This actually relates to a 1996 V70 mk 1 but as the running gear is the same as the 850 and there seem to be more CV joint related posts for the 850 I thought I would post here, hope that is okay?

I have sheared 3 CV joint shafts in around 300 miles, the last one lasted about 30 miles!
They shear in the same place each time about 1/2 inch fom the end of the splines just as it protrudes through the hub on the hub nut side.

I replaced the outer CV joint the first time and the whole axle complete with inner and outer CV joints the second time.

There has been a slight wobble when breaking, feels like a warped front break disc but that seems to check out okay.

any adivce appreciated as to what may be causing this strange and expensive problem.

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Here's probably a silly question, but were you using original parts all the while? If they are not, the material may have been inappropriate - though i doubt that'll be the case, for the third time.

And what made you suspected the CV join in the first place? Vibration at acceleration?

Sorry i cant be of much more help.

Hi,

The first to go (as far as I am aware) was a Volvo original been on for the 40k miles I’ve had it and probably a lot longer.

second was a good quality pattern part, and last was good used Volvo original.

I replaced the CV joint because the shaft had broken! see photos.

Just had another look and the hub splines are definitely worn, the cv joint spins inside the hub even with splines are engaged all the way.

I guess this has happen when the joint spins in the hub after the break and wears down the splines. The hub will obviously now need replacing.

The slight play in the splines may explain why the CV joints break so quickly 2nd and 3rd times, as the play will eventually I believe weaken the shaft but it does not explain why it happened first time?

Any thouights?

Just some food for thought, as alot of the industrial eqiupment I work on uses similar splined connections and we've had to repair a bunch of broken shafts over the years.

If you hub spline is truly worn, this can be part of the problem you are experiencing. It appears from the pictures that the splined shaft is breaking off just inside the splined hub. If so then you most likely have a worn inner section of the hub. This worn area is going to put extra stress on the shaft, because it is now only making forced contact in less than 100% of the originally designed surface area, increasing the amount of stress on the shaft to produce the same effect, and in a smaller area. It will shea at the spline normally as this is the weakest part of the shaft, especially where it can escape the hub, as that is where any shear pressure is going to exist.

At this point my initial thought would be to replace that hub with a new one (not used, or you might experience similar problems again) and preferably use a new CV joint, so that all parts mate properly and with full surface contact.

It might also be suggested to do the same on the other side, because if you have any worn parts on the other side, correcting one side could increase the other side's failure chance with added stress (inspect it as best you can to determine this).

You can have a metellurgical place test the broken shaft to try to determine exactly why it broke as it did, but that can take time and might be expensive (and most people dont know where such places are anyways...usually a local Catapillar repair place, or similar excavation equipment place, can lead you in the right direction).

Of course improper alignment can cause this as well (not front wheel alignment but installation alignment).

I suppose possible transmission problems might lead to this as well, if it isnt distributing power properly and instead forcing all driving power to one wheel all the time...not sure as I dont know transmissions very well.

Hopefully you aren't the type that aims for every pothole you see...haha.