The Death of a Flex Disc ... did I kill my 240D?
 

I'm going to lead off with pictures ... lousy cell phone picks, but they tell the story ... :(
http://farm4.static.flickr.com/3641/...2c0e8a.jpg?v=0
http://farm4.static.flickr.com/3347/...116d11.jpg?v=0
This is the 78 240D. I checked the flex discs before and after buying it, and I had thought they looked fine. The last time I drove it, it started to go do a rapidfire thudding/stuttering right after I shifted into 1st or 2nd and accelerated ... but it only lasted a flash each time and wasn't present at all in higher gears. I thought maybe something was wrong with the clutch, but I figured I'd check the flex discs anyway, and this is what I found today. I don't even know where to start. The head of the bolts that hold it to the transmission are sheared on one edge, but other than that, I don't see any major damage to the transmission or end of the driveshaft (or other collateral damage). But given what happened to the disc, and the fact that I continued to drive this (only back home, but still), I have to think there's more damage than what I can see. So where do I start? Did I ruin my car?:(

And don't ask how I could be dumb enough not to realize the flex disc was bad despite inspecting it twice. Or how I could be dumb enough to keep driving it after I felt something amiss. The only thing I can say in my defense is that the car drove unbelievably normal, other than those quick stuttering bouts, given what condition the disc was in. But basically, I'm really discouraged at my complete failure to identify what had to be an obvious impending problem. I'm glad it didn't happen going 70 down the freeway. Ironically, I bought this car as a project that could help me build confidence during a hard time. I probably should have taken up knitting.:(

looks like you got some body work and damaged transmission.

You will know when fix the body work and replaced the flex disc and anything that got destroyed.

Not a big problem. Don't take up knitting. Remove discs, replace.

You're probably not getting many responses because everyone saw the pictures and crawled under their cars to inspect. :D

Looks like you got off easy to me.

i cannot see any tranny damage. i dont think you driving it home was a wrong idea. it looks to me that all you need is a new flex disc. they come with new bolts and nuts so you should be able to drive the sheared off bolt out with a punch. looks like a no sweat job,to me.:)

hell ive driven a truck with a broken rocker arm just to get it home from the middle of nowhere

Yeah, like you said bad quality of pic, but I dont see anything that just putting in a new flex disc couldn't fix.

Do not despair young C, these things happen to all of us. Just today I checked the oil and apparently didn't get the dipstick all the way down and just rust-proofed Smash all the way back to the rear window wiper!! I of course thought of Tyler immediately. :D
Some things appear fine right up until the time that they fail. So it more than likely looked just fine when you looked at it.
As stated above, you probably just need to replace your flex discs.
Chin up! You wanted a project. You certainly have had one after another on this 240. But this is bonding time, and opportunities to gain more knowledge and experience.
OK, granted, it has been quite a few "opportunities".........;)

I changed both of mine last year. There were some cracks on the front, but no deformation or visible fibers.

Is it wise to change the drive shaft carrier bearing while you have the flex discs out, even if you have not identified any problems? In other words, is it one of those "while I'm at it" jobs?

Thanks for the answers, guys. I guess it's not as bad a catastrophe as I thought ... but enough to motivate me to change the discs on the 300D, too, for good measure.
Couple questions:
1) The alignment of the bolts now does not match up with that of the new disc ... do I have to rotate the shaft, or can I rotate the yolk on the transmission? Maybe that's a silly question but I haven't done anything with the tranny/driveshaft before so I'm not sure what moves where.
2) Is there anything else I should inspect or replace while I'm working on the driveshaft (I will be also replacing the rear flex disc)? Any specific damage I can look for, other than basic damage to the tranny and frame?

I guess in a way the fact that I'm a "beginner" at driving stick probably worked to my advantage ... I drive around like a granny so that probably helped avoid a high-speed disaster.

Rotate the yoke on the transmission. Needs to be in neutral. Block the wheels well before climbing under there. There wont be any resistance to rolling in the drivetrain.

either do like kerry said or block the rear up and rotate the shaft. either way will get it done. you might want to change the center support while in there.

I like to have both the transmission in neutral, and the wheels unblocked. That way you can rotate the flex disc once it is in place with the first bolt and it's easier to get to the bolt heads if you can position them where you want them to be. To keep the assembly from rotating, when tightening the bolts, I have used a large screwdriver inserted in a u-joint.

Doesn't look like any collateral damage- you were lucky. Yes- replace the center support and center support bearing and inspect the u-joint while you have it out.

Be sure to mark both halves of your driveshaft before you take it out and apart . It is balanced the way it is now.

also check the centering bushing in the end of the driveshaft. It goes over the pin on the transmission yoke. If this bushing sustained damage from your catastrophe, it will not center the driveshaft properly. I would see if I could feel any lateral play without the flex-disk in there (just the centering bushing on the pin).

How is the driveshaft going to rotate if the wheels are blocked?

At least one rear wheel needs to be elevated and free to rotate.

That was a lucky break, looks repairable by just replacing the discs....perhaps the weakling power output of the 616 saved you from catastrophe!

Be prepared-compressing the driveshaft and getting the flex disc metal inserts out of the flanges can take some effort(once you get the bolts out) . They can be wedged (and rusted) in there pretty tightly. You may want to get under there a day in advance and soak everything down with penetrating oil.

Rick

Great advice, especially after your uca bolt.......

Yes X2 on this. There's a good chance the bushing got damaged in the process. That bushing is also what may have saved your car from further damage. It's easy to replace.

No need to rotate the driveshaft if the transmission turns unless you want to spin the driveshaft for better access to the bolts. Blocking whatever wheel is on the ground would work.

Started this job today ... not going so well. First problem: I can't get the large nut on the shaft to turn. I did get it about a half-turn, but the tools I'm using are impossible. I don't have the giant wrenches so I'm using a crescent wrench and pipe wrench, both extremely heavy and will barely fit. Is there anywhere to buy the 41 and 44 mm open end wrenches, and are they really expensive? Having the right tools would make this job doable, I think. The Haynes manual says you need about two turns of the nut to compress the shaft ... is that about right?

I'm also having a bear of a time getting the bolts out of the flex discs, although I've gotten the three out of the rear that attach it to the shaft, and two from the front. I'm pretty sure I've broken part of my knuckle, but I guess better that than the car, right?:rolleyes: I just got overwhelmed after 3 1/2 hours and went home. Ugh.

I've found using a small pipe wrench works fine on the nut. Try a sawzall on the nuts/bolts you can't get off. The new flex disc comes with new ones.

BodhiBenz,

You need two wrenches like this for optimal operation on the driveshaft nutes: http://www.hardwareandtools.com/invt/u714904

You can get them at Lowes, Home Depot, or your local harware store - they are around $15 a piece.

You can get big wrenches from NorthernTool.com - I have a 46mm open end wrench and it looks like a cartoon it's so big.

If you need more torque with the smaller handle adjustable wrenches, get a piece of 12" long 1" black iron pipe to use as a 'cheater'. Slip it over the existing handle for a longer handle and more force :-)

For the nuts on the discs themselves, I found that a gear wrench was very helpful as a back up wrench. It helped me put the most force to get them loose. Don't forget to douse them in PB Blaster beforehand.

If you are going to go for the full center carrier + bearing replacement you will need a 3 jaw puller to extract the bearing and a correctly sized PVC pipe section (i forget what size) to tap the bearing in.

Good luck - I did this two years ago on the '82 and Im already fuzzy on it.

Thanks to you I looked under my '85 and saw a small crack (big enough to see white thread) in my flex disc, so I'll be doing this again shortly. Thank you again.

Do you have the FSM? I remember the article on this job being very helpful along with the Haynes manual.

dd

When I replaced my transmission, I didn't need to touch that big nut, despite what the Haynes manual said. Try compressing the shaft without loosening the nut.

Thanks guys. I went to Lowe's and they didn't have any large enough adjustable wrenches, so I picked out a vice grip wrench that looks like a small pipe wrench. I used it on the lock nut and used a crescent wrench on the driveshaft and it worked great. That is, once I turned the nut in the right direction.:rolleyes: I did get the third bolt out of the driveshaft-flex disc. I can compress the shaft, but it's stuck to the tattered flex disc, which is still bolted to the tranny. I shot PB Blaster everywhere and hopefully the shaft will move off the disc tomorrow. If not, I'll try to get the other three bolts off and let the disc come out with the shaft. Really tough to get at the shaft/tranny bolts because of the flex disc wreckage. Long way to go, but at least I ended the night with some progress.

Not sure if the little incident you had is making disassembly worse than "usual", but the flex discs do not just fall out of the flanges once you get all the bolts out. You will need to get a very hefty screwdriver or pry bar in between the flange and flex disc and pry them apart (forcefully!). The metal inserts on the disc are a tight fit into the flange (even without any rust or crud involved).

Rick

Check this out!

http://www.peachparts.com/shopforum/vintage-mercedes-forum/205055-what-happens-when-you-ignore-little-driveline-vibration.html

You have to be sensitive to the small signs. I once had a blow out on the rear tire doing 60 on the highway. I could hardly tell anything was wrong.
My daughter was sitting in the back seat too. I looked back and asked her if she heard anything and she could barely hear it.
I pulled over and found the side of the tire blown out. I couldn't believe how well it ran.

BTW I love vise grips! They've got me out of a lot of jams!

Danny

More data
 

Driveshaft, Axle & Wheel bearing
http://www.peachparts.com/shopforum/diy-links-parts-category/142402-driveshaft-axle-wheel-bearing.html

Just a little update: Everything is out, after much fighting and a few minor injuries. I ended up getting the shaft off the disc (and tranny/diff) using a chisel and hammer to knock the little metal cuffs out. Lots of work in a tight, dirty space. Getting the bolts off involved holding a wrench on the nut with both hands while lying on my side and pushing my foot on the breaker bar to break the bolt lose. Good thing I'm flexible ... it worked on every bolt. I did have to buy a 6pt 15mm socket to get the sheared bolts off.
Damage assessment is pretty much what I thought before: Nothing catastrophic. The bushing at the front of the driveshaft was damaged so I will replace both of those. There are some minor scuff marks on the yoke of the driveshaft and tranny, but very surface. I will dab some POR15 on there to make sure it doesn't progress to rust down the road. Center support is a wreck, but I was going to replace that anyway.
One question: The grease boot on the center of the shaft was cracked and there was grease oozing from it. I got a new one, easy to install, but do I need to put any grease inside it? Manual doesn't mention it, but it also doesn't assume a busted boot.
I will be trying to complete this tomorrow if time allows before I have to go to work. Hopefully I'll remember to snap a few pictures for entertainment/educational purposes.

no grease needed, the bearing is sealed. its just a dust boot.

Update and some pics:
Well, I finished everything this evening. Yesterday I spent most of the day removing/replacing the bushings at the ends of the driveshaft (that included two trips to Lowes and a trip back to my house). I drilled a hole in each one, per Haynes manual procedure (bought a new set of Bosch drill bits that could handle the thickness), stuck a mini allen wrench through it and tried to pry it up using screwdrivers with the shaft in a vice. Upgraded to giant pry bars, no go. So I bought a torch and heated it ... they came right out. You can see the damage on the front one.
http://farm4.static.flickr.com/3300/...1b02c5.jpg?v=0
http://farm4.static.flickr.com/3649/...31b7e9.jpg?v=0
Today I put the center support back on, had to tap it on using a wide PVC pipe. The real tough part was torquing on the 12 bolts for the flex discs. My torque wrench is too big, everything kept slipping, and I had no space under there. Plus I have the strength of a preteen girl. But, I toughed it out and got them all done, despite lying in what was clearly not just mud under the back of the car.
Took it for a drive, everything seemed OK.
But here's the kicker (you knew it was coming, right?). When I was cleaning up a I picked up one of the old bolts, which still had the washer on it ... and realized I put the washer on the wrong side of every single bolt (i.e., I put it under the nut. Why? I have no idea). I doubt that will lead to immediate catastrophic failure, but the washers go under the bolt heads for a reason, and I have to go back and re-do all 12 bolts. It makes me so mad, because if I'd stopped and thought about it, logic alone would compel me to put the washer under the bolt head. And I was so careful about everything else. Oh well, it could be worse ... at least it doesn't look like this anymore ...
http://farm4.static.flickr.com/3607/...0b5c73.jpg?v=0

If the washers DO go under the bolt heads, I am at a loss to understand why. I probably have all mine on the way you did it. I would say the "normal" way would be to put the washers under the nuts anyway. I wouldn't change a thing or worry about it, especially if you used nyloc nuts.

Good job!

Rick

Congratulations on a well presented job, nice write and fantastic pics on step-by-step procedures. Well done!!

Just one point to clarify regarding the washers on the bolts. As you can see from your picture before disassembly the washer either go under the bolt if the bolt goes first through the flex disk to screw on to the lobe of the shaft or axle/tranny.
Conversely, the washer goes under the nut when the bolt goes first through the lobe of the shaft or axle/tranny. The washer always goes resting on the flex disk and not on the lobe of the shaft or axle/tranny.

Here are pics of your flex/shaft before dismantling and one of my own flex that I need to replace soon (thanks to your efforts, write and pics it will be a lot easier for me). BTW, there is 6 grams of pertinent grease to go on the centering sleeves.

http://i414.photobucket.com/albums/p...brokenfelx.jpg

http://i414.photobucket.com/albums/p...flexbolts1.jpg

http://i414.photobucket.com/albums/p.../flexbolts.jpg

Thanks for pointing that out ... I guess I only got if half wrong.:o Now I have to decide whether to go in there and change the six that are on wrong. rs899 ... I know the nuts are self-locking, but I don't think they were nyloc. Can they be removed and refastened without losing their locking function?

As long as the "self locking" feature still works, you should be able to re-use them. You can use some liquid threadlocker if need be. Maybe I'm not such a purist as Deltacom, but I would not remove and reconfigure those bolts. I say leave' em alone and find something more important to work on.

As long as those bolts are torqued down well and the nuts don't spin off, nothing bad is ever going to happen. All the side load is in the inserts.

Besides, just how many of these discs were put on by high school dropouts at Meineke mufflers over the years?

Rick

Yes, indeed!, you’re absolutely right!, there is a very good reason for the washer to be either under the bolt head or the nut, whichever is resting directly onto the flex disk.

Very briefly, the six holes on the disk contains 2 sleeves (bosses) each. The outer one is “Vulcanised” to the rubber, the inner one is fit-pressed into the outer. When the bolt is tightened the washer actually pushes slightly the inner sleeve into the shaft/flange/yoke recess in the lobes and bridges the 2 sleeves to the metal disk thereby securing the flex disk onto the shat/flange/yoke.

If the new bolts supplied with the new disk are Allen socket type of bolts, the head of the bolt is not wider than the rim of the inner sleeve (even the hexagonal head bolt barely bridges the 2 sleeves) and without the washer to bridge the 2 sleeves onto the metal disk the bolt is not securing the flex disk but only the inner sleeve. Without that vital support of the washer the bolts could shear off as it happened to your original one when failed the support due to surrounding rubber deterioration. Even the shape of the sides of the washers are important in which way they face, as one side is flat (facing the flex disk) and the other has rounded edges (facing the nut/bolt).

The way I understand you installed the washers just under the nuts only, it means that theoretically you could pull the shaft and would come away from the yokes together with the flex disk attached to it (since those are the only bolts that are secured with the washers to the flex disk) leaving the 3 bolts and inner sleeves attached to the tranny’s yoke/flange and the same at the differential.



Bolt without washer
http://i414.photobucket.com/albums/p...de/Hexbolt.jpg

Bolt with washer
http://i414.photobucket.com/albums/p...e/Hexbolt1.jpg

Hex without washer
http://i414.photobucket.com/albums/p...e/Hexbolt2.jpg

Hex with washer
http://i414.photobucket.com/albums/p...Hexbolt3-1.jpg

Looking at the pix from Deltacomm, he is correct in that you need to cover the bonded bit of the disc, whether it is with a washer , head of a bolt or nut doesn't matter. I forgot that the socket headed bolts they give you are so narrow.

Thanks for the pics/explanation. I was going to do it anyway, but it's good to understand the significance of the washers ... and I will pay more attention when I do this job on my 300D.

Nice job! You have also received some really good tips on this thread. I am assuming you inspected the bolt holes on both the tranny & differential yokes for any wear or damage from those flopping discs.

One more thing to note: If you ever happen to experience in the future any other drive shaft vibration, it will probably be the U-joint. These cannot be bought separately. There are 2 machine shops I know of that can replace them and rebalance the shaft. One is in Portland and the other in Atlanta. Atlanta is the more reasonable.

What U-joint?

On my W124 the washers are clearly to ensure clearance of the bolt from the diff housing.

When I replaced my transmission, I didn't need to touch that big nut, despite what the Haynes manual said. Try compressing the shaft without loosening the nut.

I am able to compress the shaft without loosening the nut, but when I telescope out I am no where near the flange on the transmission.

Thank you