It is my fear and sudden dread that it's time to replace the diff...
Thought I bounce this for mental health reasons here...

All of a sudden my '93 245 auto with a 3.73 diff started plaguing me with increased vibration and bass type noise coming from the rear.

A bit of history: I repacked the rear bearings 2 years ago and replaced diff fluid. Everything was fine since then. Curious though that then I felt that the half-shafts never turned smooth. Think that's normal???

Fast forward to now: Lifted the rear off the ground and checked out that it does not matter which wheel is spinning. Noise and vibration is more pronounced and gets loudest 20-40 mph. I have yet to pull the wheel and brake hardware off. Took a look at the diff fluid and no sign of metal, but did not take off the diff cover.

Basically sounds like I am driving on grooved side pavement from start and then have a helicopter flying right over me wherever I go faster with increased noise and more frequent vibration.

I looked at axle and the U-joints seem ok. there is a bit of play at the
support bearing.

Bearing or diff or perhaps axle?

Anyone want to help with diagnosis near Willimantic, CT?

Hi all,
I have a similar problem happening with my 91 240. It has been sitting for about 6 mos with bi-weekly strolls up to running temp etc... just to keep everything moving. About a month ago, and then today, I noticed a similar horrible vibration and bass sound when i get up to around 40 and then take my foot of the gas and let it "coast". Sounds like rumble strips. It sounds like a similar issue that This Old Brick is having... Anyway, I'm pretty familiar with the 240's having worked on them for years, but never had to really mess with the drivetrain. Is there a good starting point to begin diagnosis? Is the 700/900 faq applicable to this in terms of maintenance etc...
I suppose I need to put it up and check for play in the u-joints, strain on the center carrier bearing and the transmission mount, as well as check the diff fluid level... anything else to add?
Thanks in advance!
-Son of Bonzo...

Yeah, definitely pull the shaft and see just like I did.
Relatively easy job and cheap parts if you got a press, or a hammer and a bit of time.

Good Luck,
Yan

Bonzo,

Will let you know what else I find on my brick.

Yan

Hi,

I think you have already done the first step in diagnosing or noticing that you are having a drivetrain issue. A straight down the road rumble sounds like a bearing somewhere.
U-joints have the tiniest diameters and seldom get lubed. Next is the center support bearing that never gets lubed but is out there in all that wind, water and muck! Same a u-joints which in it self remarkable to do so well!
Lastly the outer ends of the axle that are not lubed from the pumpkin oil. They are enclosed out of weather and are given a lifetime lube, for what ever lifetime means.

The tiniest u-joint bearing does not spin or make noise, per say, as it only rocks back and forth until rust crushes the needles out. Vibration or drive line imbalance is the number one felt symptom due to dry joint tightness and then the severe looseness.

More times than not you will notice a thunk when rolling from forward to reverse. That can be a bad u-joint or torque rod bushing on the ends of the axle to the body.

If you drive slightly sideways into a driveway approach from a street dip and you hear a pop, that is a collapsed trailing arm bushing or possible panhard rod bushing.

A clank that sounds very metallic could be excessive backlash in the ring and pinion in the pumpkin hub area.
It takes a lot of wear or miles to get to that point. If the rear end ever got flooded in high water or suffered very low differential lube level you could be there. You want to save that thought or it’s finding to the last thing on a list.

Yes getting under there with hands, ears and some weight or strength you have to roll the shaft and shake.
You want it to be smooth in rotation without tightness spots. Listen for any tiny crunching clicks from the u joints. Everything needs to turn smooth and solid while side loading every which way you can.
The center support bearing has to be spun by lowering the driveline and using the hands to feel.
Feel for drag and it being glitchy and dryness. Look for an outer rusty powdered staining in the middle where the seals are located.
The rubber mount needs to be firm and supportive, not split or rotting.

If you cannot find anything then maybe a rear end issue is somewhere. They do not last forever

I do not advise anyone to only drive a car every couple weeks and expect any good battery life without a floating voltage maintenance charger on it for longer than a week.

Do not park the car over a thick grassy lawn or over coarse rock covered open area as moisture will rise up from the soil under the car and condensate on driveline parts and other underpinnings.
Tires will rot faster if they are in direct contact with the dirt. Put them on wood or use some square stepping pavers.
A whole slab of those laid down can serve “like” a concrete driveway barrier surface in a pinch. Some people put plastic and sand under them.
The tires do cold form the tread belts. This will begin to roll with many flat spots and cause a rumbling. As little as 1/8 “ acrossa 5 inch square area is a big fat thump. Imagine four slightly flat tires at once.

It’s Something to consider that’s getting progressive the worse the more times you move the car and warm up the tires and then let the car sit! Check your air pressures. Car stands can help keep them more round.
A car sitting is like us an aging humans in being that it just sits there it gets stiffer! There is No good that can come from it!
The interiors become brittle, wrinkly and start to fade away. Left alone in the sun and not used is a car that is like us, fading or rotting away!
Car patios or a garage is better or at least very helpful. If the car is seen getting dirty, it might get a bath or dusting. Father Time spares nothing.

1991 is still a young 240!

Hope this helps with your diagnosis.

Phil

Hi,

I think on the 1993 the automatic came with tailshaft roller bearings so you should not be getting wop play from there to cause a vibration. Take a good look at the rubber support mount for the transmission.
Getting some wop from a plain bearing bushing on the earlier years was a sign of that going bad and of course a seal giving some leakage.

If the driveline is whipping, I would think first you have a dry universal joint or cross spider unit on one end of a drive shaft or the other.
Most of the time differential end spider goes out first.
In most cases, the hub or pumpkin of the differential, is not in-line with the transmission or even the center of some cars exactly. The rest of the time it’s going up and down too!

A Tight cross joint bearing cap can cause the shafts to rotate stiffly and create those out of balance symptoms. Like trying to twist a coil spring from each end it wants to whip.

You got take down the shaft and feel the joints through their range of motion. It’s like the wrist on your forearm.
You might consider giving the center support bearing a look and feel of rotation too.
They later can get noisy if dried out. Just did a reply posting on that.

If you are still up in the air, with your wheels (:-), look for the shaft to possibly jump or bump up and down slightly when turning the tires. It may turn out you will have to rotate the driveline and also rock it radially.
Expect some small about of backlash but smooth rolling if it’s really good. Anything less try to pull down and push it all around from each joint and turn.
The rear end pinnion input shaft has to be solid in all directions, plus, fore and aft!

Just because these things are out of sight a whole lot you should not them be out of mind.
That’s why they put a swinging weight on tiny motors in our phones.
It gets our attention!

Phil

Phil,

You were right, my 93 does not have a driveshaft flex joint. That beast was on my no more 83 GLT manual. Cry cry cry.

Here is the diagnosis:

Tranny mount was sagging and ripped. Already replaced with shelf part.
Front u-joint is good. No play and no sticking.
Middle u-joint is barely flexing one way, good the other.
Rear u-joint is not flexing one way at all, good the other.
Center support bearing is iffy. Center support is old as expected but not rotted. Both will be replaced with shelf parts.

I have 1 NOS GMB Made in Japan (WOW) joint on the shelf.
2 more joints on order from rockauto. They will most likely be Made in China. :(

Much obliged for the help and mental support.

Till we break again,
Yan

Phil,

Thanks for the write-up.

I have only gotten to work on my 93 240 with 180K (baby miles) today.
Looking over so far only pulled the right half shaft mainly because I felt a bit of in/out play that I did not observe of the left. Grease and seals look good, bearing looks same as when I lubed it 2 years ago.

I opened the pumpkin fill plug and felt gear fluid just to be kinky. Nothing strange here. I'll pull the cover later after checking all joints, center support bearing and tranny mount.

Visually the drive joints do not seem bad. no play or much rust visible. What I did see is that there is some driveshaft weights are rusty and may be missing 50% of one piece. Imbalance?

One other thing I noticed in the preceding weeks is that so familiar smell of plastic burning up on the exhaust. Thought I picked up a flying shopping bag again, but did not see any remains every time I smelled and looked. I am suspecting center support bearing now come to think of it.

Taking off shaft to better see center bearing and all rubbers now. Another fun and sunny day outside under a Swedish umbrella.

Yan

What condition are the trailing arm bushings in? When they are bad odd noises can occur that you would not think are bushing related.
--
Bruce S. near D.C.

Bruce,

I upgraded to the poly torque bushings 3 years ago. Will check the trailing arms, but the noise is there even with the rear lifted off the ground (no load).

Yan