Volvo Maintenance Hints for 7xx/9xx - Bill Garland's Nuclear ...

Master Cylinder:
Don't Ruin Your Master Cylinder While Bleeding. [Editor] Master cylinders can develop a corroded bore
outside the area swept by the seals. If you bleed your brakes using the brake pedal, press the pedal only as
far as it normally travels and no farther. If the seals enter the corroded area, they will almost instantly tear
and the master cylinder will be ruined.
Replacement and Bleeding. [Editor] To replace your master cylinder:
1. Spray the brake fittings under the master cylinder with PBlaster. Place rags under the master cylinder
to protect your paint (brake fluid dissolves paint).
2. Disconnect the brake fittings and 7mm master cylinder mounting nuts.
3. [Manual transmission cars] If you have a hydraulic clutch, disconnect its hose from the reservoir and
block the hose connection.
4. Remove the master cylinder
5. Don't consider rebuilding it: buy a rebuilt unit from an auto parts store
6. The end of the servo pushrod should extend slightly beyond the face of the servo body by the
following amounts:
Models to 1991 Models from 1992+
10" 2 X 8" 10" 2 X 8"
Without ABS 2.5mm 2.5mm
33.4mm incl
2.5mm 2.5mm
With ABS 0.5mm
spacer 2.5mm 2.5mm
7. Install master cylinder and tighten nuts to 23 Nm or 17 ft-lbs.
8. Reconnect brake fittings and clutch hose.
9. Bleed brakes. To bleed the master cylinder, pressure bleed the system WITH THE OLD PADS until
the fluid runs clear, then press the pistons back in the calipers without loosening the bleed screws and
install new pads, thereby reverse bleeding the master cylinder. Don't do this on ABS-equipped cars.
10. Pressure test by pressing hard on the brake pedal for 30 seconds and inspect the master cylinder for
leakage.
Brake Hoses
Brake Hose and Line Replacement. [Inquiry:] Can anyone explain the details of replacing brake hoses and
lines on a 1985 740? How long can I expect the factory originals to last? Do the hoses suddenly fail when
old? [Response:] It is very unlikely that the original hoses will suddenly fail at ages less than 15 or 20 years
unless the hose had been subjected to abrasion, cutting, or severe stretching/bending while working on the
car. The mode of failure is usually loss of rigidity allowing the hose to 'balloon' under pressure so that the
brake system pressure is not completely transmitted to the caliper - result - soft pedal. The other potential
mode of failure is that the inner liner of the hose becomes soft and collapses inside the hose - the brake