Help. Vac Brake Conv Problems

[alwndup]

I converted to vacuum from the PM early this year and since then I can't stop the car. It's easier to stop a '48 Peterbilt. I can stand on the brakes and the car slows to a stop. There's no way to get them to lock up. I can't figure out what's wrong. I've got a used booster and pedal (81 Regal) with a new master cyl. and I've bought 2 new check valves for the booster. The booster holds as much vacuum as my 98 GTP. I've got a billet TTA vacuum block on the plenum. I've bled the system 3 times over 500 miles, and I bench bled the master cyl on the car (cracked the lines at the cyl).

Any guesses what to try next. I really don't want to put the PM back on and buy an accumulator to get this pig to work.

Thanks in advance,

Mont Hunt
87 GN

 

[John Larkin]

The booster bladder is likely malfunctioning. I had to exchange my booster once and it improved things dramatically. I think they can get oil soaked from previous applications if the engine was allowing alot of oil into the intake system. Oil will break down rubber eventually. Be sure and adjust your rear brakes so the drums just barely slide on and off, I mean using your fist a little to install them.

 

[billsgn]

alwndup....don't mean to hijack your thread, but I did the same conversion a while back. I'm wondering what you (and others) did with the wiring harness that went to the PM and what is needed to get the cruise control to work? Also, my understanding is the lock-up feature on the torque converter is tied into the brake light switch. If the PM harness is left unplugged, is the LU affected? BTW, yes I know the brake light switch is under the dash near the brake pedal....

Thanks, Bill

 

[alwndup]

Good question. I didn't realize there would be a problem. I haven't driven the car much since the conversion. But now that you mention it, I hope someone could answer that for us.

 

[billsgn]

Well, I dont know if the LU was affected, but the cruise control definately was....

 

[alwndup]

John,

I don't get it. If the booster had a bad bladder, would it hold any vacuum at all? Mine will hold 15"+.

 

[John Larkin]

Obviously neither of us can truly pinpoint the problem. I could hear air pissing out the back of the booster on mine, right through the firewall, as I applied the brakes. The replacement I found for it did not do this. I can't say the pedal improved dramatically but it did improve.

And lockup + cruise is not affected by the removal of PM. As long as the switches are there, adjusted properly and the vacuum line is on the brake switch, it should be good to go. Under the hood, you can just leave the plugs lying next to the master cylinder. Wrap them with black tape if you like.

 

[alwndup]

Thanks for your insight, John. That gives me something else to check.