Bachmann Class 46 (31-075) gears slipping

[Shrimpy]

Just got an old class 46 out of the attic (model 31-075).  Tried it on the track and it's very noisy and it sounds like the gears are slipping as it's very slow.  I've got the top off, but presenting with a metal block that contains the motor and drive mechanism.  There are a couple of screws at the top which seem to release the wiring bars, and two screws at each end which seem to attach the block to each bogie.  But it's still solidly in place when I remove all four screws.  I've downloaded the service sheet which shows how it all comes apart, but there seems to be two screws or posts that I can't get to as they seem to be under the drive shaft at each end.  I can't see any screws underneath.  Anyone know what I'm not seeing as to how to get this block off?

[34theletterbetweenB&D]

You have to remove the PCB and both bogies, Then you can pull out the drive shafts and access the screws that secure the plastic moulding to the block, (there should be easily accessible screws either end of the block too).

 

But you may not need to go that far. When this type of mechanism doesn't run well, despite getting power so that the motor is definitely turning, once you have the drive shafts out check the plastic drive couplers that plug into the flywheels. If one of these is loose, there's the trouble: when it slips one bogie gets no drive, so you have a loco with traction on one bogie, and the other bogie stopped (thanks to the worm drive) exerting equal brake force. Net result, very slow progress.  If this proves to be the problem, a dab of cyanoacrylate to secure the drive coupler and you are done.

[Shrimpy]

Brilliant thank you.  It was exactly as you said.  Now sorted and running much better.