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73-87 Chevy _ GMC Trucks => 73-87 Chevy & GMC Trucks => Topic started by: jman340 on May 13, 2013, 01:49:55 pm

Title: vacuum switch attached to brake?
Post by: jman340 on May 13, 2013, 01:49:55 pm
Just got my 86 GMC 1500 back on the road, but still have the dash pad and other dash pieces off. I noticed a vacuum sound when I stepped on the brake, and looked under and noticed a vacuum switch attached to the brake petal. What is this, and should I be hearing it?
Thanks
John
Title: Re: vacuum switch attached to brake?
Post by: zieg85 on May 13, 2013, 01:58:35 pm
It disengages the cruise control
Title: Re: vacuum switch attached to brake?
Post by: Boone83K10 on May 13, 2013, 03:16:48 pm
yes it is cruise. I tried to take my cruise off and I lost converter lockup.
Title: Re: vacuum switch attached to brake?
Post by: jman340 on May 13, 2013, 06:31:29 pm
I'm guessing it shouldn't sound like a vacuum leak. I no longer have cruise, so can I just cap the line to it, or will that disable the converter lock also?
Title: Re: vacuum switch attached to brake?
Post by: frotosride on May 13, 2013, 07:45:57 pm
Quote from: jman340 on May 13, 2013, 06:31:29 pm
I'm guessing it shouldn't sound like a vacuum leak. I no longer have cruise, so can I just cap the line to it, or will that disable the converter lock also?

It will disable lockup because the vacuum switch is part of the lockup wiring.
Title: Re: vacuum switch attached to brake?
Post by: zieg85 on May 13, 2013, 08:21:56 pm
Your vacuum power booster may be what you are hearing.  Disconnect the vacuum to the booster and determine if you still hear the hiss.