Is the driveshaft balanced with the flex disks attached? I think not.

As for the u-joint, you rebalance the driveshaft after you replace it.

No

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

Guys, I have to replace that rear flex joint. Will that rear flex joint come out when you loosen those big nuts in the center by the carrier bearing? What size wrenches do you use? Would two large cresent wrenches work, or is the space to limited. Would like to know the size of the standard wrench instead of metric since I have to borrow them. I have been trying to get a better picture of this operation and it seems hard to come by. Since I am also pulling both axles, could I gain the necessary space for removing the rear flex when the differential is is loosened and lowered? Thanks

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Junqueyardjim
Christianity, if false, is of no importance, and if true, of infinite importance. The only thing it cannot be is moderately important. C.S. Lewis



1983 Mercedes W123 240D 4 Speed 285,000 on the road with a 617 turbo, beautiful butter yellow, license plate # 83 240D INDIANA

2003 Jaguar Type X, AWD. beautiful, good mileage,
Mom's car, but I won't let her drive it!

are 46mm on my 300td but I didn't have to touch them to replace mine. The shaft will separate with them in place. It seemed to me that the nuts were keeping the shaft from shortening, not lenthening which is what you will do to pull it apart. Mark the shaft pieces well, I used a straight edge and white-out (correction fluid).

I thought my son in law had the wrenches for that job, but he did not have them that big. So it was with the channel locks. A pair of those big things will put a lot of twist on any pair of nuts I think. Well any way, I did loosen it and it does allow the rear shaft to slide forward about an inch, after you loosen the bolts that mount the carrier bearing. However, I still could not get the rear shaft far enough forward to drop the flex joint. Well, since I was going to replace both axles, I decided to drop the differential to pick up a little more space. When I pulled it all apart, I then found that the centering "bushing" that mounts inside the rear flex joint had disintegrated and was all balled up, inside the short tube. Maybe that is why it would not come apart. I do hope my "U" joint in the center of the shaft doesn't have any rough spots. Drive shaft and axles are really bad. The rest of the bottom on this new car, (1984) which Bio Pete salvaged from the crusher is so nice that I think it is beautiful. The undercoating is thin in places, it seems to have had many miles on gravel, but the floor is perfect and just like new. Anyway, I got the driveline out and I thought it was a very difficult job and I am glad it is out. Compared to pulling the driveline, the axles are a snap.

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Junqueyardjim
Christianity, if false, is of no importance, and if true, of infinite importance. The only thing it cannot be is moderately important. C.S. Lewis



1983 Mercedes W123 240D 4 Speed 285,000 on the road with a 617 turbo, beautiful butter yellow, license plate # 83 240D INDIANA

2003 Jaguar Type X, AWD. beautiful, good mileage,
Mom's car, but I won't let her drive it!

My front flex disc, on my extremely low mileage 560 SEC, just grenaded last night. There are chunks of rubber, and Nylon string coming out of the U-Joint, and it did a small amount of damage to the undercarriage insulation, but none to anything else (luckily). Was told today that in some cases these things will go bad, and send the driveshaft through the floor into the cabin. Now, I'm putting a new pair on the car, front and rear.
I cannot be totally sure, but I have a feeling it's only a result of my heavy foot, and not really due very much to wear. The car barely has any miles on it, though it's 17 years old. It sat for a long time, and the original tires were dry-rotted when I got it, so to say it could have also been dry-rotted, is not totally out of the question either.

Nick

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[SIGPIC][/SIGPIC]

Here's a little something we all know but refuse to admit.
If you bought an old (older) car and the tires were showing 'dry rot' and you replaced them, how long would it take the next pair to 'dry rot'?
This is how long ALL the rubber components on the car have in existance.
Notice the period at the end of existance........

I had to have the transmission rebuilt and the tech checked every part with a micrometer and found nothing worn. 3 little rubber valves inside were shoot and that caused all the problems. Had a flex disc fly apart... rubber. Have front strut mounts ready to come through the hood.... rubber.
Water hoses, spark plug wires, roof seals (convertible), door seals....
rubber, neoprene, foam-rubber, ............PERIOD...

Mechanicaly these cars WILL last a lifetime, unfortunately rubber deteriorates.

of why we replace these at the first sign of deterioration.

Attached Thumbnails

 

Hey, Bill, check out this pic of what-used-to-be-a-flex-disc. . . from a '95 E320.

Looks like this guy 'waited' abit too long . . . although he drove the car into the shop!

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Regards . . . . JimF
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'94 S500 Cpe

Visit my Mercedes Web Page

Considering the potential damage, if they look original or very old I would replace both of them. Flex discs are cheap and nothing lasts forever, its just part of owning old cars really.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

is there a diy writeup with pictures anywhere that shows newbies how to replace the flexdiscs? Anyone in the chicago area willing to help me out for a nominal fee? The indie by my house wants $340 just for labor.

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Where are you located?

They are quite easy to replace, the only hard part is the large clamping nuts where the two driveshaft parts join, and you may not even need to touch them. Just remove the bolts that hold the flex disks, shift the driveshaft back an inch or so and replace it.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

Hah!!, You're not joking. That's exactly what my front one looks like though, on my 126 coupe. I can't even drive the car, 'til it's fixed. Plan to do a whole driveshaft, and U-Joints/Flex-Discs, whatever you call them. All in one job. It's actually a LOT easier to replace everything involved, than it it to just replace one disc. Also, the complete driveshaft assembly costs $380.00 from "The Driveshaft Shop.com" It comes witha warranty, and is fully assembled. Easier than the old "edge of your seat" feeling you get wondering if your driveshaft bent a little bit during the whole mis-hap to begin with. They bend very easily, and the slightest bit of abnormal movement, very often will bend a driveshaft. Even if it only bends a couple of thousandths, it could prove catastrophic, or atleast cause a vibration. Just change it all, and get it overwith, once and for all. It's also a great opportunity to replace your engine and tranny mounts, and all of your exhaust hangers, and any leaks you might find along the way.

Nick

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In answer to the "twice asked---never answered" question in this thread about whether a "clunking" sound when changing gears or relative shaft directional torque could be associated with damaged/aged flex disk(s)---YES---it can be a sign of a disintegrating flex disk. I had a 300SD which made ugly clunking sounds when switching relative torque rotation (forward to reverse, or vice-versa, or switching from accelerating or coasting into downshifting mode). I looked under the ends of the driveshaft and saw "Einstein's hairdresser" had done major work on one of my flex disks (similar to the worst photos of above posts). The disk was letting go---vehicle may even have been unable to drive (can't remember the sequence perfectly, but I already had new disks in the trunk). The other disk was relatively mildly cracked. After replacing both flex disks, the clunking sound was no longer evident. ALSO, now my 300E 4Matic is making a low frequency "rumbling" sound, starting at 40-45 mph (which condition originally was noted 500 miles ago as a "tick-tick-tick" sound---like a cell-phone on vibrate mode on a hard table, and occasionally like a half-wet bundle of spaghetti being slapped on a window) from the transmission shift lever area at 60-65 mph, where if touched, perceptible associated vibration could be felt. The front flex disk has one of its six inter-bolt sectors with a v-shaped derangement of fibers, flying outwards as a mini-Einstein coif. If I am dutiful, I will post a follow-up after replacing both flex disks (expect that they are of the same vintage, so the rear one is worth replacing even though cracks appear only minuscule and restricted to along the circumference of the six bolt washers, as observed from below the vehicle).

Is the flex disk on all 300 diesels w123 the same or did the non turbos have a different flex disk?
If the rear one looks bad should one change the front one as well?
Is it ok to replace old ones with good used ones as long as they don't look torn?