The
most challenging part of this little project was making a new boss in the NP205
tail housing to hold the GM speed sensor. A traditional speedometer gear on
the output shaft of the T-case drives the speedometer cable by a gear that sits
below the output shaft. In contrast, the VSS must be oriented exactly perpendicular
to the output shaft and reluctor ring. This required filling in the old speedometer
boss and machining a new one for the VSS. I was worried about welding so much
on the cast iron tail housing and the potential for warping the housing. I called
on my friend Senkovitch who has expereince welding cast iron. The procedure
we used included slow heating to bring the entire housing to a temperature of
near 700 degrees. We then welded in the old boss using a TIG welder and a large
cast iron welding rod. Following completion of the welding, we insulated the
housing and allowed it to cool overnight. The next day we put the housng on
the lathe and checked for any warpage. The runout on the bearing journal was
less than 0.002" so we were satisfied we had not induced any deformation
or warpage.The imnage on the left shows the housing with the original boss --
note how the speedometer fitting angles down toward the bottom of the output
shaft. The image on the right shows the new boss machined
into the tail housing. I build a jig to hold the housing on the table of the
milling machine and machined the weleded area flat. I then drilled and tapped
the hole to fit the GM sensor.
The
image to the left shows the output shaft of the NP205. The inner set of splines
held the original teflon speedometer gear. Some of the later model NP205s used
a reluctor ring instead of the traditional speedometer worm gear. I purchased
a 40-tooth reluctor ring for a 1992 NP205 and that fit perfectly on the output
shaft. The image on the right shows the output shaft with the reluctor ring
installed.
The
image to the left showns the completed tail housing with the VSS installed in
the newly machined boss. The image to the right shows the tip of the VSS (arrow)
located approximately 0.040" from the surface of the reluctor ring.
The
most challenging part of this little project was making a new boss in the NP205
tail housing to hold the GM speed sensor. A traditional speedometer gear on
the output shaft of the T-case drives the speedometer cable by a gear that sits
below the output shaft. In contrast, the VSS must be oriented exactly perpendicular
to the output shaft and reluctor ring. This required filling in the old speedometer
boss and machining a new one for the VSS. I was worried about welding so much
on the cast iron tail housing and the potential for warping the housing. I called
on my friend Senkovitch who has expereince welding cast iron. The procedure
we used included slow heating to bring the entire housing to a temperature of
near 700 degrees. We then welded in the old boss using a TIG welder and a large
cast iron welding rod. Following completion of the welding, we insulated the
housing and allowed it to cool overnight. The next day we put the housng on
the lathe and checked for any warpage. The runout on the bearing journal was
less than 0.002" so we were satisfied we had not induced any deformation
or warpage.The imnage on the left shows the housing with the original boss --
note how the speedometer fitting angles down toward the bottom of the output
shaft. The image on the right shows the new boss machined
into the tail housing. I build a jig to hold the housing on the table of the
milling machine and machined the weleded area flat. I then drilled and tapped
the hole to fit the GM sensor.
