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U-Joint Replacement - Part 1 of 2

I had to break up this posting into 2 parts because it was too
long the first time I submitted it.  The first part will detail
the disassembly of the u-joints and the second part will describe
the reassembly of the new u-joint.

I had quite a few requests for the instructions for replacing
driveshaft universal joints so here goes.  FYI, I worked as a BMW
mechanic in the early '70s and was trained at the factory training
center in Santa Monica by Hoffman Motors (the sole distributor of
BMW automobiles at the time).  I worked in a small independent
shop for a German master mechanic who had 16 years of experience
at the BMW factory.  Obviously, I never worked on any of the 3
series or later cars although I have owned them and serviced all
of them myself.  Also please keep in mind that I am giving these
directions from 25 year old memories so I might not be 100%
accurate any more... (enough of the disclaimers!)

Remove the driveshaft from the car.  I will not go into the
details of how to do this as it varies from car to car. 
Generally, remove the exhaust system, heat shields, center bearing
and remove the "doughnut" (that's what we called it back then,
it's now called a "guibo") that holds the driveshaft to the
transmission.  The attachment to the differential is solid (no
"guibo") and needs to be removed also.  One thing to keep in mind,
mark the location of the center bearing on the chassis.  I usually
use an awl to scribe the location of the edges into the mounting
bracket.  You will need to put the center bearing back at the same
location when you reinstall the driveshaft.

Now that you have the driveshaft out, take it to your workbench. 
The u-joint is the "+" shaped object(s) that connect the pieces of
driveshaft together.  The places on the driveshaft pieces that
hold the u-joint are called the "yoke".  I'll refer to the "+"
shaped piece as the "joint".

If you look at the outside of each yoke, you will see a retaining
clip inside a bored hole in the yoke.  Remove all 4 of these
retaining clips with cir-clip pliers (you can usually work them
out with small screwdrivers if you need to).  The flat metal parts
that the clips were retaining are the tops of caps that fit over
the arms of the "+" shaped center of the u-joint.  These caps have
needle bearings inside them between the cap and the joint itself.

The caps are pressed into the yoke from the outside inward and
there is a "stop" in each yoke that prevents the cap from being
pressed too far into the hole.  The clips we just removed prevent
the caps from moving out of the hole once it is seated.

You don't need to worry about damaging any of the caps or the
joint piece during disassembly.  All of these pieces will be
replaced by the new u-joint.  If there is a grease fitting in the
joint piece, remove it by unscrewing it (counterclockwise).  If
the joint has a grease fitting, note the orientation of the joint
so that the new u-joint will be in the same orientation (assuming
it also has a grease fitting).  If the new u-joint doesn't have a
grease fitting, don't worry about it.  It can be installed in any
direction.  Some u-joints have grease fittings and some don't.  I
don't know what determines whether they have one or not.

I will assume that you don't have either a hydraulic press or even
an arbor press in the following discussion.  If you do have a
press, your job will be a little easier (but not much).  I am
assuming that you do have a vise handy.  If not, you might still
be able to do this is you have a LARGE pair of channel lock pliers
or the equivalent.

The first thing we need to do is remove one of the caps.  To do
this, take a hammer and a good sized punch and drive the joint
piece into one of the caps which should cause the cap to move
toward the outside of the yoke.  You can't drive the cap on one
side inward in the hope that it will drive the cap on the opposite
side outward.  Remember that the caps have "stops" that prevent
them from moving too far inward.  You need to actually drive the
joint piece into the cap from the inside and thereby drive the cap
to the outside of the yoke.  I usually drive the joint by putting
the punch near the intersection of the cross piece at the center
of the joint and giving it a good whack.  The caps are usually
pretty tight and you will probably need to hit it pretty hard. 
Start off with a moderate whack and if the cap doesn't move, hit
it harder until it does.  If the u-joint you are working on is
very dry and rusty looking, you might want to put a little WD-40
or Liquid-Wrench on the cap to help it along.  Drive the cap all
the way out of the yoke (and watch out for the needle bearings
when the cap comes out).

When you have one cap out, it is an easy matter to put the joint
back into the opposite cap (again, watch out for loose bearings)
and then drive out the opposite cap by punching out the joint
piece through the hole in the yoke where the cap you just removed
was.  The cross arm of the joint usually has a nice hole in the
end of the cross piece that you can put your punch into so it
won't slip when you hit it.  Again, drive the cap all the way out
of the yoke.

Mark the orientation of the two pieces of driveshaft so that you
can reassemble them in the same relative orientation.  If you
don't do this, you can get them reassembled 180 degree off from
the way they came apart.  This might not matter and then again, it
might unbalance the driveshaft.  Play it safe and mark them.

Once both caps are out, you can remove the joint piece from
between the yoke and separate the two pieces of driveshaft. 
Repeat the same procedure on the two remaining caps in the other
yoke.

Clean up the parts if need be and you are ready to install the new
u-joint.


Don Mies
85 635CSi (The latest of 8 BMWs) - Wonderful car!!
Thinking (very hard) about a Z3