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Old 07-17-2008, 08:09 PM
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Power brakes and vacuum

I recently picked up a 79 z/28. The engine is a 350 and is original except for the cam, intake, and carb. I have no idea what kind of cam is in the engine, but you can definitely tell it has one because it has that lopey sound at low RRMs. Anyway, the brakes are fine when I'm driving down the road, but when I begin slowing down the pedal stiffens up. Also, the vacuum canister is not hooked up (I'm not sure if it absolutely needs to be). Where should I start to fix this issue? Do I need to put some kind of vacuum pump in because of the cam?

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Old 07-17-2008, 09:15 PM
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When you say "vacuum can", are you refering to the hose that goes to the power booster for the brakes? If so, it MUST be hooked up for them to work. It's possible the booster is/was bad and the previous owner was too cheap to replace it but you really need to get it working.

Mark
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Old 07-18-2008, 08:15 PM
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I'm referring to a black can near the radiator. Maybe it's something else. I'm new at this.
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Old 07-19-2008, 08:06 AM
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The vacuum can near the radiator is usually just a vapor recovery canister for the fuel system. It won't affect your power brakes.

The stock vacuum line for the power brakes is a flexible hose that goes directly over from the power brake booster to a fairly large diameter metal line (about as big around as a ball point pen) that is connected to the back of the quadrajet. This provides direct manifold vacuum to the power brake booster. This line must be connected and the rubber must be in good shape.

To check vacuum - There will be another small diameter vacuum line that leads from the back of the manifold over to an HVAC vacuum canister/ball, which is usually mounted on the firewall on the passenger side. Disconnect this line and connect a vacuum gauge. With the engine idling you meed to show anywhere from about 10-12" (aggressive cam) to about 20" (stock) of vacuum. Any lower vacuum may affect your power brakes. Based on your description of how your car runs (just a lopey idle), I think you probably will show enough vacuum. You might just have a leaking booster, or need to bleed the brakes.

If you need to buy an electric vacuum pump, you'll find that the ones from Summit and other sources are very expensive. A cheaper source is the electric pumps that were used in the 70's on heavy GM motor homes, and even on a few cars. It might take a little junkyard searching, but it will be much cheaper than a brand new vacuum pump.

Bruce
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Old 07-19-2008, 04:19 PM
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85 and 86 front wheel drive cadillac devilles had electric vacuum pumps.. they are located just behind the driverside headlight.. these cars seem pretty plentiful in the yards..
-Christopher
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