Headed to town in the Grabber and then....

No, I don't believe so. The pushrod is not what activates the brake lights if I recall correctly. The pushrod connects directly to the pedal and there is another spot on the pedal higher up than activates the brake light switch.

So remember the brake pedal system is a fulcrum lever that moves more the further you get from the pivot point. The Pivot is roughly at the top of the pedal, then there is the brake light switch, then the push rod.

Man this is hard to explain purely through text...

The pushrod length is determined by the distance from the point it attaches to the brake pedal as it sweeps from its "home" position to the floor (essentially). So the design is for there to be roughly a 1/2" of slack from when you press the pedal to when the push rod engages. In that 1/2" of slack the pedal should engage the brake lights before it engages the pushrod.

If your pushrod is too long it will engage the push rod before the brake lights so your brake lights would not come on until after the brakes come on. Which means that too long of a push rod could not theoretically have a situation where the brake lights are ALWAYS on, because the longer push rod would actually be interfering with the brake lights being casually engaged. I.E. it would be pushing the pedal away from the switch.

Now if your push rod was to SHORT it would pull the brake pedal down and that would result in the brake light always being on... EXCEPT there is a helper spring to pull the brake pedal back, and that would make the push rod fall out of the master cylinder.

So that brings us to the next scenario.

Your brake pedal itself is somehow adjusted too far forward. This would make sense with the brake lights being ALWAYS ON, and could even cause your brakes to jam up and get stuck on, because the push rod would not be able to fully disengage the master cylinder.

TL/DR - start with ensuring your brake pedal is properly installed.

I also missed the point where if you had too short of a push rod, combined with a incorrectly set, damaged, or worn out helper spring it would also describe the events you have occuring.

 

The pedal is not adjustable. It's a fixed location between the firewall and support

The pedal doesn't have an end to it's travel range. The end of it's range is when it hits the pedal support. If it goes this far you won't be able to see the pedal. The retaining clip on the end of the pushrod is what is keeping it from swinging too far up.

The problem sounds like a bad brake light switch.

 

you say it's not adjustable, that doesn't mean it cant be out of spec. The number of times someone told me something wasn't adjustable and then I found out it just wasn't supposed to be adjusted...

But yes I agree with you it could also be a bad brake light switch. Except that he also has other issues with his brakes, that sound an awful lot like a problem with his pushrod and pedal.

No matter what when I get home I'm refreshing myself on the diagrams for the brake pedal, and I'm gonna look at mine again before I drive it home. When I got my new MC it came with the wrong pushrod, but I can't remember WHY it was the wrong pushrod.

 

but if the pedal is not disengauging the brake light switch would also not disengauge, the brake light switch hooks up on the same post of the brake pedal as the pushrod, the switch actually saddles the pushrod correct?
I know this is a later model pic but it's the same hook-up

 

The pedal can't be adjusted and it can't get out of spec. The brake light switch is spring loaded and works on pressure when the pushrod runs out of free movement to close the switch. When 71gold and I was doing his master cylinder...we had an adjustable pushrod that didn't have a retaining clip to hold it in the MC. If we adjust it too long the brake pedal would be too high off the floor. Adjust it too short and the pedal would almost touch the floor. After We figured out how long it needed the length to be we made a pedal stop and bolted it to the pedal support to keep the pushrod from falling out of the master cylinder.

 

yea refreshed myself on it, I even remember why I didnt use the rod that came with my new mc.

length of the pushrod should only affect the pedal height. and there is no spring to return it. otherwise I was kind of correct, just too general not specific to our car. but I agree that its probably a bad switch. push rod would have to be way way too long.

 

And an inch longer than stock......would that be way to long?
Seems to me an inch longer would make quite a difference in pedal travel/location at the pedal.
I found a slightly better picture and explanation of the switch and how it works....so if the pedal still has pressure on it the brake light would stay on according to this pic.

 

Bringing this back up because I finally got around to looking into it better, my brake pedal has a point where it does top out on the swing, the pushrod was actually keeping some pressure on the master cylinder at the top of the pedal sweep and also causing the brake light switch to stay activated and thus the brake lights staying on, now I just need to figure out how long the pushrod needs to be, I have one that is 1/2 inch shorter than the one I had been using but I am not sure that's shorter enough to fix the problem, has anyone got a pushrod they can measure the overall lenght and let me know?

 

1/2" on the rod is lot of travel on the pedal...

Mustang unlimited sells an adjustable M/C rod.

 

Ok, I can't get these brakes to bleed, when I changed the rod all I did was loosen the M/C and pull it away from the firewall 1/2 inch, put some small wood blocks behind it and went to the pedal and pulled it till the rod popped out, I then pushed the shorter rod in with my thumbs and bolted the M/C back in and hooked everything back up, hit the pedal and it goes to the floor, I have bled them out AGAIN twice since then still pedal goes to the floor, before I touched it I had excellent pedal and no problems other than too long of a pushrod, I did not unhook any lines at all for the pushrod swap, can't get any pedal at all back unless I pump on it and then it gets a bit, but once you let it sit a minute and push it, no pedal at all, bad master? it is/was new!

 

maybe you jammed the piston or ruptured something in the M/C with the rod that was too long...

 

Ok new master cylinder and still no brakes, yes I bled them.... again! no fluid loss, no leaks, pulled wheels and everything looks good, still can pump them up and have some pedal but release and hit a few seconds later and it goes to the floor, I can't figure this one out.

 

Bad master cyl...Did you bleed it on the car or bench bleed it??? If bled on the car...You cut a piston on the compensating port and damaged it (Too much travel when useing the pedal)...Allways bench bleed master cyls...You cant manually push the piston far enough to damage it that way.

 

Bench bled the old fashioned way, bleeder hoses ran back into the MC, then install, vacuum bleed system then pushed pedal....nothing.

5:28 PM Just got back in from bleeding them once again, 5th time on all 4 corners, ran a whole quart through the system, still no pedal