Brake brake unit, location/task/function - GF43.10-P-3102GG

MODEL 460, 461.217 /219 /223 /227 /229 /238 /239 /249 /266 /267 /302 /321 /322 /323 /326 /327 /328 /329 /331 /332 /335 /336 /337 /338 /341 /342 /345 /365 /366 /367 /368 /401 /402 /403 /404 /405 /450 /451 /452 /454 /455 /456 /458 /459, 463

Task

Boost the leg force at the brake pedal and actuate the flange-mounted brake master cylinder

Special maintenance is not required

General function

The brake unit is a leg force assistance unit which uses the pressure gradient between the vacuum produced and atmospheric outside pressure as a power source. The brake unit has two power pistons in series and a dual diaphragm. It is a dual diaphragm unit.

The area of the power piston is doubled by means of this arrangement of the power pistons.

Fig 1: Identifying Flange-Mounted Brake Master Cylinder

Courtesy of MERCEDES-BENZ USA

Release position function

The outside air port and vacuum port is closed in the release position. The same vacuum prevails on both sides of the power piston. The compression spring keeps the power piston in its right-hand rest position.

A Vacuum

B Atmospheric pressure (outside air)

Fig 2: Identifying Brake Unit Release Position Function Diagram

Courtesy of MERCEDES-BENZ USA

Partial braking function

When the brake pedal is operated, first the vacuum port is closed and opened in the further course of the movement of the outside air port. The vacuum behind the power piston is reduced until the brake master cylinder piston, thrust rod and valve piston come to a standstill due to the hydraulic pressure produced in the brake master cylinder. The pressure is transmitted via the reaction segments.

At the same time the poppet valve contacts the valve piston and thus interrupts the outside air supply.

A readiness position is now achieved, in which any slight change in pedal pressure causes an increase or reduction of pressure difference on both sides of the power piston, resulting in an increase or reduction in retardation.

A Vacuum

B Atmospheric pressure (outside air)

C Reduced vacuum

Fig 3: Identifying Brake Unit Release Partial Braking Function Diagram

Courtesy of MERCEDES-BENZ USA

Full braking function

The vacuum port and outside air port are closed and the outside air port is permanently open in the full braking position. Consequently the largest possible pressure difference prevails on both sides of the power piston, achieving the greatest possible assistance.

The force on the brake master cylinder piston can only be increased further by increasing the leg force.

A Vacuum

B Atmospheric pressure (outside air)

Fig 4: Identifying Brake Unit Release Full Braking Function Diagram

Courtesy of MERCEDES-BENZ USA