Several months ago I replaced my vacuum pump. I was getting hard brakes and the brake light would light at each startup and during long idles. I put in an A1 Cardone remanned unit and the issues got noticeably better but now I've been noticing that the blend doors on the HVAC are slow as Christmas and sometimes on startup the air is blowing through the defrost vents when the control was left on AC.

I checked all the hoses to the pump, vac manifold, brake booster and they seemed to be fine. I did fresh coolant recently. Could there still be air in the system causing a problem? Would air in the system even do that? I also can hear the vac pump barking during cranking. It's the sound it makes when you have one off and turn it by hand. Any thoughts?

 

I would put a gauge on it and see what you have there for vacuum. If you don't have a gauge, I would suggest buying one of these:
Mightvac.

They make bleeding brakes a cinch and the pump has a gauge on it that can be connected to your vacuum system to check things like this.

 

Thanks Nate. I'll try and get a gauge on there soon. Which hose do I tie it into; the one directly connected to the pump? And then just crank the truck and read the pressure?

 

Same problem here. Please post what you find out

 

It shouldn't matter which hose you tie into. If it were me, I would remove one of the caps off the vacuum manifold that are capped off and tie it in there. There's always the possibility that one of the lines has a leak in it and if you don't have all the lines hooked up you may not find the leak. If the vacuum level ends up being low, then I would connect the gauge directly to the pump line and see what you get there. If the pump produces more vacuum with just your gauge connected to it then you have a leak in the system somewhere.

 

Do the manifold end caps pop off or something? It's got 2 large (i think 11/32") ports and 2 small. 1 big from the pump and 1 to the booster. 1 small to, what I assume is, the vac sensor and 1 small across the cowl the the heater box. I'm not near it now though so I can't look at the moment.

 

One to the pump, one to the brake booster, one to itself (vacuum switch) and one to the heater box area.

 

How much vacuum should I be pulling directly from the pump? And should that change through the booster?

 

Jacob, I'm not sure but I think it's either 12 or 17 .

 

17 sounds familiar to me too but I really don't know why...

 

I think that's it.

 

Ah hah! 17-21 inHg. It is in this thread in post #9 by none other than Jose.

 

I knew it was somewhere on here cause I remembered reading it, but I couldn't find it. Glad you found it, Thanks Jose!

 

Does anyone have some tips on diagnosing a vac issue? I'm losing it somewhere. Directly to the pump is pulling a solid 26 in Hg and through the manifold to the hose where it connects to the driver's side booster is holding 25 as well. I took the hose to the booster off at the manifold-

^^the fartherst back in this pic and tried to apply vac to the booster from there but can't build any at all. And I'm having trouble finding anything in the shop manual on it.

 

If the pump / manifold are pulling good vacuum, but the booster isn't holding it, sounds like the booster is bad. Did you test it with the check valve (on the front of the booster) in place, or did you go right into the booster? If you had the check valve in place, that could also be what's leaking.