Mercedes M-Class W163

since 1997 release

Repair and operation of the car

Manual box of gear shifting

Specifications

Due to the energy emitted at combustion in cylinders of air-fuel mix a bent shaft of the engine develops torque, at the same time the frequency of its rotation lies within rather narrow range. The majority of modern engines of an OHV design develop the maximum torque at turns about 2500 a minute. At increase in frequency of rotation of the engine up to 4500 rpm the size of its torque decreases so that further increase in power is not possible any more. Engines with the top arrangement of the camshaft (OHC) are capable to develop considerably bigger torque, however in much narrower range of frequencies of rotation.

Use in the transmission line of such component as the transmission allows to regulate relationship between turns of the engine and speed of rotation of driving wheels of the car, providing rather high efficiency of return of the power unit practically in any service conditions of the car.

Smoothness of torque transmission from a bent shaft to a main shaft of the manual box of gear shifting (MBGS) is provided by coupling assembly which design and the principle of action are sorted in the Head the Transmission line of the present manual. Consecutive gear shifting in the course of change of speed of the movement of the car is provided due to use in the transmission of a multistage reducer. The transfer relations of each of five/six steps of RKPP provide maximum efficiency of transfer to the power developed by the engine to driving wheels of the vehicle at various speeds of the movement.

On two of the all-wheel drive Mercedes-Benz models of the M-class considered in the present manual besides automatic transmissions (see the Head Automatic transmission) manual transmissions (RKPP) of one of two types can be used: 717.461 (ML 230) and 716.644 (ML 270 CDI). Both boxes have the standard design used on the majority of the Mercedes cars with the classical back drive (series 717.4 and 716.6).

Developed by the engine the torque transformed in a reducer by RKPP is removed since the back end of the main shaft and is transferred to an entrance shaft of the transfer case which is carrying out its further distribution between forward and back leading bridges of the car. Detailed information on a design and the principle of functioning of the transfer case is provided in the Head the Transmission line of the present manual.

In both transmissions synchronization of all five (717.4)/six (716.6) steps of switching of all forward transfers is provided.

It makes sense to pay a little attention to features of functioning of more modern six-step RKPP.

Boxes of a series 716.6 belong to the class of completely synchronized 2-valny 6-staged check points with one reverse gear which were widely used both on rear-wheel and on the all-wheel drive cars equipped with both petrol, and diesel engines.

General view of RKPP 716.6

1 — the Main shaft of the check point 2 — the Synchronizing ring of 5/6 transfers 3 — the Shaft 4 — a backing bearing Insert	5 — an inclusion Cam 6 — an inclusion Axis 7 — the Flange of connection with the driveshaft

RKPP 7.6.6 design

Competent use of the 6th transfer allows to achieve essential economy of fuel consumption due to decrease in working turns of the engine. In view of design features 6-staged transmissions have bigger weight, than 5-staged.

The box perceives torque from the engine by means of usual coupling of the dry type equipped with the automatic compensator of wear. The case of RKPP has a tight design and refuels the gearbox oil which is not needing replacement.

Accuracy and ease of the switchings having the short course is reached by the following features of a design:

• Use of the shtokovo-trosovy drive of switching with the central rod fixed in needle bearings;
• Use of multiconical synchronizers of switchings of the 1st, 2nd, 3rd and 4th transfers;
• Full synchronization of the reverse gear.

Reduktorny assemblies with shaft are located between two bearing planes. The third bearing plane used in earlier 5-staged boxes in this design is eliminated.

The two-section separate case is made of light alloy and pressurized by means of a special liquid compound.

The entrance shaft (1) is recorded in a flywheel by means of the directing bearing, and a transmission case - by means of the ball bearing with a profound flute. Main (2) and entrance (1) shaft are jointed among themselves in the general plane of a case of transmission and fixed by means of ball bearings with a profound flute (see in the same place).

The intermediate shaft (3) has the facilitated hollow design and is fixed in the roller coupling and the ball bearing with a profound flute.

In view of the minimum production admissions of semi-cases and gear wheels, and also due to use of roller couplings, need for adjustment of axial side plays of shaft disappears.

Movements of the lever of gear shifting are transmitted through drafts on a box. Removal of RKPP can be carried out separately from the engine, need for removal arises at coupling service, and also in case of need carrying out recovery repair / replacement actually of RKPP.

In view of complexity of a design of RKPP, absence on free sale of necessary replaceable internal components and need of use of the special equipment, authors of the present manual do not recommend to owners of cars to carry out capital repairs of the transmission by own forces. Repair of a box in the conditions of a workshop of car service is rather expensive operation, in a type of what, it is necessary to consider alternative options of replacement of the failed block new or restored. Any useful information on repair and replacement of transmission can be received at car repair shops of the Mercedes-Benz company. Regardless of the chosen way of elimination of problems (repair or replacement), independent dismantle of a box from the car will allow to reduce material inputs significantly.

In this Part of the Head descriptions of processes of implementation of such, lying within qualification of the average amateur mechanic procedures as the general adjustment of the drive of gear shifting and removal/installation of assembly of RKPP are offered attention of the reader. Councils for management of switching ми are stated to RKPP in the Head Governing bodies and methods of safe operation.

Information on the automatic transmissions (AT) is provided in the Head Automatic transmission.