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Thread: Just Installed rebuilt Treadle Vac Low Pedal

  1. #1
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    Just Installed rebuilt Treadle Vac Low Pedal

    HI guys this afternoon I finally finished my brake system rebuild. I've replaced all the hardware, cut the drums, installed new shoes, brake hoses, wheel cylinders and got my Treadle Vac professionally rebuilt. They replaced the big disc, and the rod and piston as well as sleeving the master. I filled it with Dot 3 brake fluid from a fresh container. Then I gravity bled the system, followed by having someone bleed it with me using a pedal. The brakes are set so the shoes rub slightly when you spin the wheels. If you jack it up and spin the wheel it does roughly a rotation and a half before stopping. So I think they are set right. The small shoe is in the front on each wheel so they're not swapped. I adjusted the pedal so it's all the way up at rest, without pressing on the plunger. I've only drove it in my drive way but when I push the brake to the floor the pedal is about a half inch off the floor. Also they don't seem very grippy it still feels like I'm pushing the pedal pretty far to stop the car. Whats going on?
    Last edited by My55buick; 11-23-2017 at 08:58 AM.

  2. #2
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    Follow the details in the service manual for the rod adjustment from pedal linkage to master cylinder. Also worn joint in this linkage will translate in up to 1 inch of pedal free play.
    You may need to drive it (carefully) to break in the shoes. Sometimes the edges of the shoes will contact the drum on initial assembly and after worn will allow more adjustment.
    Sleeving the master cylinder does not make sense since the rod rides in seals to displace fluid, not seals in a bore that is sleeved (manual brakes).

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    The car sat from 1973 and when I got it in 2008 I readjusted the brakes and bled the system to get fresh fluid, it had a decent feeling brake pedal so I decided to try to drive it. The brakes were horrible and slammed would barely even stop the car. Then it sat for a couple years and the treadle vac seized completely. The re builder told me there was pitting in the bore, and the rod was rusted and pitted so he re-sleeved the bore to take away any pits, and replaced the rod.

    The pedal linkage seems very tight, my first thought was sloppy joints are causing the problem. But it seems like there is no slop anywhere.

    I took it for a ride around the parking lot next door to my house today, and at roughly 15 mph I couldn't even lock the brakes up. I slammed them and it felt like a normal gentle stop. The front shoes are natural linings could that be the problem? I was told semi metalics are a bad idea. I see the nose start to dip when I slam the brake but it never really gives me that hard grab, also the brakes don't feel like they're applying until the pedal is almost on the floor. The fluid level isnt any lower so I dont think its leaking anywhere, when I got in it this morning there was still assist so I know there isnt a vacuum leak or anything. If I pump the pedal until there is no assist left the pedal is fairly firm with minimal pedal travel. It feels a little easier to push than the manual drums in my 65 Mustang.

    The worst part is the car stopped the same before replacing everything....

  4. #4
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    I looked at the shap manual and I may have the pedal adjusted wrong... The part I dont understand is in step 4 it says compress the Pedal grommet 3/4 of an inch. What is a pedal grommet?
    Attached Images Attached Images

  5. #5
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    There is a grommet in the toe board that the pedal goes through, often missing, so adjust at 3/4 inch from toe board.
    Source or brand of shoes?
    Drums turned and shoes arced to fit?
    Similar discussion right now: http://forums.aaca.org/topic/302043-...brake-mystery/

  6. #6
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    Quote Originally Posted by My55buick View Post
    HI guys this afternoon I finally finished my brake system rebuild. I've replaced all the hardware, cut the drums, installed new shoes, brake hoses, wheel cylinders and got my Treadle Vac professionally rebuilt. They replaced the big disc, and the rod and piston as well as sleeving the master. I filled it with Dot 3 brake fluid from a fresh container. Then I gravity bled the system, followed by having someone bleed it with me using a pedal. The brakes are set so the shoes rub slightly when you spin the wheels. If you jack it up and spin the wheel it does roughly a rotation and a half before stopping. So I think they are set right. The small shoe is in the front on each wheel so they're not swapped. I adjusted the pedal so it's all the way up at rest, without pressing on the plunger. I've only drove it in my drive way but when I push the brake to the floor the pedal is about a half inch off the floor. Also they don't seem very grippy it still feels like I'm pushing the pedal pretty far to stop the car. Whats going on?

    When installing new brake shoes, I would take a different approachto adjusting them, as they can be not completely centered and even though youllhear a slight drag, they may not be adjusted correctly:
    Adjust to the point that the wheel completely locks up, way tootight. Then back off from here to the point you can spin the tire by hand, witha little resistance. the rear wheels will have more resistance because of thedifferential, so theyre a little more difficult to gauge. With new brake shoes,youll want to re-adjust them pretty quickly as they’ll bed in.

    A great upgrade to your factory brakes are 10 psi residualvalves, in your front and back brake lines. These are cheap and you willnotice an improvement in the brake pedal. These basically pump up the brakesfor you, but wont cause any drag.

    I struggled with my original rebuilt treadle vac system fora couple years. At best, I could expect it to have pressure at halfway to thefloor, and right on the floor for a quick stop, without any hope of locking upthe tires. A disc conversion actually made it worse. If you decide its time forfirewall mounted, modern power brakes just send me a message 😉

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