vacuum brakes

[kjhansen]

Originally posted by Steve Wood
If you cannot get a solid pedal, most likely you have air in the system. Has the iron proportioning valve been replaced withteh brass one on your car?

There should be no problem with vacuum brakes...most people that reported problems had a mechanical problem with one of the components...be sure the vacuum booster/check valve is working properly, and that you use the correct pedal. A new master cylinder is probably a wise investment.

If the above mentioned valve has not be replaced, this would be a good time to do it...

Make sure that the master cylinder is properly bled and then all four wheels... I use either a vacuum pump or simply gravity bleeding to do the wheels...

Proportioning valve was replaced and master cylinder rebuilt when the vacuum brakes were put on--the brake pedal (really the lever since the brake pedal is technically just the pad at the base that you put your foot on) was part of the vacuum brake setup from the other car, so yes it was replaced too. I put a new check valve in, then later added a vacuum reservoir and another check valve is on that. The brakes have been bled and bled by myself and professional mechanics--I've gone through several sets of pads and shoes since the mod back in '96 so they've been adjusted too. The brakes still go down almost to the floor before engaging. They'll lock up the front tires in a panic stop, and they do stop the car OK. Just a really long throw and not the firmest feel--nothing like my Chevy G20 van for example, which has about an inch of throw before firmly engaging. I dunno... as long as they stop the car they're OK I guess.
Keith

 

[FlyinGN]

sounds like maybe the pushrod that goes from the 'lever' to the master cylinder may be the wrong one?

 

[TurboJim]

Originally posted by Roger
I tried vacuum brakes & went back to the PM.
With a daily driver, you'll have problems when pulling out into traffic from a side road. The braindead about 100 - 200" farther down the road trying to pull out into traffic with a SUV or an "economy" vehicle will also pull out because you did. In about 100' you'll be doing better than 45mph & have maximum boost when you suddenly notice the braindead idiot now has blocked the road in front of you. Since you are at maximum boost, you'll have no vacuum to enable the vacuum brake booster to function.

Thats cuz the dingbat installer didnt install the little plastic check valve

Also, why are you pulling onto a busy road at full tilt? You need to drive farther ahead....

I have never had a problem with my vacuum brakes. I did however lose my PM (ROCK hard) pulling to an intersection on the way to work one morning. Bent my seat trying to stop

Least if I lose vacuum, its a little harder than manual brakes, but I know I can stop.

 

[kjhansen]

Originally posted by FlyinGN
sounds like maybe the pushrod that goes from the 'lever' to the master cylinder may be the wrong one?

Well, the lever, the rod, the master cylinder. and the booster were all from the donor car. While I complain about how far down the pedal goes, fact is I've never had a a brake failure since replacing the Powermaster. On the other hand, the PM failed twice in the first 6 months I had the car. As far as reliability and cost go, the vacuum brake system is far superior.
Keith

 

[tego]

Question!! Is just did my 86 grand national convertion to vacuum from a 85 el camino master,booster, and pedal.. i oready bleening the brake all 4 of them.. the car will stop the first time you hit the brake but after the 3 push of the brake they get hard.. my check engine light comes on... is the vacuum that i use the wrong one or what do i do with the plug from the original brake booster

 

[tzque]

Did you change the brakelines

 

[tego]

No when i was readying in the forum it did not mention that..