A/T - LImited Production Automatic Brake Band Adjustment: Overview

91mercedes02

TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS

DATE: February 1991


REF. NO. 27/85


SUBJECT: ALL MODELS WITH CERTAIN AUTOMATIC TRANSMISSIONS 722.5 AND 722.3 BRAKE BAND PISTON B1 WITH AUTOMATIC ADJUSTMENT


The brake band piston B1 with an automatic adjustment of the release clearance was installed from July 1990 to September 1990. On these transmissions only, measuring or adjusting of the release clearance is not required.


Effective Serial Number

Transmission Transmission End Number Range
from to

722.3/722.5 03 420 691 03 450 408





Function of Automatic Adjustment

The brake band B1 is engaged by the oil pressure build-up between the brake band piston (37) and the brake band piston cover (40). The brake band piston is shifted against the force of the return compression springs (35/36) until the brake band B1 is applied. This lifting action of the brake band piston causes the diaphragm spring (37a) to pull along the pin (37c), while the stroke "L" (inset) is covered first. If the stroke is greater, the lock (40a) retains the pin and the diaphragm spring (37a) is shifted on the pin (automatic adjustment) (Figure 1).


For releasing the brake band B1 the oil pressure is reduced. The force of the return springs (35/36) forces the brake band piston back until the pin contacts the brake band piston cover. The locking action of the diaphragm spring (due to the shape of the diaphragm) cannot be overcome by the force of the return pressure springs. During this release action, the brake band piston B1 is moved back only by the stroke "L". This corresponds to a release clearance of 1.9 to 2.4 mm.