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Discussion Starter · #1 ·
Hi guys, I wonder if anyone has any ideas on what is causing this. I have a 67 Chevelle that when I apply the brakes it works fine but then it doesn't want to release the rear brakes. This was happening with the rear drum brakes. I thought it might be a wheel cylinder problem or something similar. Anyways I changed them over to disc. I still have the problem. At this point I've changed the master, proportioning valve, and just removed the line to see if it was blocked. The line was clear. Not sure where to go next, Could the booster cause this somehow. Its the only part I haven't changed?. The front brakes work fine. Thanks
 

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No, but it looks fine, its not blocked. Something is not allowing the pressure to release after the brakes are applied
It's my understanding that at least some of those rubber lines are double-walled, and if the inner wall ruptures, or develops cracks inside, then fluid pressure can build up between the inner and outter walls of the line, which can hold pressure even after you let off the brake pedal. So maybe that's why Jeff asked that question in post #2. I'm curious how you found out in the first place that the drum brakes you had in the rear weren't letting off. How did you diagnose that as being the problem?
 

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Discussion Starter · #5 ·
When I applied the brakes you could just feel the car was not releasing the rear. The brakes got super hot. This problem I had for awhile. It seemed to be getting progressively worse. Its to the point now. If I hit the brakes 3 or 4 times hard they are barely releasing at all. I put it in the garage last night and pulled the line today thinking maybe there was some blockage. Anyways line seems clear. I can blow through it no problem. I'll remove the rear flex hose and check it out, I doubt its that though
 

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When you pulled the line to check for blockage, did the brakes release? Maybe the rear is holding pressure from the proportioning valve after the brake is released?
 

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1964 Chevrolet Chevelle Malibu 4 door
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Grab a wrench that fits the rear bleeders and go for a drive. When the rear brakes won't release crack a rear bleeder. If you have fluid under pressure, replace the flex line between the axle and frame. As Billy stated, that was my reason for asking. There's only so many things that can hold fluid pressure.

Blowing through a line and applying 1200 psi of hydraulic pressure are two totally different operating differences..
 

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Try loosening the nuts from the master cylinder to the brake booster. In addition you can disconnect the rod at the pedal
 

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1966 El Camino 350/370HP 5 speed TKX 3.31 rear.1967 Chevelle 454/430HP Th400 w/Gear Vender 3.73 rear
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I experienced a similar problem with my Chevelle. It was operator error in my case, I had the actuator rod from the pedal to the booster too long and was not letting the master come back to the stop. I assume it held just enough pressure on the master to hold the brakes. Maybe another item to check.
 

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Discussion Starter · #13 ·
I experienced a similar problem with my Chevelle. It was operator error in my case, I had the actuator rod from the pedal to the booster too long and was not letting the master come back to the stop. I assume it held just enough pressure on the master to hold the brakes. Maybe another item to check.
Yeah I thought that might be a problem. Slacked it off to the brake pedal and then just to be sure I added a washer between the master and the booster. I definitely have clearance now. Didn't help
 

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X5 on the flex hose. I've seen this more than once, and -- no offense intended -- have had more than one person say "it's not that". But it was. As posted, the hoses fail from the inside. They come apart in a way that the inside line shreds and makes little one-way valve like shapes inside the hose itself.

Is there ANY chance that something other than brake fluid ended up in the master. I have seen it exactly 2 times in 30 years where the wrong fluid was put in the master. Anything oil based will swell and cause to stick the the rubber parts in a brake system. Gets worse as things heat up, goes away when things cool down.
 

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Discussion Starter · #16 ·
Hi guys, Thanks for all the input. Turns out it was that flex hose in the back. Hose looked fine on the outside but was blocked on the inside. I never would have thought that would be the problem. Anyways finally got a new one and all seems well now. Now I have a nice chrome spare master (lol). Thanks again for all the input
 

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1964 Chevrolet Chevelle Malibu 4 door
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Thanks for the follow up and glad it was something simple! Drove a 67 Camaro home for a buddy, had the driver's front locking up, would get out, open the bleeder to release pressure, then coast coming up to lights/traffic trying to keep from hitting the brakes. It was a fun day.
 
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