You might want to consider a pressure bleeder. It won't take much to push fluid through the system just a few pounds.

I have in the past run the engine at idle to pressure the system as you pump the brakes to move fluid. This is usually a two person job. One pumps the brakes, one opens/closes the valve at the caliper checking for air bubbles in a glass jar. Pump a few times all the way to the floor and then check the fluid in the reservoir, trust me you don't want to run out!! By using pressure you force the fluid into those cavities where there is trapped air, moving it along out of the system.

 

I have used a pressure bleeder without success (others have I might admit). My theory is that pushing the fluid into the small orifice without having a place for the air to vent will just compress the air. It needs to bleed out but the base of the compensator plate prevents it from moving that far.

Actually I think you could use a pressure bleeder to pre-bleed the booster with a little bit of plumbing. Then you could, as I'm recommending remove the entire compensator valve to allow the check valve to move far enough out of its chamber to vent to atmosphere.

 

GP I know this is a couple of years old, but have you figured this out? My 69 has rebuilt M/C, rebuilt boosters, new pads, rotors, some lines. I've bled this thing until I was bleeding....still the pedal feels off. It brakes ok, but if I press the pedal, hold, let go and repress it makes more pedal pressure. I'm close to plumbing out the boosters all together.

 

Sorry for the late response. The answer to your question is yes, I did figure it out. I figured that the boosters aren't worth the time, money and space I've given them over the years. I now routinely pull them out of the system. I have no problem with the extra pedal effort except when I get into my boosted late model cars and jam on the brakes...

A simple L shaped tube with females on each end does the trick. Don't forget to plug the vacuum line.

 

I finally have my system (dual) bled and firm. No idea if the boosters are doing anything..

I've lost my brake lamps.. The inline pressure switch seems to have been affected by all the bleeding, I'm over it frankly

 

I have found that if the system has been dry, you can wind up with an air bubble under the switch that makes the brake lights only come on when you use max pedal effort.
I got so sick of the booster needing re-building regularly, and bleeding the frigging thing that I tracked down a remote reservoir, tandem master that was the right size for going boosterless, designed a bracket and pushrod, and converted to dual circuit and boosterless (How people put up with 2 of those freaking boosters I don't know). I've made a few sets of the mounting brackets, if there was a call for it I could probably be persuaded to knock up another batch.

 

Love the idea of going boosterless. Is it necessary to change the MC as opposed to just plumbing them out? I was hoping a simple disconnect of the input and output brake lines with a connection.

 

My 69 spider had the original ATE master cylinder on it and its a 22mm. The replacement one I got from Alfa back in the early 80's which they told me was the last one available was also a 22mm.

When I bought my car the boosters were already gone. I never had a stopping issue and actually like it better the the hanging pedal cars.

Also when I restored mine I eliminated the brackets and all the extra lines for the booster. But I'm still running the dual master cylinder.

 

Need to change the master, other wise the pedal is extremely heavy.
Unfortunately my bracket design won't suit LHD cars.

 

AFAIR, the booster MC was 20 mm diameter, and the non-boosted now was 22 mm. the difference is about what the booster provided. You can get a "modern american car" feel (lots of brake with less pedal pressure) by putting the 22 mm MC on cars with boosters.

Be sure you check the rear pressure limiter very closely. It's on all cars after 69 or so. This often is gummed beyond all recognition, and the rears barely work as a result. I replaced mine with a Tilton adjustable valve, and can shift the f/r ratio pretty easily for road, track, AX.

Robert

 

Other way round. The non boosted cars used a 3/4" (19mm) master, the Boosted cars use a 7/8" (22mm).
Of course, there's another approach, 4 piston Outlaw calipers (4 1 5/8" pistons) on the front with stock rear calipers and an adjustable proportioning valve - the larger front caliper surface area workswith the 7/8" master.

 

One point I wanted to mention concerning the trapped air: the main piston seal has a hole in it which comes into play during bleeding. As you push the pedal, fluid enters the booster and forces the metal cup (which also has a hole) and seal away from the actuating rod allowing fluid to pass to the outlet port of the booster. As the small bullet valve is usually mounted under the booster body, the air is (or should be) carried out with the fluid, although it takes a fair amount of pedal pushes to do it.
I just rebuilt my Bonaldi so I had a lot of time to cogitate on how it works. Was I successful? Only the shadow knows...
Mark S.

 

I just finished this on my 69 on Sunday. I had previously gotten most of the way there by myself. I made a pressure bleeder from an old reservoir cap and a quick disconnect from my air compressor. I set the regulator as low as I could and it was enough to push fluid through the system. The key, of course, is to not let the reservoir empty. I could not quite get the pedal fully firm so I had a neighbor come over and help by pumping the brake pedal as I went around the four corners. I suspect there was some air trapped in the MC that did not purge until the pedal was pumped. Another 20 minutes and it was done. I have not driven it yet but it feels great.

Years ago I had another 69 and tried to do this with one of the check valve hoses that you put on the bleed fitting. That wasn't worth a darn because air could get back into the caliper around the bleed fitting on the brake release motion.