Brake Pedal Not Returning

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FragginDale

FragginDale

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Hey everyone.
So I've got a problem that's been stumping me. I've got brand new master cylinder, brake booster, and front calipers on my 1974 Scamp (front disc rear drum). I've gone through and bench bled the master cylinder then installed it and bled all my brakes. But when I got in the pedal feels good but it doesn't return. So I'm trying to figure out what I need to do or what's messed up. Any advice would be greatly appreciated!
 
If the pedal assembly swings free not hooked to the booster, then the problem in the booster master cyl assy. Push the pedal down and take the master cyl loose and see if the piston is stuck in the master cyl.
 
Unless I'm mistaken, is there also a brake pedal return spring? If it's missing that could be the problem.
 
I had the same thing happen to me. When I first went through my car to make it streetable, I replaced the master cylinder with a reman NAPA unit. Not even six months later, it seized up and would lock my brakes if I touched them. I replaced it again and haven't had an issue with it. I would say take the master cylinder back and exchange it for a new one.
69_340_GTS said:
Not that I know of. Spring is inside the master cylinder, AFAIK.
Click to expand...
Yeah, the return springs are inside the master cylinder. They sit in the end of the cylinder bore and push back against the end of the piston.
 
Chained_360 said:
I had the same thing happen to me. When I first went through my car to make it streetable, I replaced the master cylinder with a reman NAPA unit. Not even six months later, it seized up and would lock my brakes if I touched them. I replaced it again and haven't had an issue with it. I would say take the master cylinder back and exchange it for a new one.

Yeah, the return springs are inside the master cylinder. They sit in the end of the cylinder bore and push back against the end of the piston.
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Yep, now that I've had time to think about it, there is no external spring on the pedal. Sorry about that.
 
I will check the pedal assembly tonight after work. One of the things is that the rod going into the master cylinder is adjustable. I adjusted it out thinking that was it and drove home the other night. I got out and you could tell the brakes were dragging a bit. So I'm thinking that got adjusted too much. Is there a certain way that is supposed to be adjusted? My current plan is to check the pedal assembly, adjust the master cylinder back, and bleed the fronts again (they were the ones dragging). Anything else I should check while I'm going over everything? I just want to check everything out one more time before trying to get a new master
 
In the FSM there is a horizontal measurement between the floor and the pedal (if I remember correctly). Then you adjust the brake light switch. Also, there is really no way any of that could cause the brakes to drag as you say. Maybe that master cylinder is toast.
 
Make sure the bolt going thru the pedal/pushrod isn't binding. Loosen nut and re-test. Clean and/or lube as nec.
 
I can walk you through taking the booster apart for inspection if this doesn't fix it. I think it should though.
 
If the pushrod is too long, the fluid in the lines cannot return thru the compensating port, then the weight of the pedal can keep the brakes applied.
If the pushrod is too short, it just wastes pedal travel. And if the rear shoes go out of adjustment, then eventually,you may not have enough pedal travel.
 
I could not find any spec for brake pedal height in the FSM. I think the reason is because the OEM pushrods were not adjustable. But IMHO the brake pedal should be just a little higher than the gas pedal.
 
FragginDale said:
... the rod going into the master cylinder is adjustable. I adjusted it out thinking that was it and drove home the other night. I got out and you could tell the brakes were dragging a bit. So I'm thinking that got adjusted too much. Is there a certain way that is supposed to be adjusted? ...
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Yes. If the adjustment is too far out, the MC piston won't retract enough to expose the "fill port". That will leave pressure on the brake tubing, thus dragging. I just use common sense when adjusting the booster output tip.

Keep offering the MC to the booster. Your brake tubes should be flexible enough to allow this while bolted up. Start with the adjuster full in. That should give play in the brake pedal. Keep screwing the tip out and testing, until the adjustment just gets rid of the play, and just barely pushes the MC in as you bolt it up. You should be able to tell as you hold the MC against the booster. Not much different than adjusting the cable brakes on a bicycle. While in there, assure that the MC piston has a strong spring, since that is all that returns the brake pedal. With MC off, insure that the brake pedal swings easily, without drag from booster or linkage. With vacuum from engine idling, the booster should follow the pedal motion and you shouldn't hear vacuum hissing, except as you move the pedal (lets in atmospheric air to produce forward force). Insure the booster also retracts smoothly.

Re brake pedal height, if you drive w/ 2 feet in an automatic (as I think driver's ed teaches today) it doesn't really matter. If you brake w/ the right foot, you don't want the brake pedal much higher than the throttle pedal or your foot might snag when moving between pedals. Back off the brake lamp switch until done adjusting the pedal. That is the biggest mistake. The switch should just sense pedal motion, but not affect it. For some reason, many people assume the pedal is supposed to bottom-out on the switch, which makes no sense if you think about it (flimsy sheet-metal bracket). But, do adjust it so the switch assuredly turns off, otherwise your brake lights will be on all night and you won't drive to work in the morning.
 
BillGrissom said:
Yes. If the adjustment is too far out, the MC piston won't retract enough to expose the "fill port". That will leave pressure on the brake tubing, thus dragging. I just use common sense when adjusting the booster output tip.

Keep offering the MC to the booster. Your brake tubes should be flexible enough to allow this while bolted up. Start with the adjuster full in. That should give play in the brake pedal. Keep screwing the tip out and testing, until the adjustment just gets rid of the play, and just barely pushes the MC in as you bolt it up. You should be able to tell as you hold the MC against the booster. Not much different than adjusting the cable brakes on a bicycle. While in there, assure that the MC piston has a strong spring, since that is all that returns the brake pedal. With MC off, insure that the brake pedal swings easily, without drag from booster or linkage. With vacuum from engine idling, the booster should follow the pedal motion and you shouldn't hear vacuum hissing, except as you move the pedal (lets in atmospheric air to produce forward force). Insure the booster also retracts smoothly.

Re brake pedal height, if you drive w/ 2 feet in an automatic (as I think driver's ed teaches today) it doesn't really matter. If you brake w/ the right foot, you don't want the brake pedal much higher than the throttle pedal or your foot might snag when moving between pedals. Back off the brake lamp switch until done adjusting the pedal. That is the biggest mistake. The switch should just sense pedal motion, but not affect it. For some reason, many people assume the pedal is supposed to bottom-out on the switch, which makes no sense if you think about it (flimsy sheet-metal bracket). But, do adjust it so the switch assuredly turns off, otherwise your brake lights will be on all night and you won't drive to work in the morning.
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Thank you for the great info! So I adjusted the master cylinder back and started to drive home but it started to grab again. I pulled over and pulled the master off and adjusted it alllllll the way back. Got it home safely after that. Then I matched the rod length to the old master cylinder I pulled out. I was able to drive to work and back home no problems. The pedal still feels way low so I'm going to play with adjusting it. Also when I was putting the new one in I used all the hardware I had. But there is a bolt that goes through where the brake booster attaches to the pedal. After looking at photos that's supposed to be a solid piece with a cotter pin. So today at work I think I found one that will work. I will change that over at lunch and see if that helps. Thank you everyone for all the help!
 
The bolt that holds the pedal to the linkrod is special. It has a large bearing shoulder to enter the eye, and a reduced shank where it enters the pedal. The nut then retains it and the cotter pin is a safety so it can never fall apart if the nut come loose,......cuz that could be fatal.
Do not use a common bolt here, unless it was specifically engineered for this application.

The pushrod spec is .920 from the tip to the filter retainer
 
AJ/FormS said:
The bolt that holds the pedal to the linkrod is special. It has a large bearing shoulder to enter the eye, and a reduced shank where it enters the pedal. The nut then retains it and the cotter pin is a safety so it can never fall apart if the nut come loose,......cuz that could be fatal.
Do not use a common bolt here, unless it was specifically engineered for this application.

The pushrod spec is .920 from the tip to the filter retainer
Click to expand...

The pedal part in cab looks to be all stock. It's where the booster attaches to the linkage by the firewall. When I purchased the car I got a bucket full of random parts. I will search that's and see if I can find anything that matches the description :) thank you!
 
FragginDale said:
The pedal part in cab looks to be all stock. It's where the booster attaches to the linkage by the firewall. When I purchased the car I got a bucket full of random parts. I will search that's and see if I can find anything that matches the description :) thank you!
Click to expand...
The part that the booster attaches to is called a blade. That is where the special bolt goes
 
I just want to thank everyone who posted on this thread. When I bought the '67 Valiant someone had wrapped a couple bungee cords around the brake pedal arm. I 'assumed' it had a return spring that was missing. To read that there is no return spring is awesome news for me. As a professional parts guy it's pretty damn embarrassing to be searching for a part that doesn't exist...lol. thanks everyone. Now I can 'stop' searching... Pun intended....
 
cgray521 said:
... someone had wrapped a couple bungee cords around the brake pedal arm. ..
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Great result and good you asked here. One should never wing it with brakes. Sounds like a prior owner barely missed a "Darwin award" and not reproducing.
 
My 74 Duster has a "dragging" pedal as well. For the few times I've moved it around, I just lifted the pedal back up with my foot, not too distracting and works. Would be nice if I didn't have to do it though.
 
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