Please see the link posted about the drive shaft interchange.
1988 740 GLE automatic

The car is on stands & with the gear selector in Neutral I can turn the shaft while holding on to one of the wheels with the other hand.
I'm not sure if it takes a certain amount of torque to "catch" so to speak.
It does still drive but with very little pulling power and some noise (this noise appeared one morning and i thought it was the center support bearing finally going out after two weeks of squealing)
Turns out the squealing bearings were the least of my problems. After placing a good drive shaft with good center bearings and all, the noise and lack of pulling power are still there.

Is there a True test that tells me the rear end is completely shot?

I want to make sure before i pull the rear end from my '90 745 turbo & place it in my good ol' 740 GLE.

Any comments appreciated.
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"Many people fail in life, not for lack of ability or brains or even courage but simply because they have never organized their energies around a goal." Elbert Hubbard

Pull the rear discs off. I suspect the parking shoes have come apart. Because you can't see them they usually get ignored. This should be included in a yearly, bi-yearly in salt country inspection/maintenance. Make sure the parking brake cable rubber boots are in good shape & the backing plates haven't rusted away.

OK, Here's the Update.

After pulling the differential cover off and taking a look inside I found the oil inside to be in pretty good shape; no metal shavings or metal dust. I also found that in between the Crownwheel and Pinion Bearing there is a bent metal ring.

(looks like it was once part of the Pinion Bearing. Maybe the end of the bearing that holds the Ball bearings in place OR the Shims. It looks similar to coat hanger metal and follows the circumference of the Pinion bearing, that is...from what i can see while looking through the Crownwheel teeth)

The piece in question isn't broken apart, just bent in a few places.
Anyway, I'm one step closer to driving my own car again.

Thanks for all the comments & suggestions.

Now I could either trade rear ends with the '90 745 or just fix the bearing. Tough choice.
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"Many people fail in life, not for lack of ability or brains or even courage but simply because they have never organized their energies around a goal." Elbert Hubbard

Nothing you have said indicates a rear end problem. If there is a lack of power that is more likely a problem up front. Rear ends get noisy but do not cause "lack of pulling power".
Can you be more specific about pulling power?
Does it shift through the gears OK?
Are shift point rpm's higher than normal?
Are you applying more pedal (ie more torque) to get moving?

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David Hunter

Thanks for the input, I do appreciate any & all comments on this.
It's hard to explain but i'll try.

The closest way i could describe it is I feel like the parking brake is lightly applied.
Or that I'm driving up a slight incline.
(This could just be me trying not to break it any further but it feels like it has less power)

It sounds & feels like a gear tooth has bent or something like that.
I do know that when it happened, it started with a loud "clunk" as if a wooden mallet hit the rear end and the back wheels slightly locked up for maybe a 1/4 revolution after that.
With the back of the car on stands i can put it in drive and let the wheels turn and it sounds as if a dented metal sleeve has been placed over the axle causing a grating/knocking sound once per revolution. It isn't real loud, it's not a constant grating/knocking.
I'm 100% sure the sounds are coming from the differential.
Before it happened the car ran great( it actually chirped the tires in 2nd gear on occasion)with a strong transmission.
I'll take a closer look when i get home as I'm at work right now.
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"Many people fail in life, not for lack of ability or brains or even courage but simply because they have never organized their energies around a goal." Elbert Hubbard

With the car on stands, set the parking brake and see if you can still turn the driveshaft (assuming the park brake works on both wheels). Being able to turn the drive shaft with one wheel locked tells you almost nothing since that is normal.

Charley

I just tried what you suggested Charley and thanks for commenting.

The drive shaft won't spin freely with the parking brake applied.
With the car still able to drive down the road (although with little pulling power) it seems i might have a rear end that's partially defective.
I started and put the selector in drive while it was up on stands to let the wheels spin and the noise seems to be coming from the rear end.
I was the unfortunate victim of having two things going bad at once.
When i heard the "clunk" and the car slowed to a stop the other morning; I assumed it was the center support bearing finally calling it quits.
When the problem was really the rear end.
I'm 100% sure the shaft and center support bearing is in great condition. I've also made sure that it wasn't binding brakes.
Is it possible to have a bad rear end and still be able to drive down the road or would it only go out completely and give me nothing in drive?

I just want to be sure there's nothing else i could try to fix before i go through a complete replacement of the rear end.
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"Many people fail in life, not for lack of ability or brains or even courage but simply because they have never organized their energies around a goal." Elbert Hubbard

Doug,

Yes, it entirely possible to drive a car with a bad rear end. In fact, they can be driven that way for years if you can put up with the noise.

When you say, "The drive shaft won't spin freely with the parking brake applied" do you mean that you cant spin it at all by hand (other than to rock it back and forth a bit to take up the gear lash)? If the parking brakes are on, you should not be able to turn it.

Have you verified that the rear end is full of gear oil? Significantly reduced power seems like an odd symptom for a failing rear end unless it is actually seizing up.

At the very least, before swapping rear ends, I would pull the cover off of the rear axel (drain it first) and see what it looks like in there, and see if the gear oil looks like metallic paint from metal shavings.

Charley

That is correct, with the parking brake applied I cant spin it at all by hand (other than to rock it back and forth a bit to take up the gear lash.
I'll try what you suggested and take an in-depth look at it.

Thanks.
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"Many people fail in life, not for lack of ability or brains or even courage but simply because they have never organized their energies around a goal." Elbert Hubbard