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Drum Brakes Again

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Alan W.

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I know four-wheel drum brake issues have been beaten to death on the forum, but my wife is ready to commit me to the psych ward. Trust me, I have read every brake thread in the forum and have tried all of the suggestions: new MC isolated, system pressurized-no leaks, power bleeding, two person bleeding, wheel cylinders compressed, every pipe and hose connection opened and bled, steady pins adjusted etc, etc, etc.

Pedal is extremely low, almost to the floor. It is firm, but not real hard. Pumping the pedal does cause a slight rise in height.

What other possible mechanical issues could be causing that much fluid movement? Appreciate any additional suggestions.

1959 BN6 - MC bore .750 -1” wheel cylinders.

Alan
 
Sound like you have checked everything well. To me, firm but low pedal suggests shoe adjustment rather than air in the system - air compresses but fluid doesn't so results in spongy pedal. Since you say the pedal is firm, I equate that to mean no air compressing (firm vs hard is pretty subjective).
I would re-check shoe adjustment - tighten until wheel rotation stops and then back off just enough to turn the wheel with only a very slight drag (another subjective term :smile:).
Were the drums turned (or worn) oversize? If so, were the shoes arced to the match the drums? If the shoes and other parts are new, it is normal to require a bit of bedding in but if the shoes are not arced to match the drums it's much worse - you can have contact with the drum in the center but not the rest of the way and the pedal ends up low because you are flexing the shoes a bit as you apply the brakes.
Dave
 
Dave, thx for your response. I had the shoe adjusters tightened all the way to compress the wheel cylinders while bleeding and then backed off to a slight drag. I did check the front left shoes to the drum and there was no rocking, appears they were arced. I'll check the other wheels to see if one may be out. The pedal was low when I purchased the car which had a previous total restoration-something wasn't installed correctly.
Alan
 
I believe this is correct, but looking for any possibilities. Is this the correct orientation for the front cross pipe and bleeder screw?
1959 bn6
Alan
 

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I am sure the Nipple should be on the top, otherwise you may have a problem getting all the air out,
 
I have a friend who reverse bleeds them, i.e. uses a large syringe to inject brake fluid from the port shown, and then pushes it up to the master cylinder. He states it's not difficult, and avoids the chance of air in the system.
 
Let’s start with the pedal and linkage assembly. First, is there any free play in the pedal before it engages the MC? Grab the pedal with your hand. Can you raise it from its resting spot? If so, by how much? Check to see if this free play is excessive. When you start to press on the brake pedal, is the brake actuator rod moving into the cylinder immediately? If not, how far do you press before the rod starts moving? Again check to see if this play is excessive. When you depress the brake pedal all the way, how far has the actuator rod traveled into the cylinder? You may not be getting full sweep of the bore if any of the pedal and linkage assembly is worn, misassembled, or even the wrong part (like too short an actuator rod). Second, is the MC piston and seal assembly returning all the way to the circlip of the MC bore? I have seen cases where the piston gets hung up and does not return. Lastly, did you bleed the MC first?
 
I would be curious to know if there is excessive pedal travel with the shoes adjusted tight against the drums?
 
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All I can add is I chased my BN2 brakes for weeks and ultimately I followed Michael Salters Blog exactly with multiple Bleeds. And I was able to get them back. The pedal is not hard, but firm and I can lock the wheels at 35 mph.
Michael’s Austin Healey Blog or
Precision sports car.com/blog/
 
I just may of found the culprit. With all three hoses clamped, the right front when released showed pedal loss. I pulled the drum and started to inspect everything again. I lifted the boot on the rear right front, wheel cylinder (boot facing up) and it was full of brake fluid. None of the fluid had leaked out of the boot under pedal pressure, which is curious, and so was never noticed. I'll repair and report back.
Thanks for all your suggestions, hopefully this was the problem.
Alan
 
Alan, that is very curious. I can speculate on why the fluid didn't blow past the boot, but a boot that holds hydraulic pressure better than the piston seals just doesn't make sense to me.
 
It may be improbable but maybe possible. I need to replace and then see what the results are.
May be hanging from a rope of sand here, but the seal could expand after letting a very small amount of fluid out and retract bringing air into the system??????????
 
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Alan W. said:
I know four-wheel drum brake issues have been beaten to death on the forum, but my wife is ready to commit me to the psych ward. Trust me, I have read every brake thread in the forum and have tried all of the suggestions: new MC isolated, system pressurized-no leaks, power bleeding, two person bleeding, wheel cylinders compressed, every pipe and hose connection opened and bled, steady pins adjusted etc, etc, etc.

Pedal is extremely low, almost to the floor. It is firm, but not real hard. Pumping the pedal does cause a slight rise in height.

What other possible mechanical issues could be causing that much fluid movement? Appreciate any additional suggestions.

1959 BN6 - MC bore .750 -1” wheel cylinders.

Alan
Click to expand...
 
Alan, see my post Big trouble with BN4 brakes dated nov 23, 2013. Read the entire thread and see if any of it helps. My breakers remain firm to this day, and clear fluid. Good luck!
Larry
 
That’s brakes, not breakers🤣
 
On my 61 BT7 the bleeders on the rear, are on the high side, as per the manual. Even if it isn't on your car, this would help to bleed.
 
I had a similar problem with my BN2. Someone on an email list suggested pushing the pedal until hard stop, propping it in place and let sit overnight. The next day I had decent pedal; can't explained why it worked but it did.
 
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