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September 20, 2014
Rear Half Axles and Hubs

[Click the pics for a larger view.]

The TR6 uses a semi trailing arm rear suspension where each arm carries a wheel hub connected to the frame mounted differential by a "half axle".  The half axle must accomodate the swing of the trailing arm by changing its length and the angles between the differential and hub flanges.  It does this by using a pair of universal joints and a sliding spline.

My axles were apparently in decent shape, with no obvious problems.  The hubs and joints all had smooth action.  On the other hand, they were old, and had a fair number of miles on them.  In keeping with the spirit of the rest of the project, I decided to rebuild the shafts and hubs.

This is a job that is widely considered not to be a DIY undertaking, which unfortunately comes across as a dare to me.  In the end, I'd have to consider this one of the more difficult jobs on the car so far, but not out of reach for someone with moderate mechanical skills.  The manuals list a number of required special tools which probably aren't available any more, but I found that there are ways to inprovise around them.

I found a note written by me in the back of my Haines manual, dated 1980.  It said that I had replaced the wheel bearings in the right  hub, but that I couldn't get the left one apart, and had slghtly bent the wheel flange in the attempt (probably with a two- or three-arrm wheel puller).   This was likely the reason behind the shim on one of the wheel studs.

Separating the U joints is a pretty routine job, but getting into the wheel bearing housing takes a little more determination.  The outer axle shaft has to be separated from the wheel hub, to which it has been mated for forty years with a big-ass nut torqued to 100 foot-pounds.  Since there isn't an easy way to provide support to the back of the wheel hub, a hydraulic press normally isn't used for this.  It's tempting to break out the wheel puller like I did back in '80, but as I found, the edge of the wheel hub flange isn't beefy enough to resist the necessary force.  Here is where one of Triumph's special tools comes in.  It is just a hefty wheel puller designed to pull on the wheel studs while pushing down on the axle shaft.  Plenty of people have made their own versions of the special tool, so I did, too.

Starting with a hunk of 6-inch round and some grade 8 hardware, I fashioned a serious puller.  It weighs nearly 12 pounds.

While the right hub came apart relatively easily, the left one--the one I had trouble with 34 years ago--was being difficult.  Torquing on the puller bolt with a three foot cheater bar, I could see the wheel hub flange starting to distort.  I've read various places the opinion that a thick flange on the puller is necessary to support the thin flange on the wheel hub to keep it from bending.  I just don't see this since no matter how thick the puller flange, the force is still concentrated on the four stud bolts.  I don't believe a thicker puller flange prevents bending at all.

One thing I did do to provide more support to the thin hub flange is to drill two more holes in the puller flange.  Using the two large holes in the hub flange, I could place a thick steel bar under the flange and snug it up to the puller flange.  This does give a lot more support, and reduced the distortion greatly.

So, with enough heat, cheater bars, and swearing, the hub finally gave up.

That same hub, in an act of pure spite, also made me cut off the inner bearing race.

As an aside, I've read a number of discussions about the amount of grease that should be put in a hub--just a little, or pack it full?  Here is what was in the left hub, not opened since it left the factory.

I was concerned about all the violence done to the wheel hub flanges, so I checked them for trueness.  The right one had a variation of about 0.020", but the disagreeable left one had a difference of 0.053" from high to low.  

I played with the bad one on the press, trying to reverse the bending caused by the pullers, but couldn't get it much better than about 0.030".  These errors get magnified by the larger diameters of the brake drum and wheel, so I decided to flatten the flange surfaces on the lathe.  These flanges are already a little on the thin side, so I wanted to take as little off as possible.  Since I just needed the flanges to be flat in the areas around the wheel studs, I was able to true up the flanges by removing only about 0.015". 

Powder coated the larger pieces, zinc plated the hardware, and got new bearings and U joints, which are common types and easy to find.  I try to buy these kinds of items at local industrial suppliers because I can know what brand I'm getting before I pay for them.

Now here is a mod that I'm not sure is worth it or not.  These rear hubs are not like the front ones that are easy to get into to pack the bearings.  Since it is such a chore to crack open the rear hubs, they rarely ever get lubricated.  To  address this, I decided to add a provision for adding grease to the interior of the bearing housing.  I drilled a 1/8" hole at a 45 degree angle from the outside into the cavity between the bearings.  I then drilled and tapped the top 3/8" for 1/4-28.  This will accept a grease zerk fitting, but I installed lock-type allen set screws as plugs.

Putting everything back together now.  Assembled the adjusting hardware on the outer axle, then pushed on the new bearings with shop made adapters.

All the parts for the hub assembly.

Press in the outer races and grease everything up.

Setting the bearing float is interesting.  The wrench for the big adjusting nut can only be 1/2" or so thick.  I bought a 2" wrench and took almost 1/4" off the thickness.  I had to open up the jaws a little, too.  The wrench is over two feet long.

Turning the nut a little at a time, and checking float.  The nut starts out just pushing the bearing up on the axle.  It's obvious when it begins to crush the spacer between the bearings.  A 1" pipe through the U joint yoke helps to steady the assembly when leaning on the big wrench.  I found it easy to sneak up on 0.002" float.

One rebuild hub assembly.

Installed the U joints, and we have axles ready to go.


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