Brake System Failure Light

I am pretty sure that light is tied to the master cylinder reservoir level. That thing if I remember right has two chambers, and one of them is indicating low. Could be from a faulty sender, a leak, or perhaps wasn't topped back off after the service.

 

On a 79 I think the light is connected to the brake bias proportioning valve located on the bulkhead near the steering rack. If the plunger is stuck out of position the light illuminates if I remember well. Maybe it got stuck when they bled the brakes?

Regards
David

 

Those would be the two areas to look at as they both trigger the brake warning light. Check the brake fluid switch in the MC bottle first and if it works then the bias switch under the car is the most likely problem. It has a ground wire on it and if you unplug it and the light goes out then you found the problem. If it is it then it is a rubber plug that has a thin blade contact that is centered in the housing. The problem is if the valve shifted during the brake bleed you need to recenter it.

 

Ding Ding - we have a winner. Most likely some dirt debris causing the valve to be stuck. its a very underwhelming piece of engineering... but a PITA to get to .

 

this is most likely the cause. debris / dirt causing the valve to stick.... its a pita to access and change but pretty easy once in there. but you have to re bleed the brakes again....

 

Here are photos of the carb car bias valve for those interested.

First shot is from above the steering rack showing it on the bulkhead below/behind.

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Second photo is a close up of the valve and the electrical connection to the internal switch.

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Unless your inner tub is removed, access is from the small panel in the floor.

 

If I remember well its made by Girling and loooong NLA

 

Same thing happened to me. It had uneven levels on both sides of the reservoir, but righted itself eventually. However, it didn't take 200 miles to do it.

 

If it were me, I'd want to open it up as I would not want any possible debris finding its way to the calipers. Once I confirmed that switch was the cause of the light though.

 

Please refer to post #10;
Brake Failure Light - 328 GTS

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The stuck switch is probably the cause of the light if you've checked all the obvious stuff. Any debris in the fluid should be purged with bleeding. So, remove the switch, ( it is a PITA to get to) disassemble and clean all parts of it thoroughly. Reinstall and bleed, test drive. If the valve/switch is stuck, you will NOT be getting the proper front/rear brake bias that the factory set up. Please, don't take shortcuts on your brake system. I did this on my X GT4 and it made my brakes positive and responsive as designed, where they were previously a little soft and quite frankly, dangerous.