TM 9-1829A, April 1944
54/100
2021-07-07
k.
Replace case:
Place mechanism in case, and fasten with two screws and lock washers.
l.
Calibrate:
Refer to chapter 13. Place dial in position and press pointer lightly on staff at zero. Place unit on
calibrating machine, hold in same position as it will be on vehicle, run master head on machine at 10 miles
per hour and make any necessary corrections in instrument by adjusting hair spring collet on staff (fig. 72).
Allow pointer to return to zero to check whether it returns easily. Run master at 30 and 60 miles per hour (fig.
73).
Figure 73: Holding speedometer on calibrating machine (T-170645) and testing at 30 mph
If instrument reads 5 miles or more fast at high speeds, shorten the hair spring. Cutting off one coil will
slow up instrument approximately 6 miles per hour (not more than three coils should be removed). If
instrument reads 5 miles or more slow at high speeds and is equipped with a strong-tension hair spring,
a weaker hair spring must be installed to eliminate slow ness. If this does not correct slowness, magnet
is too weak and must be replaced. Run master at 10 miles per hour again and make any necessary minor
corrections in instrument by moving hair spring regulator (fig. 59). Check instrument at all speeds. It
should now read within following limits:
Master reading
Calibration tolerance
10 mph
9-11 mph
30 mph
30-32 mph
60 mph
60-63 mph
If instrument cannot be calibrated, refer to paragraph 4.
m.
Replace dial and pointer:
Place dial onto mechanism and fasten to front jewel bracket with two screws.
Start pointer on shaft at about
1
/
3
maximum dial indication, and carefully press it on while turning it
counterclockwise to zero.
n.
Replace bezel, gaskets, glass, etc.:
(1)
Crimped bezel:
Place instrument on surface that will not mar finish, and crimp bezel at several points
with flat-end punch.
(2)
Rolled bezel:
Place lower die on base of bezel rolling fixture (T-178730 Det. 13), place speedometer
assembly face down on lower die, and place upper die over speedometer (fig. 74). Place upper portion
of fixture (T-178730 Det. 2) over speedometer, place entire assembly in arbor press, and roll bezel (fig.
75). Remove speedometer from tool.