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Ralph Cordell
10-23-2008, 11:48 AM
I am still trying to get my 87 GN on the road. A couple of years ago I installed a vacuum system after my powermaster went out. The brake pedal is pretty stiff when the engine is off but become really light (very little resistance except close to the bottom) when the engine is on. Is this normal? I have a salvage title for it and need to get it inspected before I can drive license it here in GA. My concern is that the brakes will not get passed.

They hold well when the pedal is fully depressed and stop the car fine in driveway testing and short trips down the street (car is not licensed). I checked the vaccuum at an idle and am pulling around 40psi. I replaced the old check valve with a new one (new one passed suck-blow test). I bought a vacuum pump from Summit but have not installed it yet. Given the reading - it may not be necessary.

I am thinking the vacuum booster may have gone out on me. Is there any way to test them? Also - I bought the system a couple of years ago on ebay and am trying to figure out what model/year I need to use in getting a new booster from my local parts guy.

Any help you can provide would be most helpful.

-ralph

Keller
10-23-2008, 01:02 PM
The brake pedal is pretty stiff when the engine is off but become really light (very little resistance except close to the bottom) when the engine is on. Is this normal?
To some extent. Without engine vacuum, you still should get a few solid brake pumps after the engine is off. If it goes away immediately, there is a vacuum leak somewhere. (i.e. hoses, check valve, booster, etc.)

I checked the vaccuum at an idle and am pulling around 40psi.
Not too sure about that number. Perhaps you are reading the wrong numbers on the scale. I doubt you can get more than 18-20 in. Hg. See http://findarticles.com/p/articles/mi_qa3828/is_200108/ai_n8978956 for reference.

...am trying to figure out what model/year I need to use in getting a new booster from my local parts guy.
Look at these articles. A V6/V8 booster from a Regal of the same year should be what you need.

http://www.gnttype.org/techarea/brakes/Powermaster_to_vacuum.html
http://www.gnttype.org/techarea/brakes/vacuum_brakes.html

buickgn38sfi
10-25-2008, 07:26 PM
When you converted over, did you chabe the the pedal to?

turbojd
10-26-2008, 04:28 PM
When you converted over, did you chabe the the pedal to?

It's easier to swap out the pedal when converting to vacuum brakes, although I re-drilled my power master pedal and used it when I did my vacuum conversion.

Ralph Cordell
10-27-2008, 04:20 PM
I bought the system on ebay and changed the pedal. This last weekend I tightened up the hoses and replaced the check valve. That seemed to help some. I jacked up the back wheels and tested the brakes. They started slowing the wheels about a third of the way down. It seems to be a matter of "feel" rather than effectiveness.