Excessive W123 Differential Wear - Pictures - PeachParts Mercedes-Benz Forum

Ken300D · #1 07-06-2003, 09:23 PM

Here are some pictures of the old differential I just took out of the 1982 300D at 328k miles. I believe it has had little in the way of maintenance. Most Americans don't consider the differential gear oil as something that is necessary to change. And it probably isn't for the limited lifetime of an American car.

The visible slot cut in the center gear holder (I don't know the technical name of this part) manifested itself as slop in the gear train. This was noticable as a "clunk" from the drive train in transitions between engine acceleration and deceleration. Further observable as about 45 - 60 degrees of driveshaft rotation (transmission in neutral) back and forth (when turned by hand) with the wheels not moving.

This picture is of the slot worn into the holder:

Ken300D · #2 07-06-2003, 09:27 PM

This picture is from a different angle that shows the burring of metal that is wearing away. It also shows how much material is left in the gear holder before catastrophic failure (although I think failure could have happened at any time with a gear this loose).

Ken300D · #3 07-06-2003, 09:32 PM

Here is the other side of the gear holder. The gear axle has dropped out of its support and is starting to wear down through the gear support in the direction shown by its movement.

The replacement was from a 1985 W123 that exibited no such wear at all. The driveline is nice and tight now with no slack, and the car is a pleasure to drive. Additionally, the 1985 W123 differential gear ratio was changed a bit to gear the car higher. Not all that noticable in driving - and I also went to 15" wheels and tires - resulting in an odometer error of approximately 10%.

Guess I'll have to state "True Miles Unknown" on the title?

Ken300D

Brian Carlton · #4 07-06-2003, 11:54 PM

Hey Ken:

That amount of wear is truly amazing. I cannot believe that this wear would be normal even with an axle with over 300k.
I wonder if the oil change interval never happened for quite a few years. Even so, I would have to believe that the unit was running considerably low on oil for many years to result in this level of wear. It would appear that the length of that slot is over 1.5 inches in length !!!!! Just amazing.

The metal looks like it was polished. Almost looks like aluminum. But I gather it would have to be steel.

Brian Carlton
1984 300 SD

BoostnBenz · #5 07-07-2003, 12:14 AM

Yea it sounds like there was quite excessive gear backlash there. Neither of my 300Ds appeared to have ever had the fluid changed. I drove the 84 a few thousand miles with mobil 1 in it, then changed it to redline 75w90. I think the mobil 1 cleaned it out nicely just from the color of the oil and previous posts about it.

Yea I believe the gears are all a breed of steel.

I've been thinking about getting the next size bigger sidewall for my rear tires, kind of like changing the car's gear ratio. Have you seen any (corrected) gains of fuel mileage?

md21722 · #6 07-07-2003, 03:05 AM

Yes - that's exactly the type of wear I've seen before where the rear wheels turn 4" before the driveshaft does! A shame people don't take better care of their cars.

Brian Carlton · #7 07-07-2003, 07:57 AM

Hey Jeff,

When I purchased the W126, I drove it up from Florida with the stock 195/70/14 tires. With the AC operating the entire trip, the vehicle would routinely get about 26 mpg. After getting it back to New York, I switched the tires from the W123. Now, it had 215/70/14 tires that I had purchased previously. The fuel economy remained unchanged, still about 26. BUT, the vehicle traveled 3% farther because of the larger tires. I could not tell any difference at the pump based upon the larger tires. If the fuel economy stayed the same, I would have expected a drop at the pump because the odometer had not been recalibrated.

Now, 3% is such a small amount that I could be within measuring error. I really do not have enough data to confirm the 3%. But, my sense is that the fuel economy is better with the larger tires.

Brian Carlton
1984 300 SD

bodyart27 · #8 07-07-2003, 09:35 AM

That is a lot of play!

JerryBro · #9 07-07-2003, 11:57 AM

Was the car used for towing? That wear is so excessive I can't imagine it happening without pulling stumps, or doing 4000 rpm slam it into gear burnouts for a couple of years!

Jerry

Ken300D · #10 07-07-2003, 12:30 PM

A likely contributing factor was that the previous owner had the vacuum line come loose from the transmission modulator. Thus he was getting the hard shifts that he may have felt were "normal" for an old Mercedes. The shifting was hard enough to chirp the tires from 1 - 2. So that is fairly hard on the whole drive train.

Then, when you do end up with just a little bit of slack, the constant banging back and forth from "power on" to "power off" situations accelerates the wear.

Even under these circumstances, I'd have to think the gear oil wasn't changed to get this kind of wear. It did not seem to be low of gear oil.

Needless to say I have the transmission shifting properly now and will change gear oil regulary - I think Mercedes specifies a 15,000 change interval. The replacement differential should never go bad for the remaining life of the car.

It will be one thing I can part out from the skeleton!

Ken300D

BoostnBenz · #11 07-08-2003, 12:29 AM

Quote:

Originally posted by JerryBro
... or doing 4000 rpm slam it into gear burnouts for a couple of years!

Now who would really do this?

Ok maybe I didn't run it upto 4k, but I last year when shifting hard I did more than my fair share of burnouts.

Only times I've trully tried to do a burnout I couldn't tell if it was tire smoke or diesel smoke.

Yea that is an insane amount of play, my talon states that only 5cm is alowable.

I suppose 3% is a nice upgrade, but probably not worth going out of the way to get it. Maybe when my Goodyears wear out I'll try getting them in a larger size, we'll see then.

Thanks.

Fisherman · #12 07-08-2003, 09:03 AM

Boy that really makes you think about living with a little flare in the shifts rather than tightening the shifting to get rid of the 2-3 flare...
I may have to go back and do some more adjusting.

Thanks for sharing.

BoostnBenz · #13 07-08-2003, 03:21 PM

Just out of curiousity, would anyone know what the spec is for excessive backlash or whatever they call it. (set parking brake, turn driveshaft full CCW, mark it, full CW, mark it)

Quote:

Lube oil of any sort (new, old synthetic or dino) would never prevent that hogged out metal shown in the pictures! I would think the bearings would have failed if lube quality was poor.

Yes and no, I believe some of the redline products (shockproof line) are designed to lighten the impact on the teeth in instances like that. The setback is mainly that the heavy shockproof gets so thick when cold out. I believe it is the viscosity of a 80w90, internal friction of a synthetic 75w90, protection of a 300w oil!

#14 08-12-2003, 04:41 PM

When I am using the brake, I get a huge CLUNK in the back of the car during the 4-3 downshift. At firse I thought it was just from the bad accumulators, but then I realized it was to hard to be that. Could this be a symptom of the kind of wear in the first picture?

When i first bought the car and changed all the fluids the dif. fluid was a very dark blue with what looked like speckles of glitter when I jooked at it in the light. How much do these cost for an 85+ like you used and how difficult are they to install?

BoostnBenz · #15 08-12-2003, 04:51 PM

Quote:

Originally posted by BoostnBenz
set parking brake, turn driveshaft full CCW, mark it, full CW, mark it

Measure the difference and you'll see how much play is in your rear end. The most common clunk in a downshift is when not enough vacuum (11ish) is going to the tranny while downshifting. I had a leaky control (for EGR) valve doing that to the 83, I just changed the valve, no more clunk. But typically this is heard most in the lowest gears.

I think all of us had that suprise first time we opened it up. I had to take the rear plate off at the sametime, and it was coated in fine metal. I used a can or two of carb cleaner and got it back to clean aluminum like it should be. Anyway that is probably 'normal' at least for those who've went a while without changing it.

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