Replacing Front Flex Disk on 300E
 

While replacing bushings on the shift linkage I noticed that the Front Flex Disk was chewed up so I ordered a new one from Fast Lane.

However. when I went to Alldata to check out the replacement procedure I came up empty handed.

Can anyone tell me how to remove the old disk... Is the procedure just removing the 6 bolts... drop the old disk and then replace it with the new one?

Thanks.

I haven't done a 300E but I've changed them in my cars and I expect the procedure is the same.

Yes, you remove the six bolts, and yes just replace it with the new one, but here are a few things to look out for.

The new flex disk has a front and rear facing side and the links have different hardness. So make sure you install the new one with the correct side facing forward and the correct bores bolted to the transmission (the double links must be under tensile stress). The double links can easily be determined by bending the flex disk. There is considerable difference in the stiffness between the double and single links.

My flex disks have had a short protrusion in the rubber that indicated the transmission side and a bore that bolts to the transmission.

Pay close attention to exactly what bolts attach to the transmission and which ones attach to the drive shaft and where the washers are. My bolts are of different length and the washers are not in the same place on all six bolts.

If there is ANY play between any of your old bolts and the bore on the new flex disk, you must replace the worn bolt. If you don't, within a few months, the bolt will look like an hour-glass and you'll be going through this again.

I hope this helps.

Cheers,

Yes, indeed there is a front and rear of the disk, so pay attention and put it in the right direction.

On the 124, you have quite a bit more to mess with, however. Assuming this is a US car, you will need to lower the exhaust system out of the way. You will unbolt from the manifolds and remove other hangers to lower it. You will have to remove the front passenger floor mat and disconnect the O2Sensor and feed the cable through the floorboard hole.

You then will loosen the large nut in the front driveshaft section to collapse the drive shaft. Is this does not gain enough room, lower the center carrier bearing. Before doing this mark the position of front and rear shafts so that they can be put back in correct orientation if they pull apart accidentally in the process. It is possible that you still won't have enough room to work and will have to pull the rear flexdisc down. The rear one is not subject to near as much heat as the front so it will be in good shape.

Good luck,

Thanks Robby and Larry. It appears the job will be somewhat complicated so I can plan devoting a good portion of the day to it.

I'm curious to know why the disk won't just slide out once it is unbolted. Is there a protruding flange or something that prevents it from just slipping out from between the shaft and transmission?

Yes, and the clearance needed to get the bolts out.

There is a protrusion from the shaft in the very center that goes into the center of the transmission output shaft. This is why the large nut must be loosened and the front shaft collapsed.

Good luck,

Thanks for that tid bit about the large nut.

My wrenches go up to about 1 1/4 inch and 32mm. Any idea what size the large nut is? I will probably have to go to Sears and get a craftsman wrench to fit it... or can I use a plumbing pipe wrench on it? In fact I might have an old large adjustable wrench that might work. I'll go out now and see if I can find it.

(Located a small and midsized pipe wrenches. Old but quality tools... not bulky so they might fit in a constrained area. Hope using pipe wrences on a Benz is not considered sacriligeous and cause for banishment from the forum.)

:)

I use a humongous Crescent wrench on the nut. When it is stubborn, I use a humongous pair of Channel Locks to back it up.

I'm pretty sure it is larger than 1 1/4". I have combinations to 1 5/16" and I still use my big adjustable.

Good luck,

Replacing Front Flex Disk on 300E
 

I changed mine by placing a jack under the transmission, removing the trans mount and lowering the rear of the transmission a little
the flex disk didn't fall out but with a little coaxing with a long screwdriver it dropped out. The new one was relativly easy to put in and raising the trans as I put it in held it in place.
All totaled it took me about 1 1/2 hours to replace it. Just be carefull not to damage anything at the rear of the engine as you lower the trans. This was a couple of years ago but I don't think that I lowered it more than a couple of inches. Getting the bolts loose was the hardest part as they had sucked into the flexdisk
a little and were pretty chewed up. New bolts came with the Flexdisk I got from Fastlane.

Ok Dave,

Yesterday I put the car up on ramps to put WD-40 on the manifold bolts and while looking the situation over I wondered about the possibility of moving the trans rather than droping the exaust system. In fact I was going to post the question to see if anyone had done it before and to my surprise you have already posted the fact that you have done exactly that and successfully.

Given my aprehension about dealing with rusty manifold bolts I will try your procedure. I have a very good (old) rebuilt floor jack that gives me excellent control of a load.

Wow.... what a relief.

Thanks.

:)

Flex Disk
 

Earl,
I would just like to share my experience on changing the flex disk.

- The side with the German marking should face aft (sorry- I was in the Navy) or towards the rear.

- I would try the jack-under-the-pan method first. Make sure you put a small 2x4 piece of wood between jack and transmission pan. Just as mentioned in earlier posts, pump jack to take the weight off the tranny and remove the cross member to give you more room. You will have to take out the tranny mount too to give you even more room. Once the flex disk bolts are out, try to pry the disk back and see how far it goes. You might be able to change it at this point. If not read on. ...

- I share your concern when working with exhaust components, i.e. rusted parts. Instead of taking the exhaust pipes down, take the heat shield out by unbolting one bolt in front and two in the back. You might have to play with it a bit to get it out. Once its out, you can unbolt the center bearing support. With the front sidk bolts out, remove the rear flex disk bolst also. At this point you can slide the whole driveshaft assembly towards the rear. You might have to remove a crossbar just in front of the heat shield to give you more maneuvering room. Also, try to keep the two halves together as they tend to separate if the big compression nut is loose. Once the shaft assembly is out, you can put it on a bench to make things a lot easier.

- This sounds long and winded but its actually a lot easier to do than writing it. Good luck! Be safe!

Dennis :)

Last month I replaced the front flex disk on my 1993 300se and had to remove the muffler piping.

This is not an American car. The bolts and nuts holding the pipes to manifolds are a piece of cake. Also the manifold to head is held with studs threaded into the head as it should be whenever aluminum and steel are involved, again no problem.

If I were you and planned on lowering the transmission, I would pay close attention to the jillion things at the front of the engine such as the fan hitting the shroud and the radiator hoses, stressing the expensive plastic radiator tanks.

Best of luck,

Yes Larry... I thought about what might move at the front of the engine. I'll put an extension and breaker bar on those manafold bolts to see what kind of resistance they give me. I see that they are extra heavy duty so I do not expect them to snap.

The flex disk arrived today so It looks like I have everything to do the job over the weekend.

Thanks to everyone who gave me input on this job. I now feel like an authority. Started out with a big question mark.

:)