Starting at about 30mph, there is a hissing noise from the rear of my '71 250C. It is load sensitive (i.e. present at accel. and decel, but temporarily gone between the two). Also, when I turn off the ignition in park and release the brake, the car will roll back about 6" on an incline. After I searched the archives here, I replaced the drive shaft carrier bearing and both flexible plates, but the sound is still there (the ride is much improved, however!). My next guess is the differential or CV joints. Just replaced the diff. oil, but how would I test it to see if it's the culprit? Could it be something as simple as rear wheel bearings?

[This message has been edited by wjbell (edited 02-07-2000).]

That sound is usually a diff noise, although I have never corrected it. I will be interested to see how some have.

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Benzmac:
1981 280GE SWB
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Is that to say that the noise is a "normal" part of age? If you were to correct it, what part of the differential would be suspect, or would it involve a complete rebuild?

I hate to call things normal, but I see so many with this problem. The diff will have to be rebuilt to correct the whine. The tolerances are too wide now and causing a whine.

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Benzmac:
1981 280GE SWB
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Of course, I've had that whine present in a couple of MB's I've owned and never noticed that it got any worse. Is there any kind of danger in that oh-so-common diff whine?

When you say rebuilt, do you include the gears, or mostly shims and "small" parts? I guess the only way to really tell the condition of the gears is after I open the cover. I read a response to a rebuild question in the archives and the recommendation was to only let a mechanic touch it. The question referred to a much newer model, and I understand that a differential is a differential, but is it conceivable to attempt this repair myself with a tech manual and the right tools? If so, since I would have to pull the diff., would it also be a great time to replace the CVs?

If the ring and pinion are worn smoothly all the way around, that is no chips,spalling or missing metal. What you are looking for here is a nice even wear pattern. If this is the case, then the differential will probably need new thrust washers, spacers and a new crush sleeve for the pinion gear. This is necessary to reestablish proper backlash and clearance between the ring and pinion. This type of work requires micro dial readout gauges and the all the hardware to set up the rear end for measuring and adjustment ie end play backlash ring gear runout, etc.... It is possible to improve excessive backlash due to actual wear between the gears by adjusting clearances and the like, however due to some of the inherent physical properties of hypoid gear sets, it is likely that you may never get the noise level back to new, but with a good man at the gauges, it should be a whole lot better than it was. This type of work is definitely not for the weekend warrior unless you are really patient and understand the geometry of the gears inside that case. BTW, you're right, a differential is a differential, some fancier than others, but they all share the same basic components and function, so if you know a really good mech who has experience with rear end work, let him take a look. I have a friend who sets up pro stock drag racing cars. This guy knows rear ends like the back of his hand and... he doesn't work for MB. Look around,but be careful, some people will try to sell you a new car in the process.