My '89 240 wagon has a standard shift, and I just replaced the manual transmission with a 110,000 mile used one. The car has 310,000 miles. Lately the rear end has started howling when I get to 2nd-3rd gear, and is not engine RPM related, it seems to be speed related. Sounds like a throaty medium-range howl, in the rear of the car. My mechanic thought it might be the differential bearings.
What do you think?

Differentials on 240s are extremely robust. In 30 years of driving and fixing them, I've never seen one go bad. Are you certain it is not the center support bearing on the driveshaft?

It was the main driveline medium support bearing. They spotted rust on the
edge and replaced it. A+

Hi Joning,

Your mechanic's determination that it may or may not be your differential bearings is certainly true. I hope that you didn't have to pay too much for that wisdom.

I'm not sure if I'm interpreting your post correctly. Are 'just' and 'lately' synonyms, and meant to mean that the howling and tranny swap occurred simultaneously ? It would help to know.

Bearing noise before complete failure may come and go depending on what harmonics are developing. It's not unusual for a noise to appear and then quiet down at a lower or higher speed, torque, or RPM.

If you've had someone with good ears to the floor in the wagon back when the sound is evident and you're fairly sure it is indeed in the rear end, I would then jack the rear wheels and disconnect the driveshaft from the differential.

This will allow you to spin the pinion bearing, looking for roughness or excessive pay It is often the first internal bearing to go because it's higher up and susceptible to a low oil condition.
Another check on the pinion is to crawl under the car after a drive and feel the casting around the bearing. It should not be too hot.

The only way to effectively insect the rear U joint is with the driveshaft disconnected, so I'd do that at the same time.

The outer axel bearings are also suspects, which begs the question - when was the last time they were serviced ? They don't last forever. Spin and pry the rear tires and maybe something will talk to you. If I had gotten that far without any evidence, I'd probably pull the rear tires and verify both the foot and hand brakes. They're also capable of singing a tune.

I'm assuming you or your mechanic has verified the oil levels. Don't be like me and assume an oily diff cover has a failing gasket. These covers develop rust on the inside that way weep for a long time, and then suddenly open up enough to drain the oil overnight. This may be followed by a long week-end on your back

Good luck,
Peter

I would eliminate the driveshaft bearing seeing it was messed with when the driveshaft was removed. Spray some pb blaster or wd40 on it by pulling back the rubber holder.If it solves the problem you found it. Cold weather effects the driveshaft bearing too.

Joining52.....maplebones wrote.

"
I'm not sure if I'm interpreting your post correctly. Are 'just' and 'lately' synonyms, and meant to mean that the howling and tranny swap occurred simultaneously ? It would help to know.

.......... and you're fairly sure it is indeed in the rear end""""
_______________________________________________________________________

The answer to the first question is KEY to further discussion.

My questions: when you had the tranny replaced did you also replace the 2 UJoints, the Center Support Bearing and the Rubber carrier, and the Flex Joint (Guibo) at the front of the driveshaft where it connects to the Tranny????

as you wrote: The car has 310,000 miles...when, if ever were any of these parts replaced?

Hi,

I hope you are sure it’s the rear of the car.
In being only in second or third does not make sense as the rear end or input drive shaft goes faster and faster in the upper gears of fourth and fifth. Why would it just go away?

A groan or howl is usually a bearing sound and front wheel bearings are usually easier to hear but most notably in the lower speeds range you are claiming.
Wind and road noise at higher speeds cover the sound up.

If this were higher speeds and you heard a high pitch shrilling sound it woul most likely be a main drive line support bearing. This sound really comes and goes until disaster hits.

I suggest rolling the windows down a drive in a tunnel or across a bridge with lots of side railings.
You can alternate the front windows closed or open in relation to the rear ones. Same for side to side.
This might help locate in one direction or the other or corner of the car.
You can save some fuel and jack up the car and rotate things to find something not quiet and smooth.

M47 transmissions are normally quiet except when two gears are used an awful lot more than others. If the transmission truly has only 110 k on it should not have a problem unless the wrong oil was run in it.
Getting lied too is not impossible.

I say this because I recently picked up a 1993 with 200k on it.
Second and fourth have a very slight whine to them that I did not hear right away. I had to tune my ears to it since it’s purchase.
Upon inspection about 750 miles later, I found what appears to be engine oil in it. Not ATF or anything like a gear oil smell in there! I’m now thinking how?
Who ever did the clutch for the woman, only few years back may have?
I hate to think they may have set her car up for some bigger hurt, for dollars, from an old car!
I’m glad I caught it early as the rest of the car was really taken well care of, apparently by her 10 year ago passed away husband.

I do not think it had been in there all it’s life or even near it. The sound and it’s shifting feel would be a lot worse. But second and fourth have worn in some way according to the drain plugs magnets.
The shift seems a little bit snug going in.

I usually use ATF and some 20% Lucas manual transmission friction modifier on my other M47 with 275 k so far. It makes the oil cling as it goes up on the gear train without getting thicker. I guess it gives it friction in chemical languages?

For this unknown on I’m trying the Volvo recommended pale yellow oil. I found its equivalent from Fuch’s oil company for about $10.50 a liter on line shipping included out of Colorado. About half what Volvo wants me to come get bent over for!
Others are around $22 plus and any other pluses depending on the gouger!
1.7 liters is not going to flatten the bank but I don’t like adding fuel to any run away fires!
I have left engine synthetic oils alone and now they are less than half what they were under private franchises.

So far the shifting is a tiny bit better but I’m not expecting any kind of cure from any type of oil change!
I do not believe it’s ever irreversible but time will tell me either way. I’ll check the upper magnet as I go for a while. You might want to do that too!
I have a spare, 130k, untested transmission on the shelf, so I’m not worried at this point.

Like it was said on here, you might have gotten a bad transmission, as these M47’s are not without their weaknesses given various owners and a mechanics wisdom, good or bad in our cases?

Phil

I think it's temperature related. Mine ('93 245) does the same thing, but only if it's very cold.

In both situations -- the rear end shouldn't howl or growl or whine regardless of ambient temperature. If it's doing that -- something needs attention. Could be bearings in the rear end; could be axle bearings; could be that the backlash has opened up over time -- lots of possibilities. A decent mechanic should be able to diagnose.

I do find it interesting that shortly after a gearbox was replaced, a new noise occurs....odds are something's amiss with the replacement tranny or something done related to the transmission swap.