I recently have been diagnosing braking problems I have noticed since doing and engine swap. The problem was this: During normal pump bleeding, the pedal would firm up as normal, but once vacuum was applied tot he booster, the brakes drop nearly to the floor. I tried replacing the master cylinder several times, bled about 3 liters of cheap fluid through the pipes, but nothing seemed to fix it. After searching for days, I came across one mention of the proportioning valve (the small block located in the middle of the firewall right behind the engine. This valve controls brake bias. To diagnose a broken or sticking valve, you just need to hit it with a hammer while the engine is running. I did just that, and the brakes started acting normal again. This means that the valve is bad and needs to be replaced. This is the new replacement: http://www.amazon.com/dp/B000K04CN6/ref=pe_385040_30332190_pe_175190_21431760_M3T1_ST1_dp_1 A lot cheaper than the factory part, this was made by both GM and toyota since the start of their agreement back in '84 I believe. Anyway, just wanted to put this out there in the event someone else has noticed the same issues.
I wonder if this could be my problem..hhmm. I am in the process of doing a build, and I notice my pedal gets tough at times and no brake goes to the wheels. What else if not the proportioning valve could be my problem?
