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59 American single-chamber brakes |
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Dave59
AMC Fan Joined: Apr/21/2021 Location: Harrisburg, PA Status: Offline Points: 16 |
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Posted: Jun/26/2021 at 9:10am |
Hey, folks--appreciate any guidance... I'm at my wit's end; was experiencing 'soft' brake pedal in my '59 Rambler American, so I did what I always do: rebuild master cylinder & bleed brakes. For some reason I just cannot retain a full pedal! I've rebuilt & installed two different master cylinders (& bench-bled), and bled each brake line innumerable times. STILL my pedal goes nearly to the floor. It will pump up after a couple pumps, but won't stay that way, once released. (But once 'pumped up' with pressure on it, it won't slowly descend.) There are no leaks, anywhere, system is full, and I'm using silicon fluid. Any ideas? (I can't believe that what was so straightforward when I was 18 is mystifying me when I'm 63!!!!)
NOTHING seems out of place, and everything appears to be in good condition. I keep coming back to something weird with the master cylinder, but...what? Thanks for anything! Out of ideas and losing my mind in Pennsylvania, Dave
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pit crew
Supporter of TheAMCForum Joined: Jul/08/2007 Location: delete Status: Offline Points: 5341 |
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Just a quick check. Have someone push the brakes while you inspect the soft lines. You may have a brake line that is ballooning out.
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73 Hornet - 401EFI - THM400 - Twin Grip 20 |
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Dave59
AMC Fan Joined: Apr/21/2021 Location: Harrisburg, PA Status: Offline Points: 16 |
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Excellent idea!!! Thanks--makes sense; I'll check it out.
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Trader
AMC Addicted Joined: May/15/2018 Location: Ontario Status: Offline Points: 6755 |
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Assuming "nothing is out of place and everything appears in good condition" also means you have inspected the brakes at the drums and there are no broken springs or something like an adjuster piece loose.
An adjuster falling out from a broken spring will also be a very soft pedal and no leaks as long as the pistons stay in the cylinders.
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bobsterfl
AMC Nut Joined: Jun/18/2009 Location: Orlando, Fl Status: Offline Points: 260 |
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Just my opinion, but I'm not sure about using silicone fluid. It doesn't mix with any DOT 3 that might still be in the system. Silicone fluid is usually used for extreme high temp brake applications like race cars that use a lot of brake on the track. If nothing else works, try flushing the system with DOT 3. Most shops will have a pressure bleeder that attaches to the master cylinder and uses pressure to flush the system. I have that done on all my road cars every couple of years. BTW, IIRC silicone fluid is hydroscopic, meaning it will absorb moisture. Another reason not to use it on a road car. Just my 2 cents worth.
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Bobsterfl
1970 BBO Javelin 390 - Torqueflight |
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Trader
AMC Addicted Joined: May/15/2018 Location: Ontario Status: Offline Points: 6755 |
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Dot 5 silicone is hydrophobic and does not absorb moisture.
Dot 3, 4 and 5.1 are hydroscopic and absorb moisture. They are glycol based. Dot 5 cannot be mixed with other fluids and should not be flushed out with a glycol based fluid. If you want to change from Dot 5 to any other fluid, you should disassemble everything, clean all parts, replace the elastomers that contact the brake fluid.
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Dave59
AMC Fan Joined: Apr/21/2021 Location: Harrisburg, PA Status: Offline Points: 16 |
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Thanks, gentlemen. Regarding the silicon, I've had it in this car for 20 years. Not because I imagined my 196cu.in. flathead needed the racing edge (haha), but simply because I wanted to avoid the way standard brake fluids corrode paint. I actually replaced all brake lines/master cylinder & rebuilt wheel cylinders at the time, so I'm pretty sure there's no mixing of fluid types.
BTW, I've noticed that silicon DOT 5 is now both very expensive and much harder to find (I went to 3 autoparts stores, this time, just to find some). So...while I still like the fact that it's gentle on paint, I might think twice about using DOT 5, now. I'll check everything again--and especially those soft lines. |
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billd
Moderator Group Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
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It only bothers paint if you let it get on paint ;-)
I have used standard brake fluid in my SX4 for since I got it. I find that Eastwood's clear sprayed on certain undercarriage parts delays the action of any brake fluid (used that one my 70's differential axle tubes and bleeding brakes saw fluid on the axle tubes - and I wiped it off with no impact to the clear) I powder coated the master cylinder and lid and watch really close for any leaks. If I even think fluid has touched anything, that area gets a bath - still, no problems. I just don't like having to take such care, I hate the thought of having to carry brake fluid with me at all times as I just KNOW many places won't have it, or may just top if off with regular fluid and it's expensive. Anyway, sounds to me like you may be pumping and working the brake shoes out to the drums - and then when you let up the springs retract the shoes and force the fluid back into the master cylinder until next time when you have to pump a volume of fluid out to move the shoes. In short, sounds like an adjustment thing - something tricking you into thinking it's adjusted. I get Ken's rubber line thing - but that leads to a soft pedal, not a solid pedal once pumped up. It would feel sort of like air in the line and the more you pumped, the more you'd balloon it out until POP! Your symptoms sound like it's very solid once it's there, it just doesn't stay there after you move on and need them the next time. That to me says it's taking a lot of fluid volume to move things out then suddenly when the hydraulics are full, the shoes against the drum, you have a tight pedal. |
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Dave59
AMC Fan Joined: Apr/21/2021 Location: Harrisburg, PA Status: Offline Points: 16 |
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I really appreciate it, guys. It's going back up on jacks, and I'll go through the entire system, taking off the wheels. Yes, something is taking up fluid volume and then...stops. I'll be sure to note whatever I find, but will welcome any further good ideas.
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First_Gear
AMC Addicted Joined: Jan/18/2010 Location: Mukilteo WA Status: Offline Points: 644 |
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It sounds to me like its R adjuster in the L wheel or a faulty adjuster. Come to think of it did they use automatic adjusters by 59?
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