Halfshafts for IRS: solid or tubular?

Fred Douglass · #1 (**permalink**) 07-01-2002, 09:58 AM

In doing some reading I have come across references to differing views on halfshafts. What I used to assume was that, since most of the tortional energy is transferred or carried by the outer "skin" of things like drive-shafts, the same would apply to halfshafts going from the defferential to the wheels. I noticed some Fords, SPFs and quite a few others use SOLID halfshafts. Butlers and others with modified Salisbury units went with strong (thick-walled?) tubes. Which is preferable? SPF offers a stronger upgrade...but it's still solid. Any technical hands out there offering insight will be welcome.

Thanks,

Mr.Fixit · #2 (**permalink**) 07-01-2002, 10:27 AM

I haven't seen the shaft itself break on any halfshafts yet. The CV joint can go, the splines will disappear, the diff will break, but I haven't yet seen a broken shaft. Not that it can't or won't happen though. Besides, you don't see many axles for traditional solid rear ends that are hollow like a torsion bar.

Fred Douglass · #3 (**permalink**) 07-01-2002, 11:05 AM

Thanks, Mr. Fixit,
Next inquiry is: I have heard that tubular is much to be preferred---that the solid shafts acquire a semi-permanent twist under hard accelleration. Any truth to that?

Thanks again,

wilf leek · #4 (**permalink**) 07-01-2002, 11:40 AM

Hi guys - the following is only pertinent to Jag rear ends, but I guess it is generic enough to be worth posting.

I have a friend here in the UK who drag races. He puts 750Hp + through a std jag rear end. After 4 passes, he measures the twist or "set" in those solid halfshafts - after 1/2" of twist he throws them away and fits some new (secondhand) ones.

When building my own car, I asked a driveshaft specialist for advice, we decided to uprate the half shafts/yokes/UJ's on my rear end. Mainly because those half shafts are the only thing keeping the rear wheels in position, and I wanted it to last for more than 4 passes!

What they did was to replace the original solid shafts with tubular items, telling me that "tubular shafts are stronger than solid".

Conventional wisdom here in the Uk is that a std Jag rear end is reliable for up to 450hp, after that the UJs etc need uprating. As another friend who fitted a blower to his cobra has found out.

HTH

Satanpez · #5 (**permalink**) 07-01-2002, 12:08 PM

It's quite normal for axles in solid axles to twist like you mentioned for those jag halfshafts.

People mark the shafts, and after a certain amount of twist (I think one full turn) they have to throw them.

-steve in nj-

Fred Douglass · #6 (**permalink**) 07-01-2002, 12:53 PM

Thanks Wilf,

Check my second save-the-sheep posting on the superheated "this from FFR" thread.

Thanks Santapez,

Good insight!

Bofe of yuz (and Mr. Fixit, too),
If I ever learn how to copy articles and post them---I'll send you an interesting tidbit on (I kid you not) LOBSTERBOAT (I
should say "lobstaboat") RACES...yes...RACES "Down East" (state o' Maine, Wilf). They put absolutely gargantuan "mountain engines" in "tricked up" (stripped out lobsterboats) and let 'em rip. Current record is 67.9 mph (58.03 knots).
The accelleration is phenomenal. They aren't quite in same league as the pre-Gold Cuppers on my photogallery---but the lobsterboats get up to racin' speed in about 75 yahds...ayuh!

Thanks to you all, now I'll call Bob Olthoff and get the side of my face chewed off for commiting les majeste on an SPF by
recommending tubes!

PS: Wilf, thanks for posting that photo of yourself au naturel, sauve les boots---I use it to frighten squirrels off my bird-feeders.

Chow,

Fred Douglass · #7 (**permalink**) 07-01-2002, 12:56 PM

Opps...now I've gotten the Tourettes under control, the Alzheimer's snapped back in!

I frog-gut to tell you guys that, due to the apparent initial lack of cooperation of the water, they often put 2 to 2.5 "twists" (full turns) on the lobsterboat drive shafts! Gospel.

Chow,

Tommy · #8 (**permalink**) 07-01-2002, 03:07 PM

I can't give any practical automotive advice on this topic, but I can tell you from a theoretical engineering point of view that a tube made of the same material will be stronger than a solid axle of the same total weight. So for maximum strength and minimum weight of a given material, go with the tube.

Mr.Fixit · #9 (**permalink**) 07-02-2002, 06:15 PM

One of my mentors when young raced a 57 chevy in some now obsolete stock drag racing class. He would paint a stripe all the way down the axles, when the stripe did one full turn it was time to replace the axle.

wilf leek · #10 (**permalink**) 07-03-2002, 06:47 AM

Fred - glad to be of help. but sorry to disappoint you in that the picture in my gallery is actually not of me, rather a good friend "the duke of leicestershire". Remnant of an old gasholes thread. Somehow can't bring myself to remove it, it has a certain "je ne sais quoi".

Fred Douglass · #11 (**permalink**) 07-03-2002, 09:13 AM

Wilf,
Thank Gawd for that! Hope you've kept track of events up at th' Loch, laddie. Hate to rely on infrequent UPI postings....

Carrion regawdless,

Fred

niles · #12 (**permalink**) 07-03-2002, 09:37 AM

Tommy is right on.
Tubes are stronger; a little more on this:
if your permently "setting - twisting" a shaft, your already on the direct course for failure! That fact says that you are exceeding the yield strength of the material in torsion. That being said you are now on the way to "definite" failure after X number of cycles at that stess level. NO proper design ever operates at or near the yield strength of the material in question.
Would you think it OK after a rough airplane flight to have the wings "permently" bent up a tad?

gn