Rebuilding Märklin 3084, DB 050 082-7, to digital with Märklin conversion set 60901 and new tender chassis

Updated 24.03.2013

This conversion method has also been used on Märklin 3100-2, 3310, 3315, 3319 and 3417.  This means the older variants of the Br 03, 012, 50 and 52.
As only the motor and the small parts from the conversion set are used, all the different sets for dcm motor may be used.  That is 6090, 60901, 60921 and 60760.
The Märklin motor conversion set 60941 and an separate decoder may also be used.
See Conversion sets, dcm motor.

Märklin 3084, DB 050 082-7

Tender, with new chassis, weight, coupler pocket and rear light:
The tender body is secured to the tender chassis with four clips.  The body can be removed by carefully bending the sidewalls out where the clips are located.

I rebuilt the tender in my 3084, with parts from the newer version 37840.  That means new chassis, weight and coupler pocket.  I kept the body, bogies and the pulling rod from the 3084.  I also installed a 37840 type decoder, to fit in the new tender weight.  The old tender body fits the new tender chassis without any modifications.

The decoder is installed in the tender, where the original electro-mechanical reversing unit used to be.
As I am using the new tender chassis and weight, and the 37840 decoder, the decoder installation is very simple.  Just screw it into position with two small screws.  The noise suppressors for the motor are soldered directly to the soldering pads on the decoder, and the blue and green wires are soldered to the suppressors.

A 28 volt T1 bulb with long wire ends, insulated with rubber removed from thin wires, is installed as interior light in the tender cabin.
A 330 Ohm resistor is installed in series with the bulb, to reduce the light intesity.

The connections to the decoder:

Alternative connections:

The red wire to the pick-up shoe may be soldered under the board at the left red arrow
The orange wire to the interior light is soldered directly to one of the rectifier diode's cathode (+ end)
The function end of the interior light is soldered directly to the transistor, see decoder photo above

Decoder functions:
f0 = light with directional change
f1 = smoke unit
f2 = interior light in the tender cabin, 28 Volt T1 bulb with a 330 Ohm resistor
f4 = acceleration and braking delay off

Decoder adjustments:
The decoder speed potentiometer is adjusted to minimum, yet the locomotive reaches a maximum of 105 km/h.
The acceleration and retardation potentiometer is adjusted to maximum.

With the original type tender:
It is of course possible to rebuild the locomotive by keeping the old tender chassis.

The photo shows my Märklin 3100, DRG Br 03, rebuilt with the 60921 mfx conversion set.

Rear light:
The new decoder has a bulb socket for the rear lamp, so I had to install a light guide in the tender, as 3084 originally has no rear light.  The light guide from 37840 fits perfect.  Very carefully drill holes in the rear lamps on the tender body.  Very careful, as the drill has a tendency to slip sideways in the soft plastic, damaging the lamps.

The final result looks like this:

Installation of the motor itself is very simple.  Remove the old motor and make sure that all the rotating and moving parts are clean and work perfectly.  Install the new motor form the conversion set.  Carefully add one small drop of oil to each end of the rotor.  To much oil will harm the operation of the motor.  Before inserting the brushes, check once more that everything rotates and moves normally.  Finally, insert the brushes.

Locomotive wiring:
The orange wire from the decoder leads the front lamp, so does the grey wire.  The brown/red wire for function 1 (f1) also goes to the front lamp holder, which also holds the contact tongue for the smoke unit.

The original bulb holder in the 3084 has a common contact tongue both for the lamp and for the smoke unit.  The bulb is installed directly in the locomotive chassis.  I wanted to separate the two functions, and to insulate the bulb from the chassis.

The part from e.g. 3319 fits perfect.  Bulb holder 280180, which has a separate connector for the smoke unit, and holds a 610080 bulb.  One modification to the locomotive body:  The original bulb holder has a too small diameter for the new lamp holder to fit.  It must be drilled a little bit bigger.

New front coupler pocket:
I wanted to install the new type coupler pockets on my 3084, so a 70163 type close coupler may be used.  First I screwed on a pocket on the original coupler holder, but I thought the coupler was too long.
The next solution was to install a coupler pocket from a newer locomotive, with an original close coupler pocket.
The front coupler pocket is as on Br52, 3415 and 3715.  The coupler pocket with snow plough is Märklin part 447410 and the required axle holder is 393280.  I had to make some device for the coupler's centring springs.
The support for the centring springs are quite simply two small bent pieces of wire.  At first I soldered one of them to the rivet holding the cylinder, but the rivet rotated, so the support came out of position.  A small drop of glue solved the problem.  The next support is only glued into position.
The leading truck has the old axel from 3084.  See the animated photo.

On the track:

I think I will paint the coupler pocket itself black and the spring supports red.

New drive rods:
The first thing I did with my 3084, many years ago, was to replace the driving rods for the wheels.  3084 has been produced with three different rod types, with different radius bars, but they all had the same part numbers.  See table below.

Version 1, 1974 - 1981: as in the above photo, with a wire type radius bar and a simple cross head
Version 2, 1982 - 1983: as in the above photo, but with a more detailed cross head, as in below photo
Version 3, 1983 - 1996: as in the below photo, with a detailed cross head (blue arrow) and a rod type radius bar (green arrow).

The photo is from 3308, DRG Br 85.

The parts I used to upgrade my Märklin 3084:
Märklin no. Pcs. As in Description
60901 1 - Digital high performance conversion set, motor and small parts only
602758 1 37840
c91 decoder
567190 1 Tender chassis
761710 2 Buffers for tender
463300 1 Tender weight
750230 2 Screws for tender bogies
786750 2 Screws for decoder
463330 1 Rear coupler pocket
285240 1 Cable holder
210132 1 Light guide in tender
447410 1 3415 Front coupler pocket with snow ploughs
393280 1 Front leading truck
280180 1 3319 Front bulb holder with separate smoke unit contact tongue
234630 1 3084
ver. 3
Driving rods, right hand side Note: same part nos. for all 3084 versions
These parts are used on many 1'D locomotives
234660 1 Driving rods, left hand side
70163 2 - Close couplers
610080 2 - Front and rear light bulbs
- 1 - 28 Volt T1 bulb for interior light in the tender

Screenshot from my Central Station:

The wiring diagram for my Märklin 3084:

Some facts about the prototype: (from Wikipedia)
DRB Class 50
Road numbers: 50 001–50 3171 (with gaps)
Number built: 3164
Years built: 1939–1959
End of service: 1987
Axle arrangement: 1'E h2
Gauge: 1.435 mm
Length over buffers: 22,94 m
Height: 4,5 m
Overall wheelbase: 9,2 m
Service weight: 86,9 t
Adhesive weight: 75,3 t
Axle load: 15,2 t
Top speed: 80 km/h (both directions)
Indicated Power: 1.625 psi (11,200 kPa)
Driving wheel diameter: 1.400 mm
Leading wheel diameter: 850 mm
Valve gear: Walschaerts with lifting links,
also called Heusinger
Cylinders: 2
Cylinder bore: 600 mm
Piston stroke: 660 mm
Boiler Overpressure: 16 bar
No. of heating tubes: 113
No. of smoke tubes: 35
Heating tube length: 5,200 m
Grate area: 3,89 m2
Superheater area: 68,94 m2
Evaporative heating area: 177,83 m2
Tender: 2'2' T 26 or 2'2' T 30
Brakes: Pressurized air
Train heating: Steam

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