Iv'e got a problem. Iv'e got an '89 D-250 and I dont really get how the vacuum system really works. It looks like there are two vacuum pumps that run off the power steering to assist the power booster for the brake master cylinder. Is this correct???? And if so how do I determine if my booster is bad or the vacuum pumps are bad???

 

The two pumps are plumbed in parallel to provide more pumping capacity. They supply vacuum for the brake booster, HVAC system, and cruise control. To test the pumps, pull the line off the pumps and hook up a vacuum gauge. As long as you get 8.5" they are within spec, most of them will pull around 20" though.

To test the booster, use a Mityvac or similar hand pump and see if you can pump the booster down. If you can't pull a vacuum on it, it's bad.

 

Thanks alot I'll give that a try!