ZF Half Shaft Bad Vibes

[Chuck]

Good info. Appreciate the educatin'. Looks like we keep the ends on the same plane. No 90 degree offset.

Mike: You mentionind balancing the half shafts. I removed a few grams of metal at the yokes to assure no clearance issues where it fastens to the stub axle. I see nothing to indicate that they were ever balanced. Should I be removing the entire assembly and taking it somewhere to get it balanced? Or is this of more academic concern in a car that will be used primarily on the street?

And for those of us out in the country, who would balance a half shaft? I am guessing it would take something more than rolling it on a couple of sharp blades to see where it ends up amd sticking on a lead weight.

 

[Terry Oxandale]

JacMac;

Excellent example of the induced "de-phasing" that camber gain forces on the entire assembly. I had not thought this deeply into the dynamics and always made assumptions that the axis of the axle was the same as the ouput stub in the transaxle (and my specific application puts the transaxle forward of the axle axis by about 8º (which does not exist at the axle). So I'm out of whack from the get-go (if I didn't use CVs) :thumbsup:

Chuck, would a drive-shaft balancing shop be able support your needs? I know at some point in time as we were kids working on our hot-rods, we've all done the "double hose clamp" balancing at one time or other. Tedious and time consuming, but it does work for those small offsets.

 

[John]

you should use one type or the other. do not mix. the c/v joint make the drive shaft travel at a constant speed and the u joint makes it travel at a non constant speed , so you are constantly twisting and un twisting the drive shaft. not good

Lynn,

Thanks for your advice - I thought mixing joint types was a problem. I have a KVA which uses a 930 Porche transaxle (CV-joints) mated to Corvette Hubs (U-joints) and this is the source of the problem!

Are you aware of any adapter kits that could convert Corvette (U-joints) to CV-joints?

John

 

[Terry Oxandale]

Are you aware of any adapter kits that could convert Corvette (U-joints) to CV-joints?

John

I don't know of any of these specifically, but I did draw up plans and partial machined (then had a professional shop finish it for me) some 930 adapter plates for a Datsun 240Z that used a very similar 4-bolt u-joint flange. I would think it to be as simple a moving the 4-bolt pattern around to match your 'Vette pattern, and you'd be through.

When I started it:

The other side of it as I drilled and taped the holes for the CV:

and the final pieces:

The adapter once it was mounted onto the axle:

The complete axle. I spent about $400 to have all four machined (I used inner and outer adapters to both the Datsun strut and Datsun R200 differential. You only needing two should be much cheaper.

Sorry for all the long post. Below is a shot of part of my drawings:

 

[Ron McCall]

Chuck,

My halfshafts are balanced. They have weights welded onto them . And I would HIGHLY recommend locktite and safety wire on the bolts that hold the straps over the u-joints!!
( don't ask me how I know what happenes when the bolts back out!!! )

John,
Give Fran Hall at RCR a call. He has stub axles to replace the u-joint end with CV flanged versions.

 

[John]

[The complete axle. I spent about $400 to have all four machined (I used inner and outer adapters to both the Datsun strut and Datsun R200 differential. You only needing two should be much cheaper.]

Terry,

Thanks for your exhaustive response and pictures - it makes using your solution all the more understandable should I decide to move to an all CV-Joints arrangement!

John

 

[Eric]

May I ask a question here?

You guys have got me thinking. My CAV halfshafts are off the car and I am
in the process of reinstalling new boots on the 930 type CV joints.


Since I have CV joints do I need to be concerned about any phasing issues??

Thank You, Eric

 

[Mike Drew]

May I ask a question here?

You guys have got me thinking. My CAV halfshafts are off the car and I am
in the process of reinstalling new boots on the 930 type CV joints.


Since I have CV joints do I need to be concerned about any phasing issues??
c

Nope, you're good!

BTW nobody has mentioned what the GT40 originally came with! The GT40 had solid, non-telescoping driveshafts with a conventional U-joint outboard, and a Rotoflex bushing on the inboard side.

I can already see the puzzled looks on many peoples faces.

Here's a good image of a pair of Rotoflex bushing from a Hillman Imp, resting against a brake drum:

It's a six-sided rubber donut, reinforced with an external steel strap. In practice, a three-eared flange is used to transmit the output from the GT40 gearbox, and the driveshaft has another three-eared flange, which attaches to the other three of the six available holes on the coupling.

This system helps to absorb shock in both directions (from rapid acceleration and deceleration), and also allows for slight in-and-out movement of the driveshaft as it moves through its arc. It's a typically quirky, British solution to the problem, and this technology was only ever widely used on British cars (and a very few Italian front-engine, rear-drive cars, in the coupling between driveshaft and transmission).

These bushings were still used on Land Rover products through the 90s--old traditions die hard!

Although probably effective on low-horsepower applications, they are almost assuredly near their limit when used on a car like a GT40. Lots of 1960s race cars used them as well, and it's possible to still see them being used at vintage races etc.

They do have a distinct advantage over CV joints--they are MUCH lighter. They are hard to find and expensive though.

CV-joint driveshafts are typically also very expensive--it's not unusual to have to pay $2000-2500 for a pair, whereas conventional U-jointed sliding driveshafts (with splined shafts which allow them to telescope) are normally $500-700 for a pair.

 

[Mike Drew]

Mike: You mentionind balancing the half shafts. I removed a few grams of metal at the yokes to assure no clearance issues where it fastens to the stub axle. I see nothing to indicate that they were ever balanced. Should I be removing the entire assembly and taking it somewhere to get it balanced? Or is this of more academic concern in a car that will be used primarily on the street?

>>>The answer is, 'it depends'. It's possible that your shafts were so perfectly made that they didn't need any external metal added to balance them. Depending on how much material you removed, you could have screwed them up a little bit, or a lot, or not enough to notice.

The only way to find out is to take them to a driveline shop and have them balanced. Make a note of where your clearance issues are, and perhaps mark the driveshafts so that the technicians know NOT to add any weight in those places. Driveshafts can be balanced just as easily by removing weight, as by adding it, although of course you don't want to go too far and weaken them.

Another thing that should be obvious but is worth mentioning is that regardless of what style of driveshaft you use, the bolts that affix them to the hubs and the output flanges need to be really, really tight. A friend had a horrible vibration problem in his Pantera that he couldn't sort out. He tried having his wheels balanced, tried different wheels, to no avail. Eventually he discovered that one or two of his driveshaft bolts had worked just ever so slightly loose, which was allowing the yoke of the driveshaft to rock just a little bit. Snugging them up to FT spec fixed the problem for good. :thumbsup:

 

[Terry Oxandale]

This appears to be true with the CV joints as well. It seems that the 6 bolts holding the Porsche CV joints are susceptible to this. I used a little low-grip Loctite on the threads and never had a problem.

 

[Chuck]

So much good information . . . .

Just remounted the half shafts. Used blue loctite. Cranked down tight. Ideally would be wired - a project for another day. Expect to mark and regularly check those bolts.

Waiting for the snow to go away . . . .

 

[Jim Rosenthal]

As someone said above, the original cars used Metalastik joints (big rubber donuts) so the only Ujoint was on the stub axle.

I don't think that CV joint shafts are as expensive as you had thought. Google 'driveshaft shop' or something like that- there is a man in Kansas City making dual-CV joint axles with Porsche 930 type CV joints on each end, and they are about a thousand dollars for a pair. He makes them in versions up to 1000hp- evidently drag racers are using these on some cars. I got my halfshafts from Safir, or I would have bought them from this fellow.