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Discussion Starter · #1 · (Edited)
At 147K miles, and after rebuilding the brakes I am now in need of a new master cylinder. The brake pedal sinks to the floor. I have bleed the system several rimes in the crisscross order and still after several days the pedal begins sinking again. I am now getting a new Mobis master cylinder.

I have read up on bench bleeding the new master. Cardone has new instructions that state, "SLOWLY press in and release the master cylinder piston using short strokes of 3/4” to 1”. NEVER STROKE PISTON MORE THAN 1”. Repeat this step until resistance to piston movement is firm and less than 1/8”. I am OK with the procedure up to this point.

After installing the new master usually you loosen the brake lines that attach to the master one at a time and after pushing down on the brake pedal they are tightened back up. This last step removes any air that may have entered the system while installing the master.

I am concerned about pushing any residual air into the ABS control module. My thought is to leave the lines tight on the master cylinder and crack them one at a time where they attach to the ABS module. This way the line from the master would be bled and any air from the bleeding would escape before entering the ABS module.

Any help on installing the new master? I also anticipate flushing using a pressure bleeder and about two quarts of new fluid. I am trying to avoid paying the dealership to run the ABS pump using their computer while bleeding the brakes. I know that it is double the work but I've read where you bleed the brakes and get a good pedal - take the vehicle out and lock up the brakes several times on loose pavement to fire the ABS. Then one last time re-bleed the whole system again. Your thoughts...

Be Safe, Mark V.
 

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Master cylinder is not a typical fail part for us.. you have ABS and crappy pedal.. we install more ABS module than you can shake stick at.. they leak internal and by-pass fluid, hence the poor pedal.

For bleeding, pressure bleed is the way to go and get it done.. pumping the pedal back-forth only agitates the air into foam.. direct pressure will just use wad of fluid to push the fluid and air out at bleed screw.

Because I have ability to pressure bleed, I would just put cylinder on, and pressurize from there and crack nut loose at first joint away from master..

After bleeding, then run HECU using GDS in pump bleed mode, and let it run.. I usually do it 2 or 3 time.
 

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Discussion Starter · #3 ·
SBR, wow, I sure hope that this isn't the ABS module going bad. I have a pressure bleeder setup and a new master cylinder.

So as I understand it you are saying to replace the master cylinder and then pressurize the system followed by cracking the flare nut where it enters the ABS module? Let any bubbles leak out and re-tighten. There are two lines that lead from the master into the ABS so I would need to do this twice. This would purge any air that gets into the lines between the master and the ABS module.

What PSI do you pump your pressure unit to for bleeding? Next I would bleed the rest of the brake system in the following order - from RR, LF, LR, RF. Rather then pay the $100 I was planning to engage the ABS several times on loose road conditions followed by another round of bleeding the calipers using the pressure bleeder. How does all this sound to you? It is necessary to have the key on or the engine running when bleeding? I read about having the engine running while searching this topic.

Time I have plenty of - money is a limited resource...

Be Safe, Mark V.
 

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Discussion Starter · #5 ·
Tom, bench bleeding a new master cylinder (MC) is fairly simple. Youtube offers helpful videos showing the process. I got a good deal on Ebay for an OEM master cylinder. Mount the MC in a vise and fill it with fluid. You have to have a clear tubing bleeder kit attached to the front and side ports that route the fluid back into the MC reservoir. You then use a blunt tip object to push the plunger which cycles the fluid out the ports and back into the reservoir. I read a tip that said to only push the plunger an inch or less each time. The idea is that pushing the plunger all the way can damage the front seal on the plunger. After about a hundred pushes there should be no air bubbles evident in the clear tubes. Remove the MC from the vise and install it on the vehicle. Remove the bleeder lines, top off the fluid and install the hard lines. You still need to do a final bleed. Have a partner sit in the car and gently press the brake pedal several times until the pedal is firm. While your partner is holding pressure on the pedal loosen the front hard line allowing some fluid to escape and the pedal to sink to the floor. Have a shop towel on hand to contain and catch the escaping brake fluid. Do the same for the side mounted hard line. Once the MC has been installed and bled you will need to bleed the wheel cylinders. Bleed the wheel cylinders RR, LF, LR, and then RF. Go through about 2 quarts for the whole bleeding process. A pressure bleeder can make the whole process a one person job. You can make your own (search Youtube) or buy a Motive Products kit that includes the MC cap that you would have to buy anyway.


Hopefully you don’t have a failing ABS module like I did. That was my most costly repair to date.


Be Safe, Mark V.
 

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Thanks FireMark. Sounds like it's an ordinary bleeding process. I just wanted confirmation it was not some unique process specific to the Santa Fe. I'm also hoping it's not the ABS module.
 

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Helpful hint from your Uncle Rich: On older car pad/shoe replacements. Using a small vise grip, gently squeeze and lock down onto the rubber brake hose where it enters to the calipers, etc. GENTLY. Just enough to crimp the hose line shut. Then, open the bleeder valve before you push back the caliper pistons. All of that dirty brake fluid will now exit thru the bleeder. Not back up the lines to contaminate the fluid upstream. Eventually it can work itself upstream and into the master cylinder as you're "pumping the pedal" and adding fluid to top off during the process. Ultimately, this nasty looking stuff can cause your MC to fail.

Not sure about how this applies to ABS systems. Pumping, etc. If there's a bleeder valve, it would seem plausible to do it for the piston retraction. I do know it sure simplifies the bleeding process and cuts down on the time required.

When it comes time to replace my pads, it will be my first rodeo with ABS.
 

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I guess the procedure has changed for cars with ABS. The recommendation is similar to what you suggest except they omit squeezing the hose. My Hanes manual only says to compress the pistons. I've always done it that way without a problem. Until now.
 

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Compress piston with bleeder screw cracked so old fluid is purged out and doesn't back flow up into master and abs. Clamping hose would be an extra guarantee of no back flow; although I have not bothered , can' really criticize it.
 

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Problem solved by replacing master cylinder

Just finished replacing the master cylinder and bleeding all four corners. The only part I replaced was the master cylinder. After replacing the master cylinder I had no problem bleeding any of the calipers, using the "old school" method. The problem appears to be solved. I guess when I compressed the pistons I blew out the master cylinder.

Thanks for all the advice and encouragement. I'll update if a problem recurs with the brakes.
 
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