Question about 2006 Buick Grand National

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Buick Grand National vacuum brake conversion

I recently changed my '87 Buick " T " over to vacuum brakes, I used a set-up off an '86 Caprice 10 3/4" booster w/master cyl. All the parts bolted up ok but I had to drill and tap the intake plenum in order to get 16.5-17" vacuum. The pedal is pushed all the way back to it's limit installed. Pedal seems Stiff to push, and is Hard then goes down off panic stops. Will not even lock up front brakes on hard stops. This set-up does not work much better than the Powermaster. Whats going on here???? Any help would be greatly appreciated.

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^ Turbo Cars have Lots of Vaccum, Where did you ever get this idea from. I have personally converted 10+ Turbo Buicks to Vac brakes.

Make sure the check valve is okay at the booster. but it does sound like you have a bad booster.
Also, did you change the brake pedal to a Vac brake pedal?
They are not interchangeable.

Also, you should not have drilled the plenum, you can get a vaccum block to replace the plastic one on the top of the plenum with a vac brake port.

Posted on Jan 29, 2009

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  • Bill Jan 07, 2010

    The only time a Turbo car has no Vaccum is under boost.

    This is why we use check valves when converting to Vaccum brakes.

    I have a Boost/ vac gauge on my car and see 17' of vaccum at idle.

    Turbo cars HAVE LOTS of Vaccum because they do not usually have cam shafts that have overlap.

  • billg87 Sep 12, 2010

    i need info on getting the vac block/vac port and any other part needed to change to vac system on buick gn

  • macguyver126 Dec 19, 2010

    please call 803 477-6065 have to covert one myself hope this gets through haveing trouble with this site


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It sounds like the vaccumn canister is not holding vaccumn.( weak or cracked diaphraim) Also did the swap come with a regulator valve (porposting) to set rear and front psi? Make double sure the system is bled well.. In addition the master cylcinder has a shuttle rod that must be centered up in order to porposition the fluid front and rear.Have a fun day and good luck.

Posted on May 14, 2008

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Turbo cars do not have enough vac. for a system like that. Get a vac. pump.

Posted on Jan 06, 2009

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