Author Topic: Flex Disk replacement - Drive Shaft procedure question (Read 17914 times)

Iconic · « **on:** October 31, 2014, 01:02:25 »

I'm deep into the flex disk replacement on my car.
I've read most everything on the forum on the subject (I think).
I have the large drive-shaft nut loose and the drive shaft moves backward to give me clearance to change the flex disk.
I have one concern/question.
I read that once I've changed the flex disk and put everything back together, I should not tighten the big drive shaft nut (46 mm).
I should leave it loose, put the car on the ground, bounce it and then tighten the nut, while the car is on the ground.

Well, my car is on jack stands, and i don't believe I'll be able to get under there with two big wrenches once it is back on the ground.
Can someone tell me if they have done this on the ground, or if it is really neccessary?

It seems to me the drive-shaft will go right back to it's original position once the new disk is in (while it is still up on jack stands). It doesn't seem like there is anywhere else for it to go.
What am I missing here? I'm getting nervous ... for a change.

Please help !
Mark

Shvegel · « **Reply #1 on:** October 31, 2014, 01:23:17 »

Because the differential is not solidly mounted to the chassis the movement of the suspension will effect the length of the driveshaft. Although you may get it close unless you allow the suspension to settle it may bind of cause other issues. I would suggest putting it back together as best as you can and driving it down to the nearest place that does wheel alignment. An alignment shop will have a roll on lift that will allow you to crawl under and re-set the driveshaft length while the car is in the air. You will probably be better off this way than just dropping the car, bouncing it and crawling under. The wheels hang down while the car is in the air and when you set it down it will not return to it's normal position without rolling the car a little bit.

Iconic · « **Reply #2 on:** October 31, 2014, 01:45:14 »

Thanks for the reply.
That sounds like a good idea.
This might be silly, but do I need to tighten the large drive shaft nut up for the short drive to the alignment shop or do I leave it loose? (Obviously I don't completely understand the drive shaft / nut assembly.

Any other different suggestions out there?

awolff280sl · « **Reply #3 on:** October 31, 2014, 02:06:59 »

When I replaced my flex disc, I rolled the car back and forth with the nut loose and then I was able to crawl back under and tighten the nut. I can't remember but it prpbably was not easy. This was a few years ago and I've had no problems with the disc since.

georgem · « **Reply #4 on:** October 31, 2014, 20:21:16 »

Is there a difference between a 230 and 280 drive shaft? I am replacing the flex disc on my 230 and I don`t understand the discussion re setting the length - is this only a 280 proceedure?

George Des · « **Reply #5 on:** October 31, 2014, 22:33:53 »

It depends. Some of the early 230Sls have the self adjusting drive shaft. There is a slip joint between the two rear section that is splined and allows it to self adjust. Now I have a 230sl with the 5 speed and my drive shaft is similar to the later versions with the large nut. So you will find 230s with both type of driveshafts.

georgem · « **Reply #6 on:** October 31, 2014, 23:12:56 »

Thanks George - I checked and I have the splined slip joint and thus no nuts - if you know what I mean

Iconic · « **Reply #7 on:** October 31, 2014, 23:21:01 »

Yes, I did read about an earlier version of the drive shaft on this site.

georgem, there are lots of things to be careful of when replacing the flex disk to insure long life. Plenty is written here on the site.

So, Andy and Shvegel, thanks for relieving my anxiety !

I still don't know: Can I drive it around a little bit to settle everything with the drive shaft nut loose, or does the nut have to be tight to transmit power to the rear end?

George Des · « **Reply #8 on:** October 31, 2014, 23:41:58 »

I did this job by driving the car up on to ramps. I was able to gently drive the car off the ramps, give it a few bounces, rolled it back and forth a bit, jacked it back on to jack stands and then tightened the nut. Make sure you use on of the new improved version flex disks. unlike the old, original ones, it is almost impossible to install it incorrectly.

George

Iconic · « **Reply #9 on:** November 01, 2014, 00:03:53 »

George, Thanks !
Yes, I've got the new design flex disk. I know all about the direction of the bolts, the washer position, etc also. I do things very slowly, but hopefully correct and only once. At least that is the plan.

So, you drove off the ramps with the nut loose? That is what it sounds like. That would answer the question about me being able to drive a little with the nut loose.

You put the car up on jack stands to tighten the nut? I thought the idea was to tighten the drive shaft nut when the car's weight is on the suspension and settled. It seems by you jacking it back up onto jack stands you are putting it back to where I am right now.

Ramps might be a good way for me to keep weight on the suspension if I can't tighten it up on the ground. As long as the nose up or tail up angle of the car doesn't put the drive shaft in a "bad" position.

awolff280sl · « **Reply #10 on:** November 01, 2014, 02:52:44 »

I used the new flex disk, designed for the 108 chassis I think. Going by memory, I remember having to add a washer or two to the existing hardware to keep the bolts from hitting the flange. /just in case you run into the same issue.

RonB · « **Reply #11 on:** November 02, 2014, 02:20:53 »

If I may ask - why are you replacing the flex disc?

If it is wore and coming apart - check your SUB FRAME MOUNTS!

Worn sub frame mounts will cause a flex disc to go by by.

When I first got my 280 we replace the flex disc and lo and behold about 2 months latter and 2k miles it left me stranded on the side of road with a blown flex disc. On checking the sub frame mounts and they where shoot. At the time they where only $100 or so each. Now they have increase considerable in price

It stands to reason that anything that 35+ years old, the rubber seals deteriorate just from age. Check rubber gourmets, seals and etc. and they all become hard with age. Good preventative maintenance would be to replace sub frame mount, engine mounts and the rear suspension rubber mounts. It them will ride nearly like a new Mercedes Benz W113.

Iconic · « **Reply #12 on:** November 04, 2014, 01:15:59 »

RonB,
I had a vibration. I've been replacing all the rubber anyway, so I was hoping that the vibration was the flex disk. In fact, it does have torn threads visible plus cracks in the rubber. So, I can't wait to drive the car to see if the vibration is gone.
A couple of years ago (not that many miles) I replaced the sub-frame mounts, engine mounts, and the transmission mount.
It is possible that it is the original flex disk with 83k miles on it.

All I have left to do is tighten the drive shaft nut.
I plan on backing the car onto ramps at the rear wheels. Then floor jack up the front so the car is level. Bounce the rear a few times and then tighten it.
I've already driven it 1 block, so it is settled.
Thanks.

RonB · « **Reply #13 on:** November 04, 2014, 18:41:16 »

I found the same problem (shutter under power) torn the new flex disc to shreds - ending up being the sub frame mounts where total shot.

I got the original information from a retired MB mechanic that cut his teeth on 50's + 60's MB.

It seems you are covering all the bases in my reverse order.

Good driving
RonB

GGR · « **Reply #14 on:** November 04, 2014, 21:21:14 »

If the transmission output flange and the differential input flange rotate in non parallel planes, it may induce vibrations. It may seem that having everything perfectly aligned is the best option. However this causes the universal joints in the drive shaft to remain static relative to the rest of the shaft. The consequence is that the forces are always applied to the same points on the joints, inducing premature wear and play which in turn will induce ... vibrations. So, the solution is to have the trans output shaft and the differential pinion shaft slightly misaligned, though rotating on parallel axis. This will have the joints work a bit and ensure their longer life. This is despite having the w/shop manual recommending for alignment, if I remember well.

As mentioned before by others, sub-frame, engine and transmission mounts play a role, and the position of the running gear is usually fine tuned by adding shims under the trans mount if necessary. Worth checking also is the rear axle center mounts, especially the lower cylindrical one: when it goes bad the rear axle usually rotates upwards on the pinion side, modifying the rotation axis of the pinion shaft. Position of the rear axle relative to that same mount can also be adjusted, resulting with variations of the rotation axis.

If everything is in good nick and positioned as it should and vibrations are still there, then it may be a shaft balancing problem. To be noted that the shafts are balanced as complete units, and the position of the front part relative to the rear part must be maintained (i.e. splines should be marked when both parts are separated so as to put them back in the same position relative to each other). So if one suspects the vibration to be due to a balancing problem, it is worth trying shifting the position of the shafts relative to each other by moving them around the splines. A bit time consuming, but it can yield good results.

Not sure if all this is very clear, I can try to explain differently if needed. I looked into this quite extensively some years ago, as I had a vibration at highway speeds that was driving me crazy on an otherwise very well sorted W109 6.3.

georgem · « **Reply #15 on:** November 05, 2014, 11:37:10 »

Iconic,

You mention there being plenty of traps for the unwary and lots of posts about the proceedure. There seem to be plenty about the original disc, but not too much about the new style which is basically a single thichness disc. If I missed any, I would appreciate a hint where they are.

I am currently replacing the disc I put in about 2 years ago because I stuffed it up (to put it bluntly). I thought I had tightened the bolts but all I had done was tighten some of them against the shoulder on the bolt. Consequently I had to replace the centering spider as one of the three bolt holes was badly enlarged as was one of the holes in the flange on the end of the drive shaft - which also had to be replaced - double unhappy.

Any guidance would be appreciated - from anyone. Can I use washers to ensure the bolts are squeezing the disc and how tight can they be. Can all bolts face the same way?

cheers

ja17 · « **Reply #16 on:** November 05, 2014, 16:03:14 »

Hello George,

Yes the new style flex disc is more robust. It is also symmetrical and does not need to be oriented as with the early versions. As before, it uses three long bolts and the same three short bolts. Be sure to place these correctly. Also note that the flat washer is always next to the rubber flex disc, so it is between the bolt head and the rubber flex disc on the short bolts and then between the flex disc on the and the nut on the long bolts. Two rubber seals are involved. One is on the tail shaft of the transmission, (nested in the flex disc) the other is an o-ring on the centering flange at the driveshaft. These seals keep grease from escaping onto the rubber flex disc, during normal driveshaft lubrication. Grease on the rubber can shorten the life of the flex disc. The grease nipple on the driveshaft is used to keep the centering flange lubricated.

Iconic · « **Reply #17 on:** November 05, 2014, 18:37:45 »

GGR, Lots of interesting information there. Since mine did not vibrate until recently (mileage-wise that is) and I found the disk is damaged, hopefully all that needs to happen is drive and enjoy (first drive after replacement should be tonight).

georgem, No additional warnings due to the new disk. Just many of the same warnings minus the orientation of the disk. So, as I understand it, all of the same points apply to the new disk. Joe covered them all (except maybe that the bolts need to all face towards the transmission with the bolt heads facing the rear of the car).
I believe the torque on the six nuts/bolts for the flex disk is 31 ft-lbs, BUT someone else please confirm this.
My disk came with new bolts and lock nuts from the Classic Center. The lock nuts are the "oval" style as opposed to the ones with a disk of nylon. I'm glad they are the all metal oval design ! I used NO locktite. I hope I don't regret that.

After you tighten everything up, then grease the drive shaft. You will know at that point if your seals are working. I actually had a little seepage out thru the o-ring at the same time as the grease came out of the other side of the drive shaft. I wiped it off and I am not concerned.

georgem · « **Reply #18 on:** November 05, 2014, 20:54:53 »

Hi Joe and Iconic,

So in summary:
1. Washers are always next to the flex disc
2. Short bolts therefore have washer near the bolt head and vice versa for long bolts
3. All nuts are on the gearbox side.

I don`t want to turn this into a "Flex disc for Dummies" book but I don`t want to stuff it up again so is this procedure ok.

Starting with the drive shaft :
Insert the three long bolts into the holes on the tail shaft flange, heads to the rear.
Assemble the centering spider inc the "o" ring and place over these bolts
Place the flex disc over these bolts, add a washer then finger tighten the nut
Place washers on the remaining short bolts and slide the washer down to the bolt head. Insert these bolts into the three remaining unused holes in the flex disc - bolt head (and washer) to the rear
Insert the rubber sealing ring over the shaft of the gearbox
Insert the three protruding bolts from the flex disc into their corresponding holes on the gearbox flange, install nuts and finger tighten
Tighten all six bolts to 31ft/lbs??
In summary:
The three long bolts hold the tailshaft, the centering spider and the flex disc together.
The three short bolts hold the flex disc ( or the above assembly) onto the gearbox
The centering spider and the flex disc can be assembled on a bench before inserting into the tunnel

As I said, the above is "Flex disc assembly for Dummies" but if the above could be confirmed I would be appreciative

Iconic · « **Reply #19 on:** November 06, 2014, 03:47:54 »

George,
You've got the orientation of all the bolts, nuts, and washers correct as far as I can see.
Everything else sounds correct, but you have the early drive shaft, and I don't really know how that works or how much clearance you will have.
I didn't have much clearance even after I loosened the drive shaft nut. I needed to push the drive shaft back and hold it because it would "spring" forward if I let go.
I removed the grease nipple, but that didn't change anything.
Anyway, I had to struggle to get everything sandwiched back in.
I needed to be very careful not to cut the o-ring or move it's position.
I was not a smooth process for me. It was my first time.
Of course, Joe is a much better source than I am.
I don't have much more to add.
Good luck ! I'm glad it is over for me.

ja17 · « **Reply #20 on:** November 06, 2014, 21:00:29 »

Looks good George, I think we have a nice picture in the tech manual. Yes, I have seen the all -metal locknuts being supplied also. Locktite is not needed in any case as long as you are using locking nuts.

Don't worry Iconic, it will go easier the second time !

Hopefully, not anytime soon.

Iconic · « **Reply #21 on:** November 06, 2014, 22:47:59 »

Thanks for all your help, Joe !

georgem · « **Reply #22 on:** November 25, 2014, 07:41:50 »

A bit more help is needed I`m afraid.

I partially assembled the flex disk out of the car on the bench - using the long bolts I attached the drive shaft, the centering spider and the flex disk and tightened the three bolts - no problems.

I then slid the front of the drive shaft into position and used the three short bolts to connect the flex disk to the gear box flange. Here lies the problem. When I tightened these three down, the thread on the bolt protrudes past the nut enough to hit a flange on the back of the gearbox and stop the prop shaft turning. Hmm. I tried to reverse the bolts ie have the head on the gearbox side but there is not enough room between the flange and the gearbox to allow them to line up.
The back yard mechanic in me is telling me to cut 3mm off the end of the bolt. Is there a more "Mercedes like" option or should I listed to the back yard mechanic.

cheers

Jonny B · « **Reply #23 on:** November 25, 2014, 16:36:53 »

I would wait to hear more back on this. The bolts should fit. A friend and I changed the flex disc on his car a year or so ago when he re-sealed the transmission (manual) and I recall we had to do a couple of different trial fits to get everything to fit correctly. If the parts are all correct, you should not have to "backyard mechanic" anything.

A very good friend told me, "This is a MB, the parts fit!"

Iconic · « **Reply #24 on:** November 26, 2014, 02:11:32 »

georgem,
I did not have this bolt hitting gearbox issue.
Did you compare the length of the bolts you took out to the ones you put back in?
Look at the awolff280sl post earlier in this string. He had to add washers. It sounds just like your situation. But frankly, I wouldn't double or triple up the washers (I'm conservative). I would try to figure out why it is hitting, like comparing the bolt lengths.
Maybe it has something to do with the early drive shaft?
My only issue was the inner diameter of the washers that were provided were slightly too small to fit over the bolts.
So, for the places where the washer had to go against the bolt head, I used the old washers ... but only one on each bolt.

Otherwise, no other problems with the hardware.

News:

Author Topic: Flex Disk replacement - Drive Shaft procedure question (Read 17914 times)

George Des

George Des