No Brakes When Cold (1 Viewer)

[NewToFJs]

1991 FJ80 restoration project -- when the ambient temperature is above the high 20s or low 30s, or if I let the vehicle warm up thoroughly, the brakes work great.

Below the mid 20s and if the engine is cold, the brakes do not work at all. Hard pedal at the right height, just no stopping power at all.

The vacuum fitting for the brake booster at the intake manifold is clear. The hose looks OK. The one-way valve at the vacuum booster seems to be working, blowing on it (pressure against the booster) it's tight, no leakage. Drawing against it, a little vacuum in the intended direction, there seems to be some restriction, it doesn't flow freely. Is this normal?

I can't tell how that vacuum fitting, the one-way valve, is held into the booster. I see a little friction pin (like a split roll pin) and a neoprene grommet. Is it just a press fit?

Should I just replace the valve? If so, how does it come out?

Is there any reason to not shoot a little PB Blaster into the valve and see if it frees up?

Is there some other problem causing this that is unrelated to the vacuum booster?

Thanks!

 

[NeverFinis]

Maybe you have moisture in your lines. Dot 3 will absorb water over time. Do a flush with fresh fluid.

 

[LandCruisinMy93]

The one way valve should be pretty free flowing in the direction of vacuum.

 

[NewToFJs]

The one way valve should be pretty free flowing in the direction of vacuum.

I think that's it then, thank you.

Parts are ordered.

 

[NewToFJs]

The one way valve should be pretty free flowing in the direction of vacuum.

That was it. New one-way vacuum valve on the vacuum booster and the brakes work great.