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Dual Diaphragm Power Brake Booster Conversion Kit (87-90 Jeep Wrangler YJ)

Item J12008
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$465.99 (kit)

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      Product Information

      Features, Description, Reviews, Q&A, Specs & Installation


      • Dual Diaphragm Power Brake Booster Conversion Kit
      • Converts Single Diaphragm Setup to Dual Diaphragm Setup
      • Kit Includes Zinc-Coated Brake Booster, Master Cylinder and Bench Bleeding Kit
      • More Braking Power
      • Less Pressure
      • Advanced Installation
      • Fits 1987-1990 Jeep Wrangler YJs


      Brake Conversion Power. This Dual Diaphragm Power Brake Booster Conversion Kit can replace worn parts and improve your braking power. This kit will convert a single diaphragm design into a dual setup and that means more power with less pedal pressure in your Jeep Wrangler YJ.

      Components. You get a dual diaphragm, zinc-coated brake booster and high-pressure master cylinder. You also receive a bench bleeding kit in your pursuit for the best braking ability for your Wrangler.

      Installation. Putting this Dual Diaphragm Power Brake Booster Conversion Kit to use is an advanced installation. It will take 3-5 hours to complete and there's more. Engine vacuum needs to be a minimum of 18 inches of vacuum at idle when engine is warm for power brake setup to function properly.

      Application. The Dual Diaphragm Power Brake Booster Conversion Kit fits 1987-1990 Jeep Wrangler YJ models.

      Fitment: 1987 1988 1989 1990 Details

      MPN# DDBYJ1

      CA Residents: WARNING: Cancer and Reproductive Harm -


      Customer Reviews (4)

      Write a Review

      Ratings Summary

      3 out of 5 overall rating from 4 customers

      • December 13, 2018

        1 2003 Wrangler - Leoner

        The fit was fine but...

        The fit was on par with the stock one, however, I installed it and it was leaking, I took it to a shop to fix it because, well, at this point, why not. They took it apart and put new seals in it. Also, the product image is not even close to what I got. I should post a picture of the one I got to show the differences. I'm honestly really disappointed.

        Helpful (13)
      • February 28, 2018

        2 1999 Wrangler - StevenM

        Fitment isn’t exact (99 TJ)

        Im in the middle of installation. So far, old brackets havent matched up to the new studs on the booster so I have to do some cutting. Also, it doesnt mention in the kit that you literally have to special order parts for 2 new brake lines that YOU have to custom make yourself. Thankfully they provide the part numbers.... towards the end of the instructions.

        Helpful (15)
      • January 26, 2017

        4 1989 Wrangler - Jking

        Significant difference

        Got this to completely rehab a brake system on my yj and boy did it! Braking is now really noticeably better and quicker! Install went pretty well and quick but removal of the old one was a challenge

        Helpful (18)
      • January 11, 2017

        5 1997 Wrangler - Justin

        Improved braking

        Really improved my braking.probably vut my braking distance in half

        Helpful (15)

      Questions & Answers (4 answers)

      4 Top Rated Questions

      Does this master cylinder have the same 1/2 and 7/16 port as the stock master cylinder

      • Yes, this item would have the same 1/2 and 7/16 ports as the stock master cylinder.

      Helpful (0)

      Hello. Does this come with the proportioning valve as pictured?. Is this a direct fit for a 2004 LJ or are modifications needed?

      • This does not come with a proportioning valve, you would re-use the existing one.

      Helpful (0)

      Will this conversion work with rear drum brakes and is it simple bolt on replacement? Thanks so much, Aaron

      • The Crown Automotive Dual Diaphragm Power Brake Booster Conversion Kit is designed for the 1991 - 1995 Wrangler YJ Equipped with 4-Wheel Disc Brakes, so unfortunately it would not work with rear drums. The install is also on the Advanced level of skill to install this conversion kit, it is not a simple bolt on install.

      Helpful (0)

      What is the size of the booster in inches

      • The Crown Automotive Dual Diaphragm Power Brake Booster Conversion Kit will have a 1 1/8" Bore master cylinder, however they do not have a listing of the booster diameter for this kit.

      Helpful (0)
      Post Your Question

      Installation & What's in the Box

      Installation Info

      What's in the Box

      • (1) Dual Diaphragm Brake Booster
      • (1) Master Cylinder
      • Installation Hardware

      Will It Fit My Wrangler

      • YJ Wrangler 2 Door - 87, 88, 89, 90

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