The Stovebolt Site Forums The Shop Area Driveline brake peddle locked up

i have my truck almost finished its on a 77 chevy running gear 350/auto tran's an the 77 chevy brake system for some reason i got it all back together an when i tryed the brakes the peddle that goe's to the master cyclinder / booster is froze stiff with no give any1 tell me whats wrong ?

Hi Toy Chaser. Welcome. I see you are new. You might be able to find a better forum for a 77 but I'll tell you what I know and see if that help and maybe someone will jump in to correct me and that way you might have some clues.

You mentioned you have a 77 Chevy running gear and the 77 brake system so does that mean the master cylinder is stock? Is it on the firewall with a vacuum brake booster like it was from the factory or has it been changed someway? Just wondering why you mentioned that. #1 How long has the truck sat without being used? That will make a difference on how to proceed. The whole system if sitting a long time will need to be serviced. Is there 2 compartments in the master cylinder for fluid for the front and rear brakes? The pedal goes on a pivot from the firewall and then a rod is pushed through the vacuum assist and into the master cylinder. That rod pushes brake fluid through and out the front of the reservoir into the 2 lines on the front. They were curled from the factory to accept some bumping and moving. If they were rigid they would crack. The master cylinder has a nut on each side. About a 1/2 inch or 9/16 if I remember correctly.

I would make sure the brake fluid is clear and clean. If the reservoir is rusty inside you would be smart to replace it from here. Loosen the nuts and pull the master cylinder out from the vacuum assist and then see if you can take your hand and move the brake pedal back and forth to see if the master cylinder pressure rod is frozen. If the pedal moves under the dash, through the firewall, and through the vacuum booster then the master cylinder is frozen and needs to be rebuilt or replaced. If all is OK and no problem is found I would look for a pinched brake line not allowing the fluid to flow to the brakes thereby it feeling to you it is stuck. If you don't see a pinched line then open the bleeder on the right rear wheel furthest from the master cylinder and the right front and press the brake pedal down when you have it reassembled from the previous test. The fluid should flow from the bleeders. If it does then I would take the master cylinder off and clean it and rebuild it and then refill with clean clear fluid and then bleed all the brakes. Also if the calipers from the front disc brakes are frozen that would not let the fluid flow through. So there are a lot of things to check to see why it is "frozen stiff".

I hope that gives you a starting point and remember as soon as you start cracking the first bleeder or line the whole system has to be bleed to be safe before you drive the truck even in the driveway. Good Luck. John