Powermaster Pump Runs Master Cylinder Dry

[thundertracks]

This started 6 months after installing new SBCC dual piston calipers and new stainless braided hoses, somehow banjo bolt worked itself loose on passenger side, lost almost all brakes. Was about half mile from home, I limped home with it. After tightening bolt up and bleeding brakes, every time I turn the key on the pump doesn't stop, it will suck the pump side of the master cylinder dry. Hoping someone might have some info as to the cause of this, whether it might be the pressure switch, or it damaged seals inside or something else.

 

[Chuck Leeper]

You did bleed the system, right? You bleed the brakes with the key off.
If the fluid isn't going on the ground, it has to be filling the system, including the accumulator ball.
Until the system is full, and the pressure rises to shut the switch off, the pump will run. This assumes the switch is working.

 

[KC87]

What's the fluid level in the master cylinder after pumping the brake pedal 10 times with key off. Seems that there's not enough fluid in it to begin with if going dry while pumping.

 

[BEATAV8]

Yeah sounds like there's not enough fluid present.
The powermaster should be filled when it's depressurized (accumulator is empty).

Key off, gently pump the brakes until the pedal gets hard and it's obvious that there's no more power assist. That's how you know the accumulator is emptied out. The reservoir should be filled when it's in this state.

There is some variety out there too.... I've seen some smaller reservoirs that are not as large as "normal". I think they are earlier units.... if you have a smaller reservoir and a larger accumulator like the newer Hydac unit, you might not have enough fluid present to fill it up all the way. Kirban sells replacement reservoirs and seals that are the larger version, but you'd need a lid and gasket to go with it.

 

[thundertracks]

Thanks for the replies, had a buddy stop over after work today to bleed the system. Got a good deal of air out of it, gravity bleeding I had done previously didn't work well. Found a small leak at the distribution block I installed, fixed that. Then did all four wheels again. First turned the key on had to turn key off and add more brake fluid, then pump finally shut off. Any idea how much fluid should be in pump side of mc after pump stops? Have to mount wheels and try it out soon. Thanks again.

 

[KC87]

Thanks for the replies, had a buddy stop over after work today to bleed the system. Got a good deal of air out of it, gravity bleeding I had done previously didn't work well. Found a small leak at the distribution block I installed, fixed that. Then did all four wheels again. First turned the key on had to turn key off and add more brake fluid, then pump finally shut off. Any idea how much fluid should be in pump side of mc after pump stops? Have to mount wheels and try it out soon. Thanks again.

About an inch or so.

 

[Chuck Leeper]

AIRC, there's a mark on the side.