After rebuilding my MGA three
synchronizer gearbox, I could just barely feel some roughness when
third motion shaft and holding the first motion shaft still. Disassembly and inspection
found the bearing
surfaces were in great condition, and the needle bearings were clean
undamaged. I had used a light grease to place the needle bearings while
inserting the third motion shaft assembly in the case and into the
shaft. All other functions were good.
Running out of ideas, I used
my micrometer to check the diameter of the 18 needle bearings taken
transmission. The diameter of the needle bearing was .117 to .118. This
sense out of nonsense. The
all turning at a slightly different rate and were rubbing instead of
The roughness was the rubbing action caused by the variety of diameters.
Digging thru my Transmission
building kit, I came up with 100 or so needle bearings. As it was a
day in Michigan, I sat at my workbench in good sunlight and measured
needle bearing. When
all was done, I had
sets of: .117, .1175, .118, .1185 and a few odd balls that I threw out.
This time on reassembly, I
tried the .1175 set, as this tranny has had over 300 races in the last
years. The rolling action was smooth & quiet, but I felt that
there was a
bit of wobble in the nose of the unsecured 1st motion shaft after all was
assembled. I took
the unit apart and tried the .118 set.
Again very smooth and quiet, and noticeably less wobble in the first
installation of the front
cover and shifter bits, I put the CR transmission back in # 49 MGA.
weekend I ran the Alfa Romeo Track Day at Grattan. After 10 laps of
4-3-2 and 2-3-4 the unit was performing better than before.
I cannot explain the variety
of dimensions, but did turn that to my advantage with a custom fitting
most important bearing.
Rowdie Racing # 49 MGA