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Discussion Starter #1
Back story, 74 GTV, was in good running condition when rear-ended at a stop light, in 2002. Rough body work completed in 03, car sitting otherwise untouched since. I am now beginning a thorough restoration. The engine and transmission are out.
Is there a way to test the functionality of the brake vacuum booster and the brake junction valve (with electrical pressure sensor located on right side inner fender), as they are? I plan on removing both to refurbish and paint the engine bay. How can I check them and be sure that they are in good working order, before I reinstall everything? Thanks, Andy
 

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If the system is still all connected I guess you could put a vacuum pump on the booster. The pressure switch you would just check for continuity under pressure.
Old boosters are not reliable. Even if it tested ok today it might fail a month after the cars back on the road.
The pressure switch can be replaced with a generic one from an auto store.
 

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@alfettaparts2, I too thought about the vacuum pump test. All of the brake calipers are in a varying state of seized (I was able to move enough of the pistons enough to slide the brake pads out to push the car), I haven't depressed the brake pedal; I think it best that I don't.

I was looking for guidance on (maybe?) how to test booster while it is still in car with master cylinder removed, or with booster on bench.

Honestly, I have had pretty good luck with old Alfa boosters like this one.

I understand that the pressure switch on the brake junction block could be matched to a generic part, but what about testing the brake component? Isn't there a sliding piston inside that moves if you lose pressure on one circuit, and then triggers the failure light? I've heard stories about taking things like that apart and never being able to put them back into service.
 

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Yeah, you'd need to put vacuum on the booster and see if it holds it. That's the most common way they fail and will give you a bit of confidence, though there are other failure modes that will be a lot tougher to test. Personally I'd probably replace it with new if I was planning to keep the car.

I understand that the pressure switch on the brake junction block could be matched to a generic part, but what about testing the brake component? Isn't there a sliding piston inside that moves if you lose pressure on one circuit, and then triggers the failure light? I've heard stories about taking things like that apart and never being able to put them back into service.
Yes, the sliding piston is how it works. It's no a pressure switch, just a plunger that grounds the wire if there's uneven pressure between the front and rear brakes.

It's an archaic concept not really needed, IMO: the '74 has a dual-circuit master so if one circuit leaks you won't fully lose brakes, and the differential pressure warning device was dropped on later cars. As long as it's not leaking I just wouldn't worry about it.

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Discussion Starter #5
@Gubi, your post jogged my memory that it isn't a pressure switch as much as a position switch. I am leaning towards just reusing it (after I wire brush and paint it of course).
I will do some internet searches about the booster. Hopefully I will be able to test it easily and it will be ok.
 

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Sorry guys the cars here don’t have those. I can’t remember ever seeing a picture of one. Our cars just have a brass fitting with a pressure switch on the top. The brass fitting is just a three way joiner.
 
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