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Discussion Starter #1
I have a fairly new-old-stock Bachmann GP-40 that has a problem with the powered back truck assembly. When I got the unit out of the box for the first time ( I don't remember if I bought it years ago or inherited it from my dad ) it ran for a minute and then it lost drive to the wheels on the back/powered truck. I took it apart and there was a lot of lubrication oil on the entire drive shaft assembly. It took several cleanings until it would stay together; however in the process I think I somehow damaged the assembly as now the front axle of the drive truck is slightly higher than the rear axle (see photos) and it frequently derails. I tried taking it apart and reassembling it. If I get it loose enough that it sits level, when I stop the engine, the rear axle on the drive truck derails to the right. If I tighten up the assembly to where the truck sits level, it's too stiff to navigate the curves. If I run the engine in reverse, where the powered truck is leading, the engine runs fine. Any idea what I've done wrong and/or can remedy the problem ?
 

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I don't own any Bachmann engines.

But...
As I look at the pic with the shell off, I notice that the worm gear doesn't seem to have a "snap on cover" over it.

This cover (on other locos) both holds the truck assembly in position, and properly positions the worm on the gear that transfers power "downward" to the truck gears and the wheels.

Could you take a pic of the OTHER truck, shot from the same angle, so we can see what that looks like?
 

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Discussion Starter #3
I don't own any Bachmann engines.

But...
As I look at the pic with the shell off, I notice that the worm gear doesn't seem to have a "snap on cover" over it.

This cover (on other locos) both holds the truck assembly in position, and properly positions the worm on the gear that transfers power "downward" to the truck gears and the wheels.

Could you take a pic of the OTHER truck, shot from the same angle, so we can see what that looks like?
Thanks for your response. The powered truck has a circular piece that swivels and holds the truck assembly to the body of the engine; there's a single screw that goes through the body into the center of this piece. In the attached photo, it's to the right of the worm gear. It's held on by two screws. The screws are secure but it's like the whole assembly now is tilted. I don't have another Bachmann engine to compare it with so your's is an interesting theory: I'm missing a part.
 

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Discussion Starter #4
I don't own any Bachmann engines.

But...
As I look at the pic with the shell off, I notice that the worm gear doesn't seem to have a "snap on cover" over it.

This cover (on other locos) both holds the truck assembly in position, and properly positions the worm on the gear that transfers power "downward" to the truck gears and the wheels.

Could you take a pic of the OTHER truck, shot from the same angle, so we can see what that looks like?
Here's a photo of the truck that's been removed from the body. A part of the circular piece snaps into the worm gear housing and that's what holds the worm gear to the wheel gear.

It's frustrating; the engine runs great, it just derails constantly.
 

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Discussion Starter #5
[/QUOTE]
Here's photos of both the front truck and the drive truck.

I went on the Bachmann site and verified that I'm not missing any parts.

Update: I loosened the screw holding the drive truck to the body so that the truck seemed to be the same as the front truck. Now, even if I just slightly push on the back of the engine, the rear axle of the drive truck kicks out to the right just like it does under power. From reading in other forums, could the problem be that the rear axle is out of gauge ? Again, if I run the engine in reverse where the rear drive axle is now the 'front' axle, the engine runs just fine.
 

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Thanks for the pics above.
I was under the impression that the engine would have both trucks powered.
I guess Bachmann "did it differently" on some of their products...
 

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...I had two Bachmann GP 40s. Both trucks are powered and
the loco has great pulling power. Never a derail. But to your problem:
I also had 2 Bachmann F units.
One had a problem similar to what you have experienced. I fiddled with
that truck a lot to no avail. I found, however if used as the trailing
unit in a consist there was no difficulty. It ran fine from then on
and I never had any further derails. I suspected that it needed
a 'break in'. I also had a Mehano SW 1 with a derail problem. I found that
the derailing truck was not putting all 4 wheels on the rails evenly
thus losing the 'guide' of the flanges. It took quite a bit of 'adjusting'
to bring it under control.

Don
 

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Discussion Starter #8
I found that
the derailing truck was not putting all 4 wheels on the rails evenly
thus losing the 'guide' of the flanges. It took quite a bit of 'adjusting'
to bring it under control.

Don
I don't seem to be getting anywhere with my adjusting. If I tighten the screw holding the truck assembly, the truck is too stiff in the turns and derails. If I loosen it too much, the front axle of the truck is too high and not sitting correctly on the rail. This is a fairly old unit and only the back truck is powered.
 

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Discussion Starter #9
I was under the impression that the engine would have both trucks powered. I guess Bachmann "did it differently" on some of their products... [/QUOTE said:
I got to thinking about this and went back & looked at the diagram for the 'regular' GP-40 on Bachmann's website. Their diagram indeed shows both trucks powered. But looking at mine, there's no attachment to the motor shaft for a driveshaft to the front truck; and there's no gear mechanism between the axles in the front truck. Could this possibly be a defective unit ?

I'm starting to wonder if my best recourse is to send it to Bachmann. Even if they replaced it with another GP-40, at least I'd have a usable one. . . .
 

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You could try sending it back, but my suspicion is that it is far out of warranty. Did you purchase it new?

Interesting looking at those pictures, I thought that all Bachman engines with the big metal frame were AWD, but as you say, yours is not, despite the frame clearly being designed with space for dual driveshafts.

One thing I thought of, how tight is the driveshaft? Could it be pushing the truck forward enough to force the front wheels down and the back wheels to lift?
 

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Discussion Starter #11
I thought that all Bachman engines with the big metal frame were AWD, but as you say, yours is not, despite the frame clearly being designed with space for dual driveshafts.

I'm not the original owner so no warranty. This was a part of a 3-piece set distributed by the "Great Planes Model Distributors Company". It has a powered GP-40, an unpowered dummy and one of the cheapest-looking cabooses I've ever seen. So my concern is that if I send it to Bachmann for repair, they'll just send a replacement that very well may have black trucks and then it won't match the dummy's dark gray trucks. So . . . I wonder if I could just buy a new engine and set of powered trucks as there's space in the frame for AWD.

One thing I thought of, how tight is the driveshaft? Could it be pushing the truck forward enough to force the front wheels down and the back wheels to lift?
I'll check this - it's a good theory. It's the front axle on the back truck that's too high but if the driveshaft were too tight, that'd quite possibly do it.
 

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Discussion Starter #12
Update: I spoke with the Bachmann Service Department and I've decided to send it to them. They have the parts and if they have to do an exchange they assure me they can accommodate my desire to stay with dark gray truck frames. They did confirm that this was a special production run for Great Planes Model Distributors, likely early 80's, which explains the can motor but a different one from Bachmann's regular units.
 

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Update: I spoke with the Bachmann Service Department and I've decided to send it to them. They have the parts and if they have to do an exchange they assure me they can accommodate my desire to stay with dark gray truck frames. They did confirm that this was a special production run for Great Planes Model Distributors, likely early 80's, which explains the can motor but a different one from Bachmann's regular units.
Wow,
That's pretty great that they'd still have parts. Are they charging you for the repair and/or return shipping?
 

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Discussion Starter #14
Wow,
That's pretty great that they'd still have parts. Are they charging you for the repair and/or return shipping?
Yes, they're charging me; even if I were the original owner, the engine is so old that they'd charge even in a warranty situation. And what they're charging is about the same as I'd pay for a replacement engine.The only part that's different is the motor. The one I have is a 4-wheel drive can versus the 8-wheel that's in most of their GP's. I'm hoping that they will either just put in an 8-wheel motor and two new drive trucks or just send me another GP-40 with dark gray trucks so it'll match the dummy unit from the set. The bottom line is that it has to run right. They were surprised that it didn't have a pancake motor.
 

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I have a fairly new-old-stock Bachmann GP-40 that has a problem with the powered back truck assembly. When I got the unit out of the box for the first time ( I don't remember if I bought it years ago or inherited it from my dad ) it ran for a minute and then it lost drive to the wheels on the back/powered truck. I took it apart and there was a lot of lubrication oil on the entire drive shaft assembly. It took several cleanings until it would stay together; however in the process I think I somehow damaged the assembly as now the front axle of the drive truck is slightly higher than the rear axle (see photos) and it frequently derails. I tried taking it apart and reassembling it. If I get it loose enough that it sits level, when I stop the engine, the rear axle on the drive truck derails to the right. If I tighten up the assembly to where the truck sits level, it's too stiff to navigate the curves. If I run the engine in reverse, where the powered truck is leading, the engine runs fine. Any idea what I've done wrong and/or can remedy the problem ?
Slomopilot;

It looks to me that the whole truck assembly is tilted, and that may be because the drive shaft is somehow "too long" since you reassembled things? Could the shaft be part way pulled out of the black plastic coupling between the motor and the drive shaft?

Good Luck;

Traction Fan 😕
 

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Could the shaft be part way pulled out of the black plastic coupling between the motor and the drive shaft?

Traction Fan 😕
Thanks. Someone in another forum suggested that; I tried adjusting the drive shaft several ways and it didn't correct the problem.
 
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