Diff swap question-help
 

Hello. I've got a 300TD wagon that has a whinning diff. I believe the diff is specific to the wagon and the 85 year with a 2.88 ratio or thereabouts.
Can I swap another diff like the 85 sedan diff with a 3.?? ration in it's place? and Will it be a direct fit? My 85 sedan has the 3.?? ratio with the same engine as the 85 wagon, so I'm wondering why I need the 2.88 diff.(the whinning one). I don't want to have it come apart on me on a trip somewhere and have another diff from a gas car (1982) same ratio as the sedan (3.??) Pardon my ?? for the ratio. I think it's really a 3.4something.

Any help would be greatly appreciated.
Mike

The sedan is a 288 also.

Tom W

whirring doesnt allways mean its bad... unless your just swapping it because its annoying.

Yes the '85 sedan does have a 2.88 ratio differential.
But if you do happen to install a 3.07 ratio differential, your speedometer will not be accurate.

Any diff from a W115 or W123 will bolt in without modification unless you have ABS.

If you change it to anything but a 2.88 your speedometer/odometer will not be accurate.

The ratios used in the W123 cars are 3.92 3.69 3.58 3.54 3.46 3.07 2.88 depending on year and model of the car.

Mercedes Benz dealer parts guy told me the ratios were different. I'm glad I've asked you folks. Next question is that I have a donor car. 1982 Gas 123 sedan with a twin cam automatic trans. No id on trunk, but sticker on cross member say 2746cc. Anyone know what final drive that diff might be? I guess I could drain it and remove the cover and count the teeth. I'm wondering if I'll screw up the milage with this diff. Free is good, but not if I get crap milage. Any help would be appreciated.
Mike

if the gasser diff is from a 280e it will be a 354, iirc. if it is a 380se (did they make them that year?), it iwll be a 247 if us spec.

both of these are drastically different from what your car came with. I would recommend against both of them. ONe is too low the other too high, imho. If I had to choose between them I would go with the 247 and sacrifice acceleration for gas mileage.

Tom W

Is there a link to a "chart" with diff specs and models and years of cars? I'll want to search out a donor diff that is close to or the same ratio as what I've got. BTW, I'm running mostly waste oil with an occasional splash of fossil diesel. When the cold weather comes, I'll switch back to full fossil.
mike

The only models that used a 2.8x ratio are the 1985 300D/CD/TD/SD.

gear ratio
 

I have a 1985CD do you know what is my ratio?

...

What does it mean? Mine whirs in my 82 SD, and my indie told me it was an indication that it was on the way out. Why would one whir and another not?

It means that the gears have no lube, or are worn from lack of lube at some point in time.

A diff that is quiet in a sedan may reveal all sorts of noises in a wagon.

Also, If it has the proper fluid a 'whiner' may still out last other parts of the car.

Unless it's just really annoying to you, I'd say change the fluid and continue to drive the whiner.

Hmmm... I just sunk $150 into a used diff... but now do I want to sink another $300 into having someone else replace it (I don't have time/skill to do this job myself), or just live with the whiner? Will it become very obvious when it is really on its last legs, or would it just go someday without warning?

My gears aren't dry now, and I have driven for about 5-6k miles without any noticeable increase in the amplitude of the whine, unless I am just getting used to it as it slowly gets louder.