Brake Pedal Does Not Always Fully Return To The At Rest Position

[RRChris]

I have a 71 Satellite with Power Front Disc Conversion, using a general purpose 8" dual diaphragm booster.
The brake system has been fully rebuilt - new rear wheel cylinders, front calipers overhauled, new hoses all round, new master cylinder, and new booster. The booster pushrod to master cylinder is confirmed as the right length. I have also gone through the pedal linkage and ensured that everything is free to move. Brakes have bled well and pedal feel is good.
As I drive the car the pedal does not always return back to the at rest position. This seems to get worse as the car is driven longer. From time to time you can feel the brakes dragging. If I put my foot behind the pedal and lift up it releases - telling me that it has to be between the pedal and the booster (no direct mechanical link to the master cylinder). The booster holds good vacuum. Is it possible the booster has an internal problem? Can the booster get hot and tight to operate? Has anyone experienced similar before? Any tips would be welcome before I spend more money chasing guesses.

 

[PurpleBeeper]

Wow, that is a tough one! I'm just going to think out loud here for a second....

1. you said "from time to time I can feel the brakes dragging", to me that sounds like at least one of your brakes hanging up, or the master cylinder or "maybe" something in the pedal linkage you mentioned (maybe check the brake pedal linkage one more time?).

2. Now, if when the brakes drag & you lift up on the brake pedal and instantly, the brake dragging goes away, then it's not an individual caliper/wheel cylinder/flexible brake hose. To me, that would say it's in the master cylinder, "maybe" a proportioning/bleed-off valve, the brake pushrod (you mentioned this) or the brake pedal linkage (which hopefully you eliminate for sure in step #1). My first guess here would be some type of issue with the master cylinder, and maybe make sure I'd pulled out the little pin on proportioning/bleed-off valve when I bled the brakes. I've "heard" that not doing this can trap some air & the brakes do weird things, though I've never experienced this.

IF the brake dragging continues for even an instant after you lift up on the brake pedal, I'd guess you had at least one caliper/wheel cylinder/flexible brake hose that was not working right. I'd try to see if I could figure out if it was front/back and left/right to narrow down my search.

3. I've had a booster go bad before and all I experienced was very hard pedal. The brakes worked fine & the pedal returned as normal.... just my one experience.

Hmmmm…..I'd re-bleed rear brakes with pin pulled out, if not that then replace master cylinder again....and if not that, take a real, real close look at the proportion valve/hold-off valve (rare to go out, but possible). That's all I got

 

[dual fours]

Now you know why all the cars following you were keeping there distance behind you and cussing you out for riding the brakes. Your brake lights were on. Sorry I don't have the correct answer for you but I will be watching the prognosis on your trouble.

 

[RRChris]

Thanks for your input.
Just to help me understand this a little more please. The booster push rod is not mechanically linked to the master cylinder. So if I lift the pedal and everything comes back (immediately) then if the hydraulics were a problem (for example air in the system) wouldn't they stay there without releasing the brakes? If the hydraulics were the problem wouldn't the pedal have returned home anyway under it's internal return spring.
I'm not trying to disagree, i'm just trying to understand the mechanics behind the problem, so I do welcome any discussion on this.
When bleeding the brakes on all corners of the car the fluid passed under gravity. Bleeding was done using the traditional means of pedal pumping. But as you suggest I did not pull the pin on the proportioning valve. As stated earlier I have gone through the linkage from the pedal pivot to the booster and everything is free. The stop light switch is not interfering with the pedal assembly.

 

[multimopes]

Were the rear shoe return springs replaced? Also the emergency brake cable springs. Can you tell which wheels brakes were dragging? Touch each one after stopping and see if any are hotter than the others or use a temperature gun. Also, some cars used a brake pedal return spring and others did not as some had an adjustable brake light switch and others had a fixed one.
Also, a belated Welcome Aboard from yesterday!

 

[beanhead]

Not necessarily a pedal/pushrod area problem. Your rear drums being out of adjustment or worn can cause this also. Make sure they are tightened up and good first. Are you using an adjustable proportioning valve in the system? Make sure that is dialed in properly as well. Then look at the booster/master cylinder otherwise you'll be chasing your tail..

 

[RRChris]

No I didn't replace the rear drum shoe springs. Had wanted to, but got sent the wrong springs despite ordering for 11" drums. It's tough on the other side of the Pacific when you get sent the wrong spares!!
Also, I will admit that the rear drums are out of adjustment - seized adjusters. Looks like I still have a project on the rear. The fronts do get hot, but this would be due to the rears taking a bit longer to take-up.
Non adjustable proportioning valve.
Appreciate everyone's input. Unfortunately I go away for work for a month now so cannot try to fix until I come back.
I'll keep people posted on the results. Hopefully helpful to others.
Thanks for the welcome!!! 18 months I have been slowly sorting the car out - really close now!!

 

[RRChris]

Well I've had another crack at this.
New springs on the rear drums and brake adjusters re-built.
I have put a tension return spring on the pedal and used silicone grease to lubricate the seal at the back of the booster that works on the bakelite / plastic piston. When pressing the pedal you can hear a noise of the seal wiping on the bakelite piston.
On taking it for a short drive yesterday whilst the pedal initially felt the same it started to get better. Would seem to return more often and not hang-up as much. I hoping with a bit more driving / use / lubrication it will come good.
Thanks for people's input to this discussion!!
Now onto my last big challenge - rear main seal. Already done it once but had issue with getting the pan on (Magnum 360 in situ). Have bought the one piece pan gasket this time. What sealant should be used on the rear main bearing cap halves? Is Loctite 515 or 518 critical. I used Permatex #2 Non Hardening Form a Gasket and I'm wondering if this is where I went wrong? Maybe I should start a new thread?