Replacing a rear flex disc - unexpected complexity

[Zarniwoop]

Do you ever get that sinking feeling when you realise a job is going to be a lot more complicated than you thought?

I've been getting a sort of thrumming vibration through the car at motorway speeds both when accelerating and at constant throttle (though not decelerating), and from what I've read here and elsewhere, a tired flex disc seems a likely culprit. I got under the car, and the rear one looked tired and the front looked pretty new, so decided I'd replace the rear.

All the guides that I found seemed to suggest that all you need to do is undo all 6 of bolts and then with a bit of levering and use of the appropriate swear words, the rubber donut should just come out.

Sadly not so simple - somewhat unexpectedly, I now see that there is a slim shaft still joining the propshaft to the diff. Wasn't expecting that!

Does this mean that I'm going to also have to remove the front donut and slide out the prop forwards in order to get the rear disengaged? Or is there a trick to this I don't know about? Looking at it, I'm going to have to remove the under tray and the exhaust to get the prop out if that's the case. And there was me hoping that this would be a quick job!

The car is a C209 2002 CLK 270CDi.

Would be very grateful if anyone can demystify this for me, even if it's just to confirm that I will indeed be spending tomorrow removing the exhaust and propshaft...

 

[Naraic]

It may only be short:

 

[Naraic]

I think it's a fail safe. If the donut lets go, the shaft in a shaft will prevent the full shaft falling to ground.

 

[Zarniwoop]

I think it's a fail safe. If the donut lets go, the shaft in a shaft will prevent the full shaft falling to ground.

Ah, of course, that makes sense. Good engineering, but a pain for me! I can lever the prop and diff apart an inch or so, and the shaft just seems to disappear into the diff - no idea how long it might be.

 

[mioba]

These are a service item at 15 years. If you need to remove both to get to the one thats a pain I would be inclined
to change them both even if one "looks" ok.

 

[Uncle Benz]

It isn’t long, but you need to drop the centre bearing in the middle of the prop. 2 bolts. You can then jack-knife the prop a little and it’ll come out

 

[M80]

While at this I would remove the prop and check UJ's and bearing/s, even if it's just for peace of mind.

It is said that the ends should be marked, with paint or at least chalk, so that they go back as removed. In truth I could never see good reason as a balanced shaft is a balanced shaft, but I do anyway.

 

[Zarniwoop]

OK, that all seems like really sound advice. So it is going to be more effort than expected but, as you say, it's a chance to check over some other things at the same time.

Thanks all for being so helpful!

 

[Zarniwoop]

Thought you might be interested to know that everyone was right!

I ended up removing the other donut and the centre bearing, plus the gearbox mount and the exhaust heat shields. Happily it was possible to slide out the prop without removing the exhaust.

With everything off the car I discovered that the front donut, despite looking pretty good in-situ, was probably the original, and certainly ripe for replacement. I also found that the rubber mount for the centre bearing was split, and the bearing a tiny bit noisy.

Unfortunately I have no option but to put most of this stuff right back, as there seems to be nowhere in Brizzle that actually stocks these bits, and I can't get either of my other cars out until the Merc is mobile again.

My plan is to stick the one new donut I have at the front, move the slightly better front one to the back for the time being, and then hope next time to be able to remove the rear of the propshaft without taking the gearbox mount off. Hopefully a second donut and a bearing and mount will be in the post to me early next week, though don't suppose I'll get it until after the long weekend.

What really stands out to me is how amazingly easy it was to get everything apart on this 20 year old 100k mile car. If any of you have spent much time working on old British or Japanese cars, you'll understand why I find this so joyous!

 

[Flyinspanner]

If the bearing has a part number on it, any decent bearing supplier will be able to supply a replacement.
or via a carefully measured ID, OD, and width.

 

[Zarniwoop]

If the bearing has a part number on it, any decent bearing supplier will be able to supply a replacement.
or via a carefully measured ID, OD, and width.

I'm sure you're right, but with the rubber mount also split it probably makes more sense just to replace the whole thing