Bachmann 'Peak': Modifying the Bogie Drive

This section describes the modifications to be made to the Bachmann Drive Units, taking one bogie at a time.

Dismantling the Bogie

Unclipping sideframe moulding Unscrew and remove the pony truck assemblies.

Using a small screwdriver, gently unclip the bogie frame/undertray moulding from the outer end, then the inner end, of the bogie drive unit. Put the moulding safely to one side for now.

Drive unit Discard the inner wheelset, bearer and spring.

Unclipping wheelsets Unclip the two driven wheelsets from the drive unit moulding and put them to one side.

Removing pivot Undo the two cross-headed screws holding the bogie pivot/worm retainer moulding to the tops of the two pivot towers and remove the moulding.

Removing pickup strips Remove the metal pickup strips from the side of the drive unit moulding.

Removing worm Lift the inner end of the wormshaft to ease the outer worm bearing out of its plastic housing - support the housing firmly with the fingers to prevent it being bent outwards - and remove the worm, shaft and bearings. The two plastic upstands to either side of the inner worm bearing splay outwards to permit this, but take it gently.

Worm gear idler shaft If the idler axle for the worm gear sticks out either side of the moulding like this…

Worm gear idler shaft marked for cutting …push it in so that one end is flush with the side of the moulding and make a nick, with a slitting disk, on the length projecting from the other side, as a marker for cutting it to length. (You'll have already removed the worm, which avoids the risk of damaging it with the disk).

Pressing out idler axles Gently press out the idler axles. We found that the axles are a tight fit in one side of the moulding only so, once you have removed the first one and thereby determined which side that is, press them out from the tight side and, when the time comes, replace them from the loose side.

As you push out each axle, remove its gearwheel and record its position in the drive train so that you can replace it later in the same position.

When removing the idler axles, support the moulding on a hard surface with some kind of slot or hole to receive the axle. We used the blind end of a 1.4mm drill, held in a pin chuck, to push the axles through.

Cut the worm gear idler axle to the length marked. Chamfer the edges of the cut end with a file.

Altering the Drive Train Mouldings

Modified and unmodified drive unit mouldings Referring to the 'before' and 'after' illustration here, and using your favoured combination of saws and craft knives, files, or burrs, cutting discs and grinders in a mini electric drill, modify the drive train moulding as follows:

Exercise some care as, in spite of being somewhat 'soft' and 'soapy', the plastic can crack in a brittle manner if overstressed. Take great care at all stages not to damage the retaining lugs for the main axle bearings.

Inner Worm Bearing Retainer

Worm bearing retainer etch Remove one of the Worm Bearing Retainer etches (D1) from the fret.

Worm bearing retainer, fold 1 Make the first fold as shown and reinforce it with a small amount of solder.

Worm bearing retainer, fold 2 Make the second fold as shown.

Worm bearing retainer, side folds Fold in the side ears of the retainer.

Worm Bearing Retainer in position Fit the inner worm bearing into position between the two plastic upstands. Fit the slots formed at the sides of the Worm Retainer around the upstands and slide the Retainer downwards so that it rests on the bearing.

Drilling worm pillars Ensuring the Worm Retainer is firmly held in place and well supported, use the holes in the Worm Retainer as drilling guides to drill 1mm holes (to clear 14BA) in the pillars.

Work gently, from each side, using a hand pin chuck and take care that the drill does not wander and break through the edges of the pillars.

Worm Bearing fixing screw Insert one of the supplied 14BA screws through the holes, and trim the screw to length, leaving sufficient exposed threads to fit a nut.

Trimming worm pillars Trim the parts of the plastic upstands which protrude above the Bearing Retainer. Make sure they are well supported while doing this.

Remove the screw, Worm Bearing Retainer and worm bearing and put them safely to one side.

If, for any reason, such as variation in manufactured dimensions of the drive unit, the etched Retainer can not be fitted, a perfectly serviceable arrangement is to omit the etch and secure the bearing by the 14BA screw and nut alone. The holes are drilled such that the shaft of the screw is in contact with the top of the bearing.


Give the Drive Unit moulding a thorough wash and degrease to remove all traces of swarf and dust.

Refit the worm gear and the three idler gears and axles (the worm shaft can be left to one side for the time being, to allow for unpowered testing later on).

That concludes the modifications to the bogie drive units.