Class 25/33: Step 3 – Armature & Driveshaft Removal

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  • Now look closely at the shafts and bearings. The white bearings have a sleeve (raised collar) on one side only. It is important that you note which way around they are, and you will need to re-insert them later in the same orientation (assuming they were correctly inserted in the first place). If we label the bearings 1-6, with 1 being far left and 6 being far right, the bearings should have their sleeves orientated as follows: bearing no.1 facing inwards; bearing no.2 facing outwards; bearing no.3 facing inwards. Bearings 4/5/6 should be symmetrical to bearings 1/2/3. Notice also how the drive springs, which couple the armature to the worm shafts are centred between the bearings, they do not touch the bearings. Likewise, the commutator and worm gears also have a gap between themselves and the bearings. This should be noted, since it will be important during the rebuild.
  • The next steps must be undertaken with delicacy and patience. Read this entire page before attempting to go any further. You will see that you cannot remove the shaft assembly in just one step, but need a raft of methods to tease it out step by step. If you try to remove it all in just one step you will most likely damage the components. There are some holes at the top of the chassis. Cut both ends from a cocktail stick and push out the shaft and bearings as much as you can (using the holes in the chassis to get at the shaft / worm). Apply force as required. We are not aiming to get the entire assembly out at this stage – just the ends where the worms are. Do not push the worms too far out as this will damage the shaft coupling springs (if you have white plastic drive dogs instead of springs, see below). Also do not put the cocktail stick against the motor or commutator to force them out – these are dealt with in picture 3.

Note: The reason to cut both ends from the cocktail stick is so that at one end you have a flat surface area to apply pressure with, and the other end is flat so that it doesn’t stick into your hand. If the cocktail stick method won’t budge the shaft, then there is a second option. A small flathead screwdriver can exert greater pressure and get the stiffest of fittings out. However – proceed with caution! The screw driver could damage the brass worm gear. I have used this option on many occasions and if you really must put screwdriver to worm gear, get the flat head in between a groove on the worm gear, not across the wrom. This will minimize chances of damage. You really should try the cocktail stick method first.


  • Gripping the chassis as in picture 3, tease out the motor with your index fingers. The bearing next to the commutator is often tight in the chassis so you might not be able to remove the entire assembly yet (see next steps for that).
  • You should now have removed the armature and shafts as per picture no.3. Be careful not to lose the carbon brush and brush spring. These can be seen resting in the chassis here. Put them in a small pot with the other dismantled components.
  • With the hook in place, apply upward pressure to pull the assembly out of the chassis.
  • To remove the final stiff bearing(s) we need to make a small hook tool. Flatten out a paperclip with a pair of pliers. Make a hook at the end which is small enough to hook under the shaft next to the stiff bearing.

What if you have white plastic drive dogs instead of springs on the shaft?

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  • The picture above shows the white plastic drive dogs, which were used on earlier models of the class 25 diesels.

Note: If you have a class 33 then it is unlikely that it will be fitted with these. The shafts are easier to remove if you have these fitted and instead of removing the enitre shaft as one piece, it is removed in three pieces; worm gear … armature … worm gear. See the steps below for a step by step guide.


  • Removing worm gear 1: Firstly, hold up the chassis with the commutator end at the bottom – as per picture 1. Next, align the”tooth” of the drive dog (at the opposite end of the commutator – again, see picture 1) so that it is pointing upwards out of the chassis. This will make removal of the worm and lay shaft possible.
  • Removing armature: As per picture 2, use the cocktail stick method to push out the worm gear and lay shaft. This should come out relatively easily (unless the bearings are jammed into the chassis).
  • Removing worm gear 2: With one worm gear removed, now rotate the chassis 180 degrees so that you have the other worm gear at the top (see picture 3). Align the “tooth” of the drive dog again, just like you did above when removing the first worm gear. Now, with thumbs gripping the chassis and index fingers gripping the armature, push outwards with the index fingers so that the armature comes out of the chassis. Do not put fingers on the commutator or exert any force on the commutator. You will now be left with one worm gear in the chassis, which should be straightforward to remove.

 

 

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