Whooshing air from brake booster
 

Hey Guys,

Been dealing with soft brakes for a while now. ALL new brake parts aside from the booster and MC. Put about 6 Qts of Brake fluid through the lines after bleeding so so so many times. Ive tried just about everything you can think of.

Brake pedal currently goes about half way down before it starts to really feel "harder". Last night a guy yelled at me on the road telling me I had no brake lights. Checked this morning and the lights arent activating till I hit that "harder" spot. Replaced the brake light switch this morning to no change but I did notice that when I press on the brake I get a sort of Whooooosh of air till it hits the hard spot.

I held my hand around the brake rod/booster around the interior firewall. While pressing the pedal I can feel air coming from the booster pictured below. Air does not continue to come out when i hit the "harder" spot.

Am I looking at a failed brake booster? I know the MC is not leaking out of the rear seal.


https://cimg8.ibsrv.net/gimg/www.for...44af181349.png

Your symptoms are similar with a failed vacuum brake booster. My old 1992 F350 had the same issue. A new booster made the pedal more firm.

I just got a new booster installed this morning, because of the wooshing air.
Unfortunatly My pedal didn't firm up as I was hoping it would.So I'll be taking it back to see what they can do about it.

Be sure to adjust the actuator rod. It makes a difference.

Installed a new booster today after finding the only one in town. Installed and there has been no change in pedal feel or brake light activation.

2 things i've noticed since installing the new booster.

1: If I pull my pedal all the way towards me (Farther than it would naturally rest) I can consitantly create a hissing sound comming from the booster. If i press the pedal, even the slightest movement, it will stop.

2: While bench bleeding the master cylinder, I noticed while pressing the plunger the front line hole will squirt fluid first and the rears will squirt second. This seems backwards since the MC order goes Booster rod>MC plunger>rear lines>Front lines

Any expertise is greatly appreciated. This problem is sucking the life out of me...

is it a Motorcraft booster? All the others are remanufactured.

The actuator rod can be adjusted by pulling the master forward (no need to disconnect the lines), and screwing the tip of the rod out if it's too short. There are instructions for how to do this in the Hyanes manual, but basically you grip the knurled part of the rod with a pair of pliers, and using a 7mm combo wrench or socket turn the tip of the rod with the wrench.

You need a bit of clearance between the end of the rod and the inside of the socket inside the master plunger- like 20 thou. Engine should be running when you do this so vacuum is applied to your booster. Unscrew the tip a half turn and try fitting the master back onto the booster. If the actuator rod bottoms out inside the plunger, the master won't seat onto the booster. You don't want that because you brakes will drag. Keep adjusting until you are at zero play, then screw the tip in 1/2 turn or so. The spec is for the rod to protrude 0.995 inches from the booster body and it can be measured, but this way works too.

Sorry to see the booster did not help your issue. It sure did for mine. About the only thing left is the master cylinder to replace, correct?

Your previous description of your bench bleeding session does seem odd.

As noted before, the actuator rod adjustment is another item frequently overlooked.

Went ahead and replaced the Master Cylinder because I do think something was wrong with mine. It mainly pumped through the front brake hose and little through the rear brake hose when bench bleeding. New one was much more smooth.

I was able to get my core back in time and return the brake booster. The hissing I was hearing in the new booster is no longer there with my old one in place.

Sad to say though, my 50% soft 50% hard pedal is still there. Still on the hunt.

I'm starting to suspect a vacuum leak of some sort. I tested the vacuum on the brake booster line and the needle fluctuated rapidly from 15-19psi. I found a couple other lines with the same fluctuation and others that sat dead at 20psi.

The booster has a pretty big reservoir of vacuum, so a fluctuating vacuum signal should not affect it once it is fully "empty".

What was your brand of new booster? Seems like Cardone is a very available, but perhaps not the highest quality unit out there. The Motorcraft BRB22 is widely avaliable and at $160, probably a better deal in the long run.

Here is a picture of the gauge I made to check the actuator rod protrusion. The plastic is 2 15/16" wide, the slot is 3/4" wide and is 0.995" deep. The tape is on there because I filed it a hair too deep. These measurements are provided in the Haynes manual. I would measure the rod on yours as suggested by rla2005.

https://cimg2.ibsrv.net/gimg/www.for...7f82dab7e2.jpg

The booster was a re manufactured Cardone one I picked up from a local parts store. I measured the Rod at .995 inches which is the same length as my original one.

The brakes actually do feel like they engage a little bit during the "soft" section of my pedal, but don't have enough force on the rod to activate my brake lights.

I will say that if I fully push the pedal to the floor, then release the engine will surge a couple hundred RPMs. This was making me think it was a vacuum issue.

I agree, something is amiss here. I am not a fan of Cardone products. But I do not want to spend your money on a blanket response of my view and experience with their products.

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I'm experiencing the same whooshing/hissing issue with my '84 but without the pedal travel or brake lamp switch issues. I did replace the vacuum hose with no change. Strange that my braking is unaffected. I'm going to present the question over in the Bullnose forum also and see if it gets any hits. :-wink

Sorry if I didn't mention before but I'm back to the original booster that came with the truck. I was able to get my original back after returning the Cardone one that resulted in no change

Does the pedal really go to the floor? if it does, you probably have air in there somewhere. How did you bench bleed your new master cylinder?

Sorry for the confusion. It doesnt actually go to the floor, I meant till it fully stops. I bench bled the MC according to the instructions and videos I found online.