Bad power brake booster?

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The Mechanic

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Hey guys, I have a question. While driving my 1967 Dodge Polara the brake pedal suddenly went rock hard and could barely stop the car. I am assuming this is the power brake booster failing. If this is correct can anyone tell me what year, make, model, boosters would be compatible with my car? I am currently using a single diaphragm booster but would upgrade to a double if I can find one. (good luck!) I am finding boosters to be very rare in scrap yards in my area so I am trying to make sure I have broadened the search as far as possible. The car has been fitted with a Scarebird front disc conversion using 1976 Chrysler Cordoba front calipers, and proportioning valve, with stock rear drums. Any help would be greatly appreciated!!
 
Check valve could also be problem. Should be able to suck air through it but not blow air through it, using the hose that leads to it. Generally has one-way action.

Brake booster lets in air pressure on firewall side of diaphragm but has vacuum on engine side to create assist. If the valve to create that difference in pressure is bad or the diaphragm is bad the pedal will feel hard.
 
Could be a number of things:

Booster gone bad
Collapsed flex hoses - unlikely though, as all would have to fail at the same time in such a way as to prevent fluid movement.
 
If the booster hisses when the brake pedal is applied, that is usually going to be a bad diaphragm as previously mentioned. The vacuum line coming from the manifold to the booster also sometimes has the inner lining collapse and that cuts off the vacuum to the booster. This line should be replaced if the booster is going to be rebuilt. Be sure to replace this hose with a vacuum rated hose as the hose construction is specific to vacuum applications. You mentioned that you installed an after market disc setup, did you use the booster supplied with the kit or did you retain the original Midland-Ross booster? You should be running a Bendix dual diaphragm booster with the disc brakes. A lot of the kit disc brake conversions supply a ChiCom booster that is not much good and is usually not rebuildable.

Dave
 
Thanks for the info guys! I will check the valve to be sure thats not it. I did not hear any type of hissing noise at all, and I kinda doubt the flex line have collapsed for #1 they are pretty new and #2 it just happened all of a sudden, one stop I had perfect brakes and the next stop I had to push like crazy just to come to a slow stop. I am planning on sending the unit to " Booster Dewey" but I have a car show in 2 weeks so I am trying to just get a cheap replacement from a yard to finish out the season. I am really looking for info on what other years, and models, will work to help me scour the scrap yards for anything that will help me get the car back on the road for a couple more months. Should I just look for full size cars? If so what years??
 
The Mechanic said:
Thanks for the info guys! I will check the valve to be sure thats not it. I did not hear any type of hissing noise at all, and I kinda doubt the flex line have collapsed for #1 they are pretty new and #2 it just happened all of a sudden, one stop I had perfect brakes and the next stop I had to push like crazy just to come to a slow stop. I am planning on sending the unit to " Booster Dewey" but I have a car show in 2 weeks so I am trying to just get a cheap replacement from a yard to finish out the season. I am really looking for info on what other years, and models, will work to help me scour the scrap yards for anything that will help me get the car back on the road for a couple more months. Should I just look for full size cars? If so what years??
Click to expand...
For c-bodies, Bendix dual diaphragm booster '68-'70 some '71 c-bodies also used this booster as did some '72 c-body police cruisers and wagons with the tow package. Failing to locate one of those, if you are running the Midland-Ross factory booster, you could probably replace it with another Midland unit to finish out the season. This booster is not as powerful as the Bendix unit but it will still stop the car, just not as quickly. Midland booster was used on '65-'69 c-bodies with drum brakes.

Dave
 
Thanks for the info Dave, So get this!!..... I moved the car out of the garage to do some work and when I pulled it back in the garage the brake pedal was completely normal! Nice and soft and the brakes worked just fine. What would cause them to work sometime but not all the time? I am going to change the vacuum hose today and see if that could be it but I will have a hard time trusting the brakes if they can just work one minute and not work the next! In the mean time I am going to look for a dual diaphragm booster.

Keith
 
The Mechanic said:
Thanks for the info Dave, So get this!!..... I moved the car out of the garage to do some work and when I pulled it back in the garage the brake pedal was completely normal! Nice and soft and the brakes worked just fine. What would cause them to work sometime but not all the time? I am going to change the vacuum hose today and see if that could be it but I will have a hard time trusting the brakes if they can just work one minute and not work the next! In the mean time I am going to look for a dual diaphragm booster.

Keith
Click to expand...
Usualy, if a booster has gone bad, it will not come back. Be sure that the hose on the unit is a vacuum rated hose, fuel line or transmission line will not work. The inner liner on a vacuum hose is supported so it can not collapse. www.yearone.com sells the correct hose.

Dave
 
The Mechanic said:
The car has been fitted with a Scarebird front disc conversion using 1976 Chrysler Cordoba front calipers, and proportioning valve
Click to expand...
I'd look into these item's before blaming the booster.

When the conversion was done, was the original booster and master cylinder used?

In my experience bad boosters usually have a soft sinking pedal. Hard pedal could be master cylinder or many other things, including possibly the booster.

Have any pictures?
 
Sorry, no pictures right now. When the Scarebird conversion was done I replaced everything else with new, complete hard lines, brake flex lines, proportioning valve, and master cylinder. I guess the only thing I didnt replace was the booster and vacuum hose. Thanks Dave for the tip on yearone having proper vacuum hose. The over the counter stores around here want to sell me fuel line. I will keep this post alive while I hunt down a correct vacuum hose. Thanks to all who chimed in! I appreciate all the wisdom this site offers on these old cars!!

Keith
 
The Mechanic said:
Sorry, no pictures right now. When the Scarebird conversion was done I replaced everything else with new, complete hard lines, brake flex lines, proportioning valve, and master cylinder. I guess the only thing I didnt replace was the booster and vacuum hose. Thanks Dave for the tip on yearone having proper vacuum hose. The over the counter stores around here want to sell me fuel line. I will keep this post alive while I hunt down a correct vacuum hose. Thanks to all who chimed in! I appreciate all the wisdom this site offers on these old cars!!

Keith
Click to expand...
Ok, I can understand why you're focusing on the booster. Best of luck in your search!
 
Thanks for the info big John. I will check that out on Amazon. You can’t beat it when it comes right to your front door. Lol.
 
Are there complete Midland-Ross rebuild kits for sale ?
 
I have a 1966 Fury a few years ago I did The Ram Mans factory disc brake conversion kit, it went really well and I have fantastic brakes. The Ram Man told me that I needed the tandem diagram booster that Mopar introduced in 1962. He also told me this was the booster used on all c bodies with factory disc brakes. He sent me the link to this youtube video to watch

Come to find out, that they are so busy there are many products that are not even listed or advertised. He has the 2nd generation model booster, which you see all over the internet for B and E bodies. This full size booster combo has been available since 2013, I was blown away. What he does is install the correct length rod for any C body or Imperial just like the original bendix booster. It bolted right up on my car just like it did for this guy.
 
Trace 300 Hurst said:
Do you hear a hissing sound when applying the brake? Ruptured diaphragm.

You're aware that you can send that booster to Home | Power Brake Booster Exchange, Inc. ? Many of us here and with any other car in the world have used "Booster Dewey and Booster Steve".
Click to expand...
Many videos on this
10,000 plus MOPAR boosters rebuilt since 71
Almost never the diaphragm……talk to any legit builder
Not me.
90% of all booster failures control valve in rear hub…. Rebuilder lingo….poppit valve
Dozens of videos on this.
Still needs a send off…does not change
 
TheRamManINC said:
Many videos on this
10,000 plus MOPAR boosters rebuilt since 71
Almost never the diaphragm……talk to any legit builder
Not me.
90% of all booster failures control valve in rear hub…. Rebuilder lingo….poppit valve
Dozens of videos on this.
Still needs a send off…does not change
Click to expand...

What?
 
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