Justinlb Posted June 17, 2021 Share Posted June 17, 2021 I was driving around my 1940 buick super yesterday and my brakes started going soft. I didn't think much of it other than needing to bleed it sometime soon. It sat overnight and I get in to take a drive a bit ago and I have zero pressure whatsoever. I had my brother help me bleed the brakes, fluid is coming out of all the lines but it isnt building pressure. I bled the lines as the manual states (drivers side first). I see no brake fluid leaking anywhere on the lines; allthe fittings are snug. Perhaps theres a hole somewhere pulling in air and it's just time for new lines? Im lost 😬  Master cylinder is brand new also. Link to comment Share on other sites More sharing options...
1939_Buick Posted June 17, 2021 Share Posted June 17, 2021 26 minutes ago, Justinlb said: Master cylinder is brand new also. Is that your problem? Internal bypass? 1 Link to comment Share on other sites More sharing options...
Rock10 Posted June 17, 2021 Share Posted June 17, 2021 If you had a hole you would see a leak. If it won't build pressure it has to be the master cylinder. Is the fluid level OK? When did you change the MC? 1 Link to comment Share on other sites More sharing options...
27donb Posted June 17, 2021 Share Posted June 17, 2021 Modern master cylinders need to be bled on the bench before installation, are 1940 master cylinders similar? Link to comment Share on other sites More sharing options...
Bloo Posted June 17, 2021 Share Posted June 17, 2021 (edited) Well.... err... Â Bench bleeding helps you get the air out of the system much faster. If the cylinder is full of air that is mostly going to go in and you will have to bleed it out. I think on a 1940 anything with the master cylinder under the floor it would probably be full of air anyway by the time you got it stuffed up in there and the fitting hooked up, and most of the brake fluid would be in your eyes and all over the paint. Edited June 25, 2021 by Bloo (see edit history) 1 Link to comment Share on other sites More sharing options...
Justinlb Posted June 18, 2021 Author Share Posted June 18, 2021 2 hours ago, Rock10 said: If you had a hole you would see a leak. If it won't build pressure it has to be the master cylinder. Is the fluid level OK? When did you change the MC? Fluid level is full, I changed the cylinder about 2-3 months ago. I've driven the car quite a few times after that. Is there a good way to check if the master cylinder is working or not? Link to comment Share on other sites More sharing options...
Rock10 Posted June 18, 2021 Share Posted June 18, 2021 (edited) Disconnect the line at the back and put a plug in there? Do they make a flare plug? Â https://www.amazon.com/JEGS-63087-Steel-Plug/dp/B078WJKPBF/ref=sr_1_10?dchild=1&keywords=brake+line+plug&qid=1623980791&sr=8-10 Edited June 18, 2021 by Rock10 (see edit history) Link to comment Share on other sites More sharing options...
Rock10 Posted June 18, 2021 Share Posted June 18, 2021 That will be messy though as all of the fluid will drain from the MC and some of the lines. How did you bleed the brakes if it won't build pressure? Â Link to comment Share on other sites More sharing options...
Justinlb Posted June 18, 2021 Author Share Posted June 18, 2021 1 hour ago, Rock10 said: Disconnect the line at the back and put a plug in there? Do they make a flare plug? Â https://www.amazon.com/JEGS-63087-Steel-Plug/dp/B078WJKPBF/ref=sr_1_10?dchild=1&keywords=brake+line+plug&qid=1623980791&sr=8-10 Good idea. I'll try that in the morning, im sure I could find a flare plug at my local hardware store. Â As far as how I bled the brakes: there was already fluid in all of the lines, but there's the smallest bit of pressure when the brake is fully depressed allowing me to crack it and close it back up. But it wont build any pressure past that. 1 Link to comment Share on other sites More sharing options...
Rock10 Posted June 18, 2021 Share Posted June 18, 2021 (edited) Very strange. Does the pedal come back up to the normal height? Is there resistance when you push it or does it move like it's not attached until the very end? Almost sounds like the piston is stuck in the back of the MC. You might try giving it a couple of raps with a hammer before you take the lines loose. Edited June 18, 2021 by Rock10 (see edit history) Link to comment Share on other sites More sharing options...
Justinlb Posted June 18, 2021 Author Share Posted June 18, 2021 13 hours ago, Rock10 said: Very strange. Does the pedal come back up to the normal height? Is there resistance when you push it or does it move like it's not attached until the very end? Almost sounds like the piston is stuck in the back of the MC. You might try giving it a couple of raps with a hammer before you take the lines loose. Found the issue, I went and got a fitting from the hardware store like you suggested, put thread tape on it and put it directly on the master cylinder. Theres almost no resistance in the pedal at all, but it does come back up. Thanks for the help rock10. Â Now it makes me wonder why it went bad already. The brake fluid in the cylinder doesnt seem dirty or anything. Time for another one. 1 Link to comment Share on other sites More sharing options...
Rock10 Posted June 18, 2021 Share Posted June 18, 2021 Can you pull it apart? Either the piston is stuck or the spring is broke. Was it new or rebuilt? Warranty? Link to comment Share on other sites More sharing options...
Justinlb Posted June 18, 2021 Author Share Posted June 18, 2021 Just now, Rock10 said: Can you pull it apart? Either the piston is stuck or the spring is broke. Was it new or rebuilt? Warranty? Yes, I can pull it apart. I might just do that now actually. Its a remanufactured one from Cars LLC, but I bought it off of Ebay so I doubt theres any kind of warranty haha. 1 Link to comment Share on other sites More sharing options...
Rock10 Posted June 18, 2021 Share Posted June 18, 2021 Interested to see what you find. 🤓 Link to comment Share on other sites More sharing options...
Justinlb Posted June 18, 2021 Author Share Posted June 18, 2021 (edited) Bought a rebuild kit. I'm going to have to take it to work tonight and use some real tools. They must have used thread lock or the biggest cheater bar in the world putting the nut on the back side. But from what I can tell I'm almost positive the spring is broken, i can only push the cylinder in and out a quarter inch. (It does move but not far) It looks bottomed out to me. Edited June 18, 2021 by Justinlb (see edit history) 1 Link to comment Share on other sites More sharing options...
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