Brake lights driving me nuts

[philbird60]

Sometimes, the brake lights stay on. If you put your foot under the pedal you can turn it off.
I changed the master cylinder, and the stoplight switch. I'm glad I replaced the master, but that didn't solve it completely.

I may adjust the rod between the booster and the master, but I have noticed that this problem seems worse when the car is hot. In fact, the last time they stuck, I unscrewed the filler cap and they went off. So is this common? Is the brake fluid expanding.
Is the filler cap vented, and could that vent be blocked?
I defer to your vast experience, and than you for your help in advance.

[DKheld]

Sounds mostly like there is still air in the system. It's a real pain to bleed these systems. The air is trying to come up to the highest point (the master cyl) and you're trying to push it to the wheel cyls which are lower. May sound stupid but probably needs bleeding about 6 more times each wheel.

I have seen failed flex hoses cause this. They fail closed and act almost like a 1 way valve. You can push fluid through them because the master cyl produces about 1000 lbs of pressure - the return is left to some springs on the shoes which can't overcome the failure of the flex hoses so your pedal stays on the floor.

Is the booster under the dash? There is some kind of funky pressure valve on those where the master cyl rod has to be adjusted just right - can't remember what it is called at the moment.

Did the previous owner use silicone fluid and you are using DOT3/4 or vice versa?

Just some initial thoughts.
Hope they help,
Eric

[philbird60]

Thanks for the ideas. I should have been more thorough.. the booster is outside. It's the original, but at this point, it's one of 4 parts part of the brake system older than 8 months. The others being the distribution blocks.
New steel lines, wheel cylinders, drums, shoes , hardware..
the car stops wonderfully, booster seems to be boosting.
I will endeavor to bleed some more, but I'm feeling like that might not do the trick.

[simplyconnected]

There are TWO adjustments. Both are equally important. You already know about the brake pedal rod, and how it needs a slight 'jiggle' adjustment.

But, what about your booster to master adjustment???

If you take the master cylinder loose and let it hang, there is a small rod inside the booster. Have someone push the brake pedal down to see it stick out of the booster.

It sounds like the new master has a different depth than the old one. It also sounds like that small rod needs to be retracted just a little bit. It isn't letting go of your M/C plunger.

Try both of those adjustments, starting with the booster rod and finally with your pedal rod. - Dave

[philbird60]

I think maybe I wasn't thorough enough in my first post.
Yes, I'm aware of the adjustable rod between the booster and master. The brake lights were hanging up worse with the original master cylinder.
I have confirmed that the problem only comes when the car is hot, or the ambient temperature is (and it has been lately).
The brakes feel great, and if I have to slacken the adjustable rod (which is by no means small on this car) then I will. However, I am reluctant to add play to what feels really perfect.

[DKheld]

If you have the shop manual there are some adjustment tips in section 10-12. I couldn't copy the pics from the Adobe format to the forum .
I measured my master to booster rod but apparently wrote the length down in my manual rather than storing it on my laptop - not sure it would be the same since mine was used with a disc/drum master cyl. Think it was 3 1/8 inches but I'll double check.

Hope you can find the trouble....
Eric

SLOW BRAKE PEDAL RETURN OR FAIL TO RELEASE

This condition may result from a clogged air cleaner or improper master cylinder push rod adjustment. Internal causes may be a restricted air passage, Sticky valve plunger, broken return spring, or the atmosphere poppet valve stuck in a closed position. The air passages should be checked for restrict ions and blown out.
The valve plunger may be touched up lightly with crocus cloth. DO NOT OIL. Replace if necessary.
If the return spring is broken, weak, or distorted it should be replaced. The power piston must be dissembled to locale and correct the cause of a sticking poppet valve. If the poppet valve appears faulty it should be replaced.

[simplyconnected]

Now that all your parts are new, let's let the Brake Light Switch tell the story.

It only comes on when pressure is present in the brake lines.

When the master cylinder is retracted the brake line ports are open to the reservoir (which allows the brake shoes (and pads) to retract).

Old OEM master cylinders had a hole in the cap which made them 'open to atmosphere'. New masters use a rubber bellows-type bladder to cover the top but above that it is open to atmosphere. In both cases, the fluid level easily moves in the reservoir.

If the cap isn't vented, fluid cannot back up into the reservoir.
If the master spool is partially engaged, fluid cannot back up into the reservoir.

Brake fluid naturally expands and contracts with temperature changes. If the lines are closed, pressure builds with added heat, your Brake Lights will come on and your brakes will apply themselves. That is why it's important to keep the line pressure equal to atmospheric pressure. Air in the lines will not close the system but it will produce a spongy pedal.

Bottom line... find what is closing off your master cylinder. - Dave

[philbird60]

Great suggestions guys! The master cylinder is a wagner, which came with shipping plugs, so I re-used the original cap. It's clearly vented, given it's shape and design, but it's entirely possible the top surface has a clog. If it's got a hole, it's pretty hard to spot. I'm going to just get Mac's to send over a new one. I should put them on the payroll....

[simplyconnected]

...I changed the master cylinder, and the stoplight switch. I'm glad I replaced the master, but that didn't solve it completely.

...I unscrewed the filler cap and they went off...

...I re-used the original cap. It's clearly vented, given it's shape and design, but it's entirely possible the top surface has a clog...

Alright, now we're getting somewhere. By your first post, I assumed you got a new cap with the new master. In fact, I had no idea you bought an OEM-style master. Most folks upgrade to a more modern dual master for safety reasons.

There is no reason to buy another cap. Carefully look around the hex for a vent hole and clear it out. You can use a small drill bit.

These brake systems are not friendly to DOT3 brake fluid. Venting to atmosphere only introduces water into your fluid. BE SURE you change your brake fluid every two years. All brake fluid is clear when new. That reddish-brown stuff you see in your master after awhile is from internal steel brake line RUST. That indicates the fluid is long passed it's anti-rust/water saturation stage and your lines are rusting. That is why new cars have a bladder/bellows-type seal and they are NOT vented to atmosphere. I have buddies that refuse to check the master level on a rainy day. That's how much DOT3 sucks up moisture. - Dave

[jopizz]

I've bought many master cylinders over the years and I've never seen one that didn't come with a new cap. Although the new ones are plastic I prefer them over using the old rusted original one.

John

[philbird60]

now I'm wishing I had gone to a dual chamber master. Is there a swap part from a later year, or is it a custom part? the cap that was on the new Wagner was definitely not intended to be used. my old one isn't the least bit rusty though. I'll try cleaning it and report back.

[jopizz]

Unfortunately there isn't a four bolt dual master cylinder made that will fit the stock booster. A two bolt drum/drum dual master cylinder from a late 60's Ford will technically bolt up to the booster but I don't know what kind of problems you might run into only using two bolts. Your stock booster can be modified to use a two bolt master cylinder by Dewey's Booster Exchange.

http://boosterdeweyexchange.com

John

[DKheld]

I rebuilt my entire drum system and ran that for a year before switching to discs - just keep at it and you'll find the trouble.

The modified boosters do work great. Booster Dewy is "the man" when it comes to booster work. He rebuilt and modified mine 10+ years ago and it is still going strong.

And ....this will also make it easier to change to a disc/drum master when the time comes......although the newer dual action boosters are probably a better choice for the disc conversion if originality doesn't matter.

Eric






Hummm - could you put a plug (bolt with Teflon) in the end of the master cyl then press the pedal - if the pedal goes to or stays on the floor then the problem is still in the booster or master. I would think that the pedal should not move very much at all with the plug. Get that right then hook the lines back up and troubleshoot on down the line.
Dave? Would that work?

[philbird60]

Wow, look at that.. You know, that's definitely in my future. I have pillaged a disc brake setup from an early 70's cyclone, the knuckles look like they should work, height wise. I wasn't yet ready to tackle that, so I just changed all the original brake parts 1 for 1. I'll try adjusting the intermediate pushrod in a couple of days, and I do think that'll do it. even 1/16" might alleviete this. I'll also vet that cap to make sure it's venting to atmosphere.
I should mention that the car is stopping confidently and straight. Pedal isn't spongy and the booster is doing its job well. It's just this last piece of the puzzle, and with your help, I'm certain I'm close to getting it right. Thanks to all!

[simplyconnected]

There are several choices in doing brake systems based on your fundamental belief in the definition of 'classic car'. If you are a purist, simply buy oem parts and maintain your brake system, but do not expect to share our highways with modern cars with great brake systems. Back in '60, all cars had drum brakes so drivers maintained safe stopping distances. Today's drivers have no clue about heavy classic cars or drum brakes. They only think of themselves and the law says, 'you must maintain complete control of your vehicle'.

My albatross is this little voice that perpetually rings in my ear. It's Mom saying, "S a v e - y o u r - m o n e y." (I was tempted to include that in her epitaph.) So, rather than doing the brake system many times and different ways, my philosophy is to do it ONCE but do it RIGHT. That produces the cheapest and most efficient way to a solid system.

I have two old Fords, one uses the Granada setup and the other uses the Scarebird setup. They both have two-stage boosters with dual master cylinders and they both work equally well. The difference is, I purchased the Granada setup from a Florida bone yard for $150 (complete). I did have the rotor snouts turned down for $15, so stock 1955 15" wheels would fit ('55 Fairlane stock wheels were 16").

Adding a power brake system requires a good knowledge of hydraulic fundamentals, mechanical aptitude, fabrication and setup skills. If you're that kind of person, adding power disk brakes to your classic car is VERY rewarding. If not, pay a good mechanic to do it for you. Either way, all cars on today's roads need power disk brakes. - Dave