jwillman

So I did shock replacements on the front and had the calipers off but did not disconnect any brake lines. Fluid level is good.

After reassembly I now have a flashing brake pressure light. Owners manual does not provide allot of insight nor does the wiring diagram. What is considered "brake circuit" as referenced in the owners manual?

What should I be looking at?

dr bob

There are two switches on the master cylinder that detect when pressure in one system is significantly higher than in the other. It indicates a leak in the system, possibly bad switches, possibly air in one circuit. Think about what you've done to the car during the last work and if you might have caused any of these problems.

jwillman

I did pull the calipers off the disc but did not disconnect any lines. I did not touch the reservoir. I will check for leaks. Brakes seem to work fine. Light did not start flashing until the first time I engaged the brakes. Should I bleed?

Thanks.

dr bob

Did you twist the hose or let the caliper hang from the hose at all during your work? Especially if yiu have original hoses, the failure mode is an internal radial fracture that then becomes a check-valve when the hose is re-bent. You can try bleeding, remembering that your car has dual-diagonal brake redundancy. So RF and LR on one circuit, LF and RR on the other. No worries if you are using a pressure bleeder, more important if you do it with the push-and-bleed manual method. Instruction for other dual-diagonal cars have a non-standard sequence of bleeding when done manually. Check the WSM's just in case.

James Bailey

To get the caliper off you had to push in the piston.....when you reinstalled it had a gap so when you pushed on the pedal it moved the caliper piston very easily.....that could be interpreted as dissimilar pressure.... Reset it and try again.

jwillman

Lines were replaced within the last year.

Reset? I have not found that procedure in the operators manual or WSM. How do you reset?

pcar928fan

Do you not have an "!" button somewhere on the dash or center console on the '79 cars? My '81 has the "reset" button that is the red button with white "!"... I think it was dropped in '89, but I thought the 78/79 cars had it too...

The "hard" reset would be to just disconnect the battery for a little while and then reconnect...

jpitman2

Press the red ! light - some errors can be reset this way. Others require disconnection of battery briefly. Get a normal high pedal back with a few strokes of the brakes, try restting the light, do the battery if necessary....
jp 83 Euro S AT 53k

WallyP

Just for the sake of completeness, I'll throw the standard brake warning tutorial out again...

Up thru 1983, the brake lights are operated by twin pressure switches on the bottom of the brake master cylinder. From 1984 - up, the brake lights are operated by a simple plunger switch mounted on the brake pedal under the dash.

The earlier brake light switches do double-duty, operating both the brake lights and the brake pressure warning signal. These switches can cause some problems.

The switches are identical - one in each hydraulic circuit. They are single-pole, double-throw switches. This means that you have only one circuit (single pole) thru each switch, and that the switch chooses one of two outputs (double throw).

Each switch has three connections: power, central warning computer, and brake light.

Not Activated
There is a power feed into each switch. When the switch is not activated (no pressure in the brake circuit) the power isn't hooked to anything.

When the switch is not activated, the central warning computer and the brake lights are connected inside the switch. Nothing happens, since there is no power applied on either circuit.

Activated
When the switch is activated by brake hydraulic pressure in one of the circuits, the central warning computer connection is broken, and the brake lights are hooked to the power feed. This removes the central warning computer from the circuit, and puts power on the brake lights.

(This might be easier to visualize if you think of three wires: one for 12 vdc, one to the brake lights and one to the warning computer. The lead that goes to the brake lights is connected to the one to the warning computer until brake pressure pushes it off of that wire and over to the one going to power.)

All three leads go to both switches.

When you apply the brakes, both switches should activate. Both switches disconnect the warning computer and connect the power to the brake lights. The brake lights come on, and no signal is sent to the warning computer, so it is happy.

If only one switch activates (either no pressure on one side of the brakes, or a bad switch), then things change.

On the switch that is not activated, the brake light circuit is still hooked to the warning computer.

On the switch that activates, the brake light circuit is hooked to 12 vdc.

The brake lights come on.

In addition, power flows on the brake light circuit back to the non-activated switch. Since in this switch the brake light circuit and warning computer are hooked together, 12 vdc is applied to the warning computer circuit. This sets the Brake Pressure Warning light.

James Bailey

Minor warnings reset with the button....things like low fuel, overheating,brake pads, burned out light bulbs. BUT brake pressure issues which could cause an accident require unhooking the battery so the warning brain forgets !

jwillman

Thanks James, James, Wally, Dr Bob and JP. I will give the battery disconnect a try. The clutch / brake reservoir was out of the car when I bought it last May because of a blown clutch line. When I put the system back in I did replace both brake switches as I was told they were problematic so I am at least know the history on those.

jwillman

So resetting by disconnecting the battery solved the issue. Brakes are solid, no leaks and not flashing pressure light.

pcar928fan

Excellent! On a 928, when in doubt disconnect the battery for a little while...solves SO MANY problems for these silly cars we love so much!