Rear end question

[psaboic]

Folks,

Been helping my brother in law with his W123 and it has an issue I have a few questions about. The car runs great, but when it is in 2nd gear, if you are accelerating hard, or climbing a hill, there is a thumping type vibration coming from the back end. If you back off the power it goes away. Almost feels like something is slipping, but the engine does not start revving and the car keeps accelerating normally. So far we have replaced the rear shocks, rear sway bar links and mounts, transmission mount, differential mount, both flex disks, and driveshaft center carrier bearing. The exhaust donuts and hangers look fine. The only thing I can possibly think of is the rear axles. The boots on them are fine and they are not torn or have grease leaking from them.

Any suggestions?

Glenn

[Do D Do]

Rear axle bearings? Brake calipers? Ebrake shoe? I took my wheel off and checked the hub, lots of play and grinding at a certain spot. Was the wheel bearing

[barry12345]

For the time and effort. Remove the clamps on the small end of the outer boots. Take a turkey baster or something with a small neck and shoot some heavy oil in. Just replace the clamps with screw clamps.

The rear cv joints where originally lubricated with heavy oil. Over the years some seems to escape. If the car had replacement axels at some point. Sometimes grease was used.

When I examined failed cv joints on front drive cars. Plus they were far newer than your car. Frequently I saw the carrier or the soap had been pushed out of the way and the evidence of lubrication really was no longer present.

In any event I have always felt it is bêtter to add a couple of ounces of heavy oil per joint. On any new acquisition of these cars. Than not. Call it preventative in nature.


A cv joint running dry can make noise under load. I am just suggesting this as a possibility. Yet not a certainty in your case. Also I would look at the center bearing rubber mount on the driveshaft.


Typically dry or under lubricated cv joints get noisier after or on a highway run. If lubrication is not present the parts heat up and expand. If you had that symptom I would almost be certain it is the issue.

[t walgamuth]

I concur that it sounds like CV joints.

[chasinthesun]

The rearend has a lot of play most likely , Ihave the same issue in my 300cd and living with it til I have time for a swap with a good without the slack .You can Check it by having the car on a lift or jack up the rear end and support the car very well .Simple turn the driveshaft by hand and you’ll see how much play it has in the gear as it mesh’s forward and reverse.

[Stretch]

Another vote for the axles

Don't forget they were originally filled with oil (for most if not all of the W123 production run they had the crimped can type ends as opposed to the annular versions that also exist out there)

If money is tight after replacing the rest of the vehicle you might want to try swapping the left side for the right etc to see if the immediate problem goes away. You might get a few extra miles out of what you've got whilst you save up for decent replacements. (Balls wear into the driven side - swap sides to get the wear on the place where it used to be reverse)

The easiest and most conclusive way of checking axles is to remove them from the car anyway and then check for play.

There are many reports of cheap axles not lasting long - so it seems best to buy a good brand if possible.

[psaboic]

Well, that pretty much settles it. Aside from checking the play in the rear end, I too concur that it is in the best interest to replace the axles. Looking at them, they look like the factory originals and with almost 300K on the car, they are probably well worn. Funny thing that was mentioned is that as it warms up, it will become noticeable, and that is exactly the case, it is fine for about the first 5 miles then as the parts warm up, it does its thing.

Thanks for all the advice folks!

Glenn

[jsp300D]

2nd on the axle. Who makes the original axles?

[Bengoshi2000]

I've always wondered if the factory axles on a w123 are rebuildable...

[tangofox007]

Originally Posted by Bengoshi2000

I've always wondered if the factory axles on a w123 are rebuildable...

They are. Here is a place that does them:

https://www.cvjreman.com/mercedes/

[Mxfrank]

CV's typically click while turning. If they lock up, it would be more obvious in a turn. Bearing noise increases as you turn away from the bad bearing. A rhythmic thump when driving straight ahead seems more like a differential pinion bearing. I've had one of these let go at speed, spun the car around like a top.

[t walgamuth]

...but the diffs are so rugged they rarely fail. The CVs though are a common failure point. I've had worn cvs make a little vibration when going over a dip in the road with a load in the car. Just a little change in the happy noises of the car.

[BATComm1966]

Not to steal the thread, but have a question... just acquired a 81 240D with the 300TD conversion, runs great 4spd car..also got a replacement diff from the owner which he states are more highway"friendly" gears.

I drove it home about 60 miles and agree a 5th gear or higher gearing in the rear would do it some good.

My question, what gear ratio is stock, he believes this set is 3.32 but I havent got any numbers off of them yet.

Looks to be a pretty straight forward swap.

[barry12345]

I suspect Mercedes got it really right with their rear cv joints. If you do not drive them too much under lubricated. It seems adequate to just add the oil. In general they may be the toughest part in the car. Rather than using an oil recirculation system but grease instead. I do not believe they could have both lasted the distance or time. For all practical purposes they rate of wear if kept heavy oil lubricated is virtually nothing.

As with many things in life some subjectivity has to be applied. They have to be running for a time in a semi lubricated condition until they are audiable in some fashion. This implication to me is some wear has occurred. How much will vary with circumstances. Yet if they settle down with new lubrication I consider it not is an indicator they need changed.

There is even a too much wear indicator may be present in this type of scenario. If the noise is there constantly all the time. To me running then too dry has been left too long. Taking time to warm them up before the noise occurs to me is an indicator there is not much existing clearance yet or they would not be capable of binding. After they warmed up a little. since your noise starts in about five minutes. I would suspect yours are still pretty unworn. Just do not put off getting some heavy oil injected.

With the thermal expansion of the friction heat. Noise from the first use of the car and constant in nature. I would change them. These joins if properly relubricated say every five years might go an indefinite amount of milage. Well beyond the rest of the car surviving is a strong possibility. Anyways I just add a little heavy oil before one of these cars goes into service. Anything is better than dealing with a road breakdown today otherwise.

I also have no ideal of where the oil migrates to over the years. Probably a tiny amount gets by a seal with time. Another thing or reason they should be on a maintenance list. The original axels with their high quality are really expensive. Plus any road breakdown can cost real money and time before you are mobile again.

Driving a thirty to forty year old vehicle is just a little more demanding to keep reliable. Actually with some effort and time this is achievable in my opinion on these cars. .If the accumulated milage is not really excessive. At reasonable cost and effort. Actually at far cheaper costs than one would expect.

Three hundred thousand is not too high for the rear cv joints. In my opinion. Tragically I never believe the odometers unless there are some indications they might be right are present though. Even then it is a tough call at least for me. Instinctivly that you want to believe what you see to me is human. Described as the wearing of rose colored glasses usually I have found pretty accurate.

[barry12345]

Originally Posted by BATComm1966

Not to steal the thread, but have a question... just acquired a 81 240D with the 300TD conversion, runs great 4spd car..also got a replacement diff from the owner which he states are more highway"friendly" gears.

I drove it home about 60 miles and agree a 5th gear or higher gearing in the rear would do it some good.

My question, what gear ratio is stock, he believes this set is 3.32 but I havent got any numbers off of them yet.

Looks to be a pretty straight forward swap.

The ratio is stamped on the rear of the casing. When changing the rear end you need the speedometer from the same car or from another that has the same rear end ratio. You probably have the original 3.69 ratio in the 240d now. The 3.32 ratio mentioned for some reason does not ring any bells for the five cylinder naturally aspired diesel engines. It still might be right though. Check for the ratio on the casing of the rear end you where given. .I found that even the original rear end ratio for the natural aspired five cylinder engines. Like in my 1977 300d seems not quite low enough. Yet I agree the 3.69 is really inadequate. Even for the four cylinder engine. I live close enough to sea level with no really serious hills. Needs can vary on location topography altitude and climate. Use as well. If you had a turbo engine I would jump to the 2.88 without a second thought.