Novak Conversions Jeep Wrangler JK engine mounts

J8 booster talk

WSS

WSS

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Looking for some info on the J8 booster upgrade.

I bought a J8 booster from Jeephut. Full master cylinder and booster kits are hard to find, so i bought just the booster. Can I swap JUST the booster? or is the OE master cylinder different and will not work with the new J8 booster?

Thanks for any input!
 
I found all this reading:

Matching Components:
The Mopar J8 booster and master cylinder are designed as a pair, with specific dimensions and features that ensure proper functionality when used together.


  • Not Compatible with OEM:
    Attempting to use the J8 booster with an OEM master cylinder will likely lead to compatibility issues, improper brake performance, and potentially damage to the components.

    Heavy-Duty Application:
    The J8 booster and master cylinder are designed for heavy-duty applications like those found in Jeep models with larger brakes and/or one-ton axles, according to a Northridge4x4.com listing.


    Performance Upgrade:
    The J8 booster and master cylinder are considered a performance upgrade, providing better pedal feel, more brake bite, and improved braking performance, according to a Reddit post.




 
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Ok I read the questions. Can I buy a replacement master cylinder? Anyone have a breakdown of the parts that are included in the kit?
 
I found this part number for the master cylinder, the source is 50/50 reliable. My local auto supply cannot find the number.

68048757AA
 
WSS said:
I found this part number for the master cylinder, the source is 50/50 reliable. My local auto supply cannot find the number.
Click to expand...

This is the same part number I've found on a couple other forums. But there is a noticeable design difference in the 2009-2014 master cylinder and the one you need for your 2007. Check this link and look at the "other brands" section down the page. The W0133-2775579 specifically says it's not designed for heavy duty brakes.

https://www.partsgeek.com/htxk2t7-j...VjSsq1PhcNwvUlHQRLVjpJMvPow_fGHhoCXYEQAvD_BwE
 
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The bore you need for heavy duty brakes is 1 1/16" whereas most of the masters are a 1". I did find this on partsgeek:

https://www.partsgeek.com/hlpxwgp-jeep-wrangler-brake-master-cylinder.html

1747055646165.png
 
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Big difference! The bore sizes need to match. I did buy the quadratec kit over the weekend. I hope it ships soon, it says in stock. It has a 1.125" bore and designed for 60's. research is showing I will have to play with the pushrod adjustment, everything else should line up. It is crowded around my booster and master cylinder, should be fun.

Here is the quadratec kit:

https://www.quadratec.com/p/mopar/brake-master-cylinder-booster-jk-dana-60-axle-P5160050
 
This is from my kit I still have in the garage. I really do want to install it, but I have an underhood air compressor that I need to relocate or just put in a little tool bag.

The kit number is P5160050

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Last edited:
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I ordered the booster and master cylinder from jegs and the o ring/gasket from quadratec. Still need to find a reservoir. There are alternates to the kit res but still pricey.
 
Update. I have the booster, MC and "seal" (o-ring really) in hand. I just sprung for the very $$ 68048758AA reservoir from mopar parts giant. I confirmed it is in stock,so I should have it soon. Then, onto the install. Hopefully have it done before the coilover kit arrives.
 
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started the project this evening. Got the clip off of the pedal arm, air compressor removed and the pcm/abs tray loosened up.

Has anyone heard that it takes a scan tool to bleed the abs? I’ve heard it twice in videos today.

IMG_9893.jpeg


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IMG_9895.jpeg
 
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WSS said:
started the project this evening. Got the clip off of the pedal arm, air compressor removed and the pcm/abs tray loosened up.

Has anyone heard that it takes a scan tool to bleed the abs? I’ve heard it twice in videos today.
Click to expand...
I've read the same as the ABS system needs to be inactive to bleed the individual calipers, and the system needs to be reactivated to purge the air:

1. Preparation:
Ensure the vehicle is level and the brake fluid reservoir is topped off. Gather necessary tools, including a pressure bleeder, a brake fluid container, and the diagnostic scan tool.

2. Initial Manual Bleed:
Begin with the right rear brake caliper, then proceed to the left rear, right front, and left front, following the standard bleeding order. Use a pressure bleeder to push fluid through the system, ensuring all air is purged.

3. ABS System Activation:
Use the diagnostic scan tool to activate the ABS pump and valves. This will help force any remaining air out of the system.

4. Second Manual Bleed:
After activating the ABS pump, repeat the manual bleeding process using the pressure bleeder to ensure all air is purged.

5. Final Checks:
Once the process is complete, inspect the brake pedal for firmness and feel the brake pedal during a few stops, as the brakes may feel soft or spongy after a bleed,
 
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Anybodyhome said:
I've read the same as the ABS system needs to be inactive to bleed the individual calipers, and the system needs to be reactivated to purge the air:

1. Preparation:
Ensure the vehicle is level and the brake fluid reservoir is topped off. Gather necessary tools, including a pressure bleeder, a brake fluid container, and the diagnostic scan tool.

2. Initial Manual Bleed:
Begin with the right rear brake caliper, then proceed to the left rear, right front, and left front, following the standard bleeding order. Use a pressure bleeder to push fluid through the system, ensuring all air is purged.

3. ABS System Activation:
Use the diagnostic scan tool to activate the ABS pump and valves. This will help force any remaining air out of the system.

4. Second Manual Bleed:
After activating the ABS pump, repeat the manual bleeding process using the pressure bleeder to ensure all air is purged.

5. Final Checks:
Once the process is complete, inspect the brake pedal for firmness and feel the brake pedal during a few stops, as the brakes may feel soft or spongy after a bleed,
Click to expand...

I don't have a pressure pot/bleeder. will check with my local parts place and see if they rent one. I do have the jscan that can disable the abs though. I did stuff silicone taper stoppers in the lines immediately when I disconnected. Hopefully very little air is present. Not that it makes the process easier!. Thanks for the info.
 
I have made some progress. It is all out. Not fun or easy but out. I had to cut a bunch of wires that went through the firewall AND brake booster adapter. I pulled another 20 feet of unused and zip tied wires while I was there too. More PO wire clean up. This rig must have had a hell of a mall crawler sound system at one time. Lots of rca jacks, stereo type wiring etc..

The main "non usual" parts of the project are the pushrod length and the compressor mount. The new J8 booster will need to be shimmed .25" out. I may wait till Monday to get some proper spacers instead of stacking washers.

IMG_9901.JPG


The calculations:

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Here is the bracket mod:

Stud spread is closer....
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Test fitting before welding......
IMG_9909.JPG


Down to the man cave to do some grinding.....
IMG_9911.JPG


While in the man cave, I did some bracket clean up. First a blast with 120 AO, the a finish with fine glass bead....
IMG_9904.JPG


IMG_9913.JPG
 
Ohh, here was a poo finding, The O ring or seal between the MC and booster was not seated correct, it was pinched and half inside the booster:

IMG_9898.JPG


IMG_9897 3.jpg
 
It’s in. There is about 1/4” free play on actual brake pedal, about the same as before.

I put the spacers between the booster adapter and the firewall, not between booster and adapter. That was the common thread online. Now I have a 1/4” gap between firewall and adapter plate. I could use some foam tape to seal it. Hope I have this right.

IMG_9914.jpeg


It is freaking tight in there.

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IMG_9920.jpeg
 
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