The Mystery of the Power Brake Booster

Ok when I was getting the 73 Mach 1 ready to go to the MOM, Mustang Owner's Museum I did not even bother to assume the PBB was good. I pulled it off and sent to Booster Dewey in Oregon. The shipping was more than the repair.

My booster has been out on the 73 vert but I drive it. You can stand on the pedal and still slide the tires with no brake booster. 

So I decided to see what is inside the booster that costs so much to repair. I had an old one that was not exactly for Mustang but still a Bendix booster. 

I put my engineering background to work. I built a fixture to hold the booster housing so I could un crimp the areas around the diameter of the housing. You cannot hold the housing in a vise and on the bench is like a monkey F&(%&$% a football. So I have some of the very thick material that is same as the covering on your kitchen counter that is 1/2" thick. I cut a piece and layed out a 10.5" diameter and cut out with saber saw. The housing of the booster drops into the hole. I bolted to the work bench so nothing is getting away. SEE PICS. 

I used pickle fork, chisel, seal bearing puller to back the areas off that clinch the two halves of the PBB together.

When I got it all apart there is nothing in there but a spring and the rubber seal. 

I should have looked a little long but I tried to pry on the center part and it broke. The rubber seal stretches and goes over the center does not come apart. 

I will see if I can find supplier for the rubber diaphragm and post up into we are getting ripped off on the rebuild of the PBB for sure. The most simple part on the darn car.

The housing on this one was trash was rusted into on the inside half. The diaphragm looks good.

Sand blasting and painting the housing is the biggest expense here.

Remember i have one available for sale if interested.

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I have several I just wanted to take one apart to see what was there. If I can find the parts I will then do a replacement for mine. I think the shipping was like $175 to rebuilt was I think $150 so not cheap. The sand blasting will be the hardest part. 

I will add a lever to my fixture to clamp the two halves together while I push the crimps back in.

Hey could open up an east coast rebuild shop. NOT I am retired.

Look at how much effort it took you to take one apart; that is why it is so expensive to refurbish them.

Agree with Randy here. Dave, I just do not understand why your shipping was 175 bucks! I shipped mine from Omaha to Booster Dewey for $20 each way!

It was sent by USPS cheapest way I could find. I am in N.C.. He sent back by 2 day it was over $70.00 each way. 

I am sure they have made a fixture to pull the bent tabs back. Would only take a big toggle clamp in reverse. NPD has some of the diaphragms will need to pull a real one apart to see what the size is. 

In production they would put in a die and would bend all of them at once.

[i think the shipping was like $175...]

[He sent back by 2 day it was over $70.00 each way. ..]

We all hate math anyway

Great autopsy!

I wanted do same as I still have my old 11 inch one. Doesn't look that complex.. Sealing it back properly is likely the biggest challenge.

For the diaphragm replacement, I see for a bendix

https://www.npdlink.com/product/rebuild-kit-power-brake-booster-dual-diaphragm-bendix/205442

This is quite a deal breaker. You said you paid +-150 for the repair at BD no?

$25 shipping back to Illinois. Didn’t think that was that bad. Ryan

David, thanks for the writeup, this really helps advance the knowledge of us hobbyists, and I get the points you are making.... Its' on my project list to either repair or replace my BB and your post gives more insight into what will be needed if I choose to open up and refurb....

question though - is there a way on a bench (i.e. not fitted in car) to check if a booster is functioning correctly ? (without opening it up ?) if I know mine works I'll just sandblast and paint....

Connect a vacuum pump to the check valve and see if you can get it to hold vacuum, with a hand pump it will probably take one to three minutes. If you haven't started showing vacuum on the gauge after three minutes your booster diaphragm is probably bad. If it does hold vacuum push in on the brake pedal push rod and watch the rod that goes to the master cylinder, it should move. It should be a lot easier to push the push rod than trying to keep the master cylinder rod from moving. Push the push rod three or four times, it should get harder to push, indicating that the booster is working.

Connect a vacuum pump to the check valve and see if you can get it to hold vacuum, with a hand pump it will probably take one to three minutes. If you haven't started showing vacuum on the gauge after three minutes your booster diaphragm is probably bad. If it does hold vacuum push in on the brake pedal push rod and watch the rod that goes to the master cylinder, it should move. It should be a lot easier to push the push rod than trying to keep the master cylinder rod from moving. Push the push rod three or four times, it should get harder to push, indicating that the booster is working.

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thank you.

When I got mine back from Booster Dewey I tried to test with a hand vacuum pump used to bleed brakes. I use to check fuel pumps also. I could never get any vacuum and pumped till beat. I could not get my AC vacuum pump hooked up to is either. I called Dewey and he assured me he tested and would work. It did but still a mystery why I could get not vacuum.

I still have not located the parts can get 1970 back easy just not 71 -73.

I just recently rebuilt the 8" PBR booster in my 73 Mach1. Parts are still available and not that expensive. I'm not sure with the Bendix units but the 2 halves of the PBR boosters unscrew, no need to unpick the tabs. Not easy but with a jig in the vice and plenty of leverage, they come apart. I bought another one cheap in case I needed parts but both were in as new condition inside, no rust and the diaphrams looked as new although I did replace them. One had very little rust on the outside so cleaned up easily. The small seals/check valve seem to be the main cause of problems.

David

I just recently rebuilt the 8" PBR booster in my 73 Mach1. Parts are still available and not that expensive. I'm not sure with the Bendix units but the 2 halves of the PBR boosters unscrew, no need to unpick the tabs. Not easy but with a jig in the vice and plenty of leverage, they come apart. I bought another one cheap in case I needed parts but both were in as new condition inside, no rust and the diaphrams looked as new although I did replace them. One had very little rust on the outside so cleaned up easily. The small seals/check valve seem to be the main cause of problems.

David

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i see  your problem you put  it on the wrong side of the car  :whistling:

No, it's on the RIGHT side. ha ha