Drive shaft replacement for W124 cautionary tale

[joe prosser]

My wife went to pull away the lights and heard felt a loud thump. The car (W124 estate automatic) failed to move. I towed the car home and found that the near side drive shaft had sheared just inside the rubber boot (see picture). My wife suggested that if it broke on one side it was possible that not before long the other would go the same way and so I ordered two new drive shafts from J&R at £110 the pair (Part #DS687). Shafts arrived next day, excellent! I dutifully put the car up on stands and swapped out both drive shafts. I torqued up the diff connecting bolts to 70Nm and lowered the car to the ground. Torqued the spline shaft nut to 200Nm on drivers side, but when I did the near side I thought I heard a click from the torque wrench but it did not feel quite right. It turns out that the spline shaft had simply pulled right off the end of the constant velocity joint (see picture). I put the old, intact, shaft back on since it was operating smoothly. It was a sod of job and if I have to this again I will go for the SKF (VKJC 3244) at three times the price, believe me its worth it.

 

[brucemillar]

Ouch.

 

[John N]

Calling on my previous engineering experience I would say that's most definitely broke!

 

[joe prosser]

Calling on my previous engineering experience I would say that's most definitely broke!

Glad for the technical assessment, and there was I thinking it was JUST well f****d but what do I know LOL. I don’t know where these cheap shafts are made but i would guess they have a high proportion of chinesium in the casting. The end of the CV joint was about 6mm thick, it simple should not tear out the way it did. Having said that the original Mercedes shaft of 25mm diameter should not have torn apart either. The drive shaft material in both cases seems to behave more like cast iron than steel.

 

[WDB124066]

Where will you get the replacement bits from now...?

 

[optimusprime]

I may be wrong but did you install them while the car was on jack stands . I think reason this broke on assembly is the car should be on the floor to fit the drive shafts .

 

[joe prosser]

The car was on jack stands so the wheels were on full drop. I fed the outer splined ends of the CV shafts into the back of the wheel hubs and then lifted the inner CV joint to mate to the differential hubs. The splined ends slipped in very easily without any fight and so there was absolutely no chance of any damage or breakage possible at this point. You need to have both wheels at full drop at this stage to allow enough room to mate up the inner CV joints to the differential. I bolted up the six inner differential mounting bolts to 70Nm torque then lowered the wheels car to the ground, since they spin if you try to tighten the wheel hub nut. I finger tightened the wheel hub nuts then applied 200Nm torque (148 ftlbs) or at least tried to. The specification is 200 to 240Nm. The drivers side torqued to 200Nm no bother but the passenger side clicked just as I thought it might be getting close to 200Nm but in fact the sound was the splined end detaching from the cv joint. I have worked on cars for years and have never seen this before. There is no way that I, with a 18” long torque wrench with a 210Nm maximum, could exert enough force to begin to pull a splined shaft off a CV hub like this. I would expect that the first sign of over tightening would be the threads of the wheel nut becoming stripped or the corners of the nut becomming rounded off since it is made of quiet soft metal and it has a low profile.

 

[joe prosser]

Where will you get the replacement bits from now...?

SKF shafts are supplied by ‘buycarparts.co.uk’ and ‘autodoc.co.uk’. At the moment I am reusing the one shaft that I had replaced as a precautionary measure, it seems to be OK for now.

 

[optimusprime]

Joe you know what your doing . And may be a fault in the manufacture of the shaft . .Will you return it to the supplier for inspection .