Volvo Coupes/Sedans/Wagons 1970-1989 Repair Guide

Power Brake Booster


All models are equipped with a mechanical tandem-type power booster device located between the brake pedal and the master cylinder. Either intake manifold vacuum (models through 1974) or a camshaft driven vacuum pump (1975 and later models) is used to supply power to the booster. When the brake pedal is pushed, the vacuum acts on a diaphragm inside the booster; this in effect amplifies the brake pedal pressure.


See Figure 1

  1. Remove the master cylinder, following previously listed procedures. On 140 Series, remove the ignition coil if it is in the way.
  3. Disconnect the vacuum hose and the check valve from the brake booster. The check valve is a press fit and may be removed with gentle prying.
  5. On 700 Series, loosen the fuel filter from its mounts and move it aside. Remove the vacuum pump.
  7. Disconnect the link from the brake pedal. Remove the bracket with the clutch pedal stop.
  9. Remove the retaining nuts (4), pull the power booster forward and disconnect fork from the link arm.
  11. The brake booster is non-serviceable; any failure requires replacement of the complete unit. To reinstall, transfer any necessary parts to the new unit. Remember to transfer the rubber seal for the check valve. Make sure it is properly seated in its groove.
  13. Install a new sealing ring on the booster. (The DBA 9 in. (228mm) booster found on some 200 Series does not have a ring; it requires sealing compound to be applied to the firewall.)

Click image to see an enlarged view

Fig. Fig. 1: Remember to position the seal when installing the power brake booster

  1. Attach the brake booster to the firewall. Connect the brake rod to the pedal. Secure the soundproofing under the dash.
  3. Install the master cylinder. Connect the check valve and the vacuum hose.
  5. On 700 Series, reinstall the fuel filter and the vacuum pump. On 200 series, reinstall the ignition coil if it was removed.
  7. Bleed the brake system completely.