Vacuum Brake Conversion


Mar 28, 2021
Ok. Since the powerboost is broken I'm converting to vacuum. I will be starting this weekend once parts arrive. I'm going to document the conversion but I have a few questions to those who have done this in the past.

So far I have ordered Monte booster and master cylinder. As far as finding a new pedal I'm not sure I can find one in any local yards so will either be drilling or welding mine. I haven't found any pictures documenting the pedal modification. If anyone has tips for pedal mod please post it.

Next is check valves and vacuum source. Does the check valve on the booster suffice or do I need another inline? What is the best spot to tap vacuum? I'm thinking PCV for now but may order one of those aluminum vacuum blocks in the future. How does the vacuum ball come into play? Does it actually assist in braking?
Well parts arrived today. Went ahead and did the easy part. New booster and master cylinder are installed. I'm going to try and source a clevis pin tomorrow for the pedal.

Only advice I can give this far is take off the top bolt on the pass side first. The other three can be reached with extensions on an impact.

If I can find a proper clevis tomorrow I plan on drilling the pedal arm then welding the clevis in place.
I went with the dual diaphragm monte booster and master cylinder as well.
I put a tee in the PCV line just above the check valve in the intake manifold. I routed the hose under the coil packs over to the booster. I have a stock booster check valve in the booster.
I have a stock engine with bolt ons and have plenty of vacuum.
Some guys say there isn’t enough vacuum going this route, but it may be because of a larger cam and their setup.


Ok pedal welded up and installed. That was the hardest part. Managed to bleed the master but still some air in the lines. However even with air will hold the car in gear and lock the brakes when rolling around the driveway. Will get the system fully bled and flushed in the daylight.

Not much to write up about this I will say the hardest part was scribing the circle on the pedal with all the wiring and stuff down there.

Hopefully my engine bay will look that clean one of these days.
I ran a T above the PCV line like described above. It worked fine for cruising in a stock car.

It didn't fare well once I started to demand a bit more from the brakes. A dedicated vacuum source is required.
Vacuum brakes are fine for the street and in an occasional emergency stop. Looks like you're on the right track. Make sure you don't have any vacuum leaks elsewhere so you get enough pressure. Might be time to upgrade your old hoses to silicone if you haven't already.

I have only ever had vacuum brakes on my GN and when my old booster went I upgraded to a Caprice (not sure the year). I saw somewhere on the monte forums years ago that the caprice was the monte guys upgraded booster.

One day if i feel the need i'll upgrade to hyro but i'd do a aftermarket steering box before that.

Good luck
If memory serves you can drill a new hole in the pedal for a pivot point. You could search it on here for the diagram.
Don't use a T in the pvc hose. It's a controlled vacuum leak to pull vacuum from the crankcase and has lower vacuum than other sources.
When I delete the EGR tower from the manifold I weld up the tower solid and tap it to 1/4" pipe and install a hose to the booster. I also weld the bottom of the plenum, contour it and drill a 5/16" hole for the vacuum to the passage. Some don't weld up the inside of the plenum when removing the tower, but I prefer to do it that way.


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