We have disassemblied the gearbox and we have found a large play on tapered roller bearings ... they are not defined at all ... on tapered roller bearings a preload:
http://workshop-manuals.com/volkswagen/golf-mk4/power_transmission/5-speed_manual_gearbox_02j/gearboxmechanicsgearsshaftsinternal_operation/adjusting_output_shaft/ of approximately 0.2 mm must be applied, but for example the most important one, bei constant gear (output shaft) has a play of 0.3 mm !!!
Although all the permanent gear nuts are tightened, the shaft is completely free ( see video ):
https://drive.google.com/file/d/0B2dlgPu8jrboaklmSVl5R0ZyUTQ/view
There is no adjustment shim under the bearing thickness 0.5 mm. The same is on the imput shaft, there is 0.35 mm
This does not happen by usage, it is a poorly assembled gearbox.
This gearbox could not work, the malfunction would occur even if it was not modified.
The gearbox we got has very poorly set preload on tapered shafts. The video shows how the shaft swings in the permanent gear area. The shaft must not move at all and must have a preload as explained below.
For this reason, the customer can not claim warranty, because that is only applicable only if all the other parts are in perfect condition, but this is not entirely evident in this case, yet we have not agreed upon this case...
Therefore, I will describe how to set up tapered roller bearings again:
Preload and its reason
Poorly laid shaft without preload:
Each shaft in the tapered roller bearings must be separately preloaded.
This is achieved by:
Tightening the nut or the washers under the outer ring of one of the bearings.
If we did not preload the shaft, the condition shown in the picture would happen. The outer rings would then be too far apart and the shaft would move in them, which would have a disastrous effect on:
Lifetime of bearings.
Lifetime of gears on shaft.
Noise of the device.
Reason for the required preload:
In order to achieve the proper functioning of the shaft mounted in tapered roller bearings and to avoid the condition described in the previous paragraph, it is necessary to achieve a certain but low "squeeze" of the shaft and of the two bearings. This is called pretension or preload.
Required accuracy:
Arrangement of tapered bearings into X, preload applied by washers under the bearing.
Reaching the required preload - individual mounting of each shaft.
If we want to achieve the correct preload, in practice we have to install each shaft separately. For example in the case of X-type arrangement, the actual position of the outer ring of the two bearings (usually measured by the depth of both boreholes for the outer rings in both boxes) and the actual shaft length between the outer rings must be individually measured for each assembled piece of gear. All these values must make a difference within an accuracy of 0.01 mm.
From these values, for each assembled piece, the required thickness of the washer must be calculated separately, which, after mounting, will result in the required preload, which may be, for example, 0.27 mm. A qualified installer has available washers with thicknesses of 0.1; 0.05; 0.02 mm. He therefore selects 2 × 0.1 + 1 × 0.05 + 1 × 0.02 = 0.27 washers and inserts them under the outer ring of the left bearing.