Issues with Beetle CV joint failure? Options

[stownsen914]

Hi all,

With 914 CV joints being NLA now, I recently tried out Beetle CV joints when my old ones wore out on my 914/6 race car. I understand they are made by EMPI. I am using the same 914 axles I've used for years. After about 30 minutes of track time, one of the Beetle joints failed (the inner one on the right side of the car). Basically the joint seems to have been plunging too far inward and the lateral force seems to have just forced the joint apart. No broken parts are immediately apparent. The joint seems to have just fallen apart!

I also noted that the inner races of the joints seem to be gouging the output flanges on the trans. This occurred on both sides fo the car. I had noticed some of this wear previously, but it seems to have accelerated significantly with the Beetle joints (especially considering only 30 minutes of use). See the pics below. It's hard to tell from the pics, but the wear spots are basically gouged into the flanges about a millimeter or so deep.

I never had any failures or unusual wear with the 914 joints I used for years, so I am at a loss what happened here. Anyone have a similar issue with Beetle joints? I'm wondering if I should be trying Lobro or other joints, or a different setup entirely ...

[SirAndy]

Yes, they over-extend and fail. There have been several threads about this, the first failure of this kind i saw was maybe 6 years ago on McMarks car.

However, there is a version that does work and i believe PMB sells them now.
http://www.pmbperformance.com/catalog/item...868/9926705.htm

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[ChrisFoley]

Yes, they over-extend and fail.

Scott's problem doesn't appear to be related to that mode of failure.
Note the amount of "damage" inside the output flange which indicates the axles are bottoming not hyperextending.

Scott's failed CV is one of mine.
After McMark's issue we carefully inspected the CVs we work with and couldn't find anything that would lead us to believe our assemblies would suffer the same result.
What was written by Eric and/or Mark didn't just fit with our findings.

I know of only one other on-track failure of the ones I sell, which was on a Lemons car in the mid-west. That one went 4 hours before the unloaded side came apart, probably by hyperextension.
Matt Romanowski has lots of track time in his 3 liter car with our axles installed.

In both failure cases there's no evidence of the cage being damaged.
I have a test planned to hopefully gain further understanding of what happens.

[SirAndy]

After McMark's issue we carefully inspected the CVs we work with and couldn't find anything that would lead us to believe our assemblies would suffer the same result.
What was written by Eric and/or Mark didn't just fit with our findings.

Eric's article is a bit misleading as it seems to put the blame on the inner cage.

After McMarks failure, we went back and compared the new VW CVs with original 914 ones and noticed that on the VW CVs, the inner portion had significantly more side to side travel.
So both extending or compressing them can result in a failure when force is applied at the same time. At that point, they basically just fall apart.
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[ChrisFoley]

...
on the VW CVs, the inner portion had significantly more side to side travel.
...

That is true.
However, that shouldn't be enough to allow the joint to come apart unless there's a huge angular misalignment of the axle.

One idea I'm looking more closely at is possibly installing teflon (or similar) buttons on the ends of the axle to prevent the shaft from travelling so far that a CV could allow a ball to come out of the track.

[Mugs914]

...
on the VW CVs, the inner portion had significantly more side to side travel.
...

That is true.
However, that shouldn't be enough to allow the joint to come apart unless there's a huge angular misalignment of the axle.

One idea I'm looking more closely at is possibly installing teflon (or similar) buttons on the ends of the axle to prevent the shaft from travelling so far that a CV could allow a ball to come out of the track.

I've seen some CVs that have a stamped metal 'cap' that goes between the CV and the flange, presumably to limit the axle plunge and to retain grease. Taylor or someone may have one that will work.

I'll be really interested to know why the Empis allow so much more lateral movement of the axle. Is there some difference in the actual design of the joint or is it just a difference in tolerances? (IMG:style_emoticons/default/confused24.gif)

Mugs

[ChrisFoley]

...
I'll be really interested to know why the Empis allow so much more lateral movement of the axle. Is there some difference in the actual design of the joint or is it just a difference in tolerances? (IMG:style_emoticons/default/confused24.gif)

Mugs

I believe its due to longer slots in the cage.