Bad Brake Booster Vacuum Hose Can Cause Intermittent Brake Warning Light
 

Diesels do not rely on engine vacuum for brakes because there is not enough vacuum.

On the 6.0, the vacuum is generated by a small pump that is driven by the engine or electrically driven [edited thanks to Steve].

As everyone know, I have had a mysterious intermittent brake light issue for months.

Well, finally I nailed down the cause --- which is not the vacuum pump.

It is a vacuum leak caused by bad hose:

The rubber hose(s) that connect the pump to a vacuum sensing switch, and then, from the switch to the brake booster.

The rubber hose appear to be normal, black 3/8" ID fuel line.

On my vehicle (2005), it is not all that old, but it had turned into a hardened, inflexible rubber hose that is cracked.

The hard hose in turn, caused several issues:

Because it was so hard, it became difficult to maneuver, and whoever installed it the last time did not install it properly.

On the piece that goes from the Vacuum sensing switch to the brake booster (about 4" long), it terminates at a 90 degree elbow.

Because it was so hard and not inserted in properly, it caused the 90 degree elbow / filter joint on the brake vacuum booster to be "bent" at an angle and not seal properly.

That became an intermittent vacuum leak that would, as the parts heat up and cool down, seal itself just enough to repeatedly trip and untrip the vacuum sensor.

Yet, on a visual inspection, it is hard to see it unless you were actually inspecting the part very closely for a vacuum leak.


Fix:

Reinstall it with new hose, then checking for signs of a vacuum leak around the edges.


Cost: about 50 cents worth of hose.



Recommendation:

After 3 to 4 years, the hoses to the brake booster / vacuum pump should be checked and replaced if they are hardened / damaged.


Bet a lot of vacuum pumps got installed when the problem is just bad hoses.


I am investigating an alternative to the Ford 3/8" ID hose --- which seem to be not holding up well as a vacuum hose.


Anyone have ideas what works well?



PS:

On a few very cold winter days (20F or lower), I had a mysterious noise (whinning) that came from the front left.

Come to think of it now... a vacuum leak would probably create just that kind of a whirling whistling noise.....

It came, and it went mysteriously.

It should be noted that the F series pickups use an electric vacuum pump, not an engine driven pump.

Thanks Steve!

Come to think of it... is my pump engine driven?

I never got that far --- as you know --- it is buried deep in the bowels of my E series.

Ford replaced it 1 year ago... so I assumed that is good.

Beats me.....I've never looked at it.:D

Follow the hose, see where it goes.

If your pump is electrically driven, it isn't used to boost the brakes. The small electric pumps just can't produce enough vacuum. That's why there are hydroboost brakes.

If you have a vacuum brake booster, you have a belt driven vacuum pump. At least I'm 99% sure.

I think I remember seeing somewhere that F series trucks got electric pumps and hydroboost, while vans got belt driven pumps.

I'm also not sure when hydroboost appeared. I know pre-'99 trucks were belt driven pumps, because Dad's 96 is. But I don't know if those disapeared with the body style change in '99, of the change to the 6.0L in '03