Weak brakes after vac install

ThikStik

My sleep apnea is winning
Joined
Mar 27, 2002
I did the vac install, re bled, have no hissing and the assist feels fine, just have harder time stopping and pedal goes lower than it should. Also, while at drag strip the brake lights were on a few times all the way down 1/8 mile. Car also pushed thru and red lights sometimes at 8-10 lbs of boost. I had to panic stop the other day, and fronts did not lock. I may try re bench bleeding. I do have modern combination valve. Ive read that i shouldnt have converted to vac, as PM is best. Just my luck, as i sold PM. Also, there seems to be debate over MC types..24/36mm VS 24 mm. Im not sure which i have.
Thanks
 
ThikStik said:
I may try re bench bleeding. I do have modern combination valve. Ive read that i shouldnt have converted to vac, as PM is best. Just my luck, as i sold PM.

Where did you read the powermaster is best? I'd quit reading there.

What did you use for a booster and master cylinder? Did you change/ move the mounting point on the pedal?

Old as the fluid is did you bleed until it was clean? What did you use for a bleeding procedures?

Nothing wrong with a propperly working vac setup.
 
millions of car are using vac assist power brakes just perfectly.
why would anyone think they don't work well?
 
Where did you read the powermaster is best? I'd quit reading there.

What did you use for a booster and master cylinder? Did you change/ move the mounting point on the pedal?

Old as the fluid is did you bleed until it was clean? What did you use for a bleeding procedures?

Nothing wrong with a propperly working vac setup.
X2 ..... We need a bit more information Like Rich asked here so we can pinpoint the issue.... For what it's worth, my vacuum brakes work Fantastic!
 
HI,
I saw a thread on hereafter a search from 2006 that involved a guy who had marginal brakes after vac changeover. PowerbrakeMan, iirc his name, stated how the PM was best from a liability standpoint, and from a stand point of no pressure making it into booster, etc.
My procedure: Bled rr, then lr with a person at pedal, me on bleeder. Then bled rf, lf. Done twice , so clean fluid. Brakes were strong before changeover. I have pushrod in lower pedal hole. I have a billett vac block. Sorry , not sure but i think it was a Grand Prix doner for MC/booster, dont know engine or year. I have aluminum mc and booster is very lengthy so maybe its duel diaphragm. I get the sense i have enough assist, just a low pedal with marginal clamping force on hard braking. It did change when i changed to vac, so rest of system is ok. Also, i did get brake lights on a few passes that cancelled upon applying braakes. I can blow into chek valve and it stops airflow one way, so if its bad, its only marginally bad. thanks
 
HI,
I saw a thread on hereafter a search from 2006 that involved a guy who had marginal brakes after vac changeover. PowerbrakeMan, iirc his name, stated how the PM was best from a liability standpoint, and from a stand point of no pressure making it into booster, etc.
My procedure: Bled rr, then lr with a person at pedal, me on bleeder. Then bled rf, lf. Done twice , so clean fluid. Brakes were strong before changeover. I have pushrod in lower pedal hole. I have a billett vac block. Sorry , not sure but i think it was a Grand Prix doner for MC/booster, dont know engine or year. I have aluminum mc and booster is very lengthy so maybe its duel diaphragm. I get the sense i have enough assist, just a low pedal with marginal clamping force on hard braking. It did change when i changed to vac, so rest of system is ok. Also, i did get brake lights on a few passes that cancelled upon applying braakes. I can blow into chek valve and it stops airflow one way, so if its bad, its only marginally bad. thanks

The statement about the PM being the best from a Liability stand point is absolutely absurd because if the PM goes out you have absolutely NO BRAKES! so it's not really a good liability.... At least with a Vacuum system you still have brakes to stop the car even if the car is totally off and not running !!! I know because I had converted over to vacuum MANY years ago and when I needed a tow home about 4 miles (TurboDave) came and got me with his Excursion and my tow rope and I actually stopped his Excursion and my car for stop signs without the damn car running! I would like to see a PM do that!!@!

Something is wrong somewhere and we will help you figure it out one way or another....

Please answer this...

* Did you change out the actual whole brake peddle? Or at least change the mounting point of the peddle?
* Did you actually replace all the brake fluid, and bleed them until you seen Clear new fluid?
 
If you read anything from PowerbrakeBob he was a scammer and 99% of his info was BS.;) He was banned some time ago btw.:D The best holding brake system from the factory is the hydro boost system, second is the powerbastard, and third is Vacuum brakes. Cost wise is vacuum, with hydro and powerbastard is roughly about the same cost. As far as reliability, vacuum and hydro are about the same, but the powerbastard when new was fine, and now that they've gotten old you can't trust them without at least once a year flushing the fluid out, and then I still wouldn't trust it.:eek:
 
I did the vac install, re bled, have no hissing and the assist feels fine, just have harder time stopping and pedal goes lower than it should. Also, while at drag strip the brake lights were on a few times all the way down 1/8 mile. Car also pushed thru and red lights sometimes at 8-10 lbs of boost. I had to panic stop the other day, and fronts did not lock. I may try re bench bleeding. I do have modern combination valve. Ive read that i shouldnt have converted to vac, as PM is best. Just my luck, as i sold PM. Also, there seems to be debate over MC types..24/36mm VS 24 mm. Im not sure which i have.
Thanks
Try this: http://turbobuick.com/forums/thread...-diaphragm-booster.370682/page-2#post-3054720
 
in for updates, i did the vac swap and the pedal bottoms out without upto par braking (for me atleast) car ha a cam and makes 13-14 inches of vac. do you have a stock cam?
 
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