I have just brought a 1988 silverado and the previous owner had removed the vac pump which is running off the front pulleys said it was noisey .
1 : what pressure's and what is it likely to run ?
2 : oiling of cam which run's pump is done how ?

What transmission do you have> I hope its 700r4/4l60 (3spd + OD) If so it only runs cruise control I think. It should have about 20" of vaccuum at idle. Don't know about how it's oiled since mine isn't belt driven or are you saying that the belt driven unit was replaced with a cam driven unit in which case theres a hole in the shaft that goes between oil pump and vac pump and oil gets in from there.

it also runs the heater controls if you have AC

thanks for the reply smackzed .have'nt got under to find g/box numbers yet but shift positions = 1 , 2 , d , O . Pump is still run off front belt by way of a slave cam shaft bolted up under AC compressor with a bolt fitted centre of camshaft housing at the rear which I'm assuming to be a fill/level gauge for cam.Only hold's about 6 pump's from oil can?

it also runs the heater controls if you have AC

Yes I have ac and will check this out Diaric ,thanks for help ,also vacum pipe is split through electrical control? under air cleaner with ist line going to unit ? bolted to air intake just below filter at rear ,second line heading off over rear of engine drivers side ?:confused:

it doesnt run the A/C on a NBS truck. if it is a half ton then it will have electric controls.

I have just brought a 1988 silverado and the previous owner had removed the vac pump which is running off the front pulleys said it was noisey .
1 : what pressure's and what is it likely to run ?
2 : oiling of cam which run's pump is done how ?
If your '88 looks like mine (new body style):
1: If you have cruise control and/or air conditioning, those controls are electronic and not dependent on a vacuum source. If you have an automatic overdrive transmission, there's a cable that controls the shifting. Only thing left is emissions controls, that is, EGR and EPR valves on the 'C' code engines.
From what you're describing, I'd guess that the previous owner disconnected the emissions controls. It will cause you a "Service Engine Soon" light but nothing more that I'm aware of.
2: I'm not sure how one would oil the belt-driven pump. If mine ever goes, I will probably go electric or use a mechanical modulator on the transmission. You can search "Vac Pump Delete" in the 6.5 forum for more info, just to assure yourself that it's okay...

Ah, reviewed your last post. Those boxes you're describing under the air cleaner are the emissions control valves.