In the Models 45, 29 and 28 there is a small coil spring at the rear end of the drive shaft. Dial-drive slipping in these models can be corrected by tightening the two hex nuts at the end of this spring. These nuts regulate the spring tension, which in turn affords proper operation of the reduction-drive assembly. In some remote cases it may be necessary to replace this spring when it has been compressed beyond its limit of elasticity. This spring is known as Part No. 28-8256 and lists at 70 cents per hundred [1935 prices, of course].
From the Philco Serviceman – March, 1935.