Another Brake Discussion (sorry...) - JKowners.com : Jeep Wrangler JK Forum
 
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post #1 of 7 Old 02-25-2018, 06:53 AM Thread Starter
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Another Brake Discussion (sorry...)

Quick background: 2009 JKU-R, stock rear brakes other than longer brake lines that came with the JPP 4" lift, and the Mopar BBK up front that includes calipers, rotors, booster, m/c, and again the longer brake lines from the JPP 4" lift. I'm battling a long pedal throw before any brake action happens, and then the pedal is very soft. The brakes work OK, but the pedal feel is less than confidence inspiring. I've bled the brakes several times, both via the pedal pump method and a vacuum bleeder. However...

I can't wrap my head around what's going on here: when bleeding the rear brakes via the pedal pump method, the brake pedal stops roughly 1/2 way through the pedal arc when you crack the bleeder. Stops dead and will not go any further, period. I can push hard enough to bulge the firewall pretty severely, but simply no more travel. WTF???

In stark contrast, the front brakes bleed exactly as you'd expect, with the pedal travelling all the way to the floor when you crack the bleeder.

'09 Unlimited Rubicon, Deep Water Blue
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post #2 of 7 Old 02-27-2018, 12:12 PM
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Quote:
Originally Posted by tobyw View Post
Quick background: 2009 JKU-R, stock rear brakes other than longer brake lines that came with the JPP 4" lift, and the Mopar BBK up front that includes calipers, rotors, booster, m/c, and again the longer brake lines from the JPP 4" lift. I'm battling a long pedal throw before any brake action happens, and then the pedal is very soft. The brakes work OK, but the pedal feel is less than confidence inspiring. I've bled the brakes several times, both via the pedal pump method and a vacuum bleeder. However...

I can't wrap my head around what's going on here: when bleeding the rear brakes via the pedal pump method, the brake pedal stops roughly 1/2 way through the pedal arc when you crack the bleeder. Stops dead and will not go any further, period. I can push hard enough to bulge the firewall pretty severely, but simply no more travel. WTF???

In stark contrast, the front brakes bleed exactly as you'd expect, with the pedal travelling all the way to the floor when you crack the bleeder.
When you installed the BBK master/booster are you sure you got the booster pushrod seated properly in the M/C piston? some reports out there of it not seating properly. Otherwise I'd do a pressure bleed of the entire system using a Motive pressure bleeder, etc.

'09 JKRU. 4" Teraflex long arm, Teraflex R44 housing, Teraflex / Fox Resis, Poly Performance skids, Nemesis Billy Rockers, Nemesis flares, 37" ATZ P3s on 17" 5x5.5" Trailready HDs, Spyntec hubs, Teraflex BBK, Mopar BBK master/booster, Superior front & Alloy USA rear axle shafts, CTMs, Reids, Synergy drag link & tie rod, WTOR hydro-boosted steering, 5.38s, TF Dual Rate front bar, TF bumpers, Warn Powerplant, Tom Woods shafts, AA xfer case cable, Kilby canister relo, RH4x4 cage.
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post #3 of 7 Old 03-02-2018, 06:42 PM Thread Starter
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Thanks much for the response!

Yes, I have verified the push-rod is/was properly engaged a couple of different times now. I have it fully disassembled and the m/c on the bench again this afternoon. A wheeling buddy has the same BBK on his Jeep, and this afternoon I verified that his pedal also stops short on the rear circuit. So there must be some sort of internal check or something in the m/c itself? Regardless, I guess that's not any sort of clue as to my problems.

What I did find, however, is that I can actually push all the way through the brake pedal travel without it ever really firming up. Yes there is resistance to my foot pushing on it, but with not to great of effort I can push all the way to the floor. Normally this would cause me to think the m/c is bleeding internally and has failed, but when I disconnect the m/c from the system and block off the outlet ports, the push rod will only travel about 1/2" and then stops firm and holds steady. So... I'm pretty sure that tells me that I've got a massive air bubble SOMEWHERE in the damn system that just won't come out???

I will source a pressure bleeder first, and then see if I can get my hands on a factory scan tool with the ABS bleeding capability and go through that routine as well.

'09 Unlimited Rubicon, Deep Water Blue
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post #4 of 7 Old 03-02-2018, 09:03 PM
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Quote:
Originally Posted by tobyw View Post
Thanks much for the response!

Yes, I have verified the push-rod is/was properly engaged a couple of different times now. I have it fully disassembled and the m/c on the bench again this afternoon. A wheeling buddy has the same BBK on his Jeep, and this afternoon I verified that his pedal also stops short on the rear circuit. So there must be some sort of internal check or something in the m/c itself? Regardless, I guess that's not any sort of clue as to my problems.

What I did find, however, is that I can actually push all the way through the brake pedal travel without it ever really firming up. Yes there is resistance to my foot pushing on it, but with not to great of effort I can push all the way to the floor. Normally this would cause me to think the m/c is bleeding internally and has failed, but when I disconnect the m/c from the system and block off the outlet ports, the push rod will only travel about 1/2" and then stops firm and holds steady. So... I'm pretty sure that tells me that I've got a massive air bubble SOMEWHERE in the damn system that just won't come out???

I will source a pressure bleeder first, and then see if I can get my hands on a factory scan tool with the ABS bleeding capability and go through that routine as well.
Did you bench bleed the master? If not you most likely have air in the ABS system. This will have to be bleed out at the dealer or someone with the proper scan tool.
Correct way to install the master is to bench bleed the master. Then install the master and crack the brake lines into the master and bleed it again before bleeding the system. This is your best chance of not introducing too much air into the system.
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post #5 of 7 Old 03-03-2018, 06:56 AM Thread Starter
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Then install the master and crack the brake lines into the master and bleed it again before bleeding the system.
Yes, master was bench bled thoroughly before installation. However, can you explain the above statement a little? I'm not following what you mean by "...crack the brake lines into the master and bleed it again..." Sorry for what is probably a stupid question, but I appreciate ANY thoughts on this one; I'm at my wits end and ready to just throw a match at the damn thing.

'09 Unlimited Rubicon, Deep Water Blue
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post #6 of 7 Old 03-04-2018, 01:19 AM
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If there is air in the system it to late for that. You will need a scan tool to bleed the ABS system. But as far as what I meant was once you bench bleed and install the master you should loosen the brake lines where they go in the master and press down the pedal. Tighten the lines and let the pedal up. Do this 4-5 times to try and remove as much air as possible from the system before doing a complete bleeding through the calipers.
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post #7 of 7 Old 03-04-2018, 07:47 AM Thread Starter
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Thanks, I'll try that on the next go-round!

My contact with the scan tool is unavailable for a couple weeks (his wife just had baby #2), so it's going to sit for a while... Maybe the Jeep will use the downtime to think back on what it's done to me and decide to play nicer in the future

'09 Unlimited Rubicon, Deep Water Blue
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