Bachmann 4-6-0 "Big Hauler"

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Bachmann has a very famous loco, called the "Big Hauler" (There is a special  version called the "Anniversary Editon" or "Annie" that has had variations in detail, quality, etc.  See the Anniversary edition page link at the end. The anniversary edition was a 5th Generation gearbox).

It has been continually improved over the years, so it's common to try to identify the "generation" so as to know the "quality level" when buying a used one.

The typical Mabuchi motor used was 1.08" in diameter, housing legth (w/o bushings) 1.49", 1.71 wth the bushings. Short shaft versions were about .26",  the worm was .610" in length, with 8 lands series , on a series 3, there were 6 lands in the same length

On the chassis with the gears retained by pins pressed through the chassis, only one end is knurled, so when pulling apart, only push the pin out a bit, and see if it's the knurled end... if not, push it out the other way, so as not to force the knurling through the gear.

Special thanks to Dave Goodson for the majority of the information and pictures here.

1st Generation: 1988-1990

The first generation was battery powered, had a simple remote control system, and had a small motor, plastic wheels. It had a multigear gearbox. The motor was 6 volts. You can turn the drivers by hand and the motor will turn. No worm, a right angle spur and crown drive

Note--the controllers came in two frequencies--27 MHz and 49 MHz. If the loco number had a "7" in it anywhere (like, 7, or 27), it was 27 MHz. If it had a "9" anywhere (like, 9, or 49) it was 49 MHz.

Early Big Hauler flanged wheels have a plastic hub which is driven on to the axle (and quartered).

They took 6 "D" cells for power.

There seemed to be an accessory cable with a Tamiya plug to allow a standard 7.2v 6 cell packs to be connected.

There is a 4 pin connector in the bottom of the battery compartment that has a gray, a brown, a blue and a black wire... the gray and brown wires go to the square pin on the tamaya plug, and the blue and the black wires go to the D shaped tamiya connector.







Note the big battery compartment in the chassis below:

2nd Generation: 1990-1994

The second generation used the same gear train, but had a 12v motor, and ran from track power. The motor block has a smooth bottom cover. It still used the 90 degree spur and crown drive.

There were variations in the gear on the motor, the picture above shows a gear that is "cut" the length of the gear.


The picture below not only shows a cracked gear, but note that the gear teeth do not extend the full length of the gear.

3rd Generation: 1994-1998

The third generation was also called the "Plus" model. It has a better motor (but a weak motor mount), better gears inside (idler and axle spur gears). The bottom cover is still smooth, but you cannot turn the wheels to turn the motor. this is because the drive used a worm gear.  The motor mount would let the motor to move away from the cluster gear and strip it. People usually used a big ty-rap to hold the motor in place.  The worm gear diameter is ~0.68" in diameter.

In the picture below, notice that the "motor mount" ring has come loose from the motor. This helps cause problems with gear mesh.

4th Generation: 1998-1999

There is a large, wide hump centered between the rear drivers on the bottom cover.

The motor worm directly engages worm gear, which is on the driving axle.

There are 2 variations in the gearbox. The first shown is with a single axle through the worm gear. It is surmised that this was to use up the rest of the components that relied on the single axle and the splined drive to the wheels.

Ver4 4 6 0 001

Ver4 4 6 0 003


The second variation on the gearbox shown below uses a gear that takes square ended half axles. Unfortunately these crack/split differently, see below:

Sound drums split, gear hubs split, wheels came adrift. Same motor as before, just mounted to a metal channel.

(please note in the picture below the owner has moved the nylon bushings from the outside to the inside in an attempt to limit the side to side gear travel.) The damage seen here was caused before the repositioning of the bushings. This is unnecessary, as you can see, the gear was worn evenly in the center - after accounting for the extra side force from the worm rotation.

Therefore the wear occured while the worm gear was centered under the worm, the issue was not side play, but just worn out, possibly excerbated by the typical loose motor, since the screws that hold the motor in place are only accessable through the gearbox, so many people do not discover this until too late. This is a common issue with this gearbox.

030 gap to left


 Note 2 different implementations above:

There are 2 types of worm gear:

  • one rides directly on the solid axle as in previous generations (first pictures, with solid gear)
  • Later versions the worm gear hub has a square hole and you have 2 metal axle halves with a square ends. These ends go into the drive gear hub, or the chuff switch "drum" This version is in 2 pieces, the gear and a center hub. The center hub is held by 4 posts, that are "hot melted" over to hold the 2 parts together. (once separated, you would have to drill and tap and use screws to reassemble.)

The worm gear is 1.245" in diameter (the reason for the big hump).

 The gear that is made of 2 pieces and has the square hole in the center hub is pictured below, and it is quite flexible:

  Botch Gear2

When this gear lets go, it basically shreds into rubber dust.

Notice the splits in the hub on both sides. When this happened, the motor and gear would move but not the loco.

The worm gear was actually an assembly. The inner part attached to axle hub with 4 pins that was "heat riveted" to the gear. They did come apart, and there was no way to repair.


When the hubs crack, you normally put a brass sleeve on them:

Ver4 4 6 0 004

When doing this fix,  you need to put thin nylon washers on the inside of the U channel of the gearbox, so your brass sleeves do not grind into the metal sides of the gearbox.

The stock nylon bushings on the outside keep things from moving too much side to side, the brass bearings (nearest the wheels) could touch the metal chassis and make a potential short.

Note if you do this fix, you may have problems on 4' diameter curves.

5th Generation: 2000-2012

There is a 3/8" wide hump offset (not centered) between between the rear drivers and a plastic lubrication plug the size of a dime to the rear of the hump. The fifth and sixth gen wheels mount on a solid axle with plastic pieces in and around the hub. The drivers were attached to the axles with screws.  Bachmann claimed Delrin is no longer being manufactured, so wheel bushings are now made of Celcon. Lots of rotational play in the wheel and axle assembly.

The picture below shows a generation 5 BH, but with plastic side rods. Some people believe all generation 5 locos have metal siderods, but this shows it's not true.

Below you see a generation 5 gearbox. Notice the screws to hold the wheels on.

Anniversary edition is also Version 5 chassis, see link below.

6th Generation: 2012-present "all metal gearbox"

I'm working on getting a picture of this gearbox.




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