| 2manybikes | -- 12-17-2021 @ 2:52 PM |
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The brake pedel comes up to the top from about the halfway point as I drive the car eventually turning the brake lights on. It did this before adding the Boling Brothers drum brake conversation as well. After it sits about 40 minutes the pedel drops and the brake lights go off. It will do this in less than 15 miles. Checked the tire rotation this morning and there was no unusual drag from the shoes but I loosened them up anyway. 15 miles or so and the same thing. I have a gravel drive with a downhill slope off the main road so I turned in going a little faster than I normally would and pushed in the clutch, none of the wheels locked up in the gravel. I hit the brakes hard and started skidding, the brakes were definately not locked up. At the house I checked for unusual heat on the rims, nada. No hot brake odor or smoke. I'm out of ideas other than replacing the master cylinder but I don't like throwing parts at a problem before I know what it is. I'll open this up to the experts! Thanks.
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| alanwoodieman | -- 12-17-2021 @ 3:38 PM |
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pedal return spring OK, and brake rod clearance is good?
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| 2manybikes | -- 12-17-2021 @ 3:46 PM |
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Both re OK. This message was edited by 2manybikes on 12-17-21 @ 3:48 PM
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| TomO | -- 12-19-2021 @ 10:09 AM |
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It sounds like you do not have the correct pedal free play. Without the 1/4" - 3/8" pedal free play, measured at the pedal, the piston will not return enough to uncover the fluid return port in the master cylinder. I like to adjust it by listening for the push rod to hit the piston and then check the pedal movement. Tom
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| 2manybikes | -- 12-19-2021 @ 1:05 PM |
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Thanks for your reply and suggestions. I'll back it off a little more and see what happens.
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| 2manybikes | -- 12-26-2021 @ 6:53 PM |
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I'll admit to not being much of a mechanic, so I'm going to ask. Is there any adjustment to the brake pedal other where the rod enters the master cylinder? If thats it, does moving the nut and lock nut away from the master cylinder put more "play" in the travel? Still trying to figure out if the adjustment is too tight or if the master cylinder is the reason for my initial post. I backed it off about 1/8" yesterday and I'm still having the same problem. I can back it off more, but want to make sure I'm going in the right direction.
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| kubes40 | -- 12-27-2021 @ 8:08 AM |
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TomO is spot o with his advice. Your issue with the brake lights comes from the rod at the master cylinder being too long in adjustment. There is a fine line between "correct" and too long / too short. Creep up on the adjustment. Low pedal? Brake shoe adjustment... figure about .005" clearance at BOTH the top and bottom of each shoe. Arcing shoes is paramount to a properly operating brake system. Mike "Kube" Kubarth
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| TomO | -- 12-27-2021 @ 8:36 AM |
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You need to shorten the distance between the brake pedal and the master cylinder, so you would turn the push rod in the direction that would make the rod shorter, the nut would go away from the master cylinder. Here are 2 pages from the training manual showing what you are trying to accomplish and how to do it. When I am under the car, I reach up and try to pull the pedal down slowly. If there is any clearance, you can hear the click as the pushrod hits the piston. If you don't hear the click, shorten the rod about 5 turns and then listen for the click. If you can't hear it try to feel the movement before the rod hits the piston. You are looking for 1/4" - 1/2" movement at the top of the pedal before the rod touches the piston. I hope that I have cleared up your questions, if not I will try again. Tom This message was edited by TomO on 12-27-21 @ 8:48 AM
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| 2manybikes | -- 12-27-2021 @ 9:04 AM |
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kubes40 and TomO, thanks for the additional info and clarification. TomO, Thanks for the service manual pics, that helps too. I need to get some general repair info. The weather is supposed to be really nice tomorrow so its back under the car!
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| 40 Coupe | -- 12-28-2021 @ 5:36 AM |
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The brake pedal return spring must be missing or broken. With the proper spring in place the brake pedal should always return all the way and should not move by itself. This message was edited by 40 Coupe on 12-28-21 @ 5:52 AM
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| 2manybikes | -- 12-28-2021 @ 6:54 PM |
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40 Coupe, Thank you for replying. Since my initial post, I have learned quite a bit more than I did when I started. A better description of my issues is losing my "free play" and travel to a fully depressed pedal. My return spring is present and accounted for. I sat in the car and pushed the brake pedal down 100 times, stopping every 25 and checking to see if the brake lights came on. They did not. I think that cancels out the theory of a plugged hole in the bore. I even put some unnecessary slack in the emergency brake cable, and adjusted the rod at the master cylinder out another 3/16" or so. Still did the same thing in about 5 miles. I moved it another 3/16" or so but was unable to try that before dark. A couple days of rain in the forecast so I will report back when I can. Is it possible to overfill the master cylinder leaving no room for expansion if the fluid heats up? Once the car sits for an hour or so the "pressure" in the system drops, the lights go off and the pedal returns to a "normal" state.
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| TomO | -- 12-28-2021 @ 8:05 PM |
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Do you have the correct free play of the brake pedal? Until you have it, we cannot give you further advice. Tom
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| 40 Coupe | -- 12-29-2021 @ 5:12 AM |
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Here is some reading for you. Note how the pressurized brake fluid returns to the master cylinder fluid reservoir and how the piston can block the very small return hole if the brake pedal adjustment is not correct or the return spring is improper.. While driving heat can build up in the brake system expanding the brake fluid. There is a check valve at the fluid output end of the master cylinder it allows a residual very small pressure to stay in the brake lines. Any pressure in the brake lines in excess of the slight residual has to bleed back to the MC reservoir or the brakes can start to bind up and the brake lights will stay "ON".
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| 2manybikes | -- 03-07-2022 @ 4:30 PM |
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The weather has been nasty for so long its hard to remember being outside. I got the car out finally a couple days ago. I think my brake adjustment rod is close to where its supposed to be finally. This may be a hard question to answer but can anyone explain to me, or have a photo of the left side exhaust manifold pipe routing in relation to the master cylinder? I'm having issues with transferring photos from my phone to the computer or I would post what mine looks like. Basically mine runs under the frame below where the master cylinder mounts.
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| TomO | -- 03-08-2022 @ 8:46 AM |
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I like to route the pipe through the frame and along side the left side frame rail. The best size pipe for the left side to do this, is a 1 1/2" pipe. A 1 3/4" pipe is the largest that will work on the left side. I have photos of my Mercury's left side pipe but they won't do you much good as the frame on the Mercury is different from the Ford in 1939 and 1940. As long as you have at least 1/2" clearance between the exhaust pipe and the master cylinder, the exhaust heat will not affect the brake fluid temperature. The brake fluid will heat up and expand with brake usage and the correct free play is critical. I am hard of hearing and I can still hear the pushrod contacting the master cylinder piston when I adjust the freeplay. Tom
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| 2manybikes | -- 03-11-2022 @ 4:13 PM |
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TomO: Thanks for another reply to my numerous questions. I hope to get back on the car next week.
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