our track cars eating up the CV's

[962porsche]

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I'm posting this again . seams for some reason it was removed?
the cars manufacture I'm leaving out but they are a manufactured race/track car.

the problem is the cars eat up there CV joints. after some searching and taking to a few manufactures of the VW type 2 CV joints that as I knew the half shafts exceed the angles the CV's are designed to run it.
this I already knew because the bearing cages run against the cups the CV's bolt to.

now it's time to come up with a fix that doesn't require a total redesign and lots of fabrication work and high cost.
sadly I don't have a easy or low cost fix for the bad design from the manufacture.
with about 150 cars manufactured to date I'm sure the other car owners that own one of these car would also like a way to fix the problem .

the fix is to drop the rear diff lower in the chassis but what sounds simple really isn't because the lower chassis cross rail under the diff will contact the chain. the lower cross rail also has the mounts for the rear engine mounts on it. not only have two cars I personally own but we have 3 customers cars that the customers said if you can come up with a fix then we want our cars also fixed.

I was thinking of taking the adapters for the CV to the rear diff and to the hubs and putting them in the lathe and cutting some of the material away so the cages of the CV bearings would run against them. this may fix that problem but not the problem of the CV's themselves exceeding the angles they are designed to run at. both reason is why the CV's are over heating and cooking the grease out of them.

[962porsche]

sorry don't know why 3 of the same diff pics got posted.

[KB58]

You're asking the math to change for you, not going to happen. As a ghetto fix I was going to recommend the same - cutting back the cages just enough to clear, but as you pointed out, that doesn't fix the geometry problem. With 150 cars already out there, have you asked those owners if they're running into this and what the fix was? Other than that, you pretty much answered your own question, lower the diff.

Oh, a couple more thoughts. Is this happening to only your car, and if so, can you change what you're doing? For example, if - as Napoleon Dynomite asked - are you taking it off any sweet jumps? Assuming not, driving on really bumpy roads or tracks? Lastly, how are the shocks set? If they're too soft in compression, they may well be the issue, but that of course brings other factors into play. Everything is connected to everything else...

[Bent Wrench]

Bump stops or travel limiter straps?

[LoadOS]

I once read about some Porsche "race" CVs.

A racer decided to take one apart to see what made it a "race" part. Evidently the ball bearings in the street car part were slightly oversized so it would wear in quickly. The "race" part had slightly undersized ball bearings and a special high temperature grease.

A strategy of doing a rebuild like that on brand new CVs might allow them to last long enough for at least one race.

[Bent Wrench]

I fail to see how a Locost would hyper-extend a CV, they don't have enough travel.

For high travel stuff look at the side by side and UTV stuff available.

Those HyJump buggy chassis use some high angle stuff.

Those crazy Icelandic folks use a double u-joint extend usable offset.

[962porsche]

at a static ride height the CV's are just over there max angle of the 17 degrees. even for a road course racing car like these are you need your suspension to work in both compression and rebound so limiting the rebound not to go more than 17 degrees will not work.

yes every owner of these cars has the same problem with having to do constant CV servicing. I do the ones on both our cars every 4 days of track use and never more than 6 days. our cars are track day rentals cars to date each car has done over 70 track events this season I have lost count with how many CV's services I have done just this season so far.

I know the only real fix is to drop the diff and then deal with the chassis cross rail and the lower rear engine mounts.
it's either lots of work once or a few hours every week pulling the CV's and servicing them.
Im sure I will also need to have new half shafts made because dropping the diffs will also shorten the distance between the hubs and the diff's.

[KB58]

at a static ride height the CV's are just over there max angle of the 17 degrees...

Is the range of motion 17 degrees total (+/- 8.5 deg), or +/-17 deg? Regardless, if it's at the limit just sitting there, then the CV assembly itself is the droop limiter, unsettling the suspension over any extension, and probably makes terrible noises while doing so. Dumb question: is the car at the mfg recommended ride height, or - because they're track rentals and students regularly get into the rough - is the ride height been set extra high? This could cause exactly this issue.

I'm at a loss to understand how a track-only race car is exceeding the CV's range of motion because typically, race cars have about 2" total travel. I wonder if the designer arbitrarily shortened the half shafts without understanding the implications of doing so...

[Bent Wrench]

I wonder how much power those joints eat up operating at high angles?

[Miatav8,MstrASE,A&P,F]

I thought this was covered already but it has been a while. No extra spline length on the inboard end for the cv's to slide. Necessary for this type without a fixed inner cv "tulip" to float on an inner cv cup. The damage to the outer stub axle is likely being mirrored in the trans stub bearings.

[Bent Wrench]

One of the joints has to plunge or the axle will get bound up as the suspension moves.

I did not think they made axles like that, or is this shake and bake?

[Kartracer47]

Type 1 (Bug), type 2 (Bus) and some Porsche CV joints are self centering. They must be used in pairs for this to work.
Front wheel drive CV joints are a completely different design. Outboard joints that work with the front wheel only allow . The inner joint allows angular change and plunge.
Check with offroad buggy builders to find out what they are using as noted previously.

Note to others - In this instance the joints are running at a near constant high angle of change.

[Miatav8,MstrASE,A&P,F]

In the missing topic, the vw/porsche style axles had no plunge ability. Not oem axles but custom for this application. The plan was to remove a snap ring between the cv's on the inner end to provide a bit more plunge or use off the shelf aftermarket axles with what I expect are 930 size joints.

Multiple problems obviously though we can't really see anything. Considering the engineered angle problems, the issue probably is what was ordered (engineering drawing) instead of who made them. FFR ordered 18 inch Chinese axles years ago and received crap axles that were not returned by FFR and were sold as replacement parts. I bought a set for a miata I was putting a tbird diff into, didn't realize they were crap until months later, then traded them off to someone with full disclosure.

[Bent Wrench]

Don't engineer around the angle problem, the angle is the problem and must be addressed.
Plunge must happen too even with low angles.

[962porsche]

as the previous post that was removed states the plunge of the half shafts is also a problem. I did remove the inner C-clips on the inner CV joints. I had hopes this would stop the half shafts pushing the CV's into the adaptors to the Diffs. it did not ! the cars manufacture has C-clips on the inner and outer sides of both inner and outer CV of each half shaft.

the cars have about 2.75" of suspension travel from full droop to full compression. at static ride height when you lift the car up some wheels are off the ground there is about 1/4" droop.
needless to say I tried to lower the cars as much as I could but the problem with that is I can't lower the cars more than a 1/4" before under full compression the car will bottom out the floor on the ground. so in short the car would belly out before the suspension goes to full compression.

to date I did a mockup with the diff lowered in the chassis with the CV and half shafts dry fitted ( no grease and no CV boots) the half shafts are way to long to put the half shafts at the 6 degree angle as they are in a VW bus. every VW and Audi half shaft I can find lengths of are way to long! in fact they are also longer than the half shafts in the cars now.

what it comes down to is a total redesign! I would most likely have to have shorter custom half shafts made. it's also going to take many hours of fabrication work to remake the lower chassis cross bar that holds to lower rear engine mounts because dropping the dive the chain will them hit the factory cross bar on the cassis now.

I guess when you buy a 40K starting price for a sports racer new you sure get what you pay for!