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post #1 of 12 Old 06-26-2011, 06:48 PM Thread Starter
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Another brakes question

Wonder if anyone else has this issue. I was on a high mountain trail yesterday and the JK's brakes would not hold it on steep grades. Even with the pedal mashed to its stop I had to use the handbrake to hold it or it would slowly roll backwards. In all other cases the brakes are fine. They've been well pressure bled, so I don't think it's an air issue at all. I assume there's just not enough rear brake disk area and / or pressure to the rear, so on a grade the weight transfer overwhelms them. Thoughts?

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post #2 of 12 Old 06-26-2011, 07:30 PM
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I have yet to ride on steep grades but how many miles are ob the pads?


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post #3 of 12 Old 06-26-2011, 07:50 PM Thread Starter
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Only about 17k, they look perfect. It has Spyntec hubs and thus their rotors. The rear rotors are showing the usual accelerated JK wear but they have plenty of meat left and the pads are fine. FWIW, it had this same problem with the stock front rotors.

I'm wondering if something like a two or three piston front caliper might help?
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post #4 of 12 Old 06-26-2011, 09:16 PM
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The only time I have issues with the brakes stopping me is when I'm in 4low......


Maybe something wrong with the hydraulic part of the brakes?
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post #5 of 12 Old 06-26-2011, 09:38 PM
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That sounds like more of a vacuum issue, actually. Check the vacuum hose where it goes into the brake booster. Beyond that, the booster itself could be crapped out. Or, since you're at some altitude, it may not be getting enough vacuum. No amount of extra mechanical braking force would help that. Only hydra-boost would fix that, or a vacuum pump- Mark W.

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post #6 of 12 Old 06-27-2011, 03:05 PM Thread Starter
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Thanks. They have plenty of boost, the issue is that on steep grades the system won't hold the rig in place. Even with the pedal mashed to the stop it slowly rolls backwards. OTOH, if facing down the same steep slope they hold just fine. When they are being bled the flow to the rear calipers is very restricted, fluid just kind of oozes out. Dealer tells me this is normal and caused by the restrictions in the ABS/BAS unit.

This is really the only brake issue I have with the bloody thing, they are otherwise just fine.
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post #7 of 12 Old 06-27-2011, 06:39 PM
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Quote:
Originally Posted by SoK66 View Post
Only about 17k, they look perfect. It has Spyntec hubs and thus their rotors. The rear rotors are showing the usual accelerated JK wear but they have plenty of meat left and the pads are fine. FWIW, it had this same problem with the stock front rotors.

I'm wondering if something like a two or three piston front caliper might help?
2 piston calipers up front really help especially with bigger rotors and performance brake pads.

check out the Teraflex big brake kit...I love mine one of the better upgrades I have done.

or people have had really good luck with the Rebel Off-road brake upgrades


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post #8 of 12 Old 08-04-2011, 06:24 AM Thread Starter
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Well, after doing some measuring and checking it does appear the Teraflex Big Brake rotors will work on the Spyntec hubs provided the center hole is opened up. Called Matt at Spyntec and he said the center hole needs to be 4.005". Need a good machine shop to open up the hole and maintain the center. Otherwise everything else seems to be a bolt on & go. Thinking maybe Tera's larger master cylinder might be a good first step, as the system just seems to need more fluid flow. Would like to know the OEM applications fro the rotors, pads & M/C so that later on I could source common parts for it.
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post #9 of 12 Old 08-04-2011, 06:55 AM
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Just a few random thoughts here....

Is the proportioning valve adjustable? You're saying high wear on the rear brakes, maybe the proportioning valve is putting too much to the rears and not enough to the fronts? Any chance the ABS is kicking in at all?

I'd look at a higher volume master cylinder before going to new calipers. Two or three piston calipers get more pressure yes, but they also require more fluid volume at the same time. if you're already bottoming out the pedal, the problem more sounds like you're not getting enough fluid volume going to the calipers. More pistons may actually make the problem worse.

How steep are we talking here anyway? I highly doubt it, but any chance you might be uncovering the ports inside the reservoir in the master, and thus sucking air?

-Hans
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post #10 of 12 Old 08-04-2011, 07:53 AM
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There is a prob there somewhere. The hill to my house is a very steep grade(%?) and my stock brakes hold just fine. I'm inclined to agree with thaduke and go with a Vacuum issue. Like he says if the vacuum is down you can hold it to the floor all you want and it won't help.

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post #11 of 12 Old 08-04-2011, 10:28 AM Thread Starter
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Quote:
Originally Posted by HHaase View Post
Just a few random thoughts here....

Is the proportioning valve adjustable? You're saying high wear on the rear brakes, maybe the proportioning valve is putting too much to the rears and not enough to the fronts? Any chance the ABS is kicking in at all?

I'd look at a higher volume master cylinder before going to new calipers. Two or three piston calipers get more pressure yes, but they also require more fluid volume at the same time. if you're already bottoming out the pedal, the problem more sounds like you're not getting enough fluid volume going to the calipers. More pistons may actually make the problem worse.

How steep are we talking here anyway? I highly doubt it, but any chance you might be uncovering the ports inside the reservoir in the master, and thus sucking air?

-Hans
No air in the system, it's been pressure bled until the cows come home. I even had the local dealer run the StarScan tool ABS bleed routine, thinking there might be some air in the motor/pump unit. Made no difference. As JKs go mine has a relatively firm pedal, some others I've checked have more pedal travel than mine and are even less firm. The problem is on our steep mountain grades, and around here I do mean steep. When the rig is facing uphill, such as when negotiating switchbacks or trying to hold it in place, the pedal will squish all the way to the internal stop but the rig will slowly roll backwards. Even worse when power is being applied in 4-lo, like when doing a three-point turn on a switchback. I've heard other JK owners around here gripe about this so it's not just my rig that has the issue.

The issue with JK rear pads & rotors wearing faster than the fronts is pretty well documented. It's caused by the ESP system and is probably just something one has to live with.

I'm just looking at a way to resolve this for safety reasons. Try negotiating Black Bear Pass while you're worried about the brakes holding and you'll know what I'm talkin' 'bout!
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post #12 of 12 Old 08-20-2011, 10:40 AM Thread Starter
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FWIW, I installed Teraflex's Big Brake kit and master cyl this week. Write-Up section has the details.
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