on my new truck.(93 w-250 ext. cab) the brake peddle is hard half of the time, and normal the other half. also the low vaccum has set the lights. but cruise and heater controles still work.oh... previous ownew put on a new master. didnt fix the problem.

 

First, plumb in a vacuum gauge.

Second, get yourself a hand-held vacuum gauge.

Dis-connect the main line at the pump and check that it is pulling at least 20 in/hg.

Then, connect lines and work your way from the pump to the brake-booster.

If you have good vacuum at the pump, and low vacuum at the booster, plug off the various little vacuum lines and check at the booster again.

If still low, you most likely have a bad booster.


The symptoms you give are symptoms of a bad booster, but can also be symptoms of low vacuum.