussion Starter #1
Greetings all,

I've owned a '99 E320 4Matic (160k kms) for just under a year. In our frigid snow laden climate the AWD has been wonderful. Almost as much fun as my '93 Quattro and more precise than our Previa AWD. I won't mention the behemoth 7.3 Ford Extinction :crybaby2: which now sits waiting for a backwoodsman buyer.

With near 3 feet of snow on the ground (a record even for us here in Algonquin area) the car has seen more use than usual carting the kids around town. But unlike last year, I've noticed that only the rear wheels spin and I occasionally get stuck. Certainly not the grip-sure feel of last winter. I thought it may have been due to a change in tires. Testing in a large parking lot confirmed that only the rear wheels spin. I eventually got stuck and had to rock my way out.

Background:

a. CEL has been on for a month (p0141/161/136 -- both rear sensors or possibly cats going, has slight "rattle" at idle) with no performance issues. Two Bosch oxygen sensors have finally arrived today and will be replaced as soon as I can get the garage above -20C :eek:

b. weak heat in the cabin, thermostat is being replaced next week. I've taken apart the duovalve and it was in good shape.

c. I'm going to flush (dilute flush via return lines) the 722.x transmission as soon as I can find some reasonably priced 722.6 or 722.9 MB oil. The closest dealer (2 hours eastward) in Ottawa wants $26/litre CDN. I wonder if Dexron III Spec H would do?

Despite the "to-do" list the car runs fine with good gas economy and power. No issues with the transfer case in turns or wind-up but there may be sweating and low fluid. Will check this weekend. No transfer case service campaign on this for my VIN.

So my question is this -- is there an electronic control module for this TC or is it a viscous coupling activated plenary gear type like my Previa?

How does one go about diagnosing this 4Matic system?

Thanks in advance for your suggestions,

Tony
 

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Hi, Tony.

The biggest point I can try to make with you is that if you plan on using any ATF other than the OEM MB stuff, you're better off leaving it alone, better no service than the wrong service. Contact duvalmotorcars.com and see what they charge to ship to you up there. Do the same with autohausaz.com. You definitely want the real deal.

The easiest thing to do with diagnosis may be to invest $125 or so at the dealer or indie and let them plug in the star diagnostic system. That will dig in a lot deeper than can the casual mechanic or DIY-er and may end up saving you a lot of time, expense and headache as you're chasing after things.

If you have NEVER changed the fluid before, I would recommend a pan drop to clean it out and replace the filter. A flush will only do so much. Plus you may have the converter drain plug, then you just pop it out and get most of the fluid out without having to deal with the flush. Either way you need the dipstick, pm ohlord to see what he'll charge to ship up to you. Maybe he'll pack in some atf as well, avoid custom charges or something.

Last, before you start be sure to pop the electronic connector and see if it is wet. If so order the adapter and replace it while you are under there. You might just be low on fluid from that, who knows?

Take care and enjoy the ride,
Greg
 

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Those 4-Matics are so reliable that besides occasional issue with CV joint you will not find any reports on the forum.
To my knowledge there is no viscous coupling on the car. You have permanent differentials with no blockade. They advertise that like 55% of the power goes to rear wheels, but MB usually doesn't release info how the things are done on the cars. My understanding is it is all done electronically by applying brakes to spinning wheels.
Since you have several codes running, I would get them taken care of and than worrying about 4-Matic issue. It is not that you really know it is bad? Human perception is very deceiving.
 

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I think it's a 35%/65% split of the torque to the front/rear driveshafts through the transfer case. This is by using a planetary gear set rather than a standard differential, but it is open as are the front and rear differentials.
 

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With near 3 feet of snow on the ground (a record even for us here in Algonquin area) the car has seen more use than usual carting the kids around town. But unlike last year, I've noticed that only the rear wheels spin and I occasionally get stuck. Certainly not the grip-sure feel of last winter. I thought it may have been due to a change in tires. Testing in a large parking lot confirmed that only the rear wheels spin. I eventually got stuck and had to rock my way out.
Three feet of snow would swallow a Land Rover. Wheels will still spin because its not a fully locked differential.



The rear wheel was spinning here and it had nothing to do with a faulty AWD system.

I think you're probably ok. I'd fault the new tires more than anything.
 

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Discussion Starter #6
Thanks for the replies.

Greg -- I may have a local mechanic, the only one in this small community who goes weekly to keep up his training, who carries the better diagnostics. My little OBDII only pulls only the basics. The service dipstick is on the way as is purple MB 722.9 synthetic oil. You're right, I should pull the whole pan and do it that way but energy and optimism fade when you're creeping under a half frozen suspension.

Kajtek1 -- that was what I wondered. If the distribution is handled electronically is there a module somewhere that could have gone kaput! For example, backing up even on a small slope (compacted snow) such as our drive way only the rear wheels engage. I've tried this several times. The fronts do nothing. The ECT flashes in the dash but it makes no difference. I'll do the maintenance, oil and O2's, clear the CEL and see where things stand.

James -- that's the kind of picture Land Cruisers are made for. There was at least a dozen stories on a Cruiser board I once belonged to (when I had an old FJ60) that prided themselves on pulling out Rovers.

Good point though, but the 4Matic should and did handle compacted snow last winter without this kind of issue. The whole geometry and feel of the car has changed.

Would low fluid in the TC or front differential case this sort of thing? I don't think the tires would have bearing on this, would they?

I'll do some work and report back. Thanks for the advise.

Tony
 

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As Kajtek1 said, the 4M is a permanent system. Maybe you should jack up the car on all four corners and then drive the car to see if all four wheels spin. If they do, then the 4M mechanical system (transfer case, front and rear differentials, drive shafts) is good.

Do you have the exact same tires on all four wheels? Would switch off traction control make any difference?

The transfer case is prone to leak. Take a close look to see if it is a little wet. I and another member here (or on mbworld) did some hunting and were able to add fluid (automatic transmission fluid) to the transfer case. Search for my username and transfer case should get you to the thread.
 

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For example, backing up even on a small slope (compacted snow) such as our drive way only the rear wheels engage. I've tried this several times. The fronts do nothing.
In such situation the rear with more torque and less load suppose to spin unless the traction control will apply brakes on them. How long you had rear spinning?
Unfortunately there is no easy way to to troubleshoot 4-Matic.
How about parking front on ice and rear on asphalt and have somebody observing wheel spinning?
 

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Hi arcasta, I haven't had any experience with a 4-matic, but here is a possibility; since the awd system relies on a planetary gear set and brakes to apply power to the correct wheels, there may be a problem with the brakes. If it was a mechanical problem with the driveline, there probably would have been a traumatic experience leading to the lack of awd, and some serious noise at this point. If you have bad brake fluid and some air in the lines (which invariably happens over time), the effectiveness of the brakes is diminished. If you pump the brakes and they get slightly firmer with each pump, then it would indicate that you need to do a brake fluid flush. I'm guessing that the awd system only applies a certain amount of pressure to the brakes, or moves a cylinder a certain amount, assuming that it is enough to make the brakes work and distribute power accordingly. If that amount of pressure or travel isn't enough to make the rear wheels slow down, then no power goes to the front. Just a suggestion, but it is easy and cheap enough to try, and makes sense to me.
 

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winerocks just triggered a thought... About two years ago I found that both rear calipers on our E420 had frozen (corrosion) open. We were driving around with no rear brakes and we never noticed it except under hard braking.
If your ASR lights flash and no torque is being transfered to the front wheels, your rear brakes might not be working due to frozen calipers. (or air in the lines as someone else mentioned).
 

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Rear brake failure would also explain why your rear wheels are spinning with ASR/ESP engaged.
Try this test....get on some good slippery ice, turn traction control OFF. Apply the brakes and throttle at the same time to see if the rear brakes engage and control wheel spin properly. You may have to play a little bit to get a proper feel for everything. You should EASILY be able to control rear wheel spin with the brakes, If you can't, and you are on ice, your rear brakes are bad.
 

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Discussion Starter #12
Thanks for all the input. Two A/F sensors replaced. All codes clear after a Christmas shopping trip to Ottawa -- that's 4 hours round trip. The brakes were a little soft so I did a brake bleed. That helped with stopping power but 4matic is still not working.

Tested again on driveway slope (ice with about 1/2 inch of compacted snow atop -- very easy to spin wheels). I applied brakes to lock up the wheels and gave it gas. All brakes lock up fine. Past a threshold the rears will begin to spin but not the fronts. If I add some gusto to the pedal, again, only the rears spin. Even on level slippery ground only the rears spin. And yes, their is a front driveline and not just a 4Matic sticker. I checked :)

Managed to get 12 litres of synthetic ATF at the Benz dealer in Ottawa for $17.86 (that's after I asked and got a discount -- 10%, retail was $19.85/l). Will do the shortcut dilution flush today (its -20 C on the mountain here) and check the transfer case if it warms up.

I'm really stumped though -- low fluid in the TC would result in eventual lock not slip, wouldn't it? And older fluid in the transmission would not affect 4matic operation. Suspecting the rear brakes makes sense if their slowing via ABS sends power to the front differential. But they work fine. No trouble codes at this point.

I'll keep you posted. Thank you all for the help it is muy appreciado!

Tony
 

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One more time -there is no way your 4 WD is not working. If something fails in the system the car wouldn't move. What MIGHT be your problem is traction control.
The traction control takes about a second to react. A full second is long time with spinning wheels and on ML i had big wheels burred to the axle in gravel during that time.
So question is are your wheels spinning for longer than a second? You still didn't do the suggested test, did you?
 

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Discussion Starter #14
I can spin the rear wheels all day long. Will jack-up the car to test further. Have not been able to find asphalt to run your suggested front ice, rear asphalt test.
 

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Putting the car on a jack and putting it in drive is a bad idea... It's also not going to tell you much as all of the wheels will start spinning in weird directions because of the differentials and whatever part of the traction control still works will be confused as hell.

While you're spinning the rear tires is the big triangle dash light on? If so it means the traction control is detecting the wheel spin and trying unsuccessfully to do something about it. I'd check the rear brakes for seizure.

If you got no light then I'd check the wheel spin sensors. I'm not sure where they are or what they look like but someone here may.
 

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Discussion Starter #16 (Edited)
Some progress

James -- the ETS/ESP warning flashes when the wheels spin.

I tried another angle to the issue, literally. All this time I've been testing with the nose of the car facing the downward slope toward the house and backing up. Result: only the rear wheels spin if I push it and make it out only if I'm gentle on the throttle.

This time I put the rear of the wagon downward toward the house and the front facing up the incline. Result: I could see the front wheels spin sometimes (after some delay for ETS/ESP, as mentioned earlier in this post) and the car pulls forward.

That's an improvement since the brake bleed. But the 4Matic still seems skittish :)

Is this the way the system is designed?

Going backwards on a slippery incline there appears to be no power diverted to the front wheels. Is that one of those AWD black holes that the car was simply not designed to tackle? The 4Matic approach to AWD seems very different than Quattro and more akin to the Toyota AWD although our Previa doesn't use the ABS for spin/power distribution sensing.

Thanks for the help. I'll continue with the maintenance items (especially transmission/transfer case) and hope for ongoing improvement.

Tony
 

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This time I put the rear of the wagon downward toward the house and the front facing up the incline. Result: I could see the front wheels spin sometimes (after some delay for ETS/ESP, as mentioned earlier in this post) and the car pulls forward.

Toldya ;)
The MB traction control on 4-Matic is disappointment, but still big help comparing to 2 WD. On ML switching to low range helps quite a bit, no this option on wagon. I've been spinning wheels on our 2WD diesel whole day today just on morning moisture on clean asphalt. Still sounds like your system might be misaligned.
I am afraid only dealer would know how to test it better than the test above.
 

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get out of your driveway! find a huge empty parking lot with packed snow and start driving in circles. if the car is tracking in a circle with a moderate throttle, your front wheels are pulling. that is all it will take. if your car is sideways or spins out with the throttle on, your front wheels aren't pulling. trust me, if you've spent any time doing donuts in parking lots, you will know immediately if all 4 wheels are working!

you can even do it in reverse.
 

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Discussion Starter #19
meooem1 -- I did exactly that today in a nearby Church parking lot. A good test. I should do it more often -- after their services :)

Today the back end began to spin out even though the ETS tried to lock opposite front wheels. The car would straighten but nearly stop with all the ABS counters. And that's very different from last year when I did the same test after I got the car. It does not track nearly as well as before.

I'll try this again tomorrow with greater care.


Thanks again.
 

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might be time to get under that thing.

I would put it up on 4 jackstands and see if all the wheels spin. Since the diffs are open, the wheels should not spin in strange directions.

Loubapache and I were the ones who figured out the transfer case fluid situation, and we determined that the wagon is a bit harder to add fluid to, but not impossible.

The system is really quite simple, and there is no reason why it should really just break.

Have you been running different sized tires?
 
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