Things I think I know

about CV's and axles

Originally written; March 3, 2009

To start off;

I'm no hero in regards to knowing everything about Porsche and Audi stuff!

Things noted here are to the best of my current knowledge. If you spot anything that is wrong, please contact me and let me know what the reality is. Here is a link to my E-mail.

The stuff noted here is due to researching for an axle and CV solution specific to my project. It's not a typical 914 project due to wanting to use the Audi / WV 012 5 speed transmission, which is similar to the early Boxster transmission.

Stuff that I talk about on this page may be specific to the project I'm doing! Don't assume that any of this will work on what you are doing.

Worthwhile links

SirAndy has a good string on the 914World site that can be viewed by clicking here. He goes into what is required to use 944 CV's and how to modify the original 914 axles.

Eric Shea has an equally good string on the 914World site that can be viewed by clicking here. He uses 911 CV's and then purchases new axles of the correct length from Sway Away.

To get to Sway Away's web site, click here.

To get to Taylor Racing's web site, click here. They can supply modified CV's and I'll get into that latter.

There is the Blind Chicken Racing site with a page called "CV joints 101" which is good to know about and you can get there by clicking here.

Random things to know (terms) when talking about CV's?

1.    Normally a CV is referred to based on it's size. A 108mm CV has a body with an outer diameter of 108mm.

2.    A CV of 108mm may be available in different widths. The wider it is, the more the balls can move in and out within the body. This is a big thing if you need more angularity in the joint. (A big thing with the sand rail guys)

3.    Normally a CV is attached to the hub with 4 bolts and 2 dowel pins, or 6 bolts. The early Porsches had 4 10mm bolts and two dowel pins. When Porsche first went to 6 bolts, (1975?) they used 8mm bolts. The latter year CV's used 6 10mm bolts.

4.    The "spline count" is the number of splines on the axle, where it slides into the inner race of the CV. There are 25, 29, and 33 spline axles. Now there isn't any mechanical reason to dictate that an axle with a specific spline count is a set diameter, however there seems to be an industry standard that the spline count does dictate the axle size (at the splines). In other words, all axles that are 29 spline are the same size at the spline.

5.    GKN / Lobro is just about the only company that manufactures quality CV's. One problem is that they like to market axle assemblies that are complete from CV to CV. This is only and issue due to the fact that they seem to like using 25 spline axles. This axle configuration may not match what was originally in the car and you may not be able to find a 25 spline axle of the correct length.

6.    "Full floating" axles are ones that do not have a circlip on the end, capturing the CV's inner race at a specific location. The axles sold by Sway Away are floating axles. The original axles on a 914 are not floating. What this means is that on a 914, as the suspension goes through it's travel range, the axle forces the center race of the CV inward and outward. As best as I can figure, all sand rails use a floating system.

7.    Not all CV's of a certain size are the same width. It's due to this that when the SirAndy solution of using 944 CV's is done, the stock axle has to be modified to make up for the added width. He is using a wider CV.

8.    The wider the CV, the more angularity it can handle. In other word, the more suspension travel you can have before dropping out a ball. This is a big thing if you are building a sand rail. It also means that there can be more "plunge" of the inner race before dropping a ball. This could be significant if not running floating axles.

9.    A "lightened" CV is one where material is removed from the outer race. You can buy lightened CV's from GKN.

What are the different CV's?

"930" CV's are also called the "turbo" CV's. They have an outer body diameter of 108mm and have 29 splines. The bolt circle is 94mm and takes 6 10mm bolts.

"Type 4" CV's are used in the VW type 4 cars, latter bus's, and some of the 944 Porsches. They have an outer body diameter of 100mm and have 33 splines. The bolt circle is 86mm and takes 6 bolts (8mm??) These are the CV's used in the SirAndy "solution".

"914" CV's are no longer available and that's why the above noted (and linked) axle "solutions" exist.

"early 911" CV's are no longer available from Porsche individually. They do have a full axle assembly available at the price of $600 per axle. What I wouldn't feel safe assuming is that they still have a 29 spline axle. (my guess would be that they just re-sell the GKN unit, which has a 25 spline count) Some of the early 911 CV's used 6 8mm bolts and others use 4 10mm bolts along with 2 dowel pins (it's the 4 bolt version that Eric Shea uses)

"GKN" or "Lobro" CV's are ones manufactured by GKN / Lobro and I'm making up the term so I can discuss some of the ramifications should you use them.

"Empi" CV's are sold by Empi (a seller of air cooled VW stuff from the beginning of time). Empi axles and CV's are at such a low price, I've just got to question the quality.

The solution to my problems;

Here are the parts required for my set-up;

1.    930 CV's which will bolt up to the transmission output shafts

2.    28 spline axles fromSway Away

3.    Modified Type 4 CV's at the early 911 6 bolt stub axle. These are the "trick" items required to get this to work. Taylor Racing takes a "lightened" GKN 100mm 6 bolt CV, re-sizes the inner race and then broaches it for a 28 spline axle. Although not called out on their web site, they have them in stock as part number 02002521. The cost is $199 each.

So there you go.

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Wes Vann