This discussion thread has come to a successful conclusion as indicated by the following image:



Close examination of the disassembled components reveal that the upper tank had been GLUED to the chassis where the back of the tank meets the chassis.

For those wishing to follow in my steps, I leave the following guidelines and cautions:

1) I used a hobby knife to gain the release of the stubborn upper tank section.  I had initially attempted to pry under the side viewed in the picture, but release did not come until I had pried on the opposite side under the rear and middle sections of the tank.  It released with a start causing me concern that the knife may have done damage to the circuit board or wiring (which is possible).  Note the lip on the removed upper tank: use care to get the knife under this lip.

2) While loose, several more steps are necessary in order to free the upper tank.  The upper handrails need to be separated from the front of the tender.  I was able to remove one by hand, but the second one required the use of light needle nose pliers.  While holding the upper tank nearly in its original position, it is necessary to back the tank away from the front section in order to free a tongue that secures that connection.   I was surprised to yet be unable to remove the upper tank.  It took some horsing around to remove the upper tank with an upwards movement.  A view of the components and fittings explains why the upward movement is necessary.  I was surprised that the leveraging motion from the rear of the tank is only applicable to step 1).

Regarding the removal of the trucks, I find that the screws to the trucks are secured by nuts that will simply spin when loosened.  Under the each nut is a thin brass washer to which a wire has been soldered.  This is capable of winding with the turn of the screw if not managed from the open tender.  It may be necessary to remove the circuit board to manage the removal of the rear truck, but access to the front truck is not as yet apparent.

I applaud the engineering of the tender light as there are no wires to frustrate the removal of the upper tank.  A plastic light straw conducts the light from the bulb that is seen aimed vertically at the rear of the open tender.

I wish more immediate success to those who subsequently attempt the disassembly of the Bachmann HO Medium Vanderbilt Tender.

-Gary

As I have previously stated

I've attempted to open not one, but two, NIB tenders after removing the two screws.  I have been unable to get the rear tank to separate, or even give hint that it is capable of separation.  The tank remains solid! 

Does any (who has gotten one of these apart) see where I could insert a screw driver, or Xacto knife, and pry it open? 

Thanks.

As you can see from the parts explosion of the 89903, access cannot be obtained from either end.  Hasn't someone made access to the circuit board?

Here is an image of the Bachmann 89903 HO Medium Vanderbilt Tender which I am unable to open:

Sorry, Roger, you've got the wrong tender.  You have the Hicken style tender.  I marvel at the modification you did.  I have opened the Hicken style tender w/o problem but am unable to open the smaller 2 axle truck Medium Vanderbilt tenders.  I seem to be unable to attached its 11KB image as the upload folder is presently full.  -Gary

The first Medium VB Tender remains impenetrable!  I had a second unopened #89903 tender stored away.  Upon removal of the tender from the box, I removed the two screws at the center bottom and front bottom of the tender. and yet there is no give when I exert upward pressure at the rear of the tank.  I am at a total loss!  While a hammers and pry bars are tempting, they would defeat my purpose.  HELP, SOMEONE, PLEASE!

Bob, did you do further disassembly as I am unable to force any movement of the upper tank by exerting upward pressure near the rear (after having removed 2 screws from beneath the tender)?  I have left the coupler and coupler pocket in place at the rear of the lower chassis.  From the parts diagram, I do not see why this has to be removed.  Did you remove the coupler?  Thanks.

Readers!  My question remains unanswered!

Bob corrects himself in identifying the oil tender accompanying the mountain locomotive as the Hicken style tender which I also own and managed to open for decoder installation.  

The Medium Vanderbilt Oil Tender is a horse of another color...at least as disassembly goes.  I am unable to identify which, if any, locomotives the Medium Vanderbilt Oil Tender was sold with.  I acquired mine as a product unto itself, item #89903.

Thanks, Gary

I am desiring to 'borrow' the trucks from a B'mann tender, 89003, as they have electrical wipers I could use urgently elsewhere.  I have viewed the accompanying documentation (with the tender) and searched internet forums--including this one--without finding needed answers regarding disassembly.

I partially back out the screw to the rear truck, but when released, the screw head moves to the opposite direction.  I am fearful that there is an unillustrated electrical connection affixed to this screw.  The screw to the front truck remains snug, but again, I fear that I am twisting an unillustrated electrical connection.

Desiring to see what lies in the tender, I again find the accompanying documentation and internet searches to be of little value aside from affirming that access s/b possible for decoder install.  I have removed two phillip head screws from the bottom of the tender and pull upwards on the shell without indication of possible separation.

I am desiring instructions as to how to remove the shell from the chassis in order to address both the issue of truck removal, and later decoder install.  [Note: the trucks w/b returned, or replaced, before decoder install.]  

Thanks, Gary

You will not find the Digitrax DH123D 2 function decoder to be plug-n-play, but the DH123P and DH123PS variants include harnesses ending with the NMRA 8 pin plugs that are plug-n-play to Bachmann DCC ready, or as replacement decoders to  DCC On Board locomotives.  If you search the internet, you can find them for $17.25 each.

Jonathan - Thank you so kindly for your reply--and image--as to the possible cause of the racheting noise.  I have captured it and printed it.   I made my plea on the Message Board to obtain real life responses like yours.  If I can visually confirm that the driver wheel pickup brush is the cause, I will not be in a rush to tear apart the GS4 as I expect to rarely operate this in reverse.  I am entertaining the possible disassembly of the locomotive to change out the motor which I suspect to be the cause of the buzz.  I could at that time deal with the wheel pick up brushes.

I get a growling/buzz noise at mid boiler of the locomotive when putting DCC throttle to the new engine on the test track even if it is insufficient to cause it to move (as I haven't adjusted the start voltage).  This is quite unlike my B'mann Santa Fe Northern w/DCC On-Board.  Grasping the shell does not alter the buzz.  Add'l throttle causes motion and new noises but leaves the growl unchanged.  Furthermore, I hear a racheting sound when moving in reverse.  I haven't found anything externally amiss; and was utterly amazed that changing out the decoder for a silent operating Digitrax decoder failed to diminish the buzz.  Any ideas?  Thanks.