Need Help, JKU Brakes and Upgraded MC + Booster with my UD60's - JKowners.com : Jeep Wrangler JK Forum
 
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post #1 of 5 Old 05-11-2018, 10:25 AM Thread Starter
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Need Help, JKU Brakes and Upgraded MC + Booster with my UD60's

This is a bit long but I wanted to cover as many details as I could. I've bled brakes on many cars so this isn't new to me but obviously I'm not a mechanic by trade so I may be doing something wrong.

2015 JKUR, Auto. Just installed UD60's and installed Mopar booster and master cylinder plus new brake hoses for the UD60's. Bled using MightyVac, total PITA, but I bled at least 1/2 quart through each caliper. Brakes were still soft and the Brake light on the dash continuously flashes and dings every time I take off from a stop. I can hear a slight puff of air around the pedal when I press the brake, a second press does not do that.

Attempted to bleed with power bleeder but even at 20psi I couldn't get it to force fluid through the rear calipers even after 10 minutes of the bleeder being open, the fronts did some spitting and then started trickling slowly before eventually stopping. Manual bleeding seemed to be good, pedal would eventually go to the floor and then I would close the bleeder before the air bubble in the hose would get back to the bleeder (it never would fill the hose completely even though I had the end submersed in a half-full bottle of fluid.

Decided to "bench bleed" the master a second time without removing it from the Jeep. Ended up stripping the threads to one of the ports in the MC, had to replace MC. Started the process over again:

- Bench bleed new MC until no air bubbles, left bleeders and hose attached/submersed in the reservoir (no air gets back in this way)
- replaced the line to the HCU from the MC and installed the new MC
- power bleed still does nothing, even with pedal depressed half way
- manual bleeding forces a rush of fluid with no bubbles in it then slowly begins to suck it back in (pedal has sunk to the floor and is still pressed down)
- pedal is very firm with vehicle off, sinks when started
- still hearing a tiny puff of air on that first time I push the pedal so I checked the torque on the booster bolts and the MC -> booster bolts
- brake light still blinks when it is put into drive

What am I missing here? Did I get a bad booster from Mopar? Is there too much air in the HCU/ABS?
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post #2 of 5 Old 05-11-2018, 12:46 PM
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ABS system has to go through the bleed process. You will need a dealer or someone with a high end snap on modus or something of that nature to initiate the process.


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post #3 of 5 Old 05-11-2018, 12:59 PM
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I have the same setup and also the same issue. I ended up giving up and took it to the dealership. They told me my MC was bad. Went home and double checked my work and realized that I forgot to use the rubber o ring between the MC and booster.
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post #4 of 5 Old 05-11-2018, 01:24 PM Thread Starter
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Quote:
Originally Posted by ALASHA View Post
ABS system has to go through the bleed process. You will need a dealer or someone with a high end snap on modus or something of that nature to initiate the process.
I feel like something else is wrong still. Regardless of the ABS, I should be able to properly bleed the rears with the power bleeder but I am simply not getting fluid to them unless the pedal is pumped - even with 15-20psi going to it from the power bleeder.

I did see somewhere that it could be the shuttle valve (or similar) in the HCU that regulates the proportioning may be stuck.

@still in school did putting the o-ring in resolve your issue? My o-ring is there but it fits like crap. The second new MC didn't even come with one so I had to pull it off the other new MC. I went through the install carefully last night since it was like the 4th time I've done it. The *only* thing that bugs me is how difficult it is to get the cylinder and booster shaft to mate. Every other MC I have replaced in the past the pin/shaft protruded from the booster slightly so it was easy. I did make sure that there was spring tension against it as I was tightening the bolts.
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post #5 of 5 Old 05-14-2018, 09:32 AM Thread Starter
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Well, I ended up pulling the new master cylinder out because the brakes stuck on my first trip out, all 4 were smoking by the time I made it the 1/2 mile back home.
Found these metal shavings in the plunger in front of the booster pushrod. This was a Crown replacement, not a Mopar part, that I bought from ShopJeepParts. I guess it’s going back. 🤬
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