Class 25/33: Step 9 – Driveshaft Fitting (Spring Coupling)

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Note: This description assumes new style bearings with flatter collars. If you have old style bearings, click here to see how they are orientated.

To identify which bearing type you have (older or later) click here.

  • As per picture 1 above, connect the lay (worm) shaft to the armature shaft with the coupling spring. On either side of the spring there should be a bearing, with the collars, or “sleeves” facing inwards towards the coupling spring. Repeat on the other side of the armature with the other worm shaft, setting up the bearings the same way.
  • Place the remaining two bearings on the outside of each worm shaft, with the collars facing inwards towards the worm. As per picture 2, lay the attached shaft next to the chassis and roughly align the bearings and worms, ready for inserting into the chassis.
  • As per picture 3, “drop” the shaft and bearings into place in the chassis. Make sure you insert it in the correct orientation, with the commutator over the brush hole. Also, notice the little indent on the top edge of the bearings in the picture. All the bearings have to be this way, with the opposite, flat edge, dropping into the chassis first.

Tip: In summary, bearing collar orientation should be (from left to right); Inwards / Inwards / Outwards / Outwards / Inwards / Inwards.


  • Applying a small amount of pressure, push the bearings down into the chassis. You shouldn’t need brute force here, and if you do then you possibly have a distorted chassis or bearing and this needs to be investigated. If it needs a lot of force, remove the shaft and check you have orientated the bearings the correct way around – do not force it in. Use a small tool (I have used a pair of tweezers in picture 1) to give the bearings the final “push home” into position. Note that the bearings should be flush with the bottom of the chassis (picture 1 has the chassis inverted, so in this instance you can refer to it as being the top).
  • With the flathead of a small screwdriver up against the spring end, rotate the armature with your thumb to adjust the length of the overall shaft. You can move the screwdriver to the opposite end of the spring and rotate the worm if you wish. This is fiddly to do and rather than trying to explain it in detail it is better to experiment. Just be careful not to over tighten in either direction. Your aim is to achieve clearance of the bearings from the armature, commutator, spring coupling and worm. All four should have clear daylight between them and the bearings so that there is minimal rubbing during shaft rotation. Picture 3 illustrates this well.
  • Finally, with your pin and some oil, apply a drop of oil to each bearing where the shaft goes through it. Be careful on the commutator bearing that you don’t get oil on the commutator itself.

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