Merkblätter zur Restaurierung der überschweren Kräder BMW R75 und Zündapp KS 750.


Herausgeber:  ERSATZTEIL- DIENST   Hans-Peter HOMMES       D-41748   VIERSEN   Tiefenstraße 10       Tel. 02162 - 8100933

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Brake system


H - P Hommes


© 2006 h-p hommes




Brake system


The brake system of the BMW R 75 and Zündapp KS 750 is the same except for the brake line between the master cylinder to the  t-piece  and the brake line for the BW40.



 It consists of the following elements:


1.        master cylinder (3132/ 3086/ 3176)

2.        brake line to the t-piece for BMW R75 (2130), for Zündapp KS 750 (1102).

3.        t-piece (3015)

4.        brake line to the brake wheel cylinder (3190)

5.       22mm brake wheel cylinder (3133/ 3135/ 3165)

6.        brake hose to the sidecar (3050)

7.        brake line under the sidecar (3191),  BW 40 (1234).

8.        brake hose to the brake wheel cylinder SW (3051)

9.        connecting angle (3141)

10.     brake wheel cylinder 19 mm SW (3134/ 3136/ 3165)


The rear wheel brake cylinder has a diameter of  22mm, the one of the sidecar has only 19 mm.
This difference in diameter achieves a compensation when braking because the bike is much heavier than the sidecar.

The master cylinder is made of steel and the brake cylinder is made of brass.


Here are some points that should be observed :

1.    The assembly of the master cylinder must be imperatively  made in the right order.
First the bottom valve, then the compression spring, the cuff with the open part towards the compression spring and then the piston with the filler piece.
All together as to be secured with the spring clip.

 2.   The master cylinder has an original inner diameter of 19 mm.
Some competitors offer master cylinders with 22 mm diameter with a supposedly “ improved braking performance”.  
Someone has not paid attention in physics and did not understand the most simple lever principle.
Now they are trying to construct brake parts.
With this object you can put your complete body weight on the brake pedal and the brake effect is only minimal.

3. The brake lines are flanged at their ends. A proper flanging puts the material twice.
Only an adaptation of the end is no flanging and often leads to the fact that the lines are not tight or burst open abruptly under heavy braking ( this type of brake lines is unfortunately offered again and again).

Correct one



Problem and its cause.


No pressure can be built up although I have vented it and the whole system is tight.   Possibilities:


The bottom valve in the master cylinder is defect, improperly fitted or the entire content of the master cylinder is assembled in the wrong order.


The holes in the rebuilt master cylinder are not appropriately fitted. The piston, the filler piece or the sleeve are produced in a wrong version or length, so that no brake fluid enters the pressure chamber.


The brake hoses are not suitable for the occurring brake pressure and expand under pressure.



New brake pads are fitted but there is very little braking power to be felt.             Possibilities:


The brake drum is not round.

The outer diameter of the used brake pads is not equal to those of the brake drum. Repair: overwind brake pads.


The brake drum is worn out and the brake pad is only on the inner side. Repair: when mounting the brake pads put a chamfer on the edges.

The sidecar brake works well. Now, however, it slows down permanently because it does not release itself after braking.

I have adjusted the brake cylinder of the rear wheel several times.

Did not help.




Brake hoses are too old and swollen inside. The brake pressure pushes towards the sidecar wheel. The return spring has not enough power to release the brake. The swollen hose acts like a valve.

Repair: New brake hoses.


The valve  of the T-piece is not open and the pressure can only pass on one side.


The sidecar is blocked when braking.


With no load on the sidecar that means without passenger or luggage this is a normal condition.

The braking power of the sidecar brake is made for the sidecar weight plus 130 kg for a normally equipped soldier and further luggage.

I have put a bracket with a 20 liter petrol can on the outside entry. This reduces the blocking enormously, because now the wheel is loaded with more weight.

At the same time it is much easier to drive right turns because the sidecar does not tend to lift the wheel so easily.




Wir bieten an:

Ersatzteile + Zubehör + Instandsetzung
für Motor, Getriebe etc. der
Zündapp KS 750 und 600

Wir bieten an:

Ersatzteile + Zubehör + Instandsetzung
für BMW R75 und Zündapp


H-P Hommes Ersatzteil-Dienst
Ersatzteile + Instandsetzungen
repairing + restoring

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