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December 17, 2014

[Click the pics for a bigger view]

Drive Shaft

The TR6 drive shaft (or propeller shaft) is a pretty standard item.  It has a flange connected directly to a universal joint at each end, and a sliding spline joint in between.  This arrangement accommodates the changing alignment between the transmission output shaft and the differential input shaft.  All the parts of my drive shaft were dirty and rusty.  This is after pushing out the U joints.

After some cleanup and derusting:

After powder coating.  The main shaft is too big for my small oven, so it got a couple of coats of POR15.

The sliding spline has a cork seal to keep dirt out.  It was hard and brittle, and came out in small pieces.  As far as I can tell, it isn't available anywhere, so I fashioned one from some cork sheet.  The steel split washer and the cap were re-plated.

Here is where the story takes a grim turn.  Any time someone uses a powerful tool like a hydraulic press to move something, there is a real potential for unintentional carnage.  Installing U joint bearing caps is a relatively routine process, but occasionally something goes awry.  I was pressing one of the caps into the sliding yoke when something apparently got cockeyed in a direction I didn't see.  When I should have stopped and investigated the reluctance of the cap to go into the bore, I kept pouring on the tons, believing the cap would right itself.  The sad result was a bent ear on the yoke.

A disappointing Internet search revealed that no one was selling just the yoke, and that everyone who was selling a complete drive shaft apparently believed it was made of platinum.  

This made me think a little harder about undoing what I had done to my yoke.  Within limits, bending is usually a reversible process, so maybe I could unbend what I had bent.  Careful measurement showed that the extreme end of one yoke ear was bent in by about 0.080".  The deformation extended down only to about the center line of the bore.  

Another Internet search revealed that some people have successfully repaired this kind of damage, and I adapted one of the methods to fit my situation.  The head of a 3/4" Grade 8 bolt was modified so that it would slip into one of the cap bores, which would keep it centered.  A nut on the bolt presses on a stepped collar that fits into the other yoke bore.  This arrangement can apply an enormous amount of pressure--probably as much as my press.  The little shim in the last pic was inserted to apply all the pressure at the outer end of the bent ear, since that's where the deformation was the greatest.

I went through several cycles of pushing and measuring, and the ear was slowly moving.  I was able to get the ear within a few thousandths of the correct dimension.  I was prepared to use heat, but didn't need to.

After this success, I noticed that the cocked cap had also left its mark inside its bore.  There was a small ridge of upset metal in the bore.  I was also worried about some lingering distortion of the bore, so I decided to carefully ream the bores to ensure that they were  round, but also that they were colinear.  I used a cheap adjustable hand reamer for this.  Its blades happend to be just long enough to span both bores.  I opened the reamer just enough to clean up the ridge.

Of course the danger here is that one or both bores will get too big, and the bearing caps will be too loose.  Luckily, this wasn't the case, and both caps were still a nice firm press fit.

The final shaft, ready for install.   When assembling the sliding joint, it's important to get the phasing of the U joints correct.  A single U joint can produce a slight oscillation in speed which can be canceled by a second U joint if the relative orientation is correct.

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