Boots on drive shafts

Independent suspension.

Are you talking about the CV joints on the drive shafts, when you say "boots"?

I don't think those have anything to do with how much turning radius you get. It's got more to do with the wheelbase of each vehicle, plus the fact that the Jeep is only part-time 4WD, whereas the Outback is full-time 4WD (AWD).

Yousuf Khan

The Subaru half-shafts use an entirely different mechanism. The outer end is a Bierfield (sp?) joint; uses steel balls closely fit into a cup. The inner end (the CV; Constant Velocity) joint also uses steel balls in a sliding spider. Both operate in a grease bath, and so require a rubber boot to keep the lubricant in and the world out.

Your Jeep, on the other hand, uses conventional "U" joints; two U shaped sections, joined by a cross shaped yoke with captive roller bearings at the ends. Variations in the length of the drive shaft as the suspension travels thru its stroke are accommodated by a sliding spline arrangement on the connecting shaft. And yea, they probably do operate thru a wider angle than the Bierfield; desirable in a vehicle nominally intended for off-road use.

FWIW, the 4WD/AWD Subaru uses "U" joints on the drive shaft to the rear differential.

Why the different technologies? Don't know, but I suspect it has to do with long-term reliability. The Subaru half-shaft is basically maintenance free unless (until) a boot fails. If modern Jeeps are anything like the old Cherokee I used to have, you have to really keep after the various "U" joints with a grease gun, or they get noisy and fail. Sometimes they fail anyway, especially if you work them hard off-road.

ByeBye! S.

Steve Jernigan KG0MB Laboratory Manager Microelectronics Research University of Colorado (719) 262-3101

A CV joint transmits torque smoother than a U-joint. The U-joint alternately increases and decreases the output shaft speed as the the input shaft turns at a constant speed if it is flexed at an angle, which it almost always is.

The CV joint, by design, does not alter the speed of the input shaft.

Excellent answers. I learned something..I wondered why tractor trailers didn't have a jumbo version of cv joints. The only driveline part I ever broke on a subaru was the u-joint . Broke to the point of no return on the driveshaft, aftert being forced to listen to the one error on one cap until it decided to fail- with no option to replace quietly. A tractor trailer has wheel bearings... A u-joint will break more than ten times to one in chances, before the wheel bearings fail... food for thought.All that turning and strain, unlike the relatively straight line job as the driveshaft. Rather ridiculous to think u-joints are still mainstream, with todays alloys and engineering. Maybe they'll go extinct with the 258 inline 6 and all the other monstrosities with no excuses anymore....

Thanks for the excellent reply. The "U" joints on my Jeep are very reliable as they have lasted 16 years without failure. And it is full time AWD.

Frankly, I don't see the advantage of the Subaru version; I do read a lot about failures of the booted linkage. Some say that it is needed due to independent suspension. Well my '71 XKE has half-shafts on the rear drive and no boot neither. And the half-shafts form part of the suspension as well.

Are the "U" joints capable of handling more torque than the booted ones?

Yes, I keep my vehicles a loooonngg time. I run the wheels off of them. I'm the original owner of the Jag and my son wants it. He'll get it as soon as he gets a garage ;-)

Al

You know that weird jerking of the steering wheel when you put in 4WD on pavement? Subies don't do that. Those boots cover (and keep lubricated) far more sophisticated constant-velocity joints on those driveshafts under the Subie.

Turning radius is a function of wheelbase. Is your yeep a CJ/TJ/YJ? If so, it's a hell of a lot shorter than the Outback.

Rzeppa joint - I think originally invented for use in tanks or something.

The advantages of the CV design are in Jim Stewart's post. You might want to stop calling them "Subaru version", tho..that's about like calling alloy wheels "Subaru type wheels", because you have steel wheels on your Jeep. CV joints are everywhere in vehicles, and have been for years.

I guess it depends on the Jeep model. Mine doesn't jerk!

Mine is the '91 Laredo, whatever that is in CJ/TJ/YJ.

Al

I have a 2001 legacy outback wagon. It does have issues with its front CV boots. The passenger side CV boot sits right on top of the exhaust. It cracked at 60K miles. According to the dealer, it is a common failure due to the heat from the exhaust. I just replaced the boot on the steering shaft at ~90K miles. The turning radius of subaru is horrific. My honda Odyssey can turn tighter than the outback.

Regards

Not really, the wheelbase on the Jeep is about 104 inches and on the Outback it is about 102 inches. That's less than a 2% difference. So that should not really have such a big effect on turn radius.

Al