Mopar J8 Booster & Master Cylinder Alternatives?

[Crawl2Camp]

So I ordered a Mopar J8 master cylinder and booster combo last September and the ship date has continuously been pushed back due to national back order.  I just got another notice last week that the new ship date is now July 6th.. F-me! My guess is it may actually go longer than July as this is the forth shipping notice extension I’ve received now.  
I got a whole new braking system sitting here in my living room (yes my life loves that) waiting for the booster and master upgrade.  Is there an alternative to the J8 combo for the JK that will give me the same increase in pedal pressure?  

Currently have the RT Offroad/Crown big brake kit with dual piston calipers and JL Rubicon HD rear kit waiting to go in.  

[fiend]

17 minutes ago, Crawl2Camp said:

So I ordered a Mopar J8 master cylinder and booster combo last September and the ship date has continuously been pushed back due to national back order.  I just got another notice last week that the new ship date is now July 6th.. F-me! My guess is it may actually go longer than July as this is the forth shipping notice extension I’ve received now.  
I got a whole new braking system sitting here in my living room (yes my life loves that) waiting for the booster and master upgrade.  Is there an alternative to the J8 combo for the JK that will give me the same increase in pedal pressure?  

Currently have the RT Offroad/Crown big brake kit with dual piston calipers and JL Rubicon HD rear kit waiting to go in.  

I don’t know of any alternatives. I ordered one last fall from Morris and it was on back order for months. Last month I managed to snag the last one in stock from Northridge and cancelled the Morris order. Maybe look around at other vendors. Perhaps you’ll get lucky. In the meantime, I would suggest you install the big brakes and see if they work with your current MC. 

[Crawl2Camp]

50 minutes ago, fiend said:

I don’t know of any alternatives. I ordered one last fall from Morris and it was on back order for months. Last month I managed to snag the last one in stock from Northridge and cancelled the Morris order. Maybe look around at other vendors. Perhaps you’ll get lucky. In the meantime, I would suggest you install the big brakes and see if they work with your current MC. 

 

I also ordered from Morris.  I tried everywhere and they are gone and  on nationwide back order.  The dealer said there are now close to 800 on back order in the dealer system.  They were selling for double the price on EBay ($600) and completely sold out.  I sent an email to Crown asking them if they have a true alternative, as I just found a booster (J8) and two different master cylinders (One J8 without a reservoir and another that states for use with 13” rotors?) that they have.

I dont want to put the brakes on without doing the upgraded booster as my current pedal sucks already.  I bled it multiple times and also took it to as shop to have it flushed and re bled with the anti lock brake actuated and i still have a pedal that I'm not comfortable with.  This can get scary bad when idle is low or when in 4low at times. 

[Fury22]

Look on amazon. I found mine on there last summer and got it in 2 weeks. Caught them when they got a restock i guess.

[Fury22]

Oh, also look into a racing dot4 or dot 5.1 fluid. I had a brake fade issue for s long time, it was probably more that my fluid had turned to shit lol, but the dot 4 racing fluid i found from amsoil should help as the boiling points are well above the dot 3 and some dot 5.1s…Just an idea that can only help

[Crawl2Camp]

16 minutes ago, Fury22 said:

Oh, also look into a racing dot4 or dot 5.1 fluid. I had a brake fade issue for s long time, it was probably more that my fluid had turned to shit lol, but the dot 4 racing fluid i found from amsoil should help as the boiling points are well above the dot 3 and some dot 5.1s…Just an idea that can only help

 

Thanks for the suggestion and I’ll definitively make sure I upgrade the fluid. (never considered that with the slow ass jeep)  I use to run the better fluids (ATE Type 200) in my sports cars I use to drive, and they definitely had much higher boiling points.

Over the last two to three years I’ve switched most of my fluids over to performance types except brake, transmission and antifreeze.  (I run Redline motor oil and torco gear oils)  

[AJK]

1 hour ago, fiend said:

I don’t know of any alternatives. I ordered one last fall from Morris and it was on back order for months. Last month I managed to snag the last one in stock from Northridge and cancelled the Morris order. Maybe look around at other vendors. Perhaps you’ll get lucky. In the meantime, I would suggest you install the big brakes and see if they work with your current MC. 

Exactly what I did. I heard a rumor they only make the product once a year to fill backorders and plus some.

[Crawl2Camp]

OK I found the Crown J8 booster and master cylinder part numbers since the Mopar kit is on back order until at least July.  Here it is if anyone is interested:

Master cylinder: 68048757AA
Brake booster: 68048755AA

Reservoir: 68048758AA - Mopar 
Reservoir alternative: 5179927AA ,CARDONE 1R3336 for about 17 bucks from Rockauto

[Redline]

What kind of brake lines do you have? If you have stock or poor quality aftermarket lines, that can give you a soft pedal easily. 
I have a mopar kit to put in our jeep but haven’t got to it yet. I was sure that when switched to the 60s I was going to have no pedal but was surprised by how good it still was. Make sure you bleed your brakes right and the do the abs bleed. The abs bleed makes a pretty big difference I’ve found.

[Redline]

Also if switching from factory to racing dot 4 or 5, make sure to thoroughly flush the system out because most racing fluids don’t play well with others and actually end up reducing boiling point.

Also if running race fluid you should “technically” replace minimum of once a year.

[fiend]

On 3/4/2022 at 9:41 AM, Crawl2Camp said:

OK I found the Crown J8 booster and master cylinder part numbers since the Mopar kit is on back order until at least July.  Here it is if anyone is interested:

Master cylinder: 68048757AA
Brake booster: 68048755AA

Reservoir: 68048758AA - Mopar 
Reservoir alternative: 5179927AA ,CARDONE 1R3336 for about 17 bucks from Rockauto

How did this work out for you?

[Crawl2Camp]

56 minutes ago, fiend said:

How did this work out for you?

 

 

I haven’t ordered it yet, I actually was looking into a few things including the differences of the three master cylinders that Crown offers for the JK.  I got a reply back this morning from their tech guy Woody.  My last question to the was in regard to the master cylinder bore size.  I knew the one that referenced the stock brake rotor size was probably 1” bore like the pre 2012 Jeeps came with.  He verified that and also what the other two bore sizes were. 

 

680912798AB has a 1-1/16" bore with a 4" bolt spacing. (This matches/is a stock replacement the newer JK’s and will work with stock booster.  Crown state for 13” rotors though?  LOL) 

 

680481757AA has a 1.125 or 1-1/8" with a 3.5" bolt spacing. (This is their J8)

[fiend]

It’s been years since I did it and my memory is fuzzy, but as I recall my stock MC bore was 1”. When I upgraded the front brakes to a big brake kit with 2 pot calipers and a larger rotor, I upgraded to a 1 1/16” bore MC. It has worked fine for me. I don’t think there were any 1 1/8” bore MCs available at the time. 

[AJK]

I have the J8 kit in my Jeep and currently have the stock system as well if needed I can take some measurements for you.

[Crawl2Camp]

22 hours ago, fiend said:

It’s been years since I did it and my memory is fuzzy, but as I recall my stock MC bore was 1”. When I upgraded the front brakes to a big brake kit with 2 pot calipers and a larger rotor, I upgraded to a 1 1/16” bore MC. It has worked fine for me. I don’t think there were any 1 1/8” bore MCs available at the time. 

 

Greer you are correct.  

Pre 2012 = 1” master cylinder bore diameter
2012+ = 1.0625” bore
J8 = 1.125” bore

My issue is a sinking pedal on my current setup which I have personally bled a few times and then took it in to get it vacuum bled and still have the issue. (On stock calipers). I have no leaks in my lines so everything points to a bad master cylinder. I was just reviewing my options as the Mopar J8 is on back order.  I can get another 1.0625” bore master cylinder (stock replacement for me) or I can upgrade everything to Crowns J8 components. Unfortunately the J8 master cylinder will not fit the stock booster, as the bolt spacing for the booster is different. 

[Nice Little Jeep]

On 3/16/2022 at 8:57 AM, fiend said:

How did this work out for you?

Thank this helped double check part numbers, Can’t ordered the complete booster master cylinder kit right now so I ordered each part individually which cost me an extra hundred dollars but at least I was able to get the parts.

[fiend]

8 hours ago, Nice Little Jeep said:

Thank this helped double check part numbers, Can’t ordered the complete booster master cylinder kit right now so I ordered each part individually which cost me an extra hundred dollars but at least I was able to get the parts.

Let us all know how it goes.  

[Nice Little Jeep]

On 3/16/2022 at 2:38 PM, AxK said:

I have the J8 kit in my Jeep and currently have the stock system as well if needed I can take some measurements for you.

I will let you know, once I have the parts in, thank you 

[Crawl2Camp]

On 5/23/2022 at 10:37 PM, Nice Little Jeep said:

Thank this helped double check part numbers, Can’t ordered the complete booster master cylinder kit right now so I ordered each part individually which cost me an extra hundred dollars but at least I was able to get the parts.

Good to see this is helping people out.  

[fiend]

On 3/17/2022 at 8:54 AM, Crawl2Camp said:

 

Greer you are correct.  

Pre 2012 = 1” master cylinder bore diameter
2012+ = 1.0625” bore
J8 = 1.125” bore

My issue is a sinking pedal on my current setup which I have personally bled a few times and then took it in to get it vacuum bled and still have the issue. (On stock calipers). I have no leaks in my lines so everything points to a bad master cylinder. I was just reviewing my options as the Mopar J8 is on back order.  I can get another 1.0625” bore master cylinder (stock replacement for me) or I can upgrade everything to Crowns J8 components. Unfortunately the J8 master cylinder will not fit the stock booster, as the bolt spacing for the booster is different. 

What did you end up doing?

[WarthogJK]

Do Not Get the Crown version of the J8 Kit! Part numbers below.

68048757AA, 68048755AA, 68048758AA

 

I finished building my Ford SD60 and 14 bolt for my 2012 JKU sport in February.  I was using the stock MC and booster for a month or so.  It was spongy but worked.  I decided to upgrade to the J8.  Problem is no one has the Mopar J8 and Mopar has no intention of making them as far as any distributor can tell.  I was on a waiting list for months without a get well date.  I found the Crown option and part numbers listed above after extensive searching.  I made the switch.  Huge Mistake!  3 master cylinders failed before I finally gave up on that junk!  Each time I returned it hoping it was just a rare defect.  The internal seals failed each time.  So dangerous.  Would work for a week to a month or so until the brake pedal would sink to the floor and would not hold the jeep at a stop.  After endless searching and trouble shooting and bleeding and everything, I gave up on the Crown version. I went to the 1 1/16 inch bore OE MC with my stock booster and it works great!  Jeep makes the J8 which is 1 1/8 inch bore, an OE 1 /16 inch bore and an OE 1 inch bore.  Basically small, medium and large.  I went to my local auto parts store and they had the 1 inch (small) and the 1 1/16 inch bore (medium).  They have different part numbers.  I bought the medium and installed it with my stock brake booster back in the jeep.  I finally have brakes that work.  If Mopar ever makes the J8 MC again I will switch to it when I do an LS swap in a couple years.  Stay away from Crown!

 

Do Not Buy the Crown version of the J8!

[AJK]

8 minutes ago, WarthogJK said:

Do Not Get the Crown version of the J8 Kit! Part numbers below.

68048757AA, 68048755AA, 68048758AA

 

I finished building my Ford SD60 and 14 bolt for my 2012 JKU sport in February.  I was using the stock MC and booster for a month or so.  It was spongy but worked.  I decided to upgrade to the J8.  Problem is no one has the Mopar J8 and Mopar has no intention of making them as far as any distributor can tell.  I was on a waiting list for months without a get well date.  I found the Crown option and part numbers listed above after extensive searching.  I made the switch.  Huge Mistake!  3 master cylinders failed before I finally gave up on that junk!  Each time I returned it hoping it was just a rare defect.  The internal seals failed each time.  So dangerous.  Would work for a week to a month or so until the brake pedal would sink to the floor and would not hold the jeep at a stop.  After endless searching and trouble shooting and bleeding and everything, I gave up on the Crown version. I went to the 1 1/16 inch bore OE MC with my stock booster and it works great!  Jeep makes the J8 which is 1 1/8 inch bore, an OE 1 /16 inch bore and an OE 1 inch bore.  Basically small, medium and large.  I went to my local auto parts store and they had the 1 inch (small) and the 1 1/16 inch bore (medium).  They have different part numbers.  I bought the medium and installed it with my stock brake booster back in the jeep.  I finally have brakes that work.  If Mopar ever makes the J8 MC again I will switch to it when I do an LS swap in a couple years.  Stay away from Crown!

 

Do Not Buy the Crown version of the J8!

Welcome to the forum. When you get a chance jump over to the Welcome thread and introduce yourself. 

 

Sounds like you have some pretty bad experience with the crown kit. Would you say what you pieced together is better then stock and how did it compare to the crown kit when it did work.

[WarthogJK]

7 minutes ago, AJK said:

Welcome to the forum. When you get a chance jump over to the Welcome thread and introduce yourself. 

 

Sounds like you have some pretty bad experience with the crown kit. Would you say what you pieced together is better then stock and how did it compare to the crown kit when it did work.

Thank you for the welcome!

 

The 1 1/16 inch OE MC works just as well as the Crown J8 version when the Crown version worked.  Need to take it to the Rubicon for a true test.  Hopefully it will reopen soon.

 

[Crawl2Camp]

1 hour ago, WarthogJK said:

Thank you for the welcome!

 

The 1 1/16 inch OE MC works just as well as the Crown J8 version when the Crown version worked.  Need to take it to the Rubicon for a true test.  Hopefully it will reopen soon.

 

If im not mistaken, the 1 1/16” master is used in all 2013+ Jeeps from the factory.  I’m currently using my stock unit (S/B this as I have a MY14) and the pedal is spongy. I’ve bled it three times, then had it flushed and bled at a shop per requirements including ABS.  I’m a bit worried to see how it will work out on the trail, because with my stock axles the brakes would get worse in 4 low and low RPM.  

[Crawl2Camp]

1 hour ago, WarthogJK said:

Thank you for the welcome!

 

The 1 1/16 inch OE MC works just as well as the Crown J8 version when the Crown version worked.  Need to take it to the Rubicon for a true test.  Hopefully it will reopen soon.

 

 So even the J8 was spongy and the pedal would drop a bit before engaging the brakes?  Grrrrreat.