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Hello Guys, I was wondering if you can shed some light on an interesting issue i have with my GTO's manual drum brakes. Car sat for many years so the master cyl froze up and broke. I bought a replacement (re-manufacture) but found many issues along the way. I replaced all wheel cylinders, all new brake lines up front as well as the distro block. No the issue is the pedal is real hard and does not slow the car as i would hope. I know they are drum, but i would need to literally stand on the pedal to make the car stop. Any Ideas? I have bled the system so i don't think it has air in there. I am leaning towards the master cyl but i am confident as i just replaced it.

Thanks
 

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If you do a "Search" within the forums, you will find much about brakes and problems. Personally, I never buy the premium shoes as the material is too hard and will not stop so well. I always get the cheapest set as they are seemingly softer and stop better.

It could be you are too used to todays featherlite brake pedal feel and instant stopping. Drum brakes are harder to stop and do require more foot pressure. This is why many do a disc brake conversion as well as add the dual reservoir master cylinder for both better stopping and safety sake. Make sure you keep a safe distance and be ready to pull a downshift in emergency situations to help braking.

Other than that, it could be a number of things, so search our forums to get a few ideas. :)
 

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Drive it to a couple of rapid stops, then get out and either feel or shoot the temp of the brake drums with a pyrometer. If you have one or more cool drums, the brakes are not applying on that wheel. You could also get the car in the air, and have someone step on the brake and see if you can turn the wheels. To me, it sounds like you have either a port restriction in your master, or a line blockage. High, firm pedal and no stopping usually means a blockage somewhere, unless your shoes are glazed badly.
 

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Discussion Starter #5
Drive it to a couple of rapid stops, then get out and either feel or shoot the temp of the brake drums with a pyrometer. If you have one or more cool drums, the brakes are not applying on that wheel. You could also get the car in the air, and have someone step on the brake and see if you can turn the wheels. To me, it sounds like you have either a port restriction in your master, or a line blockage. High, firm pedal and no stopping usually means a blockage somewhere, unless your shoes are glazed badly.
thanks Geeteeohguy. It is a high hard pedal. the brakes did bleed as normal. i would not think there is a blockage.
 

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Primary and Secondary shoes in the correct position? Did my S-10 pick-up rear brakes about 2 months ago with the right side wanting to lock up on me when I applied brakes. Found the the Primary and Secondary were backwards which might have been part of the problem.

Could even be the "remanufactured" master cylinder. If you got it at the local parts store, they often sell generic stuff where one size fits all.........and doesn't. You might want to consider having your original rebuilt by a competent rebuilder to ensure the master is not your problem. We see "remanufactured" and even "new - Made in China" parts that are bad from day one only to replace it with another "new" bad piece.
 

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K sometimes return springs on the shoes and or a sticking binding wheel cylinder can cause the shoes not to properly return. they stay almost deployed and not much room to press down....I would relook at your spring hardware and wheel cylinders. Pat attention to any wheel that drum is hard to take off,.... as it may not be returning properly. If you have it stuck up it would feel hard, and not deploy against the drum properly.

also make sure you are getting all for wheels to deploy...if you are only getting the rear two...you have about 35% of braking power, and it will feel like it does not want to stop....so make all are working correctly
 

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Discussion Starter #8
Primary and Secondary shoes in the correct position? Did my S-10 pick-up rear brakes about 2 months ago with the right side wanting to lock up on me when I applied brakes. Found the the Primary and Secondary were backwards which might have been part of the problem.

Could even be the "remanufactured" master cylinder. If you got it at the local parts store, they often sell generic stuff where one size fits all.........and doesn't. You might want to consider having your original rebuilt by a competent rebuilder to ensure the master is not your problem. We see "remanufactured" and even "new - Made in China" parts that are bad from day one only to replace it with another "new" bad piece.
Early on when i was t/s this issue i did mix up the pads. I had the "bigger" pad in front. I double checked and corrected. I feel the same about the master cyl. I was desperate to get the car to stop somehow so made in China had to do. I did replace one before with no issues. I an gonna look at that

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Discussion Starter #9
they were brand new wheel cyl. Doesnt mean they are free from defects but i need to look over the whole system again
 

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Early on when i was t/s this issue i did mix up the pads. I had the "bigger" pad in front. I double checked and corrected. I feel the same about the master cyl. I was desperate to get the car to stop somehow so made in China had to do. I did replace one before with no issues. I an gonna look at that

Thanks
I have read on many blogs that master cylinder bore size has a big effect on pedal pressure. Was doing some research for my own car to get an idea of future system purchases. Many master cylinders will interchange and fit, but you want to ensure your bore size is for your system - same with the wheel cylinders. Double check that these dimensions match your application and some guy behind the parts counter did not give you the wrong parts. They usually can tell you the bore diameter from their catalog - I would think, at least they used to when they had paper catalogs they could reference from in the "good 'ole days". :thumbsup:
 

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From a Hotrod write-up: "In Pontiacs of the '60s and '70s generally, a 1-inch bore was used with four-wheel drum brakes and a 1.125-inch bore was used with disc/drum brakes. Most aftermarket brake companies can provide the required master cylinder to use or at least recommend one.

The larger the bore, the more fluid it will displace, but it will require more pedal pressure to create the same line pressure in the system as a smaller bore. If the bore is too large, the result will be a hard pedal with too-short travel."

Again, IF you don't find anything wrong with your rebuild & installation, I would be suspect of the master cylinder as my next item to double check - and I'm not saying it is bad or incorrect, but I would confirm it to be the correct one for your application.
 

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Remove the rubber brake hose over the rear end and check to see if it is clogged. Mine was. What was funny is that the rear brake cylinders would bleed OK, but the right rear brake would hang after driving a block or two. It would release after the car sat for a bit. Checked the hose and it was plugged to the max. I think applying pressure allowed the brake fluid move around the clog and apply the rear brakes. But, but when the pedal was released the fluid could not overcome the plug - thus the brake lock. The brakes worked great after replacing the stopped up hose.
 
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