Hello, I am looking for some guidance with the braking system on my 1995 f150. I decided to replace my brake booster today because there was a loud hissing sound that had been coming from my brake pedal when I push on it that has been driving me nuts. I ordered a new one from rock auto and installed it only to realize that it is making an even louder and worse hissing sound than my old one did. I am wondering if I got a defective brake booster or if it is something else that could be causing this loud hissing. Any help would be greatly appreciated, thanks.

 

Seems like you got a defective new part.

 

Have you checked the various vacuum lines to make sire ones not split or cracked?

As mentioned, it is possible to get a bad new part also.

 

Hissing from the booster is about normal when hitting the brakes
They come with some foam rubber crammed into the back of them where the pedal goes through
That foam wears out over time
Used to see Lincolns get SSM's to add more foam (special service messages) over Oasis at the dealer
Added foam to a bunch of trucks, Mustangs and T birds over the years (it "lessens" the hiss some is all)

 

I disagree. You should not get a vacuum leak when hitting the brake.
Over time? The booster is brand new.

 

There is always some hissing sound when you press the brake pedal. I only hear it on my brakes when the engine is off and I press the brake pedal (only once then the vacuum is gone).

The video explains how air must flow into the non-vacuum side of the diaphragm to create the force to push the master cylinder. This is probably the sound that is normally heard.


I think this normal airflow is what Ford attempts to muffle. I don't know if your hissing sound is abnormally loud.

 

It seems like a pretty large vacuum leak as it almost makes my truck die if I pump the brakes enough when I first start it. All my lines look good. The booster seams to be doing its job performance wise. i made sure to adjust the rod on the booster to the right length 0.995 inches so i know that’s correct. It just makes a lot of noise and I think it has something to do with the weird things that happen when I first start my truck.

 

Repeatedly pumping the brake pedal will take away engine vacuum, and yes it will run like chit = normal
Explain "weird things that happen when I first start my truck"
Look into how to test a brake booster (foot on brake, start engine, pedal drops) + makes some noise = normal operation
Your new aftermarket booster is just not as good as the OEM Ford one (for quiet)
Take the strip of foam from your original booster and put it in the new aftermarket one
You can cram that foam in there with the booster in the car
Fun stuff

 

Take the vacuum line off the booster, cap it off, run the engine.
Do you still hear a hissing sound?
This will determine if it is your booster making noise, or something else.

It should be a sucking sound as this is vacuum we are talking about.

 

Thanks unfortunately I don’t have the original as the one I replaced was a crappy aftermarket one. I’ll test the line when I get home but I am almost certain the sound is from the pedal area at the back of the booster.

 

I’m thinking the start up issue may be unrelated to an extent because when I start the truck up it revs up for like 10 seconds then dies or almost dies and the check engine light flashes 3 times.

 

The original piece of foam (in the booster) was only about 1/2 x 1/2 x 2 inches long
The ones they had us add (for the noise complaints) were the same size
That was wrapped into a donut shape and put around the pedal shaft, inside the housing, under the plastic water shield if equipped
If you go look at a Lincoln at the wrecking yard, they have the most foam and plastic as a sound buffer
You can just use a foam strip cut from a car wash or kitchen sponge
Your 95 cold idle issue, it should start and have fast idle cold
If not the ECT may be out of range, I'd test for codes and see what the ECT PID is (I have a NGS) that ngs will read pids on an obd1 1995
In your case you'll have to backprobe the ECT with a DVOM and see the ect voltage
Sometimes lack of fuel pressure makes them stumble or fall on their face cold
I'd check that too, I'd drive it around with a fuel pressure gauge taped to the windshield (just to see what it is and make sure it's between 30-35 at ALL times)

 

Thanks I’ll look into the foam trick and take a look at those other things.

 

I would warranty the new booster as defective. Good luck with whatever you decide.

 

I just went through this problem it took 4 boosters from Amazon and I finally got one that didn't leak at the popit valve It is important to make sure you adjust your push rod length using a tool they have for 20$ .If it is not adjusted properly it will cause your booster to leak especially if it is adjusted to long.hope this helps.cheers