Brake pedal sits too low

-
Chained_360

Chained_360

Delusional Member
FABO Gold Member
Joined
Nov 11, 2015
Messages
562
Reaction score
332
Location
Indianapolis, IN
So I'm currently working on getting my '68 Barracuda on the road, and have run into a but if an issue with my brakes. The pedal sits a little to low for my liking, which is fine, except for the fact that the pedal lever does not make any contact with the brake light switch (so my brake lights are always on). Is there a way to adjust the master cylinder pushrod to correct this issue?

Also, how is the pushrod supposed to sit on the master cylinder? There is a conical-ish rubber boot on the pushrod, and I don't know where it's supposed to sit.
 
I believe you will need to adjust the brake light switch as opposed to the pedal (I could be wrong) I will check my service manual if you don't get a definitive answer before I get home.

The dust boot goes on the push rod on the inside of the firewall the wider section pressed against the firewall. It's not a super imperative part but if you have it use it.
 
Awesome, thank you. I have a shop manual at home, but I won't be able to check it for another 3-4 hours
 
The pedal has a proper parking spot on the bracketry.
There are several ways the pedal can park too low on the factory bracketry. Do not drive it until you figure out why it is this way.
#1) is a too-short pushrod.
#2) is if the rear system is faulty. If the return springs are faulty, then the fluid that is supposed to return to the MC, after a brake application, won't. When the return springs, and the rest of the system is functioning correctly, the fluid returns and fills the front most chamber in the M/C, forcing the piston towards the driver, and pushes the pedal up to its parking spot.Anything that prevents the fluid from returning, will also drop the pedal. Like a collapsed rear hose, or rust in the line, or a faulty Residual valve, or a faulty Proportioning valve.Or a leak!
#3)If the M/C is prevented from returning to it's design parking spot, then the compensating port will not perform it's function, which is to allow fresh fluid to enter the system and compensate for that which remains in the system due to the disc brake pistons moving out, and staying out as the front pads wear.If this is allowed to continue, the pedal gets lower and lower, and one day I imagine, they would quit working.
#4)If the self adjusters quit in the rear, eventually you will be stabbing the pedal multiple times to get a hard pedal. What you would be doing is pumping fluid out to the rear. Also eventually, the pistons in a rear wheel cylinder can then pop out.You would of course no longer have any brakes in the rear. The pedal will drop and not return,but the car will continue to stop cuz the front (in a dual system, such as yours) is still working fine.

Now for #1,No biggie you can drive it til you fix it. But do not put a too-long push-rod in there. See #3
But with #s2 thru #4, do not drive it until you have proven the Cport is working, that there are no leaks, and that there are no faulty components in the system, especially hoses. Hoses often fail from the inside out. They often fail by delaminating internally. This may create a little check valve, which the returning fluid will activate , sometimes locking a brake, or brakes, in the applied position. And the resultant low pedal.
 
As far as I know, the master cylinder is fine. It is new and I just bench bled it last night after a little mishap in which the pushrod pulled the piston partway out of the bore (I was gently pulling on the pedal after I saw it was sitting low). I am currently replacing a wheel cylinder, so I cannot test it inside the vehicle until that is complete. After the piston came out (not even past the first seal) I gently pushed it back in and removed the master cylinder to bleed it. I don't think that cause any damage, and it returns to the regular position after it is depressed.
 
If pulling up the pedal pulled the piston out of the bore, you have a problem with the MC. It should not come out like that.
 
There is a washer and a circlip that follow the piston into the bore. Make real sure they are in there. really sure. Super really sure. If you pulled the pedal up and it yanked the pushrod out, the rod is for sure not matched to the system or there is something wrong with the pedal parking position..End of story.
 
I'm watching I to am replacing the mc on a 73 duster in the kit I have the rubber boot I know where that goes but there is a rubber washer 1/4 'wide, does that go into the groove at the end of the push rod that goes into the mc did not take this out so I thought it should slide into the groove then into the mc let me know if that is right sorry not to high jack the conversion but great timing
 
silver fox said:
I'm watching I to am replacing the mc on a 73 duster in the kit I have the rubber boot I know where that goes but there is a rubber washer 1/4 'wide, does that go into the groove at the end of the push rod that goes into the mc did not take this out so I thought it should slide into the groove then into the mc let me know if that is right sorry not to high jack the conversion but great timing
Click to expand...
To get the pushrod out, with pedal connected, remove the four nuts honding the MC on. pull the MC out and **** it so the bolts are under the MC, MC will be away from the body the length of the bolts. Then go in the car, and pull up on the brake pedal, pull hard and the rod will come out. Then use the new rubber part you got in the MC box. The 1/4 inch one.
 
I'm a little confused...
Both the master cylinder that came off of the vehicle and the new one that went in did not have a retaining ring. All they have is a metal plate with a tab that goes over the piston, like this:
13-1323-2.jpg
 
Guys... I... I think I've found the answer to all of the problems that I've been having...

So the little rubber washer/bushing that goes into the groove on the pushrod?
Well, there wasn't one on the vehicle when I pulled the old MC out, so when I pulled the new MC out of the box, I had no idea what it was for... and now I can't find it. How screwed am I?
 
I have never seen those separate. Just tell who you bought it from it was missing.
 
Pardon me, I got mixed up between the early type M/Cs with the bolt-on cover and the later with the wire-retainer cover.
In any case your pushrod is still gonna be too short. Cuz what will change if you install the rubber? That ring is just there to keep the rod from falling out when guys lift up the pedal to see why it is hanging so low.heehee

Before you install that puppy, reach down and grab the brake pedal and slap it up as high as it goes. When it stops it should hit a rubber stopper and you will feel it hit softly, and hear a nice little muted thunk. That would be correct. If it hits metal on metal and clanks, the stopper is gone, and you will need to replace it.

If you have a booster, there is a big spring inside it which pushes stuff back, including the pedal, to park it.But then if you had a booster, you would not have been able to yank the rod out by lifting the pedal, cuz the Outer rod is divorced from the inner rod.
 
To clarify, the OP must be talking about a manual MC.

As I recall, in the photo of post #4, you should remove the piston retaining tab and attach the dust boot to those 2 holes, while holding the piston in (its return spring tries to push it out). The dust boot has a metal plate which keeps the piston from coming out. Most manual MC's come w/ both a dust boot and pedal rod (see rockauto). Yes, you can buy the rubber bushing for the end of the pedal rod by itself. I did so when I ruined one from a test fit (before I put the boot on). Might have bought on ebay.

Always remove the brake light switch (or slide way back) when doing this. You don't want the pedal to bottom out on the switch. The MC should push the pedal back. Once assembled, then slide the switch forward so the contacts open when the pedal is at resting height, and should be slight free motion left in the switch (i.e. not bottomed out). If not, the MC piston may not fully retract to expose the refill port, and thus not work, which is a common issue discussed here.
 
You must log in or register to reply here.
-

Back
Top