Brake Pedal Inconsistent

[Paul Mcmenamy]

Just bought a USED 1988 MR2 N/A. Already own a 1987 that is fun fun fun

Anyway, just changed the slave and master on the clutch side. Not too many problems, not easy to bleed by yourself, but once I got some help, it was cake.

My new issue is the brake system. The brakes feel fine, then suddenly the pedal will get much heavier, and from what I can tell, I get rear brake failure. I still have brakes, but I believe it is only the front. Kinda hard to be ABSOLUTELY sure, but I am pretty sure I only have front. Took it off the side of the road last time it happened and applied brakes while cranking sterring wheel, and the thing just plowed. I would expect it to come around a bit if the rears had locked.

I have been unable to find a write up of similar problems, thought the manual mentions the system is designed to accept a failure in front or back but still offer functionality in the other system.

I am not afraid of the work, but I want to buy the right part. I would certainly not mind changing the master cylinder out, even though its not a cheap fix. But if that is not the problem I would prefer to address the real problem.

Apparently there are vacuum boosters in the system, but I dont understand them, how to check them or how to replace them.

Anyone had similar probs?