CV in the Drive Shaft

**101RRS** · 14th November 2006, 02:43 PM

While this question relates to a Freelander - it is general and could apply to any vehicle. Note the question relates to "propeller or tail" drive shafts not axle drive shafts

On another forum I was reading about a Jeep that had the CV on its front drive shaft fail. It failed because it was old and the car had a substantial lift. It broke at the front diff end.

Now it got me thinking because my Freelander also has a CV on the drive shaft but as there is no relative movement and the drive line is relatively straight I do not understand why LR would bother putting one in - a drive shaft uni joint is about $70 but the CV is extra special at about $500.

The drive shaft in a Freelander is 2 piece with the viscous coupling in the middle. The engine/transmission module, the VC and the rear diff are all basically bolted to the body in a straight line - there is nothing in the drive shaft the goes up and down. There are universal joints on the rear drive shaft joining the VC to the diff and where the front shaft joins the VC there is a uni. However where the drive comes out of the Intermediate Drive Unit (the equivalent of a transfer case) there is a CV. As I have said there is nothing that goes up and down and the drive shaft is basically straight - so why would LR put in an expensive CV (and it has a different design to most CV joints) instead of a uni like there is on the rest of the drive shaft.

Why do I ask? - the CV churns out grease from time to time - I have topped it up once and will have to do again at the next service and i suspect I will have to replace it soon - has covered 210,000 km though there are no other indications it has a problem. I replaced all the universals when I topped up the grease last time so I know they are all OK.

Thanks

Gazzz

causing the drive shaft to

**Scouse** · 14th November 2006, 03:14 PM

I can't say I've had a close look at the Freelander prop shaft set up but the engine is mounted transversely.
Maybe the rocking under load might be why there's a CV fitted. Does the CV slide as well or am I confusing that with something else ?

**101RRS** · 14th November 2006, 03:24 PM

Originally Posted by Scouse

Does the CV slide as well or am I confusing that with something else ?

Like all CVs there is an inbuilt measure of slide automatically provided.

Gazz

**dobbo** · 14th November 2006, 03:29 PM

I have never looked at a Freelander but as a guess, would suspension travel droop on the tailshaft have anything to do with use of the cv joint?

Aren't CV joints stronger than Uni joints?

**JDNSW** · 14th November 2006, 04:02 PM

Not familiar with the Freelander drive train, but I suspect the reason that a CV joint is used is that there is a bend in the line of the shaft without an equal bend in the other direction. The fact that the shaft is pretty rigidly connected to the body, amplifying any vibration, may also be a factor.

CV joints are not necessarily stronger than conventional U-joints - it depends on construction and size, and the design is so different that it is difficult to set equivalents other than on strength. And I presume you are talking about the common Rzeppa type of CV joint - there are others, including the Tracta joint used in early Landrovers.
John

**BigJon** · 14th November 2006, 04:08 PM

Originally Posted by dobbo

I have never looked at a Freelander but as a guess, would suspension travel droop on the tailshaft have anything to do with use of the cv joint?

Shouldn't be any variation in tailshaft angles with suspension movement. Independent suspension sees the diff centre mounted to the body.

**dobbo** · 14th November 2006, 04:09 PM

Originally Posted by BigJon

Shouldn't be any variation in tailshaft angles with suspension movement. Independent suspension sees the diff centre mounted to the body.

It was a guess I didn't even know they had Independant suspension

**Slunnie** · 14th November 2006, 04:15 PM

Its probably to prevent vibration from the angles of the input/output of the shaft. The Uni joints cycle through their rotation (speedup/slowdown) and this can be balanced when the angle changes are minimal and the input/output angles are controlled, but the CV's will keep it constant throughout the angle. Well thats my guess at least.

**ladas** · 14th November 2006, 04:48 PM

According to RAVE the freelander does not have CV joints - it has uni's and a viscous coupling.

No reference to CV's at all

???????????????

**101RRS** · 14th November 2006, 07:29 PM

Originally Posted by ladas

According to RAVE the freelander does not have CV joints - it has uni's and a viscous coupling.

No reference to CV's at all

???????????????

Well in that case the Rave has made an error - each axle has two CVs on it and the tail shaft - 3 universals and one CV (a tri-pod type CV). May Rave disk is at work so I cannot check it but my Haynes manual has a CV and as I said - I have had it out to replace the grease ad it is definintely a CV

Slunnie - and others - the drive shaft is virtually straight - at least straight enough for government work - so a CV is not really needed for this aspect - any series or disco drive train has much more of a change of direction in it.

I guess the mystery continues.

Thanks

Garry

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