Porsche 930 Transaxle, Half Shafts, Angles

[Ron Earp]

Our T70 is coming along really well and I’ve been quite pleased with the progress we’ve been making. The only thing about the setup that bothered me, and more than a few other 930 transaxle users, is the half shaft angle. It will typically be between 10-15 degrees with an inverted 930 (unless you dry sump your engine and run extremely low ground clearance) and 10-15 degrees seems excessive for a CV joint to be fixed at indefinitely.

I spoke with a few companies about the CVs and angle but there aren’t many of them with direct experience with the setup. My mistake might have been talking with transaxle companies when I would have been better served asking around the sand rail companies. At any rate, I contacted Kartech (http://www.kartek.com/), a California shop that specialized in off road race trucks and buggies. I explained my intended usage and what I was concerned about:

• Angle being too high, premature CV failure
• Due to high angle the CV boots would rupture, leaking grease, and causing a failure

And what I learned was that I was being a bit conservative, but that is a good thing. They felt that 10-15 degrees is actually quite preferable compared to what they normally race with, 20-28 degrees, and that even a normal 930 CV (their quote was a good quality German unit) should be able to deal with that at road race speeds (roughly a wheel speed of 1700 RPM at 130 mph). So from that standpoint their opinion was that the setup we have should be sufficient.

However, they do offer uprated cages for the CV joints that have elliptical openings and will not bind up with angles up to 28-30 degrees. These cages replace the stock cages, are not as brittle and are relatively inexpensive at around $75 each. And, for the CV boots, they also offer a number of “double boot” systems for 930 CVs. These are so that a thick outer boot that will protect the relatively fragile inner boot so that heat and debris doesn’t rupture the boot that contains the grease.

So I ordered up some new cages and additional boots to have on hand if we wish to install them. Also some CV bolts with head holes for safety wire. We have a test day coming up on the 17^th of this month and I won’t get them in before then, but maybe shortly after for the following track day.

Just thought the info might be interesting for some of the 930 users that aren’t dry sumped and/or ring gear flipped.

R

 

[Jack]

Good info Ron, thanks.

 

[Seymour Snerd]

URL is Kartek Off Road - Where Off Road is On! The ultimate source for off road parts..

 

[Dave Deerson]

Ron, I have an inverted 930 behind an LS6 in my Fiero GTU car and due to the length of the drivetrain and the shortness of the wheelbase,I had to run the axles "forward". The axles are at 12deg. I have been using the "uprated" CVs with the CroMo cage and clearanced housings(so they run cooler) and the "Aero"/"Indy" style CV boots . I had early temp/lube failure but after changing from Redline( junk !) to NEO, I have never had an issue since. I can practically grab the CV after a session!

Dave D.

 

[PhillipM]

Most off road places will stock the 'race prepped' 930 CV's with chro-moly cages and fettled housings.
One thing I will say is make absolutely sure they are from proper GKN cores as the durability of the GKN housings far surpasses the other offerings available.
We usually run a maximum of 26* as any more than that and the life of the joint does start to suffer, but that's well beyond your application anyway.

I'd recommend the neoprene boots over the H/D off road ones though for road/track use, as being quite elastic they keep grease forced into the joint much better, for cooler running at high speeds.

We generally use them with forged 300M shafts that are as thin as possible so they flex and take out some of the shock loads under heavy impacts (much like a torsion bar), which, if you're running near the limits of the box may be a good idea, but can induce a little torque steer over rougher surfaces so unless it's vital they're probably not worth it.

 

[Randy V]

Great information Ron! Thank you...

 

[Ron Earp]

Dave and Phillip, god info and thanks. What are these aero or neoprene boots? Do you have any other information for them or a source?

 

[Dave Deerson]

These are like the ones I am using:

Hewland Gearbox | Jerico Transmissions | Quaife Transmission | Tilton Clutch | Racing Driveline

 

[Cliff Beer]

Good info Ron. Thinking about replacing the goofy little 016 in my GT40 with a properly set up 930/G50 unit...so any tips/tricks to put together a really solid drive train south of the output shaft of the SBF is appreciated.

Incidentally, there's a place in Scottsdale called Powerhaus - they do a lot of work with porsche engines and transaxles where the power output has been increased dramatically over stock. They might have some further tips/tricks for longevity of the half shafts - just a thought.

Powerhaus
7905 E Greenway Rd # 101
Scottsdale, Arizona 85260
(480)9484788

 

[Jeff Young]

NEo is a higher quality axle grease?

Ron, I have an inverted 930 behind an LS6 in my Fiero GTU car and due to the length of the drivetrain and the shortness of the wheelbase,I had to run the axles "forward". The axles are at 12deg. I have been using the "uprated" CVs with the CroMo cage and clearanced housings(so they run cooler) and the "Aero"/"Indy" style CV boots . I had early temp/lube failure but after changing from Redline( junk !) to NEO, I have never had an issue since. I can practically grab the CV after a session!

Dave D.

 

[Mark]

Great info Ron and others. Having just shelled out big $s for my transaxle to keep the axle angle as small as possible, I can tell you there are alot of Nay-sayers out there with the old that'll never work routines etc.

I spoke to GKN and they did say that they would prefer to see less than 10* ideally. We talked about off-road racers and very accute angles etc and the reply was basically, it's all fine below 20*, but you will just need to allow for a shorter life-span on the joints and factor that into the maintenance schedule of the car in question. The average ife of a CV joint is apparently 100K+ miles. Racing may reduce that to as low as 30K. I may therefore shedule replacements at 10K perhaps. Either way, it's not too big a commitment to strip and inspect the joints on a regular basis.

Not sure of my final engine/trans location in the chassis yet, but I should be around 10* give or take. I will look into the suggestions above regarding boots and grease etc.

Cheers

 

[Dave Deerson]

NEo is a higher quality axle grease?

The Redline CV grease turned into a gray clay in 1 1/2 days at Watkins Glen. It's been almost 2 seasons without needing to touch them with the NEO(that's 15-20 days a year getting 2-3 hours of track time per day). The NEO is more $$$,but I feel worth it.

Dave

 

[Mark]

The NEO is more $$$,but I feel worth it.

You are worth it Dave

 

[Dave Deerson]

You are worth it Dave

Hey, cut me some slack!!!
"It's worth it" was what I ment
Look at the time of my post!!!
The caffeine did not have a chance to kick in yet!!

 

[Ron Earp]

Neo grease isn't cheap but I'll try some. This place has it:

Neo HPCC 1 Race Car CV Grease

$70 a tube. Is this about right?

 

[PhillipM]

We use Millers Hi-Mol 20 for ours, if it's any cheaper for you, seems to work just fine for us, it doesn't seem to degrade much even with all the water/mud/etc that ocassionally manages to get in if we snag a boot.

 

[Woody]

Good info Ron Thanks. Dave has a good point in the clearanced housings of the CV. The guy I buy my trans bits from leases out , I think 6, 996 gt3 race cars he told me he uses smaller balls for more clearance to keep the temp down, he swears they last a lot longer. and with the greese well you pay for quality

 

[John]

Do any of you guys have 930 half shafts with CV joins on one end and U-joints on the other. My transalxe is mated to Corvette suspension and has this half shaft combination. I've been advised that this combination can cause vibrations!

 

[PhillipM]

A few guys tried it years back with the off-road buggies and found the stress it sent back through the shafts made them twist/muller the diff - it's not really a CV joint with that combination so it's understandable, it may well have been the result of vibrations but they wouldn't feel them :lol:

Regarding clearance housings/smaller balls, it's a trick we often use to get a touch more angle out of the joints and let them plunge more freely without snagging (quite important when you've got 90mm+ of plunge over a foot and half of travel!). However, you can feel a noticable 'snatch' in the driveline if you're on tarmac/slicks because the driveshaft bounces slightly as it takes up the slack. It tends to make them noisier when running too.

 

[Cliff Beer]

The NEO grease is definitely good stuff, and will last well in a demanding environment (perhaps a whole season of active racing) but no CV used on the track should go longer than a season w/o at least a complete washdown and repack, if not a proper rebuild. If you go longer than that then you're asking for CV failure as a reason to be sidelined and out of the racing. Just my own personal experience.