I've posted several times here and other platforms about other issues without geting answers or snarky replies about how bad S550 is. Hopefully I can get a answer from someone who is knowlwgable and not guessing

OK, what do I mean by "scrubbing tire"? Consider an old 4 WD pickup truck with hubs locked making a slow, tight turn on dry payement making the tires scrub or drag. That is the best description I can make. It doesn't make clunk, bang, knock or any kind of noise. Rather, it is something that I can feel making the car shudder.

I purchased it from a Benz trained mechanic / shop owner, who did all the work with intent of it being his own personal car but family issues prompted him to sell. He gave me a stack of invoices for all the parts he installed. He even had the AMG wheels refinished due to some curb rash, I bouhgt it with 125,000 miles, owned for 2 yrs / 15,000 miles. It has always ran smooth on several road trips and everyday driviong. Scrubbing is relatively new in last month.

It does not do it driving straight, whether slow or fast
It is not a vibration driving anywhere from 0 mph or 80 MPH
Transmission shifts normal.
There is no clicking that would indicate a bad CV joint.
If I go around a wider turn, there is no shudder. Only turning in tight spaces, (parking lot, etc) where it is very noticeable.

Maintenance history form previous owner
The motor / transmission mounts were replaced 15,000 miles ago
The transmission was rebuilt 15,000 miles ago by a reputable Tranny shop in Chicago. There was a 2 yr warranty but only to the prev owner and even if it were covered, it is a 4 hr drive from me.,
A ton of other normal maint things were done

Harmonic balancer was replaced about 5,000 miles ago after the serpantine belt was shredded. I was told it was due to balance wobble

Curent shop suspected transfer case but now belives it is the front differential. He showed me a capful of diff oil and it had a tiny bit of "dust" (metal crumbs)

He is planning to drain and replace the dif oil next week and it has to be filled by taking off an axel because there is no way to fill it. Thise seems logical to me and other arm chair mechanics echoed this but stress the leak should be fizxed first #### BUT THERE IS NO LEAK. If the diff oil is low, did it evaporate?

Pulling the axel is a 4 hr labor job and I'd hate to pay for that and not correct the problem.

Your thoughts?

 

Hi Mr Jim,
From my limited knowledge, it sounds like your front differential has gone into full lock up mode.

There are basically two kinds of LSD (limited slip drive). Pure off-road is not LSD, but 100% lockup all the time when locked.

Mechanical LSD inside the differential pumpkin, which is added to an open differential starting design, will let the inside wheel of a turn go slower, different speed as compared to other wheel, by a mechanical slip mechanism like ratcheting the internals or clutch plates. Will have full lock up on both wheels for straight ahead driving. Same torque and burning rubber on both wheels, robust design for racing, but can affects drivability for average driver at highway speeds. Needs more fluid changes for clutch plates and mechanical component wear. Drivability example the car suspension can become unloaded on a bump in a turn at 70 mph and handle squirrelly when it comes back down on road and the average drivers are tricked on how to handle it, scary. (Me). 2002 Dodge Durango with AWD mechanical LSD front/rear.

Electronic controlled LSD is an open differential which uses the braking system to control the wheel that is slipping in a straight away throttle or lets the open differential design float the inner wheel at a different speed in a tight turn so the car doesn’t hop and scrub due to different speeds of tires. Cheaper to build as no LSD mechanical guts inside pumpkin. Mechanical vs Electronic = same functionality, sort of. Drivability is superior at highway speeds as the car is steering with an open differential. Serious use of electronic LSD down side is, as the harder it’s pushed, the braking system will overheat and be taken offline for LSD only. Now the car is back to having an open differential, which if relying on LSD, with LSD brakes offline, the open diff can cause a spill into a ditch. Less fluid changes as no metal or clutch plate particles.

Mechanical LSD, something failed in the assembly keeping it in full lock up mode.

Electronic controlled design, possibly the electronics is keeping the differential in full lock up mode all the time and in a tight turn it is a hoppin’ and scrubbin’.

We owned a 2008 Daimler/Chrysler Durango. It had AWD with the electronic LSD front/rear. The sales jargon explained the superior drivability at highway speeds compared to mechanical LSD, and from my experience they were right. The open diff electronic design was a lot more manageable at highway speeds, on that same turn, bump, at 70mph. (odds are German design)

From my experience, all differential have a fill hole/plug. They may not have a drain hole, must remove back pumpkin cover to drain, but they all have a fill hole/plug.

johnny

 

For the front differential you fill the fluid from the drain plug. Sure, the MB manual says to remove the passenger side cv axle and fill it that way, which you can. But, why do that when you can simply pump in the fluid, same way the transmission fluid is pumped in. The same fluid adapter for the transmission is used.

I have done it on my W204 without any issues.

- Remove differential drain plug.
- Drain all the fluid.
- Use inexpensive fluid pump with MB fluid adapter to fill new fluid.
- Remove Fluid adapter and quickly install drain plug with new crush washer.
- Torque drain plug.



* EDIT- I would go to another shop. I already do not trust them. but then again I do not really trust any shop. But for a shop to seriously try to claim the axle needs to be pulled because there is no other way to fill the front diff has me shaking my head. I don't buy it.

This is a job that anyone with very little experience can do. If you can go under the car and drain the oil then you can replace the differential fluid. Cost is very minimal. Fluid pump on amazon$10. Quart of 75w-85 gl5 gear oil $20. 8mm socket to remove undertray. I believe 6mm hex socket for drain plug. Torque wrench to reinstall drain plug. New crush washer 50 cents.

 

If the tires are rubbing while turning, you would see evidence of that on the fender liner/wheel arch. If that's the case, is the ride height proper? Leaky Airmatic causing low ride height?

 

lots of pics and lots of info

https://mbworld.org/forums/glk-class...ml#post8768779

 

It’s a good day to learn about a differential drain hole/plug only and no fill hole/plug. Maybe it’s due to the differential being shoe horned high up in the body, and there’s no access to a fill hole/plug if there was one?

Every diff I’ve worked on there’s a fill hole/plug, and the diff is filled until the fluid starts draining back out of the fill hole, indicating filled with correct amount.

I’d wonder about the last person to possibly under fill it causing the issue of hoppin’ in a tight turn.
Try to measure how much drains out and what kind of metal shavings are mixed in?

Johnny

 

Im thinking even if there were a fill plug on the side of the differential there is really no way to even access it easily with the subframe in the way. Would have to drop the subframe to get to it, and the cv axle has to be removed to drop the subframe so why not just delete the fill plug and Mercedes says to fill thru the cv axle? The W221 and the W204 are very similar to each other, they share the same cv axles. The W204 parts diagrams do not show the separate part numbers for the boots so I got them directly from the W221 diagrams instead.

In the repair manuals they have procedures for checking/refilling the rear differential fluid but I cannot find one for the front differential. The rear differential is wide open and easy to work on.

The only notes im finding that mention filling the front differential are in the procedures for axle or for the pinion gear below:






Heres a diagram/photo showing the differential with the subframe removed. I think that is the engine mount hanging above.




Now heres a diagram/photo showing removal of the passenger cv axle. The subframe is completely in the way of the diff.



If the goal is to just replace the front differential fluid i think draining then pumping in the new fluid is to best option. From searching around it looks like the fill capacity is 0.6l. The very odd thing is in my Operators manual it says the front differential capacity is 1.1l, which I think is totally wrong. When I drained my front differential I measured .7l of old fluid. I could not see any signs of leaks at all. So I measured out 0.7l and then pumped in a little more to compensate for anything that dripped out trying to screw the drain plug back on. The cheap fluid pump I used is pretty good, it sucks up all the fluid and will pump it all in, then will keep pumping in air. There is supposed to be some type of vent at the top of the differential so I wasnt worried about it.

When i did mine I used quick connects on the hose, disconnect it when done pumping to keep the fluid from draining back out. I have since bought a few inexpensive 1/4" barbed shutoffs which work great. Used one when I serviced the transmission.

 

Thanks for the advice. If I were still a DIY guy, I might have dived into this myself. What do I mean by "still a DIY?", I mean 20 or so years ago when I was 60 yrs old. Today, (if it was up on a lift; if I was feeling up to it and had all the time in the world), then maybe!

Getting back to the update. Muliple people advised that new diff oil was the first (and least expensive) step. Yesterday my shop drained and refilled the front Diff oil using a pump. The "shddder / tires scrubbing sensation is 80% better but on a tight, slow turn it's still somewaht noticeable. Maybe after the oil sloshes around in the diff over time, it will be 100% good, but my reservation is something is still wrong. I will drive and see what happens.

What would be the next step if the shudder sensation resumes or gets much worse?

Would a repeat diff oil drain and refill perhaps get rid of any junk (metal particles) floating around help?

Is it likely the diff needs to be rebuilt or replaced? Does it require pulling the engine / trans? Again, I'm not doing it myself but I'm inqusitive and would like to know what's involvled. On a similar subject it's highly unlikely I'd do my own caronary arteriy bypass, but I'd want to know the mechanics and can I save some money getting the "coronary parts" on Amazon?. HA

Happy NewYear to everyone.

 

One of the reasons I like coming on here is to try and figure out the issues other people are having in case I ever have to deal with it. Most things ive never dealt with or even heard of before. So i just search around.

Here is a link to 2008 S550 4matic repair manuals I look at: https://charm.li/Mercedes%20Benz/200...%28273.968%29/

It looks like in order to open up the differential it has to be removed. Have to drop the subframe to access the bolts to remove it from the side of the engine. Its only held on by 3 bolts, just cant get to them with the subframe in the way. Looks like Mercedes calls the front differential the Front Axle Gear.

Even if you could access the 3 bolts to remove them the differential still wont drop out since the subframe is in the way. Guess the engine could be pulled but that is probably much more work involved.

I had to search around online for removing the axle gear AR33.30-P-0525CWX








I dont have much experience with transmissions and differentials but im thinking the condition of the old fluid would give a good indication if something was wrong, metal in it. i recently replaced the fluid in my transmission and it looked good to me, i even took apart the filter to inspect it and while it was dirty i didnt see any obvious signs of metal.

If i knew I had an issue with my front differential I would probably look for a used one on ebay. Im finding them for around $300-$500. If anything have a shop open that one up and look for anything wrong. Then have it installed. Just because I wouldnt want my car tied up while they pull the diferential, work on it, then put it back in. I do this for alot of my repairs I do myself. If there is an issue with a gear how much will a replacement cost at that point, do they even make them? i dont know.