User:MinorProphet/Draft subpages/WW2 ZF gearboxes



Oi! You need to sort ALL THE REFS OUT, get on those sfns...

This is an incomplete list of gearboxes (Schaltgetriebe) made by ZF Friedrichshafen (ZF) before and during World War 2 and fitted to various military vehicles used during the war, including tanks, tank hunters, self-propelled artillery and assault guns, half-tracks, armoured cars (Sd.Kfz. 247 Ausf.A), artillery tractors (eg SWS, ?Maultier?) and other soft-skinned transport vehicles (e.g. Krupp Protze).

ZF designed and made gearboxes for most German AFVs and prime movers used before and during World War II, in conjunction with its sister company Maybach, who made the engines (both were subsidiaries of Luftschiffbau Zeppelin, all based in Friedrichshafen). Almost all of the gearboxes listed in the following tables are of the manual, constant-mesh 'Aphon' type (from Ancient Greek, meaning noiseless). Although ZF's founder had designed the pre-selective semi-automatic gearbox, ZF made almost none of these types for military applications: it was Maybach which designed and produced the majority.

The 'G' and 'ZG', models (without synchromesh) were fitted to half-tracks; and the rest ('FG', 'SFG', 'SSG', and 'AK' models, all with synchro on most gears) were fitted to tanks and various self-propelled guns, tank hunters etc. based on tank chassis.

Almost all the tank gearboxes included a clutch as standard, as well as some of the half-track ones (e.g. for many Sd.Kfz. 6 variants.) Gearboxes with no clutch included the ZG 55 fitted to late models of the Sd.Kfz. 7, and the G 65 VL230 in the Sd.Kfz. 9; they were paired with a Maybach TUK type engine, where the 'K' always indicates a factory-fitted clutch.

Tanks etc. which did not use a ZF gearbox included the Panzer II Ausf. D & E, which used a pre-selector, semi-automatic, Maybach SRG 14 4 79 (7+1); the Panzer III Ausf. E-G which up until late 1939? used the troublesome Maybach SRG 32 8 145 (10+1); and production models of the Tiger I and Tiger II and derivatives, which used the Maybach 8+4 Olvar OG 40 12 16 (Original, 'A', and 'B' versions). Other vehicles which did not use ZF gearboxes included the half-tracks Sd.Kfz. 10 and Sd.Kfz. 250, fitted with pre-selector semi-automatic Maybach VG 102 128H (7+3); and all Sd.Kfz. 11s and Sd.Kfz. 251s, which used Hanomag's own manual 4+1 x2 gearbox design.

While manufacturing large quantities of gearboxes for production-series tanks and half-tracks, ZF also made a number of experimental or test designs which never reached the mass production stage. Both these types are listed in the tables below.

Gearbox nomenclature
ZF's gearbox model numbering system usually consists of one to three letters, followed by a number.

The letters (e.g. G, FG, SFG, SSG), tend to indicate the number of forward gears, and the number indicates the approximate maximum torque of the gearbox (e.g. 45 kilopondmeters, abbreviated in contemporary documents as mkg). According to Jentz, Panzer Tracts 3-1, SFG 75 stands for Synchronisiert Funf-Gang Getriebe (synchronised five-gear transmission), with '75' indicating the maximum torque (Maximaldrehmoment, abbreviated Md.) it can transmit in kilopondmetres (abbreviated as mkg or mkp. See § Torque section). Although all the ZF half-track transmissions included a range reduction (hi-lo, or 'crawler') gearbox, either separate or integrated within the casing (resulting in 8 forward and 2 reverse speeds), this is ignored in the model number.
 * G = Getriebe, four forward + one reverse gears, non-synchro
 * ZG = ? (four forward + one reverse, non-synchro, like the 'G' series
 * FG = Funf-Gang Getriebe, five forward gears + one reverse, (synchro on gears 2, 3 and 4 only REALLY?)
 * SFG = Synchronisiert[er] Fünfgang Getriebe, synchronised five-gear transmission (except 1 & R)
 * SSG = Synchronisiert[er] Sechsgang Getriebe, synchronised six-gear transmission
 * AK = Allklauen(?) The AK series (whether series production or not) have the number of gears and max. torque stated explicitly in the model number. The AK 7-200 had seven forward gears, the non-production AK 5-80 (proposed for JagdPanzer(D) with Tatra Typ 103) and AK 6- series had five and six forward gears respectively. ZF also made a 4-speed synchro gearbox (possibly with pre-selector mechanism?), the AK 4 S in 1934.Find ref, fool!.

Half-tracks
All the half-tracks have non-synchro gearboxes with four forward gears and one reverse, coupled with a hi-lo range box to give 8 forward speeds and 2 reverse, abbreviated as (4+1 x 2).


 * G 'Semi-unit' construction with clutch, non-synchro. Two casings bolted/flanged together: clutch and hi-lo box at the front; and main change-speed box in the rear casing (i fink). Fitted to half-tracks with HL xx TU engines (e.g. HL57 TU in Sd.Kfz. 7 KM m9) - NB The exception is the clutchless G65 in the Sd.Kfz. 9, which really ought to be a ZG65...
 * ZG 'Unit' construction with both speed change and hi-lo mechanisms in the same casing, no clutch, non-synchro. Fitted to half-tracks with HLxx TUK engines (e.g. HL62 TUK in Sd.Kfz. 7, KM m11)

Tanks
All the tanks (including other full-tracked vehicles including self-propelled artillery, tank hunters, assault guns and vehicles based on tank chassis) have five, six or seven forward gears, all synchro (except reverse).


 * FG (5+1) - Plain gearbox with clutch, synchro only on 2, 3, 4 (not 1 + R, plus 5 removed). Fitted to Panzer 1 Ausf. A & B (drawings/pix at J&D, PzTr 1-1, p. 1-39, 1-41 (FG 35), 1-80, 1-82, good photo on p. 1-85 (FG 31) )
 * SFG, SMG?, SSG, AK (5/6/7+1) - Plain gearbox with clutch, with synchro (except 1 & R) - all fitted to tanks only.
 * EV (6+1) - Electromagnetic gearbox fitted to Swedish Stridsvagn m/42 tanks. Almost certainly with synchro. Seen as very unreliable (due to poor quality steel in manufactured internal clutch plates, perhaps not the basic design...)

Thus it appears that (apart from the above exception) all of the transmissions which ZF produced for series installation in tanks, halftracks and other AFVs were manual: all the pre-selector semi-automatic gearboxes fitted to some tanks and the Sd.Kfz. 10 etc. as mentioned above, were made by Maybach (SRG, VG, & OG series).

NB - for Maybach g/box draft: The Soden transmission used mechanical shifting; the VG was pneumatic/vacuum operated; the SRG used vacuum for the selector valves/pistons and hydraulic pressure for the accelerator & brake clutches; and the OG was completely hydraulic.

Good website about the Panzer IV: Panzer IV Universe with lots of refs.

Table 2 - Experimental or test ZF gearboxes
None of the gearboxes listed here reached series production during the war, although in the 1950s/60s ZF sold the AK series as pneumatically controlled pre-selector gearboxes (with a similar mechanism to the Maybach ones) for commercial trucks, either without synchromesh (e.g. the AK 5-35) or with synchro (e.g. the S 6-70).

Founding of ZF
Zahnradfabrik Friedrichshafen GmbH (ZF) was formed in September 1915 as an offshoot of two existing companies, Luftschiffbau Zeppelin GmbH of Friedrichshafen and Max Maag Zahnradfabrik of Zürich (later Maag-Zahnräder AG), to make gearboxes for Zeppelin airships. The head of the testing department at Zeppelin was Alfred von Soden-Fraunhofen (21 November 1875–14 June 1944), an engineer and designer who had worked at Daimler AG and MAN. He became acquainted with Graf von Zeppelin while holidaying in the area, and was offered the newly-created position in 1910. He was involved with testing the LZ 6 and LZ 7 in 1910 after the LZ 5 crashed and burned. (See List of Zeppelins.) Soden and Claude Dornier, also employed by Zeppelin, wrote a report together on airship drag in 1911.

In search of high-quality gear mechanisms, von Soden contacted Max Maag, a Swiss engineer who in 1913 had started his own factory in Zürich to make precision ground helical gears. Count Zeppelin prompted Alfred Colsman, managing director of Luftschiffbau Zeppelin GmbH (LZ), to propose a new independent company based in Friedrichshafen, which was founded in 1915 as Zahnradfabrik Friedrichshafen GmbH, a limited liability company with von Soden as managing director. By 1918 the company had 600 employees, which had fallen to 570 in 1920.

The harsh terms of the Versailles Peace Treaty forbade all military activity and manufacturing, and ZF turned to making gearboxes for passenger vehicles. The general post-war depression threatened bankruptcy, and the firm was re-financed and incorporated as Zahnradfabrik Friedrichshafen AG (stock corporation) in May 1921, with LZ as the major stockholder. Theodor Winz was the first managing director with Soden as technical director, heading the department for almost 30 years until his death from previously diagnosed leukaemia in 1944. Soden was deeply religious, and never joined the NSDAP.

After the rise to power of the NSDAP regime in 1933, the manufacture of military vehicles began again in earnest, and many other German manufacturers manufactured their own engines and gearboxes: but by 1936 the gearboxes for the majority of all tanks and half-tracks were designed and made by ZF, with the engines made by Maybach, another offshoot of Zeppelin also based in Friedrichshafen.

However, the motor industry in Germany during the 1930s was not well developed. There was very little mass-production using assembly-line methods common in the US. Motor cars (Personenkraftwagen, Pkw) were only owned by approx 5% (?) of the population, including businesses, government and richer private individuals. The motor industry was small-scale and scattered over thousands of individual businesses. Approx 90% of all goods travelled by rail. Only another 5% (?) was carried by trucks (Lastkraftwagen, Lkw). The most common mode of personal transport was the motorcycle.(ref Repairing the Panzers Vol 1, |loc=early on.)

Aphon transmission
In 1928 ZF introduced the 'Aphon' transmission (Greek for "without noise" or "noiseless"), a constant-mesh gearbox with helical-ground gears for passenger vehicles. It eliminated the inherent whine of straight-cut gears. See also § Overview of gearbox types below.

The Aphon was designed by Albert Maier (1899–1983), Maier graduated from Konstanz Engineering school and joined ZF in 1922, later becoming an engineer in the Design Office/Department. Soden and Maier designed the AK 7-200 gearbox for the Panther. See also Maier also designed ZF's only car, the post-war two-seater Champion with 200cc supercharged 2-stroke lawnmower engine with 3+1 speed gearbox. One of the managers of ZF after the war. Collector of medieval arms and armour.

These first Aphon car transmissions also featured synchromesh (except 1 & R). Transmissions with full synchro on all gears ('Panaphon') for passenger vehicles appeared in 1934. The (world's) first full synchro gearbox for commercial vehicles appeared in 1957, e.g. the ZF S 6-55 etc. - ha! see [http://www.ff-zinzendorf.de/wp-content/uploads/2016/10/Getriebe-Fibel.pdf. Getriebe-Fibel]. In military vehicles, it appears that none of the ZF gearboxes fitted to half-tracks had synchro, while all those in tanks etc. did.

None of the ZF types discussed here are of the older sliding-mesh type; all are constant-mesh. The term Schubgetriebe (abbreviated to 'Schub-') which Spielberger appears to use in referring to non-synchro transmissions is somewhat misleading, since the German term refers specifically to a sliding-mesh gearbox.

All the gearboxes described in this article and in the tables below are of the Aphon type, using helical-ground gears (except for reverse) even if not expressly indicated. They were produced in both synchromesh and non-synchro models. For example, the Aphon FG 35 fitted to the earliest Panzer Is had synchro on 2, 3, & 4 (synchro on 5 later removed.) REF?? Pz. Tr.??? Not while the Aphon ZG 45 in the Sd.Kfz. 6 was non-synchro. (US Handbook ) These appear to have separate shift-speed and range boxes. The "ZF Aphon ZG 55" in the Sd.Kfz. 7 Krauss-Maffei m9 & m10 (Spielberger 1993 p. 162), is described as "non-synchronized" (Handbook ) and appears to be of unit construction, with the hi-lo box incorporated within the gearcase.

General overview of gearbox construction
The general terminology of gearboxes may differ considerably by country. Gearboxes are often called transmissions, although the latter term is often colloquially used by mechanics and others to refer to the complete drivetrain by which power is transmitted from the engine to the driving whelks wheels. In modern terms, this may include the gearbox (which may be separate or of unit construction with the engine}, propeller shaft (or Cardan shaft, or simply 'prop shaft') and final differential gear. There are many implementations of this overall concept.

This article interchangeably uses both 'gearbox' and 'transmission' to refer only to a speed-shift mechanism. In this context, the gearbox or transmission is almost always a separate unit, either flanged directly to the engine (as in the half-tracks mentioned here) or powered by a prop shaft from the engine which is usually located at the rear of the vehicle.

The term 'transmission' may also include a separate 2-speed manual transfer gearbox, although no Wikipedia article appears to accurately define this specific simple mechanism. It is sometimes called a reduction gearbox (Untersetzergetriebe) although not necessarily of planetary construction, 'transfer case' 'hi-lo box', or 'crawler box', also often found in agricultural tractors. For the purposes of this article this type of reduction gearbox was fitted to most of the WW2 German half-tracks (except the Sd.Kfz. 10), providing a second set of low ratio speeds when very low speed and high torque was needed, such as hauling disabled vehicles out of a ditch, mud, etc. In the ZF transmissions under discussion here, the reduction box may be of separate construction and flanged to the rear of the change-speed gearbox, or of unit construction within the gearcase. This article does not discuss the differentials, steering gear or braking systems installed in tanks etc. made by other manufacturers.


 * A) Manual transmission
 * 1) Sliding-mesh type (Schubgetriebe or Schubvorgelege). This is one of the oldest gear change mechanisms, dating back to at least 1906. The gears are physically moved up and down the (input) shaft (Welle) to engage with the corresponding gear on the (output) shaft. Almost always without synchro, and often called a 'crash box'. Skilful double de-clutching is needed to effect gear changes without 'crunching' the gears as they mesh at different speeds. Very often the gears are straight-cut, which produces a pronounced whine. None of the ZF transmissions listed here are of this type, although various gearboxes are briefly described by historians (eg Spielberger) as "Schub-", perhaps possibly to distinguish from synchro boxes.
 * 2) Constant-mesh (Klauengetriebe) type. As the name suggests, all the gears are constantly in mesh. Instead of shifting an entire gear wheel on a shaft, a selector fork moves a dog clutch (in purple in the diagram) on a shaft between a pair of gear wheels. All the ZF transmissions listed here are of this type, with or without synchro, and all with helical-cut (or helical-ground) gears.
 * ZF's trade name for this type of transmission was § 'Aphon' (Greek for "without noise" or "noiseless"), a helical-ground constant-mesh transmission introduced in 1928 for passenger vehicles. It eliminated the inherent whine of straight-cut gears.
 * 3) Synchromesh gearbox or 'synchro' (Synchrongetriebe) type. A development of the constant-mesh gearbox which eliminates the need for double de-clutching by the incorporation of 'synchro rings' between the dog clutches. The rings absorb the speed difference between the two shafts, essentially acting like basic automatic inline clutches. Almost all ZF gearboxes fitted to tanks etc. were of this constant-mesh synchro type.
 * eg Aphon SSG 45 synchro in the Panzer II, SFG 75 & eg SSG 76, Panzer III & IV etc.
 * 'AK' (Allklauen) series (Klauen, 'dog clutch'), were all synchro - eg AK 7-200 (7+1) for all Panthers. Also experimental AK 6-200 (6+1) & 5-200 (5+1) for later high-revving experimental Maybach HL154 etc. engines - neither the prototype engines nor gearboxes ever reached series production during WW2.
 * B) Semi-automatic gearboxes.
 * Preselector gearbox type. Apart from the unsuccessful 6 EV 75 (see below), ZF doesn't appear to have made any series production of this type during the war, although it seems likely that they worked with Maybach on the designs of various models (eg SRG, Variorex and Olvars.) See List of WW2 Maybach gearboxes.
 * ZF Electro series - used internal electro-magnetic clutches, eg ZF 6 EV 75 (6+1) fitted to c.100 production Swedish Stridsvagn m/42 tanks in 1943–1944 (very unreliable - see table); and ZF K 12 E 185 proposed for late model Panthers but never reached series production.


 * Summary:
 * The 'G' and 'ZG' gearbox series installed in some half-tracks are all non-synchro.
 * All the ZF gearboxes fitted to a number of half-tracks had manual, non-synchro transmission with 4 forward + 1 reverse gears, coupled with a hi-lo range transfer box giving a total of 8 forward and 2 reverse speeds. This is expressed as (4+1 x 2). Some early models of the Sd.Kfz. 6 had a further hi-lo reduction box giving 12 forward and 3 reverse speeds. NB Spielberger in the English version of Halftracks has some very differing views, but I suspect he (and/or his translator) is completely in error. See talk. Some sources say that the Sd.Kfz. 9 may have had a synchro gearbox, but this is almost certainly incorrect.
 * Not all gearboxes fitted to half-tracks were made by ZF: eg the Maybach pre-selector Variorex in the Sd.Kfz. 10/250; and Hanomag installed their own gearbox in the Sd.Kfz. 11 and 251. (ref Spielberger, Halbketten in German, although the English edition makes some outlandish statements) J&D, Pz. Tracts, p. 22-2-7 state that a late trial version (not made in quantity), the H7, used a Maybach pre-selector box. Not further discussed. In some cases the range box is completely or semi-separate, as in the early 'G' series; and if of unit construction, the 'ZG' series (and, illogically, the G 60 in the Sd.Kfz. 9). NB, fool! You may be completely wrong about the Gs and ZGs, you may have got them upside down.


 * The 'FG', 'SFG', 'SSG' and 'AK' series, installed in many other tanks and SP gun carriages etc., are all synchro (except 1 +R).
 * Despite Spielberger's list in Halftracks of the German Army, ZF don't appear to have made any pre-selector gearboxes at all except the electromagnetic 'E' or 'EV' series, and they weren't a success (although due to manufacturing faults rather than design.)
 * See the interesting and fruitful discussion Talk:Sd.Kfz. 8, the reason for this article.

Torque
Gearboxes (colloquially, simply 'boxes') are generally designed to transmit a specific maximum torque.

The unit of torque used in Germany at the time was the Kilopondmetre, abbreviated as mkg in contemporary literature (sometimes mkp): modern abbreviations are kp·m or m·kp. 1 mkg = 9.80665 N·m = 7.233 lb·ft


 * Torque (lb.ft) = 5,252 x power (hp) / speed (rpm)
 * Torque (N.m) = 9.5488 x power (kW) / speed (rpm)
 * Torque (mkg) = 716.19724 x power (PS) / speed (rpm) (thanks to GNU Units and the Science Ref desk)

Max. torque of an engine is often reached at lower revs (approx 2/3 max revs) than maximum power, eg 2,000 rpm vs 3,000. Refs needed... Diesel engines (inherently lower-revving through their basic design) produce max. torque at lower revs than a petrol engine, although diesels were not fitted to most German armoured vehicles.

ZF's naming scheme almost always indicates the rated torque of the gearbox - eg the SSG 45 was designed for Maybach HL62 TR's max torque output of 45 mkp/mkg. In some cases the gearbox was uprated to handle a greater torque, but kept the same model number.Ref pls! Similarly, the AK 7-200 was apparently designed for the HL210/230's max torque of c.200 mkg.


 * I think I need a list of engines and/or gearboxes whose max. torque (Md. = Maximaldrehmoment) are definitely known. (Done: see Talk.) Spielberger's Panther tank and variants includes Appendix 18 with lots of original diagrams, graphs etc., including HL108 and HL230. NB! My thoughts below about tractability and flat torque curves may be completely wrong. They say (i fink) that a noticeable torque rise through the rev range with more gears, is equivalent(?) to a flat torque curve with fewer gears. Or something. Check, fool!

In tank and prime mover engines, the maximum power of an engine may be rather less important than its maximum torque.

Insert stuff about the relationship between the two. Not particularly easy to explain. Sports analogy: a bit like having a load of rugby players to haul you through the mud rather a bunch of sprinters to achieve maximum speed. See Büffel-Charakteristik, 'Buffalo characteristics' (Spielberger, Panther tank and variants, p. 236)


 * "A flat torque curve makes an engine much more driveable because acceleration is the same at any point on the curve. Transmission can be less complicated, not more. Engines with peaky torque curves require a lot of gears as acceleration is maximum only in a narrow rpm range.It is just difficult to get with max hp output." Put another way, a flat torque curve is desirable in a tank engine. More info needed.
 * "Torque can be increased by increasing the mean effective pressure of the engine, or by lowering the torque losses." power vs torque Includes lots of graphs for various fuel-injected spark car engines.

Clutch
Clutches, like gearboxes, are designed to transmit a specific torque from the engine to the drivetrain. The firm of Fichtel und Sachs (see also de:Fichtel und Sachs) supplied the majority of factory-fitted clutches either for ZF gearboxes or for Maybach engines/gearboxes where specified.

Most of the ZF gearboxes fitted to tanks (and SPGs, tank hunters etc.) discussed here were delivered to the various manufacturers' assembly plants with a clutch attached. These were connected by a prop shaft to Maybach engines without a 'K' in the model number (e.g. HL62 TR used in some Panzer IIs). There is at least one exception: a clutch was bolted to the HL120 TRM motor in the Panzer III Ausf. H and onwards, not to the SSG 77 gearbox. Maybach engines with a 'K' in the model number, almost all used in half-tracks (e.g. HL108 TUKRM in later Sd.Kfz. 9s) indicate that the clutch was fitted as standard by Maybach. [NB! Sort out the G/ZG series fool!]

Planetary construction
Although a number of sources (mostly websites) claim that some ZF gearboxes used planetary gears, this never appears to be the case, although some differentials and final drives (not made by ZF) did. The term 'transmission' has been used in various ways, not all of them helpful.

END OF MAIN ARTICLE TEXT

Appendix A: Soden transmission
NB! Although this gearbox was designed and made by ZF, its basic principles were generally used in Maybach semi-automatic gearboxes. It has little relevance to this article, which mostly deals with manual gearboxes. It deffo needs its own article. Anyway...

On 23 September 1921 ZF brought out the 'Soden transmission' (Soden-Getriebe) at the first Berlin Motor Show since the war. This was a semi-automatic, pre-selector gearbox representing a feat of engineering that was far ahead of its time. A series of pre-series (Vorserienstand) gearboxes had already been launched in Vienna in October 1920, aimed at taxis, light trucks and buses.

The range included types S2.5, S3, S3.5, and S4 for passenger cars (Pkw, Personenkraftwagen) and type S5L for trucks (Lkw, Last\kraftwagen) A version for railway locomotives, Typ TS18.5, had 5 forward and 5 reverse gears.

The gears are straight cut and integrally form part of a shaft which incorporates a dog clutch mechanism at one end. The selector forks... ZF photo of a cutaway gearbox:

Lots of info at https://www.sodengetriebe.de/.

- https://www.sodengetriebe.de/getriebe/ - good cutaway diagram of gear selector and g/box - https://www.sodengetriebe.de/fahrzeuge/ - list of Soden gearboxes for cars (PKW, Personenkraftwagen) and trains - https://www.sodengetriebe.de/getriebevarianten/ - more gearboxes, and pics of boxes named on the above page

Soden patents: cite patent


 * US1532564A - Coupling 1921 https://patents.google.com/patent/US1532564A/en
 * US1502701A - Change-speed gear - 1922 - locking mechanism for [semi-auto?] gearboxes https://patents.google.com/patent/US1502701
 * US2001292A - Clutch device for motor vehicles - 1933 - one-way clutch patent, like a sprag or cam clutch. https://patents.google.com/patent/US2001292

In 1925 ZF introduced the Einheitsgetriebe or 'Standard Transmission' series which consolidated and rationalised ZF's gearbox production down to a few structurally identical designs, capable of being upgraded to cope with a given of amount of torque.

The Leichttraktor of c1930 made by Krupp used a Soden transmission with 4 forward gears and 1 reverse. Changing gears was effected in two stages. First, the driver moves the pre-selector lever into the desired slot. Secondly, the driver then presses down on the clutch pedal for a full second, and then releases it. One of the pistons in the top of the gearbox moves a selector fork to actually change gear. When changing gear it was important to keep hold of the steering wheel while climbing a gradient, while turning, before going backwards or in a moment of danger. Description of gearbox on p. 15 [pdf 25]. The pre-selector lever is no. 5 in the photo, right on top of the gearbox. Close-up pic of lever on p. [40].

Soden transmission (2nd version)
NB Incorporate intro to both versions into one section!

The Soden transmission was a pre-selective, semi-automatic gearbox invented in 1921 by Alfred von Soden of ZF Friedrichshafen. See also User:MinorProphet/Draft subpages/WW2 ZF gearboxes. It was fitted in passenger cars and also in the Leichttraktor, the forerunner of the Panzer III. It is discussed here because its basic principles were developed by Maybach in their pre-selector, semi-automatic SRG/Variorex/Olvar [shaftless?] gearboxes used in WW2 tanks and half-tracks. Maybach and ZF (both subsidiaries of Zeppelin and all based in Friedrichshafen) had a close working commercial relationship, and between them had an effective monopoly of the design and manufacture of engines and gearboxes used in most German AFVs from c1935–1945.

Apart from the Soden transmission used in the Leichttraktor, it doesn't seem that ZF actually made any quantity series production gearbox of this type for military use, except perhaps the ill-fated EV series with electromagnetic clutches, fitted to the Swedish Stridsvagn m/42.(More info needed) In general, ZF made conventional, manual gearboxes, and Maybach made the semi-automatic ones.

Outline of operation - consolidate & split into new (draft) article

 * Info
 * Page on von Soden:
 * Pamphlet by von Soden (1920) about a new type of gearbox, and the Soden transmission: MAKE A CITE!
 * Pic of Soden S 3.5 gearbox (1920), showing rotor shaft and holes for shifting pins:
 * Good close-up pic of the rotor shaft and locking pins of a pre-selector Soden gearbox.
 * Good close-up pic of the rotor shaft and locking pins of a pre-selector Soden gearbox.

NB! Needs plenty of refs! eg Leichttraktor, von Soden paper (HathiYech)/ZF pamphlet (** above)

Only a complete translation from the German Leichttrakor manual will clarify - possibly... Heavily parenthesised technical German... Argh - OR: plenty of pix and tech explanation (in German) by von Soden himself here: ZF pamphlet reprinted from Der Motorwagen, XXIII. Jahrgang (1920), nos. XX and XXI, Graf von Soden, esp. pp 7-11. NB Fixed two-page layout. Not downloadable or otherwise online.

Other online volumes of Der Motorwagen: [https://archive.org/details/bub_gb_do7mAAAAMAAJ/page/n3/mode/2up IV. Jg, 1901] [https://archive.org/details/bub_gb_DpDmAAAAMAAJ/page/n3/mode/2up VI. Jg, 1903] [https://archive.org/details/bub_gb_mXTmAAAAMAAJ/page/n3/mode/2up VII. Jg, 1904] [https://archive.org/details/bub_gb_n1EfAQAAMAAJ/page/n3/mode/2up IX. Jg, 1906] X. Jg, 1907 [https://archive.org/details/dermotorwagen2519auto/page/n5/mode/2up XXV. Jg, 1922]

NBB! There is no vacuum involved at all: it is a completely mechanical operation. The pins are held in place by spring pressure, either in a hole or against the circumference of the locking rotor/selector shaft: and retracted by a mechanical lever against the spring pressure. Simples.


 * Explanation

The constant-mesh gearbox has three shafts, one mainshaft and two layshafts below and to either side of it. See page 9 of the ZF pamphlet (von Soden, 1920)

First see ZF photos of gear selector lever (3-2-1-0-[N]-R) and cutaway gearbox, so you know what you're looking at: NB Werner Beisel wrote a book about it (Beisel, Werner. Das Sodengetriebe. 2018, ISBN 978-3-00-058503-6.)

Now see. In the photo on page A6 [pdf 24] of the manual, the pre-selector lever is no. 5, right on top of the gearbox. Close-up pic of lever on p. [40]. Description of gearbox on p. 15 [pdf 25]. First part of this description refers to p. A6 [22] (eg "Trennwand 2" (bulkhead). See also picture A13 [pdf 40] showing the gear lever. Page A6a [pdf 22] has a manufacturer's explanation BY ZF of how the gearshift mechanism of the Soden gearbox works.

1. (See Fig. 1.) The gear selector lever is directly connected (perhaps by a mechanical linkage) to a locking rotor shaft inside the gear change mechanism, located on top of the gearbox. The rotor shaft sits at right angles to the main gearshafts. The shaft has five lateral holes drilled along and around its length. Moving the gear lever pre-selects (but does not engage) the next position which the shaft will rotate into, so that just one hole will be horizontally aligned with the relevant pin.

↓-↓-↓-↓-↓- locating holes for pins under spring pressure _______ __  __| O     └┘  |_ zz  |__    O        _|__|  ← gear selector rotor shaft (R) |_____O__┌┐_| zz   ← teeth on gear wheel to rotate shaft, linked to gear shift lever Fig. 1. Side view of rotor shaft

● ● ● ● ●  ← locating pins with selector fork attached below | / | \ |  ← selector forks (Schaltgabel) (all five shown) | | ∩ | |  ← end of central selector fork, fitting over dog clutch on mainshaft \ | O | /  ← mainshaft (centre) + selector forks (four shown) ∩  ∩     ← rounded end of selector forks on layshafts (two not shown) o  o     ← layshafts (Nebenwellen) Fig. 2. End view of selector pins and gearbox shafts. NB: The rounded of the selector forks sit directly over the dog clutches on the shafts (basic graphics)

2. (See above, Fig. 2.) In line with the rotor shaft and at 90 degrees to it, and thus parallel to the main gearshafts, there are five sliding pins (one per gear ratio, 4 forward and 1 reverse), which locate by spring pressure in a corresponding hole in the rotor. For any given gear, only one hole has a pin located in it; the rest press against the outside of the shaft. Put the other way round, each pin has one exactly hole it can locate into, and thus selects the desired combination of locked pinions. In the earliest versions, all the pins face the same way: in later version the pins on the outer two pistons face one way, and the inner three face the other way.

When the clutch pedal is depressed, a mechanical linkage retracts all the pins away from the shaft against spring pressure; the selector shaft rotates into the next pre-selected position, and when the clutch is released, spring pressure pushes the next relevant pin into its hole. There is a separate pin for reverse.

Small version of above diagram hidden here:§

3. (See Fig. 3.) Directly attached beneath each of the five locator pins is a selector fork, which moves a dog clutch a small distance on any of the gearshafts to engage and lock the desired gear ratio.

NB! Q1: How many pins need to be located to engage any given gear ratio? A1: One. Five pins (4+R), five holes, five combinations of dog clutches (e.g. In/Out/Out/Out/Out, or Out/Out/In/Out/Out). Q2: How many pins need to be shifted in order to select a new gear? A2: Two: one out, one in. Simples.

(R) = Riegelwalze, locking rotor in 'Prinzipskizze' diagram above |_____|== O shift pin (l.) and rotor shaft (r.) (end view). => Spring pressure to engage. | | ← Selector fork attached to sliding dog clutch <= Disengaged by mechanical linkage \ \     ~    ← gear teeth \ \    |  |    ← gear pinion ______| |___=|__|___      | |=  =|  |    ← shaft carrying pinions with dog teeth (=) ______|_|=__=|__|___           |_|   =|  |              |  |              ~     Fig. 3. Simplified section of shifter pin, selector fork and dog clutch

Translation next, I suppose. Also...


 * School of Tank Technology - Glossary of German Tank Terms - German/English Technical Glossary - 1943|

Appendix B: Non-relevant info re Panthers etc.
Spielberger's Panther tank and variants has lots of interesting and relevant appendices.


 * Appendix 15, p. 254, 'Organisation of a Panther tank maintenance unit'.
 * A report quoted in The Combat History of German Heavy Anti-tank Unit 653 (Münch, 2005, pp. 275-6), stresses that piecemeal use of tanks/tank hunters should be avoided, since the maintenance unit cannot be in two places at the same time. Various Ferdinands from the battalion were deployed in two distant locations; broken-down vehicles which could have been fixed were completely abandoned for lack of repair facilities.
 * Also, really good details of specific tech problems with engines/transmissions on Münch, p. 277. Also see Repairing the Panzers, vol. 1 (Friedli). There were basically - i fink - four levels of maintenance: man with a spanner (battery level); men with a workshop and/or mobile 3 or 10-ton? crane on a 4-wheel truck or Sd.Kfz. 9/1 (company level); men with a bloody big crane capable of lifting a turret off (battalion level); return to factory (army level). Although physical tanks themselves are the most obvious components of an armoured unit, the behind-the-scenes support sections to keep them running are considerably more numerous.
 * Appendix 17, 'Final meeting of the Panzerkommission' section 5, p. 258, Panzerjäger 38 D
 * Appendix 18, p. 262, 'Gasoline or diesel engines for the tank'.
 * Kniepkamp (either in Estes?) or BIOS report? explains how the official requirements for tanks stated a specific combat radius. Petrol engines met these specs. It's a trade-off. If the reqs. had been for a greater distance, diesels would have been used, since the increased overall weight of engine, fuel etc. is compensated for. Plus, in c. 1936/7 the fuel industry had indicated that gasoline was going to be cheaper to produce than 'artificial' diesel. This had changed by 1943, but it was too late by then. Ferdinand Porsche (who had Hitler's ear) was very much into diesel, and various other manufacturers; the Tatra air-cooled diesel was slated for the Jagdpanzer 38D by late 1944, but it was far too late by then. Also, German armaments production during World War II shows how vast amounts of money and labour were expended on useless projects (Graf Zeppelin aircraft carrier, Atlantic Wall, monster tanks, V-2 rockets etc.) when sheer numbers of much cheaper weapons might have made an actual difference.
 * Appendix 19, p. 268, 'Newer tank models'.