Been tying up the odds and ends on my 83 240D recently. Got a new windshield installed, and will tackle more of the rust soon. My fiberglass work seems to be holding up well. Anyhow, I am just curious, the car having 314,000 miles now on what I believe to be the original driveline, I assume I would need to replace flex discs? Are there even flex discs on a manual 240D? Thanks

I seem to remember a thread not long ago addressing your question KylePavao. Basically his flex disks went bad and his wife called him on the side of the road I think and his linkage ended up wrapped around his transmission. It wasn't a pretty site. That's why I am replacing mine very soon. Not that they are that bad at 134k but I try to restore any part on the car that could leave me stranded. Don't quote me but I think it was a 240d..

Kyle,

Flex discs are in every MB car back to a 1961 190D and maybe earlier, manual and automatic. They are easy to find, they are on both ends of the driveshaft. They are a black rubber disc with 6 bolts going thru them.

They are also easy to inspect for wear, just look that there is no cord showing thru cracks in the rubber.

Replacing just because they are old is another case of "if it ain't broke, don't fix it". Assuming something needs to be replaced is foolish. Inspect first and replace only if necessary.

P E H

Kyle,
That was my car that TANK is speaking of...
I cant stress this enough! Check you flex disk for ANY signs of drying & cracking. The flex disk only cost about $40, and takes a few hours to replace. Cheap insurance. My car is being salvaged now because I didnt replace mine prior to failure.
I just recently bought a 1982 300D, and I am replacing the flex disk this weekend just to be safe.
Robert

Rob,

Replacing the flex discs in your present car just because you had problems with them on a previous car is a knee jerk reaction. The reason they failed is because you or your mechanic failed to follow proper preventive maintenence procedures.

By your theory, everyone with a MB should replace their flex discs tomorrow because yours failed. This is not logical.

Are you going to replace all the parts on your present car that you had problems with on previous cars? Inspect and replace only what is necessary. If it ain't broke, don't fix it.

P E H

I think that is a little excessive, and no I would replace all of the parts that had previously failed. But I had already purchased the flex disck kit for the one that broke, in hopes to replace it and keep driving the car. Now on the '82 I am not going to wait until it "looks" bad since I have the kit just lying arounrd. My local shop has told me that they are seeing more disk failures than ever, and like I said "cheap insurance"
I am so thankful that we were not in Tenn. at 70mph when it broke. As it was it tore a hole into the passenger side of the tunnel. I just have that "hot stove" feeling regarding this, and I will not be burned again. That's just me, and my opinion.

Just completed this job on the 1982 300D this weekend, and I would like to pass along a few tips that might make the job easier for others.

First of all, the entire driveshaft can be removed without taking off the rear transmission support bracket or the emergency brake cable puller assembly. The manuals tell you to drop these parts first, but you don't need to do it - just slide the parts out the back of the transmission hump. I had the front of the car up on steel ramps.

Flex Disk:

These come with new nuts, bolts, and one washer for each bolt. So, the puzzle for me was to determine where the washers go. After researching in my manuals, it was determined that the washers always go on the side of the bolt (either the nut or the bolt head) that directly rests against the flex disk. The washers do NOT go on the driveshaft sides. Previous owner/maintainer did it exactly backwards. The six little bolt tubes in the flex disks protrude at bit - three on one side and three on the other. These must mate into the driveshaft sections - there are indentations for them.

As mentioned elsewhere, mark everything for exact reassembly - including the exact spline mating at the center of the driveshaft.

Bolts always push through the flex disks AWAY from the center of the car. So on the front disk they push towards the transmission, and on the back they push towards the differential.

Access to the front flex disk nuts is a little restricted. You can gain sufficient access with a wrench on the driver's side of the transmission. Passenger's side is more blocked by fluid lines. Hold the nuts with the wrench - access on the bolt head side can be accomplished with a socket wrench.


Center Bearing:

You need a puller with a six-inch reach. Typically not stuck on that hard, but you need a puller.

Go ahead and get a new bearing AND center support AND dust cover. I had previously inspected these on the vehicle and they looked good, but with the driveshaft down it was obvious the rubber parts were shot. So was the bearing.

You have to press the new bearing into the bearing support BEFORE you drive the bearing onto the driveshaft. I used a vise and big washers - no luck with a hammer and wooden block. What you DON'T want to do is drive on the bearing and then try to put on the rubber center support. There's a metal ring in the center support rubber that holds the bearing very tightly.

I was able to drive the bearing onto the driveshaft with a 1-1/4" by 12" long galvanized pipe "nipple" found at Home Depot. Yes they really do call it a nipple for some reason, Mr. Moderator. 1-1/4" TV mast will not work. I think the TV mast is measured on the outside and the pipe on the inside.

When you get the driveshaft pretty much in place and the flex disks bolted up, it's a lot easier to get the center support bolted up if you can support the weight of the driveshaft with a jack. Bolt the center support up last.

----------------------------------

Hope my experiences help someone else on this task.

Results were an elimination of a pretty good clunk when transitioning from "pedal down" to "pedal up" Rear disk looked good - front disk was cracked pretty good but not showing anything internal.

I still have a little vibration that seems to come from the center hump. It is either the transmission output bearing or the driveshaft U-joint. The U-joint was not dry, but seemed to have a center "detent" when moving back and forth in one direction. The U-joint doesn't seem to be made to be replaced due to two difficulties. The first is finding one the right size. The second is that the U-joint is pressed in and then the driveshaft metal deformed (straked is the word?) with something like a chisel to hold the joint sections in. U-joints really should be smooth side-to-side / up-and-down when moving.

So, if anyone ever does the driveshaft U-joint - we all need to know how you did it and where you got the parts.

I'll not take mine down just to do the U-joint unless it goes really bad, or the transmission has to be overhauled. It's not a hard job - I'm just am not enthusiastic about repeating it!

Ken300D

Ken300D
Talk about attention to detail! This is why I stay a member of this forum. Folks like this who are willing to take the time and do things right and then share their experience. Sharing breeds sharing I guess. Thanks Ken.

Ken300D,

There is a word on one side the flex disc, something like FARUD, not sure of spelling. I think this might have something to do with which way the disc is mounted, to front or rear.

Do you have any idea what is the correct mounting direction with respect to FARUD?

P E H

I've read other posts that indicate wording on the flex disks to indicate which side goes to the front of the vehicle.

The disks I used were made by Febi, and they looked completely the same on either side - totally symmetrical. No indication of anything that would imply one side must go toward the front of the car. So, knowing some disks do have words to that effect, I put the side with a few initials on it toward the front.

Kind of like a superstition thing it seemed.



Next time I need something from the dealer/stealer I'm going to ask about getting a replacement U-joint. I'm expecting they will try to sell me a driveshaft.

Ken300D

Did some more research on the MB W123 CDROM and found that only a certain type of flex disk needs to be installed with a particular orientation. (There are two designs of flex disk - they flex in different directions) The ones that require a particular orientation are for manual transmissions and say something like "Dis seide der goo-goo-meister". Sorry, my German is a little weak!

Also on the subject of driveshaft U-Joints, I found this in another thread - author is Stevebfl:
--------------------
As to "what do they do". I wish I knew! That is I wish I knew where to purchase the tooling to do it as I would do it myself. They remove the u-joint (not hard I have done it numerous times - simplest method is to burn the center out with a torch and drive the caps inward). The original joint is held in by "crimping" the yoke. Once the caps are removed the crimping is reamed or honed from the yoke. At this point new u-joints can be assembled. They need to be held in though.

The beauty of the shafts Beyer does is that they then machine the yokes to accept snap-rings such as well built shafts were built before disposability. This machining is the trick. There is more to it than just a grove cut in the yoke (I really would like to see that machine). Getting it centered is absolutely critical to balance. Other than the this part all they have to do is make sure their tubes are straight and that the whole thing is balanced and indexed properly.
--------------------

I would like to propose a simpler repair method for evaluation by the group:

1) Burn the center of the U-joint out with a torch as Steve describes.
2) Drive the caps inward and remove them.
3) Ream or hone out the crimping from the bores that hold the U-joint caps.
4) Press in the new U-joint as on any other car and get it centered as best possible.

5) Lightly tack all four U-Joint caps to the driveshaft with an arc weld.

U-joints last a long, long, LONG time - especially the replacement ones that have a grease fitting. So you probably would never have to worry about replacing this joint again. Even if you did, essentially the same method as above should work.

Now I just need someone to tell me where to find the replacement U-Joint if the dealer/stealer won't sell me one. Hopefully NAPA has a match.

Ken300D

You might try giving Cosmos International a call (218-685-4473). While I bought a boot for my axle shafts from them a few years ago, my recollection is that their main business is U and CV joints. They were very knowledgable about MBZ. Let us know if they're a good source.

__________________
LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold

I talked this over more with friends and I have to admit I'm not sure the U-Joint is capable of withstanding the heat and stress of being arc welded on the caps - even just a quick tack. Sometimes there are rubber and plastic pieces inside that might not handle this at all.

Epoxy also comes to mind but I'm not sure I want to trust my life, my driveshaft and my car's underbody to JB Weld.

Back to the drawing board.......

Ken300D

I replaced my u-joint on the 220D, then found that the shop I used couldn't/wouldn't balance it. I have some vibration, but it comes and goes, so I suspect the center bearing mount. I'm to cheap to fix that old rustbucket any more (besides, I have a new project car....) -- but the guy welded some washers behind the caps to hold it in place.

Welding a plug in is the best way to hold the caps in place if you don't have a fixture, but you could make one, I suppose, rather easily. The trick would be to set the correct cap location while straking it in.

You would also have to balance the shaft, and this presents a problem, since most driveshaft shops are VERY reluctant to shell out the $1500 or so the balancing machine maker wants for the correct adapters. Grrr. No market, I suppose.

Best bet is a good used driveshaft, much cheaper than getting one rebuilt ($650 or so).

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I'm with Ken. You have to be real cautious using a welding machine around bearings - especially if you are grounding through the bearing. You can destroy them by having a high power arc go through it.

__________________
Jim