dr bob

Bad booster alone won't cause the light to come on. It's the difference in pressure between the front and rear MC circuits, as determined by the two pressure switches. If the switches are new as stated, then you have a fault in one of the circuits that causes pressure to be less than the other. Bleed both circuits, and use a couple test lights to see that the two switches are changing over in sync. The light comes on when one switch changes state and the other doesn't as you press the pedal. Verify that all the wires are plugged into the switches correctly, too; That's kind of important.

Dennis Wilson

Bob,

I've had a booster lock up so tight you couldn't move the pedal enough to activate the front circuit and that will cause a light. This was caused by the rear seal of the master cylinder leaking fluid into the booster.

Dennis

the flyin' scotsman

From the 928 Int catalogue:

1. Operating check

a. Depress the brake pedal several times w/engine off and check that there's no change in pedal reserve.

b. Depress the brake pedal and start the engine. If the pedal goes down slightly operation is normal.

2. Air Tightness Check

a. Start the engine and stop it after one or two mins. Depress the brake pedal slowly several times. If the pedal goes down more the first time but gradually rises after the second and third time the booster is air tight.

b. Depress the brake pedal w/engine running and stop it with pedal depressed. If there's no change in pedal reserve travel after holding the pedal for thirty seconds the booster is air tight.

928ntslow

I think Paul hit it dead on! One of the switches was leaking a little and fluid had collected in the boot around the switch....THATS the good news!

The bad news is upon tightening the switch, the SOB bROkE off and I ended up having to pull the MC out. What a PITA THAT was!!! This car is screaming, "If you're gonna fix this, then you HAVE to fix that!" I had to drill out the broken piece and re-thread. I DID get to check the booster and it is dry in there. I put on a new O-ring and buttoned it all back up. I just have to bleed the brake system now, but planned on doing that anyway. The PO had red brake calipers and dust disks...stupid looking...so I was going to paint them. I have to remove the pads, calipers and rotors, so a bleed is in need. Battery is unhooked, so I do not expect this issue to come back. BTW, I put sealer on the threads of the switches.

FWIW, the car started pissing oil all over the garage floor and driveway after a drive yesterday. The **** hydraulic cooler lines to the rad from the oil T-stat gave loose at the fitting. I have to get new lines made tomorrow. I had all the other hydraulic lines remade and like a moron, I didn't do these.

Thanks for the suggestions my friends! Seems I have been needing a lot of it lately with this neglected dog.

Mrmerlin

well the good news Keith once you have redone all of the possible fluid leaking/lines( I hope you will replace the fuel lines before anymore driving) You wil have a nice DD that you can take anywhere, because you shouldn`t have any problems as you will have fixed the whole car

Dennis Wilson

Keith,

The leaking switch wouldn't cause the hard brake pedal. Did you test the booster like Malcolm suggested?

Dennis

928ntslow

Stan, the all lines are rigid tubing...this is a CIS car.

Dennis..haven't gotten that far yet. I need to get the hydraulic lines made today and back on the car. Then fill with oil, then bleed brakes, then start car....

Mrmerlin

Keith there is a point where the hard fuel lines are connected to the car with a flexible hose, maybe on the rear inner fender there should be 2 of them and they have been known to leak and burn the car to the ground

928ntslow

Good advice! I will have a look.