In reviving the '85 12A for my son we serviced the brakes. Everything works. A few days ago while out for a driving lesson the "BRAKE" warning light illuminated. OK.

Checking the reservoir showed that it was indeed low. The exterior of the master cylinder is dry with no visible leaks. Wheel cylinders and calipers are dry with no leaks. Lines are dry with no leaks.

I haven't disassembled it as yet but am wondering if there is a path between the master and the vacuum booster that could be drawing the fluid through.

 

Not a first Gen. guy but yes, it appears there is a path to the booster...—->
https://www.rx7club.com/1st-generati...-fluid-871932/

In a quick search I found another place to check...
https://www.rx7club.com/1st-generation-specific-1979-1985-18/losing-brake-fluid-rebuilt-slave-cylinder-901723/

 

the master cylinder will leak out the end where it's bolted to the booster. fluid will run down the face of the booster, bubbling the paint and possible dripping onto the frame rail.

 

What all did you do? Did you bleed the brakes? Are you sure you refilled the master cyl afterword? If you're sure the fluid isn't escaping out anywhere you can see, but is indeed escaping, it could be leaking from the rear of the master cylinder (as rxtasy3 said) and into the vacuum booster. I've never had this problem but I've read about it on the forum. The fluid will deteriorate the rubber diaphragm inside eventually, so if you double check everything and can't find the leak it would be worth worth removing the master and looking for fluid in the booster.

 

Thanks for the responses. My Haynes manual arrived and I found the download for service manuals. Now I can look for myself but it is always good to get advice combined with experience.

Yes: The reservoir was removed, cleaned and replaced. Front calipers were serviced (new seals) so refill was necessary to bleed. Rears are not leaking and have been bled.

I think the next check will be the master leaking at the rear.

Thanks to all!