Half Shaft Alignment - Education please

[Brett James-McCall]

Having read the straying in Ron's starter thread, I thougth I'd open a new one for people to share their knowledge on half shaft alignment, as I personally eould like to get some knowledge. Thanks

Brett

 

[Frank Catt]

Brett, do you have a particular problem ? Frank

 

[Brett James-McCall]

Not yet, but want to understand the principles/fundamentals, as I hopefully will soon be putting the Audi in the back of the GTD.

Brett

 

[Graeme Stebbing]

hi brett, I too am using an Audi box and after lots an lots of digging found that a cv will run at 7 deg quite happily that is about 50mm front to rear offset, and level horizontally, i have an old Toyota Corona and its done over 200,000km at 7 deg and no problems.

regards
Lambo

 

[Jac Mac]

Brett,

My post on Rons thread was in relation to them shifting the trans slightly from the chassis builders (presumably ) optimum position in order to create enough room for another component eg-starter-alternator etc, and in doing so create a halfshaft problem which would not show up until later in the build.

Russ,

There is no great problem with running CV's at a slight angle ( in fact it is preferable to running them 'straight' ), but the halfshaft plunge capability must be carefully checked thru the whole range of suspension movement to ensure that they neither compress to the point of bottoming out or extend to the point of pulling against the retainer circlips and when doing these checks bear in mind any suspension changes you may intend to make in the future to obtain the correct alignment(See the two cobra Forum items that Fran posted ). Fortunately the CV's dont suffer from 'Spline Bind' like the older splined halfshafts and suspension 'jacking' under power is unlikely.
Ideally we would place the output shaft at a height relative to the rear wheel hub in the same manner as the steering rack/steering arm when doing bumpsteer checks to keep plunge distances to a minimum, but unfortunately things like ground clearance under the trans/bellhousing/oil pan dictate this height and of course the tyre diameter sets the hub height.

Jac Mac

 

[Dave Bilyk]

Brett,
second JacMacs advice over checking driveshaft plunge through the whole range of suspension travel. One output shaft roll pin broke in my UN1 because the drive shaft had no free plunge movement on suspension droop. I now check this after every rear suspension adjustment.

Dave

 

[Sandy]

Brett

Thanks for moving the thread!

Did some more poking around and saw that the 930 CV's were capable of 25 degrees of angle before binding. One thing that I guess might also be a problem would be the length of axle is short which would seem to accentuate the plunge problem. How long is a stock 930 Porsche half shaft vs. what we might be running... It still seems like the correct length CV that is used within the bounds of it's angular constraints should be ok (if length is correct or not a crazy short shaft). Seems like a simple trigonometry problem if you know the allowable plunge and the rest of the angles. Maybe the 25 degrees after you start with some shaft angle and add suspension extremes is the issue.

While changing brakes on my wifes boxster (yes, she takes advantage of free labor) I notices the engine offset in 2 dimensions, looked like the trans was forward and up as I recall. Seemed interesting, but I guessed it doesn't matter much to the CV.

Sandy

 

[wanni]

It depends from the CV joints you are using.
You shall ask to the manufacturer of the parts you are using which are the limits by checking the efficiency diagram.
It is not a law that CV can be installed with a certain angle, it depends from how they are made for.
Normaly the worse of the CV joints can take easly 8° of composed angle. This angle is the static angle added with the suspension stroke from totaly bumped to totaly rebounded.
Going over this angle you might need also special rubbers in order to keep the grease inside and to do not overheat at high speed.
My suggestion is:
Do no invent the hot water.....just ask to the manufacturer what the product is made for and never, but never you will have any kind of trouble.
Ciao
Wanni

 

[Ron Earp]

I asked a friend of mine who races a Porsche about half shafts and getting some done, or getting technical information about them. He pointed me at one source which seem to do one-off and custom work.

Mark Williams Enterprises - Custom Work

I also found this other one kicking around on the web.

Dutchman Motorsports Inc.

Kind of light on web information on that second one, but the first one apparently does some custom work on order.

The Z I race operates at about a 7-10 degree angle, but it uses these extremely heavy half shafts that have U joints on each end with a shaft that plunges into the body of the other. I've got a bunch of them under the house as a racer gave them to me saying "these break all the time, you'll need them" but I don't believe it. These things weigh a lot and look extremely beefy. Might could be a possibility to use something like them on a rear engine build. Below is a good picture of them in position at about their operating angle.

So the main reasons to use CV joints over a U joint are smoothness of operation and greater angles of use? As Wanni says, looks like it might be fairly easy to get specs on different CV joints and know for certain what can and cannot be done with them. I've got 930 CV joints in the garage, but just messing around with them you can't tell a whole lot.

R