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1985 300d Euro
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179 Posts
Discussion Starter #1
OK so I finally got around to doing the flex discs after just replacing both rear calipers and pads. I have the bolts off, the 2 screws for the center bearing off, and the sleeve that took a 46mm wrench.

The &#$&^ drive shaft will not come down and I cannot get the shaft to move enough to go far enough to clear the pin on the differential. WTF am I missing? I am getting quite pissed and that gallon of gas is looking better and better. I even removed the emergency brake cables to see if I could pull it down...nope!

I have read and read and every damn tutorial says how easy it is...BULLSH*T!
 

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1985 300d Euro
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179 Posts
Discussion Starter #2
Oh I forgot to say that I have removed the front flex disk after much pain and cussing. The back still wont move far enough to clear. I have no idea why...I spent at least an hour just looking at it to try and figure it out.
 

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1979 & 1985 300D's
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2,537 Posts
Did you remove the two bolts that hold the center rubber bearing carrier to the body of the car? If not you're fighting that.

*Edit* I see now that you did after re-reading.

Hmm. Hard to say without being there. I didn't even loosen the big driveshaft nut when I did mine. The driveshaft moved back easily once I unbolted the center bushing like you did.

Hopefully someone else has dealt with this before. Sorry I can't be more help.
 

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'93 300CE, '84 300D, '75 450SL, '82 240D-sold,
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298 Posts
I changed the flex discs in a 1980 240D about 7 or 8 years ago and I had no issues until I attempted to fit up the aft shaft to the flex disc/rear end flange. Seems there was a centering land on one of the faces that needed to be inserted to a recess on the other face and I couldn't get the clearance I needed to do it.

I placed a bottle jack and a piece of 2X6 under the oil pan and gently lifted the engine, keeping careful to not damage the mounts. I managed to raise it just enough to get some clearance between those aft faces.

This is one of the jobs still on my to-do list for both current 123s.
 

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1983 300D
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1,248 Posts
Oh I forgot to say that I have removed the front flex disk after much pain and cussing. The back still wont move far enough to clear. I have no idea why...I spent at least an hour just looking at it to try and figure it out.
Sorry for not following this properly. But you say you totally removed the front flex disk and you still don't have clearance? That's odd. Your driveshaft currently should be free to move forward about an inch without the front flex disk and the center bearing support unmounted.

On the rear flex disk, did you pry the drive shaft yoke end to separate them?

Just trying to get a clear picture. Speaking of picture, perhaps you should take some and post them so we can see what is going on.
 

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1981 W123 300D non turbo, 1992 190E 1.8 <=> 2.0
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6,561 Posts
It sounds like the flex discs (front and back) are free from the yokes, the centre bearing is loose and the propshaft still won't come out. Is that correct?

Have you removed the transmission mount and let the engine and transmission sag? (If so don't do that!)
 

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1985 300d Euro
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179 Posts
Discussion Starter #7
I have the trans mount removed and the trans jacked up on a 2x4 for support. The rear flex disc is loose but cant clear that pin. I read that the driveshaft is supposed to telescope but mine is not. After removing the front I still lack about 1/2 to 1" to clear it looks like.

The center bearing is loose as I am replacing that as well as the boot for the 46mm nut. It is loose too but still nothing.
 

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1981 W123 300D non turbo, 1992 190E 1.8 <=> 2.0
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6,561 Posts
Well the propshaft should be collapsible. You should be able to shove it in and out. Just by the 46mm nut there's a rubber cover - pull that back and spray in some penetrating oil.

In the middle of the propshaft there is a universal joint - can you not hang on that bit and get it to bend so the ends come off?

Are the flex discs removed from the yokes of the propshaft and the yokes of the differential and the transmission? If not you might get a bit of wiggle space there.

Worse comes to the worse you could undo the two engine mounts at the front of the engine and drag that (with an engine crane) slightly forwards to give you more space for the propshaft. I think moving the engine is probably better than tackling the subframe / differential. If you have to have to go for the engine moving (which is a pain in the arse) make sure you don't slam cooling fans into radiators / yank hoses and cables out of place.
 

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'85 Mercedes 300 D Turbo Diesel
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284 Posts
Well the propshaft should be collapsible. You should be able to shove it in and out. Just by the 46mm nut there's a rubber cover - pull that back and spray in some penetrating oil.

In the middle of the propshaft there is a universal joint - can you not hang on that bit and get it to bend so the ends come off?

Are the flex discs removed from the yokes of the propshaft and the yokes of the differential and the transmission? If not you might get a bit of wiggle space there.

Worse comes to the worse you could undo the two engine mounts at the front of the engine and drag that (with an engine crane) slightly forwards to give you more space for the propshaft. I think moving the engine is probably better than tackling the subframe / differential. If you have to have to go for the engine moving (which is a pain in the arse) make sure you don't slam cooling fans into radiators / yank hoses and cables out of place.
You don't think dropping the differential would be easier??, I have changed both rear axles and dropping the dif was easy...I had a nightmare changing a motormount...
 

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1981 W123 300D non turbo, 1992 190E 1.8 <=> 2.0
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6,561 Posts
You don't think dropping the differential would be easier??, I have changed both rear axles and dropping the dif was easy...I had a nightmare changing a motormount...
The problem with the differential on the W123 is that the bolts that go into the subframe are a bugger to reach. I'd go for the motor mounts 'cos the subframe mounts are often worse!

Choose your poison my good sir!
 

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1985 300d Euro
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179 Posts
Discussion Starter #11
Well after doing the pen oil I finally got it off. Now the other issue is that centering bushing on the rear. I am trying like mad to get that out and it does not budge. Maybe some pen oil?
 

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1985 300d Euro
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179 Posts
Discussion Starter #12
I took this pic from another member but it shows the area I am looking to remove as the rubber is all cracked and I can see the little spring in the rubber because a piece is missing.
 

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1985 300d Euro
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179 Posts
Discussion Starter #13
OK I found in the FSM that is says to bang it out...So I hit a lot harder and sprayed it and it finally came out...rusty as can be...the new one went in no problem. I have to order another spline boot now though and then it will be ready to go back in. The other one looks fine.
 

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1985 300d Euro
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179 Posts
Discussion Starter #14
Now I have to wait for the driveshaft center boot to come in. no one near me had one and they had to order. I still can't believe how hard it was to get the DS out. From the looks of it no one has touched this car underneath for 30 years.

In addition to the boot I went ahead and ordered the LCA Bushings, UCA bushings, Tie rods, Blisten shocks, and the Plate spring compressor. Wife flipped out when she saw the bill, but hey it will be worth it if I get 5 years or better from it.
 

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83 W123 CDT.
I had a reinstall problem.
Car wheels hanging and couldn't get the shaft up the last half inch to mate differential.
Fortunate to have another person with pry bar and a hard hit by hand popped it in.
Try jacking the differential up to change the angle and that may give the clearance.
 

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1985 300d Euro
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179 Posts
Discussion Starter #16
83 W123 CDT.
I had a reinstall problem.
Car wheels hanging and couldn't get the shaft up the last half inch to mate differential.
Fortunate to have another person with pry bar and a hard hit by hand popped it in.
Try jacking the differential up to change the angle and that may give the clearance.
Oh man I hate to hear that! I hope it goes in smooth as I removed all the nasty stuff and greased everything back up the way it is supposed to be.

Did you replace the boot? I am looking and I though I saw something about greasing the spline and putting some in the new boot but not sure...I cannot find it again.
 

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1984 300D
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5,037 Posts
I did not read all of the Answers so this could be a repeat. Did you loosen the large Collar Nut near the U-joint so that the Drive Shaft could be collasped foward.

Also mark the Positon of the 2 sections before you pull it apart.
 

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1985 300d Euro
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179 Posts
Discussion Starter #18
I did not read all of the Answers so this could be a repeat. Did you loosen the large Collar Nut near the U-joint so that the Drive Shaft could be collasped foward.

Also mark the Positon of the 2 sections before you pull it apart.
Yes..I have to replace the boot on it now. I am trying to find out if I need to put grease in it or leave it dry. I don't see anything saying such.
 

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1984 300D
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Yes..I have to replace the boot on it now. I am trying to find out if I need to put grease in it or leave it dry. I don't see anything saying such.
Grease goes in the end of the Centering Bearings about 1/4-3/8 inch inside and the Splines inside of the Coupling and shaft should have some Grease to prevent Rust of wear if the Coupling Nut comes loose.

To center the Drive Shaft before fully tightening the Coupling Nut you are supposed to have the Car on the Ground and put it in neutral and push the Car back and forth and then tighten the Coupling Nut. Get a skinny Friend to do that as I barely made it under there to do that with the Car on the Ground.

There is a Torque for the Coupling Nut but as near as I can tell no one does that. That Nut does not need to be really tight but you don't want the 2 sections of the Drive shaft to move as it will wear the Splines.
 

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1985 300d Euro
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179 Posts
Discussion Starter #20
Grease goes in the end of the Centering Bearings about 1/4-3/8 inch inside and the Splines inside of the Coupling and shaft should have some Grease to prevent Rust of wear if the Coupling Nut comes loose.
Good to know!

To center the Drive Shaft before fully tightening the Coupling Nut you are supposed to have the Car on the Ground and put it in neutral and push the Car back and forth and then tighten the Coupling Nut. Get a skinny Friend to do that as I barely made it under there to do that with the Car on the Ground.
HA! I don't have any skinny friends that could fit under my car. Is there another way of doing it?
 
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