Propeller drive shaft CPR
Removing the propeller drive shaft (also called the center drive shaft) is necessary when you are removing the engine/transmission, changing the flex disks or removing the differential/ rear subframe.
The procedure is similar to most cars and it is exactly the same for W126 and many Mercedes models. So guide this will work for both. Expect some wrestling and sweat underneath the car since the bolts can be very tightly on.
I highly recommend to change the center bearing, the center bearing carrier and front and rear flex disks when you remove the drive shaft for whatever reason, simply due to the long time of the job it would be a waste unless you also change these wearing parts with limited life span.
Remove the exhaust, check out How to Remove the Exhaust system
Remove the parking brake adjuster cables and springs. You will have to unhook the spring from the adjuster in order to get the cables off. The system is basically an adjusting rod with three cables attached to it and a spring to keep tension on the cable whem the parking brake is released.
Now on to removing the drive shaft!
Loosen the sleeve nut in the middle of the drive shaft, this is to be able to collapse the drive shaft so it becomes shorter when removing it. Have a helper to apply the brakes so the shaft wont rotate when you try to loosen the sleeve nut. I do not like to apply pressure to the Transmission with the gear in Park due to the possible damage this may cause. Have the car in neutral instead.
Next step is to remove the flex disks, there are one at each side of the drive shaft. The bolts are of a self locking type (the nuts are not completely circular) and they are hard to remove since they are not meant to get loose when you drive. I actually broke my spanner trying to get one stuck bolt off, so here I recommend some long spanners or some form of extension on the spanners to get more torque. Remember simple physics where the torque = force x length, so the longer the better when loosening stuck bolts and nuts. To get the drive shaft off you only have to remove three nuts. The ones that are attached to the drive shaft spider. If you are planning on replacing the flex disk, then you have to remove all 6.
There might be tricky to access a spanner on the side facing the transmission, and you might end up supporting the transmission with a jack and removing the rear transmission mount.
Unfortunately you have to remove the three nuts at the differential end as well, the access here is easier though.
Now the drive shaft is hold in place by the center bearing carrier. The center carrier is just hold there by two bolts in the chassis.
Now you have to collapse the driveshaft by pushing the front side of the shaft in towards the middle to get it loose from the transmission spindle.
The drive shaft can be so corroded onto the flex disk mouting plates that you will not be able to do this easy by hand. I used a long screwdriver to place it between the drive shaft spider and the flex disk and used massive force until it broke loose.
Warning: You might end up damaging the flex disk which i did. It was so corroded that one tab of the flex disk broke off wæstill attached to the spider.
Caution: Be careful when handling the drive shaft so it doesn’t come slamming into the ground or on youself for that matter. The drive shaft needs to be perfectly straight and it is also balanced by the factory to a, so be careful eh?
The bearing is most likely stuck in the drive shaft center carrier, always replace this cheap rubber part or your drive shaft will vibrate while driving. Just rip it off or use a knife to cut it so you can access the bearing.
The Bearing is pressed is pressed on the shaft and you need a puller tool like this. Note the placement of the dust caps around the bearing, so you place the the same direction when fitting the new bearing.
After pulling out the bearing, insert the new bearing into the new center carrier.
Remember to insert the inner dust cap before tapping on the new bearing.
Use a metal tube to tap on the inner part of the bearing, be careful with the hammering and do this slowly.
Assembly is pretty much the reverse as removal, however you need to spin the drive shaft around a few times after fitting before tightening the sleeve nut. Also put the car to the ground, roll it back and forth a couple of times. Then you can tighten the sleeve nut. This is done in order to remove stress on the drive shaft bushings before tightening.
Always follow the torque specifications on the flex disk bolts!
Cheers, Robs out