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Is this a US '69? They came with two vacuum boosters in the engine compartment and a dual circuit MC, as well as a rear brake pressure limiting valve. All of these things can make bleeding the system a LOT more difficult than a simple single circuit car - just do a seach here on brakes and you'll get a picture. Non US '69's were single circuit.
For a dual cct, you must bleed two wheels at once - one front and one rear. Think of it as two seperate circuits with just two wheels per. The reason you must do two at once is that the MC has a floating piston that seperates the two circuits with no centering mechanism. If you just bleed one, sometimes the floating piston thinks that cct is failed and leaking, and slides ot one side, blocking it off completely. Then little or no bleeding occurs. Bleeding two at once keeps the piston centered.
The reason it sometimes works is if you only open the bleed screws a little, so there is plenty of pressure in the circuit, and only press the pedal a little (short stroke), you can keep the floating piston near the center and everything will work OK. Fronts usually work OK this way, but the rears have another problem.
It's the limit valve that gets involved. If you keep the bleed screw too tight and the rear pressure is too high, the limit valve will close and again no bleeding. Mostly just luck getting the right balance between too much pressure and not enough; my luck is almost always bad when I try so hard.
Best is with three people - one on the pedal and one at each of front and rear wheel. Open both F & R bleed screws, press pedal down and hold, close both screws, release pedal; repeat. Be sure to keep the reservoir full.
BTW - push the pistons all the way into the caliper, then bleed the line to get all the old fluid from the caliper out of the line. Then pump the caliper all the way out (without pads) to fill it with fresh fluid; then open the bleed screw and push piston back in all the way again; reinsert the pads (new ones, yes?) and pump the pistons into full contact. Then fully bleed the system. If you do this regularly, you will get fresh fluid into the caliper and avoid much of the corosion that occurs from moisture in the old fluid.
Vacuum gadgets don't work reliably because of the limit valve - sometimes it will lock the rear limiting valve (pressure differential higher on pedal side), and sometimes it sucks the floating piston off center.
Pressure gadgets on the reservoir work only if you do the dual bleed screw thing - same problems as the hand bleeding.
Just keep in mind the three key parts - MC, rear valve, caliper - and you can get a good solid pedal easily. Lots of dealers and minor alfa mechanics never got it really right, so you might be surprised at how good the alfa brakes really are.
Robert
Last edited by 60sRacer; 04-08-2006 at 08:59 AM.
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