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changed pads, no brakes


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hi guys, new renix owner here, 88. i just unwittingly changed my pads without reading "how to" in advance and now i have no brake pressure. it just goes to the floor, and my ebrake seems to partially engage and theres a hissing noise.  What the hecks going on here? do i need to bleed the lines? i'm reading about the load sensor in some other threads, how does that have issue with compressing a piston(s) on the front caliper(s)?

HELP? !??!??!?!!

ps did i mention this is my DD? i need a solution i can pull of asap.

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Time out. You say you changed the "pads," but everything else you mention (emergency brake, load sensing valve) is related to the rear brakes. Did you change the FRONT brake pads, or the REAR brake shoes?

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sorry, i replaced the front pads, on the discs. i didn't think that would require any bleeding. the "hissing" may be my master seal? i had my neihbor pump the brakes with the cap/lid off the ms rez and air came shooting up with the same hissing noise. put the cap back on once the air stopped and the peddle went stiff and there is still a hissing noise when the peddle is pumped and it goes to the floor. perhaps the seal on the ms is shot? theres no leaking at the front, and i did not touch the rear.

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Did you run the master dry? Not sure HOW that could happen with a simple pad change, but start with simple things. How is your parking brake "partially engaging" when you haven't touched the rear brakes? Is the "BRAKE" light on the dash on?

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if it was front brake pads,pull them off snd recheck your work,i have seen this before,hissing sound can be power booster  note reubj is right   we need to know what you did   dwa175 :doh:

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i compressed the caliper piston, disassembled the caliper, put in the new pads, reattached the caliper and attempted to drive the vehicle.  it may not be the "ebrake", but the vehicle does not roll freely, maybe the calipers are not disengaging the piston pressure? i assumed it was ebrake because of the light, not realizing that is also my brake warning light. the hissing is coming from the ms and air seems to have gotten into the line if it's bubbling when i pump the  brake peddle, right?

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When you compressed the caliper pistons, did you open the bleeders to allow the fluid to escape as the pistons were pushed back into the bores? That fluid has to go somewhere -- if you didn't open a bleeder, I don't know what might have been damaged.

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As the piston is compressed the fluid goes back into the fluid reservoir.

Do you notice any fluid around the caliper? Did the flexible line get damaged while handling the caliper? It would be quite a coincidence for the master cylinder to crap out at the exact moment the pads were replaced.

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no I did not open the bleeder valve before compressing the pistons. I've been changing brake pads on older vehicles (including several cherokees)for over 20 years without ever having to do more to regain pressure than pump the brakes a few times after reinstalling. guess there's a first time for everything, d'oh!

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no leaks that I could see on the soft lines or the calipers. and it's hard to tell whether or not there was a leak in the master cylinder because I opened the reservoir cap before checking. the hissing noises when the brake pedal is depressed and Stephanie coming from somewhere around the master cylinder reservoir. tighten everything up and its still making a hissing noise and bubbling in the reservoir when I pump the brakes.

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find out when I get home, gonna have to locate that leak and then bleed the lines. funny, several people I've talked to open vavles/lines when doing pads & consider it common knowledge and almost as many don't think you need to. even though it totally makes sense I'd never been advised to... amazed this hasn't happened before!

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The biggest reason to open the bleeder is generally to protect an ABS module, as forcing the fluid back can force contaminants into ABS modules.  No ABS, then it shouldn't be an issue.  I usually open the bleeders to get fresher fluid into the calipers as Hydrogopic brake fluid accumulates water over time through the rubber lines and seals, and can cause corrosion inside the system.  That being said, forcing the piston back with the bleeder closed generally will not cause any problems.  It may have exacerbated an existing issue within the system, or it is simply a coincidence that something else failed.  I would go over the whole system starting with the work you just performed and go backwards.

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have you tried bleeding the brakes? you may of damaged the master cylinder or caused some other problem - but getting air bubbles in the master makes me think you have air in the system from something, i'd try just bleeding the brakes and at least see if there air in the system and if it pushes it out when you open the bleeder valves and does it build any resistance afterwards

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 the hissing noises when the brake pedal is depressed and Stephanie coming from somewhere

 

Who is Stephanie?

 

Did you ever remove the calipers, like out of the vehicle?  I think you got air in there somewhere, maybe when you blew air out the MC.  I'd start by bleeding the brakes to see if you can build up some pedal.  If there is indeed air in the lines I'd do the whole bleed in the correct order, maybe even flush out the old fluid and start fresh...that is what I would do.

 

Have Stephanie help you. :dunno:

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ok, so i replaced the power booster (source of the hissing) and the master cylinder.  started to bleed the lines, rear is clear but front keeps getting significant air bubbles, mostly on the drivers side and I'm not sure from where... i've checked all the hard & soft lines for leaks, they seem solid.  my emergency bypass is open, (brake light on dash will not turn off and front brakes will not engage) despite my efforts to reset it by unplugging it then disconnecting the battery.

 

is it possible the bypass valve being open is letting air into the front lines?

is there a way to reset this valve/sensor, or is it possibly functional and reacting to the mystery leak i haven't found?

any ways to test each line idividually for leaks?

anybody been here before? any suggestions will save my $ at the brake shop, i'd hate to bring it in when i'm so close to finishing!

thanks for all those who have responded in a helpful way!

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replaced the front calipers per a jeep buddy's recomendation(sponsored racer, not just a jeep "enthusiast").  drove around without the emergency bypass switch plugged in and got the front calipers to start engaging. bled the lines in correct order one more time, and took her for a couple more laps. now i can get the front to engage but the "brake" light comes on immediately as the calipers engage, then it feels like they disengage as the brake light goes off.  the light does not come on every time, but i feel the front release and only pumping the peddle gets them to re-engage/ me to stop, peddle to the floor.  there is NO air in the rear lines, but no matter how many times i bleed the front down to no air, more air seems to appear the next time i bleed them.  it would seem that i need a new proportioning valve (only way to get a new er-bypass-valve), and/or there is still air in the master, and/or still a mystery leak(but since i lose no fluid level in the master after miles of pumping the brakes i will have to assume there are none). day 6 tomorrow.

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The front metering block on the MJ is not a proportioning valve. Did you follow the procedure for bleeding the rear brakes on an MJ to ensure that there's no air in the rear bypass circuit?

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