Intermittent power brakes

[NTOLERANCE]

Looks like my vacuum pump is on the way out.

It makes vacuum, doesnt seem like enough though.

Does the pump make as much vacuum as a gas engine?

I can put a vac gage on it tomorrow, how much should it make?

 

[franklin2]

Should be adequate for the brakes to work. Check the hose as it leaves the pump, it likes to rub against the inner fender on the pass side and rub a hole in it from the vibration of the engine.

 

[CaptTom]

18 in Vacuum.

 

[NTOLERANCE]

18 in Vacuum.

Wow....at idle?

 

['94IDITurbo7.3]

18 in Vacuum.

is that all you are putting out at idle?

my old pump right before it died was putting out about 24-25 at idle. my brand new pump puts out the same.

 

[GOOSE]

Do a little digging. It could be a host of things. I've had leaky resovours, broken fittings and rotten hoses steal vacuum from me. Isolate the pump and test that first. Then add one hose at a time until you see a sudden drop in vacuum. It's not always the pump. Good luck.

 

[bike-maker]

Like mentioned above. put a vacuum gauge on a line directly to the vac. pump. Mine stays right about 21 normal driving, about 22 going down the freeway at 2500 rpm. IIRC, anything less than about 20 and it's time to find a new vac. pump.
From my old days with an F150 gasser with a big cam, it's about 15 pounds vacuum where the brakes start having problems. Brakes worked fine under normal operation, but if you had to make a panic stop, it would lock up the tires, but it would also kill the engine. I had to put an extra vacuum canister in to cure the stalling engine issue.

 

[CaptTom]

is that all you are putting out at idle?

my old pump right before it died was putting out about 24-25 at idle. my brand new pump puts out the same.

Yeeeeup... is that why the pedal goes to the floor??

Seems counter intuitive though. The vacuum system is supposed to assist in pushing the pedal to the floor, if the vacuum gives up, wouldn't it cause one to stand on the pedal to make it stop?

I think my problem is MC.... re:TSP in hydroboost DIY section.

Have most of the parts for Hydro/Vac swap, but I've got other issues. Seems there's a 3 wire plug in the side of the MC (I'm assuming Cruise off switch), but the hydro I have, doesn't have the plug receiver in the side, but looks like a twin plug at the end. Can't find look alikes or description in even our best DIY section on HB swap. Funny thing is, the F450 it came out of is same year as my truck, yet the cruise connect isn't similar.