Brakes 2018

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Brakes 2018

Post by JGL on Wed Apr 25, 2018 10:54 am

This year I replaced the rear brake cylinders. I also got a rebuilt master cylinder from a friend so that went on too. I bled the right rear first and then the left rear...no problems so far. Then it came to the front, tried the r. front no go, then tried the left front, no go next day I tried inhaling via hose and got left front to work, tried right front and never got anything. What should i try next. Oh yeah went from DOT 3 to DOT 4 also. I have front discs and rear drums.
Maybe I should replace my flex hoses.
What should I try next???
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JGL

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Re: Brakes 2018

Post by Brads70 on Wed Apr 25, 2018 11:56 am

Maybe try taking the bleeder screws out and making sure they are clear? Use a small drill bit or something to make sure fluid can travel? If that checks out maybe crack the brake line loose at the flex line to see if fluid is at least getting there?
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Re: Brakes 2018

Post by philcollins on Wed Apr 25, 2018 6:44 pm

JG, do you have disc in front? if so,the proportioning valve is not "on center". Open a rear bleeder and try again in front.
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Re: Brakes 2018

Post by JGL on Wed Apr 25, 2018 7:19 pm

philcollins wrote:JG, do you have disc in front? if so,the proportioning valve is not "on center". Open a rear bleeder and try again in front.

I have disc brakes in front. Somebody told me that it might be the brake flex lines too so I am going to try that since they are already ordered but yours makes sense too, I never trusted that darn prop valve.
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Re: Brakes 2018

Post by AJ/FormS on Thu Apr 26, 2018 5:47 pm

I have never ever had a problem with a Mopar Combination Valve, in 50 years. Not to say it cannot happen.
You should be able to feel the pressure in the flex-line with a helper on the pedal.
 At the M/C, which reservoir is plumbed to which end of the car?
How far down is your pedal?
If your M/C has a big and a little reservoir, then the big one goes to the discs. This should be the firewall side.
Inside the M/C are two pistons separated by a little spring in a little chamber. Each piston operates a different end of the car. The chamber between them has to be filled with brake fluid in order to properly function. When the chamber is full the pedal  will be at the top of it's stroke. At the back end of each reservoir is a little fluid supply hole called a compensating port. Thru this port, the chambers draw fluid to compensate for wearing pads and shoes, and also is used for first-time charging of the system.
Now, when you step on it, the first thing that has to happen is the rear piston has to close the C-port, to trap fluid in the chamber. Then the fluid between the chambers now in a hydraulic lock, starts pushing the frontmost piston;closing it's C-port. Now can begin the braking. Now fluid travels down the lines, and out to the slave cylinders.
In your system, the rearmost reservoir, the larger one, is supposed to operate the front brakes.
If your pedal is high. then the inter-chamber is charged, and so is the rearmost chamber. That leaves the front chamber to operate the rear brakes, and that end has already been bled ok. That seems to indicate that the M/C is working properly.........if the pedal is high.
If the pedal is not high, then the M/C is operating in back-up mode, either the inter-chamber is not full of fluid or one of the other two pistons does not have resistance  to fluid travel. We know it's not the frontmost chamber , because it operates the rear brakes, and those have been bled. If you bench bled it properly, then the inter-chamber is self priming. And so that just leaves the rear chamber........ if the pedal is low.
_________________________
If you look at the C-valve, you will see that all the plumbing to it that involves the front brakes is on the top end, that's because as regards the front brakes it is just a junction block.
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So then If the pedal is not high and hard, and
No fluid is coming out the front lines, then;
Either no fluid is leaving the M/C , or it is pissing out somewhere else
In order for fluid to be pumped down the line, two things need to happen; 1) the piston has to park far enough to the rear to open the C-port, and then trap the fluid on the down stroke, and 2) the fluid must not return when you lift off the pedal.This often happens. With air trapped in the system it becomes a big spring just bouncing the fluid back and forth in the first couple of inches of the line. The cure for this is to open both front bleeders, routing the fluid into containers via attached lines, and then bleeding each joint separately from the M/C outwards. But first, as already mentioned, clear the bleeders and the bleeder ports.  Then bleed at the M/C then the C-valve, and finally out to the calipers.
Remember to lift the pedal to the top every time, to open the C-ports, and
Make sure the lid is on and secured down, cuz if there is air trapped in the chamber, it will cause a fountain inside the M/C every time you lift the pedal, and you probably want to keep the fluid in the M/C as opposed to all over everything.

Good luck.

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Re: Brakes 2018

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