PuMA measure

Rear brake - soft pressure point
US 60830088-09 - 8/26/20

Complaint:
For exclusive operation of the rear wheel brake with the footbrake lever the driver feels a soft pressure point
or a large brake pedal travel.
The conventional bleeding of the rear wheel brake temporarily creates the pressure point again. With
increasing usage the phenomenon may again occur more, little by little.

Cause
Due to currently unknown influencing variables it may happen successively that small amounts of air are
carried into the control circuit of the rear wheel brake. With increasing usage this air can, for exclusive
operation of the rear wheel brake (footbrake lever), be perceived by the driver as a "soft pressure point“
or "longer lever travel“.
Note:
For partial integral brake systems, the pressure for the rear wheel brake is generated by a pump in the ABS
modulator through operation of the handbrake lever. If there is air in the rear control circuit (between the rear
tandem brake master cylinder and the ABS modulator), the pressure build-up is not influenced by the integral
function. If there is air in the rear wheel circuit (between the ABS modulator and the rear brake calliper), the
pump in the ABS modulator can compress small amounts of air in such a way that there are no tangible
functional changes for the driver.
The phenomenon is only detectable during exclusive operation with the footbrake lever.
The very complex influencing factors are currently being determined through extensive and time-consuming
trials in the braking development.
Note:
Through operation of the handbrake lever for the front wheel brake, the vehicle can be decelerated within the
limits of the legally required deceleration values and safely brought to a standstill.
Because of the dynamic wheel load distribution, the rear wheel brake plays a subordinate role for dynamic
braking. In the case of panic braking (emergency braking), the braking power is almost exclusively
transmitted through the front wheel brake.

Measure
Bleed the rear brake circuit manually in accordance with the specifications in the Maintenance Instructions.
Then, please call up the following service programme and work through it:
Select fault pattern “Brake system: soft pressure point”, calculate test plan and perform the service
programme "Check brake pressure point". You can find a detailed description of this in the attachment.
Please bleed the affected brake circuit thoroughly over ISTA (incl. modulator). Carry out the routine at least 2
times. This may have to be repeated depending on the amount of air ingress.
After tank ventilation, apply pressure (at least 12h) to the rear brake circuit. To do this, a weight (10 to 15 kg)
can be attached to the footbrake lever.
Then flush the system again (at least 2x the contents of the follow-on tank).

Defect 34 00 90 72 00 "Rear brake system incorrectly bled"
Flat rate unit positions:
1200014 Perform vehicle test with BMW diagnosis system,
3400549 Change rear brake fluid,
1/2

If other repair tasks are necessary to carry out the repair, invoice and provide feedback accordingly under the
flat rate unit number 3499000.
Request the required quantity of brake fluid with the net price with invoicing key 04.

Validity information
Model series:

[K51, K50, K53, K42, K52, K54, K46, K47]

Engine range:

[ALL]

Body style:

[ALL]

Fault codes:

[]

Production period:

from 9/1/09

Repair overviews
34/51/001/15563, ABS 2 modulator, Cannot be encoded with VFC, , Pressure not OK, , Checking, repairing, replacing
34/21/002/43177, Rear brake, Cannot be encoded with VFC, , Malfunction, , Checking, repairing, replacing
34/31/001/14528, Brake master cylinder, Cannot be encoded with VFC, , Malfunction, , Checking, repairing, replacing

Attachments
Number of attachments: 2

2/2