Power Brake Booster in 1974

[Chief Brody]

I have no idea if the brake booster in my Blazer is original, but since I have it out is it one of those parts you just go ahead and replace or do they last forever?

And what's the difference to me if single or dual diaphragm

 

[Fordum]

In general the dual will have more power boost than a single of the same size. Up to a point, if you need more power, you increase the size of the booster, since its Pounds Per Square Inch of surface area that does the boosting.
And air pressure is pretty much the same no matter what size booster you have.

But, you start running out of room under the hood for a big booster, so they went to dual chambers on some trucks.
That way, you could have an 8 inch dual do more work than an 11 inch single.
Or you could do like Ford did on my 1966 2 ton. Put a remote booster underneath the truck mounted on the frame.
Lots of room down there.
I think its about a 15 inch booster.

 

[dremu]

I have no idea if the brake booster in my Blazer is original, but since I have it out is it one of those parts you just go ahead and replace or do they last forever?

And what's the difference to me if single or dual diaphragm

The dual diaphragm is thicker than the single. Pretty sure the single went the way of the dinosaur, but I'd replace like with like.

OTOH, they're easy to test (and very rarely go bad.) Turn off the engine without hitting the brake pedal. Wait fifteen minutes, then, without running the engine, repeatedly press the brake pedal. You should get three or four easy presses, wherein the vacuum built up in the booster gives you assist, and then have a hard pedal 'cuz there's no more assist.

If it holds vacuum that long, it's fine. If not, chase down the hose going from the booster to the carb first as they wear out and leak, and maybe the one-way check valve (plastic thing on the booster.) As I said, the booster rarely fails.

-- A