Yay!!! More brake fun for me.
93 F250 4WD 7.5L 5-spd.

Everything but the hard lines and ABS unit are new.

Basically when I start out in the morning the truck drives great, brakes feel as they should. As the truck gets warmer the brake pedal starts getting more and more wooden. Brake performance isn’t noticeably lessened, but effort to push the pedal is noticeably increased.

My preliminary research has led me towards the brake proportioning valve… does this seem reasonable? I don’t believe it’s a booster issue, as I can still hear the “whoosh” of the booster when I hit the brake pedal.

As always, any advice is greatly appreciated.


Be Safe



Jeremy

 

It's not the combination valve (proportioning is only 1 of the 3 things it does), it's the booster. If you are hearing a whoosh noise when pressing the pedal, that is bad.

 

I agree. That sounds like a booster problem. It's interesting that it gets worse as the engine warms up. This leads me to believe that it might be an after market vacuum hose collapsing as the rubber gets warm and looses it's strength.

 

Okay. That’s easy enough to diagnose with a vacuum gauge. I’ll start there. Thankfully, while the problem is intermittent, once it starts it stays until things cool down. Bad vacuum hose routing or a hose collapsing seems reasonable.


Thanks



Jeremy

 

Once you shut down the engine, the vacuum is removed from the hose and it can bounce back to it's normal shape. As the engine cools, it regains it's strength until you start it up vacuum and heat returns, and the cycle repeats itself.