brakes spongy after swap

[bohmankid]

Anybody else having problems? I put the 5.3 vortec in my 85 gmc 4x4. I have a vacuum coming off the manifold into the brake booster, transmission, and heater controls.. My brakes are very spongy, I thought I read somewhere that these motors don't put out enough vacuum. input?

[68GMCCustom]

They should put out plenty. When I installed my 22x/23x@.050 cam'd 6.0L and 1st fired up in my truck, it was set up with a carb and intake, with 6LS MSD box firing coil packs. Vacuum was good (15"-17") even with the cam. Swapped everything over to OEM EFI intake and ecm/tcm controlling everything with a custom harness. Vacuum fell to like 10"-12" and my brakes went to crap. Almost no boost from the power booster, with it occasionally working since I have a vacuum storage tank in line, which was capturing a little on vacuum on deceleration.

anyway....after plugging everything and then swapping the throttle body, new intake, verifying injectors, and more with no real change...I asked my tuner if it could be in the tune and could he do something. He said sure and changed one of the idle/air tables and made another 2"-3", finally powering the brake booster. I'm hoping an upcoming tune (different tuner) will resolve it all together, finding the 15"-17" of vacuum my motor made when 1st installed.

I'd run the brake booster "independently" off the back of the manifold and pull the vacuum for everything else from another port.

[bohmankid]

What's the best way to open up one of those other ports on the manifold?

I'm also gonna make sure I don't have a vacuum leak cuz the manifold gaskets are original. But my check engine light isn't on, so I assume no vacuum leak.

[85burb]

Are they spongy or hard to push? Hard to push would possibly be a vaccum issue but spongy that is a air in the break fluid issue.

[cableguy0]

As stated above spongey brakes would be air in the lines,bad master cylinder or a leak somewhere. Hard pedal would be booster problem due to low vacuum. A stock ls is going to make plenty of vacuum to run power brakes. Check the wheel cylinders,hoses,calipers,lines and master cylinder. Unbolt the master cylinder from the booster and check for wetness behind it.

[crazy longhorn]

Originally Posted by cableguy0

As stated above spongey brakes would be air in the lines,bad master cylinder or a leak somewhere. Hard pedal would be booster problem due to low vacuum. A stock ls is going to make plenty of vacuum to run power brakes. Check the wheel cylinders,hoses,calipers,lines and master cylinder. Unbolt the master cylinder from the booster and check for wetness behind it.

Checkin for the wet spot....I probably should not say any more..... Best of fun on your travels, I have found that a house is better to live in, than a truck(been around a few yrs)? AL

[68GMCCustom]

Originally Posted by bohmankid

What's the best way to open up one of those other ports on the manifold?

If you're talking about an OEM plastic one. The rear brake booster port has to be punched. The side port had a tab to twist/cut off? Not sure about front port by throttle body. And yes.....my pedal was HARD...not spongy.

[85burb]

The small tab on the side of the plastic intake I carefully twisted the flat part off the end with pliers. If you had a tiny saw blade you could cut it off.
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[bohmankid]

Thanks guys I didn't even think about that. I'll check fluid/leaks/air and all that tomorrow. And yes, it's spongy, almost touches the ground. And my brake light is on.
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