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Jeep Grand Cherokee HCU replacement for soft brakes - how to bleed?

I've had a soft brake pedal (goes nearly to the floor) that's slowly gotten worse. Replaced Master Cylinder (dealer - twice). Pads and rotors fine, no external leaks. Jeep dealer says HCU (in ABS system) needs replacement. Found one online at 1/2 dealer price. Question is: service procedure says to use Dealer service tool (DRB II) to bleed HCU (which turns on the ABS pump, I think). Can I just hook it (the ABS pump) up to B+? Has anyone else replaced an HCU that would have some tips or cautions? Thanks!!!

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Posted on Jan 02, 2017

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SOURCE: 1997 Jeep Grand Cherokee, hear air bubbling out

First, inspect all lines and fittings for seepage. If fluid is getting out anywhere, air is entering system as well. Fill the master cylinder and bleed it first. Make sure that when bleeding someone is holding pedal down until after you have closed each bleeder screw.(applies to all bleeders). Bleed the right rear, then l/r, r/f then l/f. While doing this keep checking master to make sure it does not run dry at any point. Make sure that at each wheel there is no more air coming out before you continue on to next one. Sometimes if there is an excessive amount of air, it's good to go around to each wheel twice.(use a small box wrench on bleeders if possible so you can actually see what's coming out.(Another way of doing this is to use a small section of plastic tubing like fish tank air hose, and attach it to end of bleeder (sometimes if hose is too small, it can be warmed in hot water so it expands over nipple.) put the free end in a glass jar with some fluid in it, keeping the hose in the fluid to prevent air from entering, using this method abslolutely prevents air from getting into system while bleeding)
Other causes of low pedal are worn rotors or drums and improperly adjusted rear brakes. If you have ABS, all of this applies but there may be a problem with abs system (usually will turn on abs warning light)
good luck

Posted on Feb 22, 2009

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SOURCE: 1997 Jeep Grand Cherokee Brake Problem. Brake

This may sound dum but its been done a few times and is a simple mistake , the bleeder screw is up top, with the caliper on the bleeder screw should be up top, if not then calipers are on the wrong side, it sounds like air in the system, also you pumped the pedal up to push out the piston so pads hit rotor after bleeding,i dont see anything else, if the pedal is good with pinched lines at caliper then it got to be calipers are wrong or on the wrong side and the bleeder is not atop caliper,also you bleed the rear also? these trucks and cars use left caliper and rt rear on one system of the master and rt front and left rear on one side, let me know about the caliper, heres a picture to show you what i mean. hope this helpsjohnjohn2_23.jpg

Posted on Nov 16, 2010

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SOURCE: i have replaced master cylinder on my 1997 jeep grand Cherokee and the petal goes straight to the floor l have bleed numerous times and yet the pedal still goes to the floor

Did you bench bleed the master cylinder before you installed it? If not you might beed to pull it off and bench bled it.

Posted on Oct 15, 2012

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I have a 1997 jeep grand cherokee. I have no

got ABS
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and skipping the MC bench bleed, will make this 100x harder.

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in late model GM and Ford cars with quick take-up master cylinders, the quick take-up valve takes about 15 seconds to reseat after the brake pedal has been depressed, so you should wait at least 20 seconds before you press the pedal while bleeding. If the pedal is pumped too quickly while manually bleeding the system, you may never get the pedal to firm up. On a side note, did you check the level in the master cylinder after every 2 or 3 bleedin procedures? you could have been pumping air right back in the lines if the reservoir runs dry during the bleeding process.

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I have replaced my brake pads I've bleed my lines several times. The brakes work fine until I hold the brake pedal down, thats when it slowly goes down to the floor in a few seconds and the brak

sounds like the brake master cylinder seals are worn buy a master cylinder kit and get a mechanic to repair it it is a lot cheaper than replacing the whole unit

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Why did you change the brake pads? Was it because there was already a problem with the brakes? Or just because they were worn out?

It's quite common for the failure of the brake master cylinder during/after bleeding brakes, especially if it's the first time for a long time that they've been bled. The reason is simple: during operation, vehicle braking systems take water from the atmosphere into the brake fluid. This does a couple of things - reduces the boiling point of the fluid; and begins the inexorable process of the corrosion of the inisde of the brake system components. This also happens within the brake master cylinder, and creates a 'use ridge' at the place where the piston stops in normal operation. When you bleed the brakes, you force the master cylinder piston beyond (across) that ridge, and sadly this often tears the fine sealing edge off the master cylinder piston seal, leading to a soft pedal (at best) or one that goes through to the floor (at worst). Obviously I can't tell you what's happened to yours, but it will need someone to check it out properly or you run the risk of having permanently unserviceable (and potentially unsafe) brakes. Good luck!

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you have trapped air in the system and need to bleed all 4 calipers. or take it someplace and have it power bled

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I have a 03 ford taurus the break pedal gose to the floor after changing the rear breaks and the front pads and after changing the master cylinder? what else could b the problem

You've done major work and now you'll need to completely bleed air out of the system, to get the fluid to go all the way through. You may also need to adjust the rear brake shoes.

First, bleed the Master cylinder to get fluid through it. This should have been done before installation. Loosen the lines at the M. Cylinder and fill up the reservior with brake fluid. Pump the brake pedal slowly with the cover on the M. Cylinder to prevent fluid from splashing out. Once you've got fluid coming through the M.Cylinder, tighten the brake lines at the M. Cylinder.

Bleeding the brakes is a 2 person operation. You always bleed the brake the farthest from the master cylinder, then the next, the next, and finally the drivers front brake which is the closest to the M. Cylinder.

If you are unfamiliar with this process, you need to remember that you can't let the brake fluid get low in the M. Cylinder, or you have to start all over when air gets back into the lines.

When one person pumps the brakes, after several pumps hold the pedal down as far as it will go and keep pressing to the floor as the other person loosens the bleeder valve. Don't let off of the pedal before tightening the bleeder valve. Then repeat until all of the air is gone.
Teamwork and communication. Both of my wives were able to assist me in bleeding brakes.

You will have to add fluid and repeat this process until you have a firm pedal.

One man bleeder valves work if used properly, but who tells you what is happening at the other end while you're pressing the pedal?

Good luck.

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