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Author Topic:   Converting from Hydroboost to Vacuum. Help!!
wrenchjockey
Member
posted February 02, 2003 10:05 AM
I'm building an 82 Monte Carlo that used to have the 350 diesel motor in it. I chucked the horsepower-robbing hydroboost in favor of a vacuum booster and a stock master cylinder from an 86 Monte Carlo for a vacuum-boosted system.

My problem is that on the hydroboost system, the 3/16" line goes to the front brakes and the 1/4" line goes to the back brakes. On the vacuum boost system, it's the other way around. I don't think I can just switch the two and have it work, because during a normal braking event, the rear brakes are applied first, and if I switched the lines, that would make the front brakes apply first, which would plant the nose and cause a push (right?). SO....do I chuck all the lines on the car and install new ones? Or do I somehow adapt this master cylinder to work with the existing brake lines?? Has anyone attempted this conversion? I put the rules for my class below. There isn't a lot of restriction. And it doesn't specifically say that I can't use a driver-adjusted proportioning valve...gray area?

Any help would be much appreciated.

BRAKE RULES

E. No after-market brake systems allowed. Steel components only. Brakes must be operating on all four (4) wheels and must lock up all four (4) wheels.
F. No rear disc brakes.


gould
Member
posted February 02, 2003 10:38 AM
im building a 81 grand prix with the same setup. im going to use the diesel master cylinder. Im also not going to use the vacuum boost. Im going to make a plate for the firewall to mount the master cylinder to, and cut the brake rod down to size. basically ill have manual brakes and wont have to worry about having enough vacuum for my brakes to work.


wrenchjockey
Member
posted February 02, 2003 06:23 PM
When I let off the throttle at the end of the straight, I'm not worried about vacuum, there's plenty...I just don't want the brakes working against me going into the corner. I want them working with me.


SLEEPY GOMEZ
Member
posted February 02, 2003 08:57 PM
Hey wrenchjocky. Just use a stock (gas engine) master cylinder, Forget vac or hyd, straight manual works OK. Make an adapter plate like Gould said. Connect your front and rear brake lines together with an "H". With rear drums and front discs getting the same pressure at the same time you will have a little rear brake bias. I have used this on several cars where we had to keep stock master cylinders and couldnt use any brake bias adjustment. Besides it's cheap.
SLEEPY


redneck bubbas racing
Member
posted February 02, 2003 11:07 PM
If you do decide to convert to manual remember to move your rod. Your brake pedal will have two holes the rod can go in, use the upper one. If there isn't another hole make one about 1 1/4 higher. If you don't it will definetly be hard to stop.


wrenchjockey
Member
posted February 03, 2003 07:59 PM
Thanks, Sleepy. I was hoping it was that easy. I need all the time I can get, and re-engineering the brakes wasn't on the agenda.

And you're almost right on the brake rod, I had to move it lower by almost an inch. and I also had to get a rod for between the booster and the master.

redneck bubbas racing
Member
posted February 04, 2003 08:57 PM
Wrench Jockey- I think you misunderstood. The rod will need to go in the UPPER hole. The farther away from the pivot point the more effort required to stop. I ran a big car (77 Olds Cutlass 4dr-3600 lbs) a year with the rod in the power-assist hole. It was very hard to stop and very hard on my front bumper. I learned the trick and switched to the upper hole the next year and it was amazing- I HAD BRAKES!


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