I have a 37 Dodge 2drsdn with a 360 Magnum and a torqueflite in it. I am having a problem with the breaks. When I drive around and use the brakes after a while the brake pedal doesn't want to return all the way up and I have to manually bring it up with my foot. This doesn't happen continuously but seems to happen when I have to repeatedly use the brakes such as in traffic or going down hill. The car has an aftermarket mustang II front end with discs and a Ford 8.8 out of an Explorer with drums. It has a GM master cylinder and booster. Driving me crazy because when it does this the brake lights remain on and front brakes will start thumping a little because they are slightly touching. Could it be the rod between the master cylinder and booster?

Do you have a return spring on the pedal? How big?

Yes I do. Fairly stiff. Inch diameter spring with approximately 1/8 inch wire. 3 inch spring stretched with over an inch tension when pedal is all the way up.

also, has it always done this, or did it just start?

if it has always done this, then as sugguested, see if anything is binding up.

if it just started, I would consider the booster as the culprit, with the internal valve going bad.
I have had one suck the brakes down while driving. I unpluged the vacuum line and drove it home with manual brakes.
So that would be the next thing to try. if you can replcate it on a closed area then plug the vacuum line and see if it still does it.

Pedal moves freely all the way down and up. It will actual do the same thing with or without the spring. Works great for a time, while driving then all of a sudden after using the brakes a lot like in stop and go traffic it slightly sucks in the pedal just enough so the front discs are just rubbing the pads.

Brand new master cylinder and booster. Put on the car less than 6 months ago. First one on it since it has been turned into a street rod from it's original state. It has done this from the start.
Can't really find any binding. It works freely until it gets sucked in a little. Then I have to physically pull it up with the top of my foot. Doesn't take a great deal of force to pull it up, but will not come up on its own even with the spring attached.

Pads normally touch the disks. There will always be some small ammount of drag on disk brakes.

wouldn't be the first time got a bad part out of the box.
I would still look at the booster then.

the rod between the master and booster shouldn't be the issue. that would cause the brakes to have pressure all the time even with the pedal up if it was too long.


again, I would see if you can make it happen again, pull the vacuum line to the booster and see if it clears up without you pulling up on the pedal.

Thanks that was what I will try next.

Yes I know the pads normally touch the discs but these are on them hard enough to cause a minor vibration and some noise when it happens. There is actually a little force on them though not much. That's why it feels like they are being sucked in instead of something binding.

Make sure the pedal is pivoting freely in the mount and not binding there.

I have done that. It pivots freely. Only time this happens is after I am in a situation where I have to frequently use the brakes. Like in stop & go traffic.
Getting to the point here in NY where the car will be away for the winter. So I have time to figure it out before next spring.

mabey its heat,does any of the lines get near the ex.?

No. The lines are away from the exhaust. So is the master cylinder & booster.

have you checked your wheel bearings?if theyr too tight or dry they can heat up and get the brakes hot enough to expand and bind.i know its a long shot but ive seen it happen.

No it is in the brake system somewhere.

I agree thanks. Next time it happens I am going to stop and unhook the vacuum line & see what happens. Thanks guys.

Think I found the problem. 10 PSI Residual Pressure Valve for the back drum brakes doesn't appear to be working properly.

that doesn't make any sense.
the residual valve should not affect pedal height/effort.
it just traps some pressure on the other side.

broken residual would either trap more pressure or let it all go.