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Brake whoas and conundrums

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StpaulF100

Brake whoas and conundrums

I knew I need to replace my master cylinder as it would fade at a stop. So like most people I’ve had all the parts in my cart at rock auto for a solid week. Today I noticed my rear brake lights were stuck on when the truck was off and the headlights were turned off. In my past this had led me to believe I have a failed master cylinder. So I picked one up today from Napa, bench bled it and slapped it on. While waiting for my bleeding partner and finishing cooking dinner the brake light are still on! So yes I need to bleed the brakes and check for leaks but do o Have a bad headlight switch or brake booster as well as a failed master? Just putting this in writing to try and track my next steps. Any help or ideas are encouraged.

Thanks.

1980 f100 custom 4.9l c6 2.75 rear gears.

Gary Lewis

Re: Brake whoas and conundrums

Administrator

The brake lights aren't connected to the hydraulic part of the braking system. Instead they are controlled by a switch on the brake linkage up under the dash. It is base part number 13480 in the drawing below, and it seems that you either have a bad switch or something wrong with the linkage.

I'd play with the linkage to ensure that there's not pressure on the switch all the time. And maybe take the switch off and check it out. BUT, it goes on in an odd way so take a pic of how it is on - assuming it hasn't been taken off and put back on incorrectly.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

rcarlisle

Re: Brake whoas and conundrums

In reply to this post by StpaulF100

I went out one evening to get a photo of the brake light switch mounting for a fellow forum member. Couple hours later, my daughter came in and said my brake lights were on. I had moved the switch some for a better photo and it stuck on. I repositioned it and lights went off. All that to say to check the psition of the switch. Or the switch is failing, but when mine failed, it just had random brake lights. Has nothing to do with how the master cylinder works.

Randy

Mt. Airy, NC 81 F-150 STYLESIDE regular cab 2wd. 302 Auto Zone crate. 5 spd M5od-R2

StpaulF100

Re: Brake whoas and conundrums

In reply to this post by StpaulF100

Gary and Randy- Thankyou for your replies. Indeed it seems I have several problems. The switch is bad or out of position. As you both say if you manipulate it just right the lights go out. I took it out and cleaned up the contacts and put it back. It seems to function better. I will probably order one regardless. Into the brake troubles. I replaced the master cylinder as I’ve had a soft pedal for some time. The old one had the piston stuck in the bore telling me for sure it’s bad. I was able to bleed the front brakes, but the rear bleeders are froze. I sprayed pb blaster and I’ll give it one more shot before getting new wheel cylinders. My only question now is? Is the brake booster also bad? Causing the master cylinder to go out and causing the brake light switch to be out of sorts. I know the only way to tell is to get the brakes bled completely. I’ll update when I can. Please keep up the tips info and generally awesome ideas.

Thanks
Mike

1980 f100 custom 4.9l c6 2.75 rear gears.

Gary Lewis

Re: Brake whoas and conundrums

Administrator

Usually a leaky master cylinder kills the booster. That's because the leak frequently is into the booster causing all sorts of corrosion. So I wouldn't replace a master w/o at least checking the booster to see if it is wet inside, and more likely replacing it.

And it is possible that a bad booster would keep the pedal from returning fully, and that might trigger the switch and keep the lights on.

So I'd check that booster out very closely as I fear it may be bad.

Gary, AKA "Gary fellow": Profile

ArdWrknTrk

Re: Brake whoas and conundrums

Administrator

Having the booster not return won't disable the brake light switch.
It works solely on pedal pressure, and the contacts have to close before you will get any forward movement of the booster pushrod.

Signs of a failed booster are a hard pedal and hissing coming from under the dash where the pushrod passes into the booster.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Gary Lewis

Re: Brake whoas and conundrums

Administrator

Good point about the switch, Bill. And, with that, I don't know why it seems there are two problems at the same time.

Gary, AKA "Gary fellow": Profile

ArdWrknTrk

Re: Brake whoas and conundrums

Administrator

Well, I understand why a bad seal will cause a master cylinder to fade to the floor.
But if it is an internal leak (and not wet on the back when changed) then there's not a problem with brake fluid killing the diaphragm.

Brake switches eventually wear out.
I changed mine in the parking spot when I picked one up at Advance a few years back.
Didn't seem expensive (around $10 IIRC)

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

StpaulF100

Re: Brake whoas and conundrums

In reply to this post by StpaulF100

Made some progress. Life happened and had to wait for parts. Masters back in. Rebuilt boosters. And a new stop light switch. Need to put the new rear wheel cylinders in yet so I can bleed the system. One interesting update. Per Gary’s schematic it appears someone or the dealer updated my brakes from Manual to power. My pedal is the one in the manual photo. I’m assuming that may be part of my problems. As well some previous owner lost part#2474 which appears to be a bushing that may take some slop out of the pedal. Thanks for the help and wish me luck in the wheel cylinders. Everything seems to be stubborn with rust.

Mike.

1980 f100 custom 4.9l c6 2.75 rear gears.

Gary Lewis

Re: Brake whoas and conundrums

Administrator

Good luck, Mike! At least you know what needs to be done. And what parts are needed.

Gary, AKA "Gary fellow": Profile

FuzzFace2

Re: Brake whoas and conundrums

In reply to this post by StpaulF100

StpaulF100 wrote

Made some progress. Life happened and had to wait for parts. Masters back in. Rebuilt boosters. And a new stop light switch. Need to put the new rear wheel cylinders in yet so I can bleed the system. One interesting update. Per Gary’s schematic it appears someone or the dealer updated my brakes from Manual to power. My pedal is the one in the manual photo. I’m assuming that may be part of my problems. As well some previous owner lost part#2474 which appears to be a bushing that may take some slop out of the pedal. Thanks for the help and wish me luck in the wheel cylinders. Everything seems to be stubborn with rust.

Mike.

Just getting up to date on posts and seen this.
The difference between manual & power peddles is where the pin for the master is located on the peddle arm.
I dont remember what one is what with out measuring what is in my truck that is power.
Guess I could pull the non-power one out of the parts bin to measure

I also want to say the non-power master rod comes straight out so it would be the higher pin and the power the lower pin but again would need to measure to be sure.

As for the bushing I would guess that would be the same for either system and you might be able to find one at the local hardware store that would work if cant find at junk yard.
Dave ----

Dave G.
81 F100 flare side 300 six / AA OD / NP435 / 2.75 gear
http://cars.grantskingdom1.com/index.php/1980-Ford-F100?page=1
81 F100 style side 300 six/SROD parts truck -RIP
http://cars.grantskingdom1.com/index.php/1981-Ford-F100

StpaulF100

Re: Brake whoas and conundrums

In reply to this post by StpaulF100

Brakes work! At least 70% of them. Brake lights are fixed. And now to figure out how far forward I need to go to get brake fluid to the rear!!! I’m assuming the rubber lines are bad. I hate just throwing parts at it, but I suppose its what you have to do some times. Thanks for all the help. So off to order some brake hoses and some nickel copper brake line.

Mike

1980 f100 custom 4.9l c6 2.75 rear gears.

Gary Lewis

Re: Brake whoas and conundrums

Administrator

Yes, some times you just have to bite the bullet and say "while I'm in there...". And to me the brake system is one of those. If one side is bad the other has been used the same number of times, so replace it as well.

Good luck!

Gary, AKA "Gary fellow": Profile

ArdWrknTrk

Re: Brake whoas and conundrums

Administrator

Yep.
Especially hydraulics. Fixing or replacing the failed component just means full pressure is going to be applied to the next weakest link in the chain.
Glad you've spotted it early!

Hopefully the brake fluid hasn't made a mess of everything.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

85lebaront2

Re: Brake whoas and conundrums

Administrator

One item I ran into on Darth, or it might have been another vehicle, the brake light switch was in two versions, manual brakes and power brakes. The difference was the strength of the return spring in the switch. The other item, a stiff return on the pedal from excessive friction at the pivot can make the brake lights stay on as the spring in the switch isn't strong enough to overcome it.

Bill AKA "LOBO" Profile

"Getting old is inevitable, growing up is optional" Darth Vader 1986 F350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator Wife's 2011 Flex Limited Daily Driver 2009 Flex Limited with factory tow package Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413

FuzzFace2

Re: Brake whoas and conundrums

In reply to this post by StpaulF100

I measured the brake pivot to pin on my power brake system and got 4 inches.
Dave ----

StpaulF100

Re: Brake whoas and conundrums

In reply to this post by StpaulF100

Started with the front brake lines today. Drivers side will need surgery and a new line run from the proportioning valve. Passenger side went pretty well…. Until I went to bleed it. It leaks from the banjo bolt area on the caliper. I used the new copper washer the brake hose came with and it poured out. I cleaned everything very good before install. Tried tightening and that just deformed the washers. Reused the old ones which are much thicker and the leak turned to a drip. I’m going to assume I need thicker washers that havnt been crushed for 41 years and the leak will be cured. Unless there is a problem with the mating surface. Just thinking out loud. Thanks for all the ideas and help.
Mike

1980 f100 custom 4.9l c6 2.75 rear gears.

Gary Lewis

Re: Brake whoas and conundrums

Administrator

Are the new washers the right OD and ID?

Gary, AKA "Gary fellow": Profile

StpaulF100

Re: Brake whoas and conundrums

Hmmmm…??? They came with the brake lines butt, however, things can be messy sometimes. I will have to look up part numbers and dimensions.

1980 f100 custom 4.9l c6 2.75 rear gears.

ArdWrknTrk

Re: Brake whoas and conundrums

Administrator

Have you considered simply annealing the washers you have?

Copper is the opposite of steel in that it *needs* to be quenched in order to come out soft.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.