Brakes

Brakes: Bleeding and some tips.

Bleeding brakes: Quite easy if you follow the right order. According to the Haynes manual, the correct order is:

1. Left rear
2. Left front single
3. Right front single
4. Right rear
5. Right double outer
6. Right double inner
7. Left double outer
8. Left double inner

Bleeding is made a lot easier if you have a pressure bleeder available like the Gunson Eezibleed or similar. If you don't happen to have such a device handy, the services of an assistent will be needed to step on the brake pedal.

When bleeding with an assistent, don't press the brake pedal too far to the floor, especially on an older master cylinder, as this might bring the rubber seals in contact with crud that's accumulated on the wall of the m/c outside the normal path of travel of the piston, and damage the seals. While you're bleeding, it's best to take out the brake failure sensor from the little aluminum sensor housing located near the master cylinder (it's the thingy all the brake pipes go to). While bleeding, the pressure in the circuits may be unequal, causing the sensor to trigger. When you're ready and the pressures are equal again, the piston in the sensor housing tries to return to its normal position again and may damage the sensor. While the sensor is out, inspect the sensor housing for wetness. Failure of the sensor housing or piston seals in it could create an interconnection between the two seperate brake circuits, causing them to lose pressure simultaniously in case of failure of either circuit. This is of course undesirable.

Should the brake sensor have triggered, the reset procedure is as follows:

• First thing to do is to fix the brake system if it's triggered other than after bleeding
• Remove sensor
• Step firmly on the brakes several times. This builds up pressure in the system and centers the piston
• replace sensor and sensor wire

Cutting off the wire to the sensor is, in my opinion, not an acceptable repair to "fix" the sensor indication

Although modern Volvos (say about anything after 1966 or so) have a dual, triangular braking system (each circuit works on both front wheels and one rear wheel), there are still failure modes that will render both circuits inoperative.
The master cylinder and brake warning switch are shared between the systems, so catastrophic failure in either might result in non-functioning brakes. However, overheating one of the front calipers (such as in the case of a stuck piston) can boil both circuits, at which point you won't have any brakes left either. The handbrake, beind a completely seperate system, will still work

The bleeding nipples on the Girling calipers on my '70 144 are 9/16". Considering how tight those things can be and the problems caused if you accidentally round them off, I purchased a high quality ring/crescent spanner for this job. Expensive but worth every cent. The advise to spray them with penetrating oil prior to trying to loosen them still applies, of course.

Opposite calipers will in fact mount just fine on the wrong side, but when you try to bleed them you'll find out one of the bleed nipples is at the bottom rather than on top, and there'll be some air left that you can't bleed out. A point to check when getting rebuilt calipers.

The check valve on the brake booster can become either inoperative, very noisy (ticking sound), or both. Inoperative is of course a problem, and the noise becomes rather annoying after a while. The solution is part 1228272, an inline check valve (made by ATE, so probably available through parts stores as well).

Carefully remove the old check valve (if you break it, finding another one will be hard and expensive). This is usually done by turning it about 30 degrees counterclockwise and taking it out, although some later models are rumored to have a push-fit rather than bajonet. Using a small screwdriver or punch push the ball down so that it's stuck (no more noise). Put back the check valve, use a new rubber gasket or some silicone sealant to fix that vacuum leak while you're at it, and install the new valve in the vacuum hose. Noise gone, functionality restored, and if the vacuum leak was serious, your car will run better too.