J8 booster talk
- Thread starter WSS
- Start date
Buying two right now!
How in the world do you find this stuff? You would make a excellent purchasing agent for just about any industry.
I hadn't seen discussions about using spacers. Why are they needed? Granted, it's been a few years, but the info I saw didn't discuss the need for shims.
I did read a suggestion of trimming the non-threaded parts of the mounting bolts to give clearance when installing.
I watched this video a while ago, which I felt was pretty solid - although I think he ruined the booster in the process. It was a cringe moment when i heard the sucking of the fluid, for sure. He also didn't do the ABS bleed, which i do believe is necessary after reading up on it more.
I don't think I'll be able to keep my visit compressor mount. Even if I adapted the mount, I'm thinking clearance won't be enough for it and the relay box I have.
I did read a suggestion of trimming the non-threaded parts of the mounting bolts to give clearance when installing.
I watched this video a while ago, which I felt was pretty solid - although I think he ruined the booster in the process. It was a cringe moment when i heard the sucking of the fluid, for sure. He also didn't do the ABS bleed, which i do believe is necessary after reading up on it more.
I don't think I'll be able to keep my visit compressor mount. Even if I adapted the mount, I'm thinking clearance won't be enough for it and the relay box I have.
The rod on the old booster was .255" longer than the new J8 booster, the rod is not adjustable like my older rigs. This is a non issue 2012 and up, the early JK's used a shorter rod. Sometimes, it was just right or maybe a washer or two. I just took the JK for a test drive and the brakes engage right away, better than before with less pedal travel. The brakes release easy with no drag when my foot is off of it, so I hope it's all good.
I did not have to do the ABS disable (either time, I will get to that) because I did not run it without fluid, or "dry". The first bleed was very little air, as the bench bleed was solid and I plugged the lines as soon as I pulled them from the MC. I went back over the flare nuts on he MC due to them being a little wet on the bottom, there was my issue, the flare wrench slipped of the nut and rounded it. due to the small leak, I had to repair it. This was interesting. the tube and the thread are SAE, the head of the flare nut is the only "metric" part of it. So I cut about 3/8" off the bad end, put a flare nut with a 7/16" head and re flared it. I would have bent up a new one but the other end is a bubble flare. I do not have that tool. I did however buy 2 bubble flare to inverted flare adapters today at Mc Fadden Dale hdw. So, if it happens again, I can bend up my own for about 15 bucks.
I did two types of "bleeds" twice. First was the vacuum pull with my mighty vac and second was the 10min gravity bleed. No air for sure anywhere in the system.
I watched that video many times. Mostly so I would not trash the MC. That was "cringy". Poor guy. the brakes work way better than before. It has corrected three distinct problems, 1) the brake pedal does not pulse on downshift anymore, that was likely due to the o ring not being seated correctly. 2) easy stopping with light foot pressure on the streets, no more slick feeling brakes. 3) I can definetly bring the beast down quicker, way quicker, I can hear the rubber growling with the window down now.
VERY happy (right now lol). So far very good. Worth the effort on this project.
I did not have to do the ABS disable (either time, I will get to that) because I did not run it without fluid, or "dry". The first bleed was very little air, as the bench bleed was solid and I plugged the lines as soon as I pulled them from the MC. I went back over the flare nuts on he MC due to them being a little wet on the bottom, there was my issue, the flare wrench slipped of the nut and rounded it. due to the small leak, I had to repair it. This was interesting. the tube and the thread are SAE, the head of the flare nut is the only "metric" part of it. So I cut about 3/8" off the bad end, put a flare nut with a 7/16" head and re flared it. I would have bent up a new one but the other end is a bubble flare. I do not have that tool. I did however buy 2 bubble flare to inverted flare adapters today at Mc Fadden Dale hdw. So, if it happens again, I can bend up my own for about 15 bucks.
I did two types of "bleeds" twice. First was the vacuum pull with my mighty vac and second was the 10min gravity bleed. No air for sure anywhere in the system.
I watched that video many times. Mostly so I would not trash the MC. That was "cringy". Poor guy. the brakes work way better than before. It has corrected three distinct problems, 1) the brake pedal does not pulse on downshift anymore, that was likely due to the o ring not being seated correctly. 2) easy stopping with light foot pressure on the streets, no more slick feeling brakes. 3) I can definetly bring the beast down quicker, way quicker, I can hear the rubber growling with the window down now.
VERY happy (right now lol). So far very good. Worth the effort on this project.
Hi, I'm in the process of trying to do the J8 swap. I had ordered everything a few years ago, then got delayed because the master cylinder Jegs said was in stock wasn't... for a couple years! So I finally have the master cylinder and booster, but now that I finally have the master, I found out I got the wrong reservoir! Does anyone know where to get a J8 reservoir? Every place I look shows them as out of stock.
My Jeep is a 2018 JKU on tons. I've put over 30k miles on it with the tons and stock master cylinder, but the pedal travel is very long. I'm hoping to finally get this part of the project completed.
My Jeep is a 2018 JKU on tons. I've put over 30k miles on it with the tons and stock master cylinder, but the pedal travel is very long. I'm hoping to finally get this part of the project completed.
It is a worthwhile project. Fixes the spongy feel and the long push.
I bought this one:
68048758AA - Genuine Mopar Reservoir-Brake Master Cylinder
MoparPartsGiant.com offers the great deal for genuine Mopar parts, 68048758AA. Reservoir-Brake Master Cylinder for $159.75. All parts are backed by the Mopar's warranty.
www.moparpartsgiant.com
Well this was a fail. I ordered the reservoir and finally got the correct one, thank you WSS. Last night I installed everything. Of course the engineers decided to use flanged nuts with flanges larger than the access holes in the firewall, so while the aluminum mounting plate was out I enlarged the holes, "just in case I have to do this again". It was a great idea. I got it installed which was pretty straightforward once I clearanced the holes. It was dark so I held off bleeding until today.
I went to bleed the system and just couldn't get a good pedal. Then I noticed fluid dripping from the master cylinder. It was coming from the line fitting at the back of the cylinder. I checked tightness and gave it a little extra, still leaked badly. I removed the fitting and the flare looked fine, but I noticed a bit of indication on the first couple threads of the fitting that looked like it was binding. I pulled the master back off and...the threads were never machined to the full depth! The fitting is bottoming before it can seal.
Now after nearly 3 years of waiting and fighting to finally get a master cylinder, it's junk. I'll get on the phone to Jegs and see if they can send me another. This weekend's trail ride is out. Hopefully there is another master available. Otherwise I'm cutting my losses and might go with hydroboost, since there doesn't seem to be any other options any more.
Quick Q for you...
I am just getting around to getting my inner fenders put back together and boy is the ABS wiring in a terrible location with the J8 booster. I can't seem to route it in a way that doesn't cause other issues.
I'm at the point now where I may cut down the new inner ABS tray to make some room for the wiring to fall "in to" under the master cylinder...
Also, is your Hemi a LX/Car engine?
The J8 upgrade is absolute garbage. The Booster never works correctly, and the Master cylinder and reservoir won't bleed, and leak. It took 3 giant bottles of brake fluid to bleed mine the first time. Using a vacuum bleeder. Then after finally getting it bled it only lasted 2 weeks before an internal seal inside the master cylinder ruptured and the Jeep wouldn't hold at a light without the pedal slowing going all the way to the floor. I got a second master cylinder under warranty, and again it took 3 giant bottles of brake fluid and a power brake bleeder to get the job done. Now my new master cylinder leaks somewhere and the reservoir goes empty every few weeks. I have read online that almost everyone that ever tried to use the J8 or "Big Brake" system has had issues with the Booster/Master Cylinder/Reservoir. I installed my system 5 years ago, and even had the dealership bleed the ABS system for me, and the brake fluid leaks out of the system somewhere. I haven't been able to drive my Jeep more than a hundred miles since I installed the big brake kit. I finally gave up and just parked it and bought a whole new Jeep. I feel we should all get together and do a class action lawsuit... if you search online there are many people with the same or similar issues.
I've seen a number of people refer to issues with their "J8 Kit", but it seems like it was always someone who used the Crown replacements, yourself included:
Everyone I know with a real Mopar J8 - and off the top of my head is at least 5 people with JKU's running tons - have had theirs for a number of years with trouble free service and fantastic results.
And I'm not sure what you mean by "leaking somewhere"... seems like that would be an important thing to figure out to determine the root cause of the failure.
Last edited:
It is tight for sure. Your idea of cutting the ABS tray to lower it would work. I added a few aluminum spacers under the module to raise it up "slightly" over the curve of the MC, still had to add a sleeve protector cause I did not feel happy about the way it laid on the sharp edge. Your idea is better seeing that you are right there. Mine is hindsight. LOL
I was told my Hemi is out of a challenger. I believe the trans and motor were purchased together. 5.7/545rfe
Mine works great. In fact it is a game changer. No issues with mine other than it being a pain to install. I think the install is where most trouble starts, plus the non oe parts. It was my understanding the J8 kit was not really a kit but an option for the military and government JKU's. The kits are just assembled parts to upgrade the brake system.