The Stovebolt Site Forums The Shop Area Driveline Brake fluid will not flow back into Master Cylinder

Hi friends,
I am completing full replacement of my brake system, new lines, shoes, Master Cylinder, brake wheel cylinders and drums. After bleeding the lines and releasing the pedal, the fluid will not flow back into the cylinder leaving the wheel cylinder pistons extended. I have checked the brake lever to firewall measurement as described in the shop manual and it is OK.

What could be causing this?

Regards, joe

It would really help if you would tell us what your working on, ie; 19** Chevy 3100 235 with 3 on the tree. There are several braking systems used depending on Year and truck size.

Well, I hope you are bleeding with the drums on. Otherwise how would you know the cylinders are extended. I realize there is a problem, but what exactly is it. What is happening or not happening. Do you have the drums ON?????? There are lots of recommendations to give you, but not sure yet of your analysis.

Do you just mean that the drums are tight after bleeding????? How many wheels are affected with this???? Whatever "this" is.

AND what the heck truck is this????????????

Please advise if you are using stock brake system or other??????
If stock, plumbed correctly and drums are on and your complaint is that drums won't turn and you are guessing that cylinder rods are extended........most likely you just need to adjust the shoes. Just tell us more. The piston position and the brake springs will bring the shoes off tight. Lack of bleeding or not bleeding the master will not lead to your comment. Air causes spongy, not lock up. Yours is mechanical or piston position........ or possible piston kit installed incorrectly. Unless this is an upgrade to disc or power or other, therefore valving problems. (proportioning, residual, etc.)

Thank you for the replies.

It is a 49 3100 1/2 tone all 49 correct parts with Huck brakes. I do not have the drums on but the shoes are restrained by ratchet straps and the return springs.. The brake shoe cylinders will not retract back in either by tightening the straps or prying against the cylinder studs using the adjustment slots to lever against. As you can see in the picture, the adjuster cup is out away from the cylinder and will not pry back. The same is true for all the wheels. The wheel and master cylinders are new and assembled correctly.

I know nothing about Huck. I don't see that the cylinders are not retracted because I don't know what retracted looks like on those. I also see that the spring is not extended like it should be if shoes were extended. It all looks correct to me. I would put the drums on. You don't know ANYTHING until you do that. If the brakes work, they work.
I have never bled brakes without drums on. But what do I know, I'm just normal.

Did you replace the rubber flex lines on the front and mid rear. If not the old lines may restrict the fluid back to the master cylinder. I had a old ford topaz and my front brake would heat up and peddle got hard but after it sat would leak back and be okay until you used the brakes again a few times took me a while to figure it out.

To Kevinski - All the hoses and lines were replaced with new.

http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0503.htm

Item 3 is called adjusting screw. Does this actuator rod/adjusting screw need adjusted???
I've googled pics of Hucks and your pic sure does look normal. Are you new to brakes or experienced?
There are hundreds of members here with Huck. They will set me straight and I will be schooled. I don't think this ratchet strap thing is a good idea. Adjusting screws are not moving out so they can't move back. They never left bottom maybe. I think you need to see if they stop the drums and release (after adjustments), not try to peek at them.

bartomos - Good Point about the adjusting screws. Before the bleeding was complete, the cylinders were retracted.

Do the cylinders retract if you open the bleeder screw?
Jerry

Hy Joe S. and guys, my vote is for the master cylinder pushrod not being adjusted correctly, not allowing the master cylinder piston to return to its true at rest position and thereby uncovering the compensating port in the master cylinder. The pushrod for the master cylinder must be adjusted with clearance so that the master cylinder can return to its true at rest position, hope that helps.

By chance did you put on a residual check valve on? If so maybe it’s on backwards not allowing the fluid to travel back to the mc. Just a thought.

Why do you have a ratchet strap on the shoes instead of the drums? With as much force as there is pushing the shoes outward, that strap will stretch, allowing the plungers to come out too far and get bound up, preventing them from retracting back into the cylinder.
There is a special spring loaded GM tool made specifically to prevent this from happening during a normal shoe replacement operation.
Carl

Nobody has explained why the spring is relaxed if the cylinder rods are in deployed position?
I'm trying to think it shows that they are retracted all the way. The spring is not extended. It is an extension spring.
I don't see it extended more than one wire diameter. Is it real tight?
Anyway Joe, adjust the screws so the drum barley fits on. Once the drums are barely scrubbing, you are all done in there. Then put the tires on and test spin them and see if they stop. If you have trouble after that it won't be anything inside the drums. Unless your spring is sprung. What is that black gunk on the coils?

Lots of suggestions here that could be your solution. If everything is done correctly and they still don't retract, it could be a weak return spring. I've had that happen before. The old spring doesn't have enough life left to retract, and return the fluid back into the m/c.

To Bartamos: The spring is new but too short to reach to the factory holes so I drilled a hole in the shoe to compensate for the shorter measured length of the new spring's barrel compared to the old spring. None of the new springs from different vendors seem long enough although they are clearly marked with "47-50 Chevy 1/2 ton" on the packaging and catalog pages. The black gunk is grease, accidental not intentional.

To VEW & 3B: To find that adjustment I will probably have to do trial and error, the service manual is not helpful.

To Jim K:No check valve.

To Hotrod Lincoln: Yes

Thank you all