I don't think my replacement vacuum pump is able to maintain an acceptable vacuum durring multiple uses. I put a gauge on it yesterday and it will get about 22 inches of vacuum, if I repeatedly hit the brakes, vacuum will drop to almost 0 and have basically manual brakes. It takes 49 seconds at 500 rpm idle for it to build back up to 22 inches. Repeat braking process and then at 2000 rpm it will take about 39 seconds to build peak vacuum. Seems like the pump should maintain some sort of minimum vacuum with repeated braking. And it doesn't take rapid repetative brake pumping to go from vacuum assist to almost pulling the steering wheel off the dash to put enough pressure to stop the truck. Thanks.

 

22 to 25 or so is close.
First I would remove the tension from the belt and rotate the vacuum pump by hand it should firm up and release as the rotor engages the diaphragm and disengages. If nothing is detected there. I suggest remove the main vacuum line and the apply regulated air at a max pressure of 3 psig. Then soap water test the distribution plastic header and the sensor core. (Be carefull around the IDM and PCM) Soap/water test the line to the brake booster and then the lip edge of the booster. Soap test the line that routes over to the AC and its two distributor plastic lines that route through the fire wall.

If you have auto hubs they should be checked.

If nothing is found replace the hose on the vacuum pump and then apply the 3 psig of air to the vacuum pump and soap/water test it.

If nothing is found you could have issues with either the v-pump or even the damper inside the truck on the ac. The master cylinder or bad brakes or hyper extended calipers or cracked internal brake rubber lines could also be a contributor to the problem.

Hope that helps

 

if there was a leak, would it even be able to get to the target vacuum? Probably doesn't matter but the brake booster is less then 2 yrs old. That is the time the original pump went out and it took me a lot of time and some parts before finding it. This pump is actualy a replacement of the replacement because that one seized up one day when I was about 3 miles from home.

 

Is your AC switching good and firm on the damper. It should be very audible when it switches. AC off have it on high cooling and full fan and switch it on. You should be able to hear the damper switch over. If its not switching good from AC to heater to defrost then either there is a leak in the line to it or the pump is on the way out.

When you described the foot to the floor it really sounds like the pumps shot already. You may want to make sure that its rotating freely as if the pump seizes up the belt can slide on it since its a slick pully. Rotating by hand is not a good way to reall see if you have intermitant seizing. If you decide to change the pump again. Be sure and really test the belt tensioner first and make sure the idler pully is not going out too. If the idler or the tensioner or the vac pump are binding or going out the belt should be jump bouncing when its happening. I would look for the belt jump at various rpms. If the belt is streached and old, a lightly catching bearing can allow the belt to slide over the pully while not fully rotating it.

You can spot paint the inside edge of the air pump pully and run the truck and different rpms and look to see if its really spining or use a plastic tye wrap to easy it up in the center to feel if its spining. I would test that out and then post what you see and find.