One problem related to power assist brake vacuum has been reported for the 1998 Chevrolet Lumina. The most recently reported issues are listed below.
I was going 55 mph on beltway. I discovered that my brakes were very hard to push and could not stop. Pulled off to shoulder and could not pick up any aceleration. I had the car taken immediately to dealer for check-up. The dealer (fox) advised that the brake booster hose from the master brake cylinder became loose and was "crimped" near the hood and fire wall. This resulted in the flow of vacuum pressure being compromised and stopping. The dealer advised that the brake booster hose had to be "repositioned. " this corrected both problems of failed braking and lack of accelleration. The dealer would not or could not fully explain if this was a manufacturing problem or was a result of human error when work is performed on the car. The dealer would not replace the "crimped" booster hose. Lost of brakes when going highway speeds was quite upsetting. I thought I would pass this complaint on for you review and any action you deem fit. If this is a safty problem, perhaps a tech bulletin or warning should be issued by chev. Thank you. Please feel free to contact me for any other information required on your part.