Having problems w/C5,LT1 conversion on my Malibu

[white79bu]

I have been working on this darn thing since January. I have a 79 Malibu w/C5 front disc and LT1 rear disc. I have a brand new master cylinder from an 88 Monte Carlo SS. I installed a dual diaphram brake booster for better vacuum. The problem I am having is that the brakes are fine in traffic when you are using them alot and even in reverse. But when you drive the car a few blocks without using the brakes the pedal gets soft and goes down before the brakes kick in. I replaced the booster and master cylinder and that really helped. I have bleed the system so much that I have ruined my chrome lug nuts. If there is air in the system I don't know were it is. I am beat my head on the wall! I don't know what to do. I called Baer and the first time I talked to them they told me there was air in the system. So I bled the system and nothing. Today when I called they told me to cheak the vacuum. But I don't think that's the problem. I have never had a problem with vacuum. The only thing I have done to the motor was I went from a 750 cfm carb to an 800 cfm. Do you guys have any suggestions? Any help would be great. At this point I will do anything. Thanks Andy

[super74]

Isn't the master cylinder from the monte carlo for a front disc rear drum? The master cylinder might not have enough stroke for the brakes to work correctly.Check into a disc/disc master cylinder. I had a similar problem using a master cylinder from a 3/4 ton chevy but again that was a disc/drum master cylinder so it didnt help either. In the late 90's I was trying to set up 4 wheel disc with lincoln rear calipers and there wasn't alot of info out there, so needless to say I ended up scraping the project. I am going to give it another go with a set up similar to yours.Keep us informed when you get it sorted out.

[Steve68]

how about a vette master cylinder maybe early 80's

[white79bu]

super74: I thought the samething about the master cylinder. But Baer told me that they use the stock master in there kit for the Malibu. They even use a manual master cylinder for power brake set-ups.

steve68: I have thought about a master from a corvette too. I just may do that if I can't find something else. But Baer claims the master I am using is fine. But it may be worth a shot.

Thanks Andy

[super74]

Baer suggested the 3/4 ton chevy master with the 1 1/16 bore
same as my stock camaro one.But I've been told, that master will run out of stroke before the brakes are fully applied. I had trouble bleeding the brakes or so I thought. I was driving my car,the brakes worked semi decent,then while driving.....nothing! I had to drive through a red light,and back through my neighborhood with no brakes. I just let it idle home and up the driveway then slammed it in park.Please be careful until you get it sorted out. Master power brakes recommended the 70's vette disc/disc master to me to fix my problem, but my car is all taken apart right now. Let me know what you find out.

[white79bu]

Well I borrowed a vacuum gauge to see waht I am pulling. I am only pulling 14 pounds of vacuum at idle. So I called baer and they told me that I need more vacuum. What I can't figure out is why I did't have a problem before? But any way I am looking into an electric vacuum pump or switching to manual brakes. The car is a street car more than anything but I plan on going to some open track events and doing some autocrossing. So I don't know what would be the best way to go pump or manual. What do you guys think? Thanks Andy

[white79bu]

Well guys decided to bleed the brakes again before I bought a vacuum pump. There was still air in the system. I don't know were it could have been but it was there. It still didn't help. It's doing the samething. But I did notice that when setting in the garage and the car running that when you pump the brake pedal the rpm goes up. I would day around 500-800 rpm. That means there is a vacum shortage right? Atleast that is what I am thinking. I wanted to see what you guys thought before I go drop $300 on a pump. Thanks Andy