David Gersic <info@zaccaria-pinball.com> wrote:
> Before I go hunting for a shop to rework this driveshaft to flip the U joint
> around, is there a reason I shouldn't do this? Does it matter whether the
> grease zerk is on the "inside" (closest to the centre of the driveshaft) or
> "outside" (closest to the end of the driveshaft)?
I'm certainly no u-joint expert so you may want to verify this from
other sources, but my understanding is that with greasable u-joints
you want to always mount them such that the zerk fitting will be under
compression as power is applied. Apparently, the joint is stronger
when the engine is trying to compress the zerk hole than when it is
trying to pull it apart.
For example, imagine you are holding a U-joint in front of you; it
is shaped like a cross, and we'll use the points of the compass to
label each of the four caps. North on top, South on the bottom, West
on the left, and East on the right. Imagine that you are the engine,
connected to N and S, and the driveshaft is on the other side of the
u-joint, connected to W and E. If the primary rotation is going to be
clockwise, you would want the grease fitting at NE or SW.
In the photo you posted, I'm assuming that the transfer case is to
the right in the picture. I'm not sure which way the driveshaft
rotation is, but the fitting installed in that pic is correct if the
rotation is clockwise (from the perspective of the transfer case,
looking towards the front of the truck).
Naturally, even if a u-joint is installed "correctly" such that its
under compression, when you are in reverse, the rotation changes and
the opposite is the case - so technically, the u-joint may not be as
strong in reverse. But, since most driving and most of the load will
happen in the forward gears, installing the zerk so that it is under
compression while going forward is the assumption.
I don't know how much difference this actually makes in a real
world scenario. It may be more important for high horsepower, drag
racing, offroading with big tires, etc. Of course, if installing the
u-joint "correctly" means that the grease fitting is inaccessible, I
would go for an "incorrectly" installed u-joint that I can grease
every time. :-)
I hope that helps! If my clear-as-mud explanation is lacking,
please let me know and I can try to clarify. :-)
--
-Jon-
.- Jon Steiger -- jon@dakota-truck.net or jon@jonsteiger.com -.
| '96 Kolb Firefly, '96 Suzuki Intruder, Miscellaneous Mopars |
`-------------------------------- http://www.jonsteiger.com --'
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