Driveline Flex Disc

[Marchor]

The rubber/fabric connection (forgive my ignorance of terminology) between the rear of the transmission and the driveshaft is shredded. I've jacked up the engine/trans so I could remove the trans mount, etc, removed all the bolts holding the rubber/fabric piece to driveshaft and transmission, do I have to remove the driveshaft from the rear end and loosen/remove the center carrier bearing of the driveshaft in order to get the driveshaft to slide back far enough to remove and replace the rubber/fabric piece? Or is there some slick trick that will allow me to get enough room to remove the rubber/fabric coupling without removing the entire driveshaft(s)?

Thanks in advance.

Bob

1967 230SE

[ja17]

Hello Bob,

There is a telescoping section built in the drive shaft. You will see one large lock nut on the drive shaft just in front of the carrier. I think the two sizes are 46mm and 42mm.  Some large adjustable wrenches can work if you do not have the special tools.  Once the nut is loosened, the drive shaft will move back about 1 1/2".  After moving the drive shaft back you can pop the aluminum centering flange off the end of the drive shaft, this will allow  the drive shaft out of the way so your damaged flex disc can be replaced. Check for damaged bolts, damaged holes in the drive shaft flange, damaged holes in the transmission flange, damage to the aluminum centering flange, and check to make sure the rear slotted nut in the transmission flange is tight and locked in place (important).  New locking nuts are also a good idea. Make sure the two different bolt lengths and the washers are in the correct location. (check the tech manual under "drive shaft flex disc"

[Marchor]

Thank you, thank you, thank you! With your obvious knowledge I'm sure you know exactly how much trouble you have saved me; not to mention the rest of the directions which will save me even more time in the future!

[Benz Dr.]

Good info but the 230SL has the early style drive shaft. I believe the back portion has a spline on it so you can simply loosen the two screws on the center bearing hanger and the shaft will slide back in the spline section.

The jam nut that Joe refers to is found on 280's and maybe 250's but I don't think it's on 230's.

[Raymond]

Bob,
Be sure to search the site for flex disc replacement.  There is excellent advice.  One of the tricks mentioned is that after installing the new disc, hand tighten the bolts and put the car back down on its wheels.  Then roll teh car backwards a few feet and forward again.  This apparently helps center the disc.  Then torque the bolts to the specification.  I had a shop replace my flex disc, they did not do that and it shreded after about 200 miles.  I found that tip somewhere on this site and I replaced the disc myself with that procedure and had no further problems.

[thelews]

Good info but the 230SL has the early style drive shaft. I believe the back portion has a spline on it so you can simply loosen the two screws on the center bearing hanger and the shaft will slide back in the spline section.

The jam nut that Joe refers to is found on 280's and maybe 250's but I don't think it's on 230's.

If this is true, then it is very similar/same as the 190 SL.  Another tip is to remove the grease fitting at the rear near the spline, then when you slide the driveshaft back air and grease can escape and not create back pressure.

[Benz Dr.]

John,
that would be a fair conclusion. The drive shaft on a 190 would be similar to a 230.

I've replaced many flex discs on all manor of MB cars and never did I roll the car around on its wheels before tightening the bolts that hold the drive shaft to the flex disc. If it flew apart in less than 200 miles someone did something terribly wrong. The flex disc is very strong - I can't even imagine what was done wrong that would cause a complete failure in so short a distance.

[ja17]

Hello,

The original traditional MB flex disc. is directional and must be oriented correctly during installation or it will not last. These days a new heavier duty flex disc is supplied, similar to the heavy duty ones used on the MB 6.3 sedans.  Anyway, the new heavy duty style is not oriented in a certain position during installation. It can be installed in any direction.  Thus new version looks like it will last the life of the car.

[Benz Dr.]

Good point. That would be a good reason why it flew apart. I know how to install them so I guess I never thought of that.

[thelews]

On the traditional one, the tabs point toward the transmission.

Here's a discussion with pictures and WorkShop manual excerpts in the 190 SL forum.

http://forums.190slgroup.com/showthread.php?4652-Flex-disc&highlight=flex+disc

[ja17]

 Thanks John,

Those are some nice pictures to illustrate the differences.

It should still be understood that there are two different lengths of bolts (three long and three short) which have to be installed in the correct place. In addition the washers always are positioned against the rubber disc. With the short bolts the washers are between  the head of the bolt and the rubber disc and no washer between the transmission flange and  the nut. With the long bolts, the washers are between the nut and the rubber disc and no washer is between  the bolt head and drive shaft flange.

There is lots of good information and assembly diagrams on this site which will illustrate the washer positions. The long and short bolts have different shaped bolt heads. The reason for the three longer bolts is that they travel through the centering flange and drive shaft flange along with the flex disc. whereas the short bolts only travel through the trans flange and flex disc.

The big  thick rubber o ring slips on the driveshaft end to seal off the centering bushing and the thin o ring seals off the centering bushing where it fits in the drive shaft.  The purpose of these rubber o rings is to discourage grease fromm from squeezing out onto the new rubber flex disc during drive shaft lubrication service. Grease can degrade the rubber flex disc.

[Marchor]

The driveshaft definitely has 2 nuts forward of the center carrier bearing, 42mm and 46mm. Unfortunately I cannot seem to loosen them no matter which direction I try to turn. Looking from the engine towards the rear of the car, with the 42mm nut forward, and the 46mm nut to the rear, which direction do I loosen them? Counterclockwise or clockwise? Are they the equivalent of 2 nuts jammed together to lock, thus do I need to each of them with a wrench in order to loosen them? Which way would I turn the smaller, most forward-placed nut? I don't want to do damage by forcing too hard, but I can't seem to get them to budge no matter what I do or how hard I try.

Frustrating...

[114015]

Good info but the 230SL has the early style drive shaft. I believe the back portion has a spline on it so you can simply loosen the two screws on the center bearing hanger and the shaft will slide back in the spline section.

Most 230ies had the early drive shaft (propeller shaft) with the spline, up to serial 018330. That's the one Dan is referring to.
From 018331 they had the later one with the lock nut Joe describes, Schlüsselweite (span width) 41 if I remember that correctly.

 
Achim
('64 230 with early drive shaft, '71 230 with late drive shaft)

[Benz Dr.]

MB made running changes all the way through production so you can't always say always.

The bigger wrench size is the nut. It threads on to the drive shaft with a very fine thread so it will take a lot of torque. Standing under the car, the wrench that goes on the nut would need to move towards the passenger side of the car ( I think ). If the nut won't move use some heat on it. Heat will loosten just about anything.

I never think about how something comes apart. It just does, or doesn't, depending on the day. I find it easier to do something than to describe how to do something. That can take more thought writing tech details. 

[Marchor]

In the morning I will focus on loosening the larger 46mm nut with the shoulder. Heat, tapping with a hammer, and eventually varying amounts of discretionary brute force will be applied. And if all of those "techniques" fail, I will dismantle the driveshaft entirely.

I must explain my hesitancy to really whack away at this thing --  it isn't my car. The car actually belongs to a widow who lives next door, I volunteer to work on it for her at no cost.

I have several projects of my own -- 1959 Austin-Healy, 1950 RHD MGTD, etc -- but I stop and help her out whenever I can because: 1. The nearest dealer is 175 miles away and they won't touch it; 2. No one in town knows anything about it; 3. She can't afford to pay to have it worked on; 4. I once owned and rebuilt the engine and transmission in my 1969 280SE so I know a Little about Mercedes; 5. She lets me drive it whenever I want.

Out of curiosity, what function does the smaller nut perform?

[ja17]

Hello,

The smaller nut is part of the front drive shaft half and is just there so you can hold it with another wrench. The dealer has a couple of special "drive shaft" wrenches for just this purpose.

[Marchor]

Flex disc replaced, drove it around the block, all is well with the world.

No matter what I did I could not get the large nut loose to telescope the driveshaft so I ended up removing the 4 rear u-joint nuts/bolts, removing the 2 carrier bearing mounting bolts and sliding the entire driveshaft to the rear to insert the new flex disc.

Reassembled everything in revers order, drove it around the block and all is well with the world. Now on to the exhaust system which literally crumbled in several places and has holes in several more.

Thanks to everyone for helping with the learning process, one more thing I now know how to repair on a 113...

[glenn]

Think the flex disc was fun???   Wait til you try to separate the exhaust at the manifold outlets -- @*&?**!$%^&  super fun

[Benz Dr.]

No matter what I did I could not get the large nut loose to telescope the driveshaft so I ended up removing the 4 rear u-joint nuts/bolts, removing the 2 carrier bearing mounting bolts and sliding the entire driveshaft to the rear to insert the new flex disc.

By heat, I mean really hot, as in red hot; but only once. On a nut, I sometimes heat just one spot depending on the size of the nut. This should be enough to break it free. If it won't turn, I will reheat it but I let it cool off completely before I try again.

A lot of this depends where I'm working and how much paint I could remove or set on fire. As the area cools I hit it with penetratant because the heat will make it soak in quicker. I've had to really heat the snot of of those nuts before but they've never beaten me. I use a long pipe for extra leverage if I have to.
 
I should say, I have my worker do this for me. ( I supervise closely ) If I tried to do something that strenuous I'd end up in the hospital or off work for a week or two. Can't do that stuff any more.......

[Ulf]

Just out of curiosity, what kind of symptoms did you experience before discovering that your flex disc was due for replacement?
I'm trying to locate the cause of a "clonking" sound from the rear/middle when I change speed...wonder whether you have had the same symptom...

:-)

Ulf

[ja17]

Hello Ulf,

Yes, a clunking between shifts can be caused by a bad flex disc or other things. A vibration, especially under acceleration is another symptom of a bad flex disc. Do a visual inspection on your flex disc ASAP. Waiting too long can cause catastrophic damage.