JK-8 brake booster / master cylinder - JKowners.com : Jeep Wrangler JK Forum
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post #1 of 10 Old 05-01-2017, 11:29 AM Thread Starter
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JK-8 brake booster / master cylinder

I installed the JK-8 brake booster and master cylinder this weekend. Wasn't that bad of a job, the worse part was getting the new stuff back in. Anyways, I noticed right when I was done that the brake lights were on so I went back under the dash to see what was going on and the brake pedal physically will not pull back far enough to hit the little plunger that turns it off. It gets right there to it and actually may even barely touch it but cant travel far enough back to turn it off.

This sound normal to others that have installed this?

Second part, I bench bled the master cylinder but when you go to install it the ports are open for a few seconds and stuff drips out. I don't see how you CANT get air in the system right there. I used a power bleeder to bleed the system as I installed new calipers as well, the style I have pressurizes the reservoir on top of the master cylinder. I feel that I did a really good job but I am scared that I got air in the ABS module. Thoughts?
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post #2 of 10 Old 05-01-2017, 11:55 AM
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subscribed since I'll be doing this project soon.
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post #3 of 10 Old 05-01-2017, 03:16 PM
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The little plunger that makes the lights go off is just pushed in too far. pull it out forcefully.. don't worry if you yank it all the way out. it pushes back in.
don't worry about the abs unless your brakes suck. even then its not that big of a deal
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post #4 of 10 Old 05-02-2017, 05:11 PM
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following as I am doing teh same. Where did you get your JK8 master and booster from?


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post #5 of 10 Old 05-02-2017, 05:55 PM Thread Starter
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Originally Posted by geberhard View Post
following as I am doing teh same. Where did you get your JK8 master and booster from?

I think ebay was the cheapest I found the setup at. I took the plate down that holds the plunger assembly to see how it worked. you DO NOT need to do this and it was a pain in the ass to access the 2 screws that hold it up there. Just depress the brake pedal and firmly pull the plunger out. When you release the pedal it will push it back in to where it needs to be to work right.
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post #6 of 10 Old 05-02-2017, 08:54 PM
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Quote:
Originally Posted by Dkjeep View Post
I installed the JK-8 brake booster and master cylinder this weekend. Wasn't that bad of a job, the worse part was getting the new stuff back in. Anyways, I noticed right when I was done that the brake lights were on so I went back under the dash to see what was going on and the brake pedal physically will not pull back far enough to hit the little plunger that turns it off. It gets right there to it and actually may even barely touch it but cant travel far enough back to turn it off.

This sound normal to others that have installed this?

Second part, I bench bled the master cylinder but when you go to install it the ports are open for a few seconds and stuff drips out. I don't see how you CANT get air in the system right there. I used a power bleeder to bleed the system as I installed new calipers as well, the style I have pressurizes the reservoir on top of the master cylinder. I feel that I did a really good job but I am scared that I got air in the ABS module. Thoughts?
I just removed the switch/plunger bracket assy. from under the dash and bent it until the brake light worked like it is supposed to. Took a couple of in and outs. I'm an old man so having the front seat out made it do-able.

When I installed the MC and Vac booster with my UD60 install I blead the system with the new calipers and the old MC in place. Even did a test drive to prove to myself how much I needed to do the upgrade. Then did the install of the new MC/booster and used a syringe to force 50/60cc of brake fluid back up thru the caliper bleed screws (one on the pass front and one on the rear) to push the air back up into the new MC and not into the ABS module. Worked great for me. The wife said she could see the air bubbles coming up in the reservoir. 60cc not enough to push air all the way up to the ABS module, but did clear the short jumper between the ABS and MC. Then bleed the system anyway you want to clear out the calipers. Don't know if this is necessary, but sure worked for me.

16 JKU Sport
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Last edited by ChuckMRN; 05-02-2017 at 08:58 PM.
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post #7 of 10 Old 05-03-2017, 09:29 AM
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Chuck awesome tip on the syringe! Do you have any pics of teh syringe and hose you used? Thanks!


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post #8 of 10 Old 05-03-2017, 10:08 AM
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The plastic plunger un the brake switch is self-adjusting. it has a ratcheting mechanism in it that makes the distance change. when you remove the pin on the brake pedal, the pedal hits the plunger and pushes it in too far. All you have to do is pull the plunger back out and it will work again.
this upgrade is really easy.
I went through the ABS bleed procedure with the scanner and it only pulses the abs. hitting the brakes on a dirt road would do the same thing. its nothing to worry about.
This set up really stops with my super duty brakes
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post #9 of 10 Old 05-03-2017, 03:47 PM
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Quote:
Originally Posted by Dkjeep View Post
I installed the JK-8 brake booster and master cylinder this weekend. Wasn't that bad of a job, the worse part was getting the new stuff back in. Anyways, I noticed right when I was done that the brake lights were on so I went back under the dash to see what was going on and the brake pedal physically will not pull back far enough to hit the little plunger that turns it off. It gets right there to it and actually may even barely touch it but cant travel far enough back to turn it off.

This sound normal to others that have installed this?

Second part, I bench bled the master cylinder but when you go to install it the ports are open for a few seconds and stuff drips out. I don't see how you CANT get air in the system right there. I used a power bleeder to bleed the system as I installed new calipers as well, the style I have pressurizes the reservoir on top of the master cylinder. I feel that I did a really good job but I am scared that I got air in the ABS module. Thoughts?
As others mentioned, the brake light switch will self adjust after you pull the plunger out. Re: your second question, there's little risk that you got any air into the ABS system. The spools in the ABS module default to closed when ABS is not actuated. They seal well enough there's little risk any air got in there. After replacing brake lines I once had the local deal do the Star Scan ABS bleed routine and ther was no difference in brake performance. I no longer even bother if I have to crack open the main braking system. A year or more ago I installed the Mopar Master & Booster kit and did the same install procedure as you, bench bleed + pressure bleed. The brakes are much improved. I have them combined with Teraflex's BBK in front, outstanding.
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'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 #10 of 10 Old 05-03-2017, 08:15 PM
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Used for flushing naso-gastric tubes, but think I've seen variations in auto part stores



16 JKU Sport
RK 3.5 X Factor, UD 60's, Atlas T Case 4.3:1,
TR Bead locks with Toyo Open Country MT's,
VKS Bumpers and Sliders. EVO Skins,
PSC Hydro on Synergy Steering,
Fox Shocks and Bumps
"40's Baby!"
2011 JKU RUBI "SOLD"
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