No vacuum for brake booster

[Chief Master Sergeant]

Since my Explorer motor install, I’m not getting enough vacuum off the manifold to help the brake booster do it’s job. I think I read this is a common issue. Is there a better spot to connect for adequate vacuum?

 

[EPB72]

Pictures would help ,, a nice 3/8 size manifold vacuum source ..have u measured vacuumwith a gauge..stock motor or cammed??

 

[Chief Master Sergeant]

Pictures would help ,, a nice 3/8 size manifold vacuum source ..have u measured vacuumwith a gauge..stock motor or cammed??

Haven’t measured it. Need to buy a vacuum gauge. Have one, but can’t find it. This is a rebuilt 96 Explorer motor with Mustang FE.

 

[Digger556]

Did you change cams?

 

[Broncobowsher]

Did you change cams?

Explorer and mustang run the same firing order, doesn't matter for this.

 

[73azbronco]

Do a leak down check of brake booster, bet it leaks. Buy a mighty vac.

If your engine is running as equipped it should have plenty of vacuum unless cammed differently, or worn out.

Worst case, even my stock 2013 jeep uses a brake booster vacuum pump.

 

[pcf_mark]

What leads you to think you do not have enough vacuum? Not getting any assists?

Truck off pump the brakes 3-4 times full stroke. Put your foot on the brake pedal firmly. Start the truck. Your foot on the brake pedal should drop another 1/2" - 1". If it does drop your booster is functional. If it stays solid in the same place your booster is not working or your vacuum supply is bad or your booster check valve is not working.

If you have a near stock cam you have plenty of vacuum. If the booster check valve is bad you will have sporadic power assist. It will be ok (not great) assist. Easy to check - just blow some air (from your mouth not a compressor) into the check valve in the direction of the booster it should not let your air pass through.

It only takes 10-12" of vacuum for a booster to work correctly which would be a pretty stout cam with a choppy idle and need plenty of timing advance.

 

[Timmy390]

I had plenty of vacuum using the explorer cam on my 351w. I went with a bigger cam and still have lots of vacuum for the brakes. I've not measured it but know it's working well due to the brake performance.

Pull the hose out of the booster with the engine running. It should make a "spewing" sound as vacuum is released. Put your finger on the hose you should be able to tell if there is suction.

My guess is as stated bad booster or check valve.

My booster went bad and was leaking internally. Brakes worked well but I had a idle issue I tracked to a vacuum leak in the booster.

How is your idle? High by chance?

Tim

 

[Broncobowsher]

Make sure you actually have it on a vacuum port. Some intake ports are not vacuum.

 

[Chief Master Sergeant]

All great suggestions. I’ll check it tomorrow. I had the engine rebuilt and the builder said he used a stock cam. Do some of you run vacuum from under the plenum?

 

[Broncobowsher]

For power brakes they can pull vacuum from just about anywhere. Some things (like PCV) have a substantial volume of air always flowing, they need to be at the throttle body to distribute the air to all the cylinders. But the power brakes just puff a little air from time to time, doesn't need even distribution. At the throttle body or a single runner, doesn't matter. Even less so with port EFI than a carburetor.

I am still thinking you have it hooked to the water port and not a vacuum port.

 

[Chief Master Sergeant]

For power brakes they can pull vacuum from just about anywhere. Some things (like PCV) have a substantial volume of air always flowing, they need to be at the throttle body to distribute the air to all the cylinders. But the power brakes just puff a little air from time to time, doesn't need even distribution. At the throttle body or a single runner, doesn't matter. Even less so with port EFI than a carburetor.

I am still thinking you have it hooked to the water port and not a vacuum port.

I’m embarrassed to say, you were dead right. I mistakenly hooked it to a water port. What a dumb ass! Thanks brother!

 

[73azbronco]

Thanks for telling us you fixed it!