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I know there are many threads that explain this procedure but another won't hurt from someone elses experience. So, this weekend I am starting the dual diaphragm conversion on my 1989 MJ. To start off, here are the tools and equipment I have so far:

 

1996 XJ Brake Booster and Master Cylinder (bought off of JC Whitney) $170

(2) 3/16 diameter bubble flared with 10mm fitting brake lines

STANDARD flare tool (rented from auto parts store)

(1) 12mm thread 3/16 diameter line, fitting

(1) Vacuum Tool

(4) 10mm stop or lock nuts

(1) Line cutter

 

The four 10mm nuts are for the brake booster. The other two bolts on the other side can use the nuts off of the stock MJ booster.

I chose to buy the bubble flare lines because the 1996 MC takes bubble flare ends and not double flared. The MJ distribution valve body DOES take double flare though. So, I am going to have to flare one end of each line using the standard flare tool. Also, one of the ports on the 1996 MC takes a 12mm fitting which I will have to slide on the line before flaring again.

 

IMG_1438%255B1%255D.JPG

 

1996 XJ brake booster

 

IMG_1437%255B1%255D.JPG

 

1996 XJ master cylinder currently being bench bled using vacuum tool

 

IMG_1436%255B1%255D.JPG

 

Vacuum tool

 

This tool made the bleeding process a little easier. There are many ways to do it. Putting each of the hoses from both fittings into the bottle and pushing the rod in, will have the same effect. I did both methods just to be sure. 

 

That is where I am at right now. Tomorrow I will start the upgrade!!  :wrench:

Also there will be lots of more pictures!  :clapping:  :thumbsup:

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The upgrade... AWESOME! I have at least double the stopping power than
before. It took me around 4-5 hours. Well worth the upgrade. :driving: 


Before I started I took out the wash bottle and air cleaner box.



Now to start off, I took off the brake switch from the pedal assembly. 

 

IMG_1440%255B1%255D.JPG

 

Then loosened the four nuts that hold the booster to the fire wall.

 

IMG_1442%255B1%255D.JPG

 

Next I took the brake lines off of the old MC so I could pull the whole booster MC
assembly as one unit.

 

IMG_1443%255B1%255D.JPG

 

Now that I have the old booster for reference, I started the small modifications needed on the new booster.

 

IMG_1447%255B1%255D.JPG

 

I drilled out a 5/8 hole in the new push rod and filed around the hole until the small
bushing could fit nice and snug.

 

IMG_1446%255B1%255D.JPG

 

Then came to grinding the flat on the rod.
I took a grinding wheel and tried to make it as perpendicular as possible
to the axis of the push rod but it does not need to be perfect. I grabbed a
set of calipers and measured the distance from the edge of the plastic
bushing to the flat. This told me how much to grind. Now come to find out
after the project was all said and done... I did not have brake lights when
I hit the pedal. Which meant I ground down too MUCH. Grinding not enough
will make the lights always stay on. So, to fix this issue, I took two
pieces of duck tape on top of each other and put them on the flat of the
push rod. Then I had brake lights. The distance from the hole to the flat
is that critical. It only took about a 1/16" difference so they would come
on. So if you do grind down too much, not a big deal.

 

IMG_1450%255B1%255D.JPG

 

Now that I finished the modifications, its time for installation. I found I did not really
need to bend the lip of the firewall for it to fit but I did anyways...
Since it is a bigger booster, the MJ distribution valve is very close to
the booster. I somewhat bent the valve on an angle so I could get the new
lines to it.

 

From there I made my new lines. I did not get the old WJ flex lines but

that would work too. I just had regular brake line. Now, it was crazy how
it all turned out but I had four different fittings on each line. On a side
note, the NEW MC has bubble flare fittings and the old MJ valve has double
flare. On both lines I had a bubble flare on one end and a double flare on
the other. On one line there is a M12-1.0 bubble flare fitting and a
7/16-24 inverted flare fitting. The other line has a M10-1.0 bubble
flare fitting and a 1/2-20 inverted flare fitting. What I did was buy one
40" long bubble flare brake line, cut it in half using the pipe cutter, and
slide on the new fittings and double flared both of the ends. Make sure the
yoke and adapter peice is straight and square when flaring....... had a
little trouble.... Hooked up the lines and bent them accordingly. 

 

IMG_1454%255B1%255D.JPG

 

^^^^^The Fitting on the left is the M12-1.25 bubble flare. The one on the right is the M10-1.0 bubble flare.^^^^^

 


IMG_1455%255B1%255D.JPG

 

^^^^The fitting on the left is the 7/16-24 standard. The fitting on the right is the 1/2-20 standard.^^^^


IMG_1456%255B1%255D.JPG


There are some fit issues:  :rant: 

 

Do not have the brake lines stick out too much
or else they will hit the wash bottle. The wash bottle also needs to be
moved to the left about one inch because it hits the new booster. The MJ
distribution valve is very close to the booster so you can move it or
whatever you like. My brake pedal is a little higher than before but I
barley notice it.

 

IMG_1462%255B1%255D.JPG


I bleed the lines by going to the RR then LR, RF,LF. Then I did the RR
again just to be sure. I did not do the weird bleeding procedure like many
people say. My brakes are amazing so they are bleed correctly. I also did
it with my truck not running. 

 

Side Note: My booster did NOT come with a spacer and worked fine.

Installed the brake switch (mine has two hook-ups on the switch because I
have cruise control).

 

IMG_1459%255B1%255D.JPG

Flaring Tool

Learn how to use the flare tool the right way.... I had a little trouble.

 

IMG_1463%255B1%255D.JPG

Line Cutter

Then I was on the road braking like a corvette!! :banana:  This upgrade is a must do.

It is like the new booster was made for this truck. Again, I have a 1989 MJ
and used a booster & MC from a 1996 XJ.

 

Ask for more pictures or questions!!  :thumbsup:  :wrench: 

 

Here are some other links for different view points.

http://www.jpmagazine.com/techarticles/drivetrain/154_0810_cheap_jeep_brake_system_upgrades/

http://www.4x4wire.com/jeep/tech/brakes/xj_wjbrakes03/booster/

http://comancheclub.com/topic/24430-wj-booster-and-master-cylinder-upgrade/

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The best DIY conversion thread I've come across so far (and there's quite a few, no offense) - and thanks for posting your conversion up on ComancheClub.

 

The spacer would tend to lower the pedal, if that's an issue but push the washer tank further left...is that what you'd conclude?

 

Where did you source your lines and flares (AGS brand)? Have all the typical stores around here, NAPA, O'Reilly's....just wondering which has the fittings you bought.

 

I'm doing this conversion, ordering the booster/master later this week.

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The spacer would tend to lower the pedal, if that's an issue but push the washer tank further left...is that what you'd conclude?

Correct. There is very little space between the air box, washer bottle, and booster. I do not think the wash bottle would fit even with a small spacer. I'm sure you could make room somehow but the pedal is not noticably higher.

 

I bought my fittings from a local auto parts store. Autozone... Any store would have the fittings.

 

 

Oh, and maybe one picture of how the vacuum and hardline passes between the booster and the firewall - thanks!

The vacuum hose goes from the front of the booster to the intake manifold? I am not sure if that is what you are asking. And ill post more pictures of how I hardlined from the MC to the valve. 

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The 1/4" spacer between the new booster and firewall locates the brake pedal at the same level it was before the conversion, and eliminates the need to bend the firewall seam for booster clearance. Recommended it to be used if you can find one.

 

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Oh, and maybe one picture of how the vacuum and hardline passes between the booster and the firewall - thanks!

The vacuum hose goes from the front of the booster to the intake manifold? I am not sure if that is what you are asking. And ill post more pictures of how I hardlined from the MC to the valve. 

 

No, sorry - was referring to the vacuum line that passes behind the booster and in front of the firewall, it's shown in Hornbrod's pic and since there is no firewall modification with his (spacer used) the lines run pretty much as the factory intended. I'm guessing that since you didn't need to modify the firewall, that those two lines (one is steel, one is plastic) are pretty much where they were before the new XJ booster.

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Oh, and maybe one picture of how the vacuum and hardline passes between the booster and the firewall - thanks!

The vacuum hose goes from the front of the booster to the intake manifold? I am not sure if that is what you are asking. And ill post more pictures of how I hardlined from the MC to the valve. 

 

No, sorry - was referring to the vacuum line that passes behind the booster and in front of the firewall, it's shown in Hornbrod's pic and since there is no firewall modification with his (spacer used) the lines run pretty much as the factory intended. I'm guessing that since you didn't need to modify the firewall, that those two lines (one is steel, one is plastic) are pretty much where they were before the new XJ booster.

 

Correct. Another good reason to use the spacer.  :thumbsup:

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Here is a picture of a home made spacer. Some 1/4" wide flat strap and some square tubing. Not much to it.

 

This one is 1/2" wide for a hydro-boost application, but 1/4" wide for the Comanche would be ideal.

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That's way overkill. A 1/4" square aluminum plate with a center hole large enough for the booster arm movement and four 5/16" holes holes to match the booster studs is all you need. Thirty minutes of fab. If you can't grab one from the yard. Here's a pic. Unfortunately you can't buy one from the dealer; it's part of the 95-96 XJ brake booster package. Might as well do your brake upgrade right. Should have made a template of the spacer plate when I did mine.

 

 

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That's way overkill. A 1/4" square aluminum plate with a center hole large enough for the booster arm movement and four 5/16" holes holes to match the booster studs is all you need. Thirty minutes of fab. If you can't grab one from the yard. Here's a pic. Unfortunately you can't buy one from the dealer; it's part of the 95-96 XJ brake booster package. Might as well do your brake upgrade right. Should have made a template of the spacer plate when I did mine.

 

 

 

I don't have 1/4" aluminum plate just lying around. In fact, If you were to purchase some, how much would you have to buy, and at what price? See where I'm going?

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Whats the difference between doing this or a WJ booster? Is it all pretty much the same?

 

I don't know, but would like to get an educated answer to your question too. If logics ruled, you would think that the newer WJ booster might be engineered to be more efficient than the 95-96 XJ booster, especially since I have disk brakes front and rear. I've searched for an answer, but there is nothing definitive out there pro or con for either one that I could find. Since I could not, I went with the easier 95-96 bolt-in solution. But I would change it all out in a heartbeat if someone convinced me that the WJ mod resulted in a better system for my application. Either way, XJ or WJ booster, it beats the crap out of the stock single diaphragm setup.

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Would the 1/4" spacer have to be metal?  I have TONS of Lexan and Lucite scraps and all are 1/4" thick.  I could easily cut the proper hole in the middle with a fly cutter and drill the 4 mounting holes and ge tthe space that I need.

 

Would such materials be appropriate?  I can't figure why they woudl not but I wanted to ask and not assume.

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Would the 1/4" spacer have to be metal?  I have TONS of Lexan and Lucite scraps and all are 1/4" thick.  I could easily cut the proper hole in the middle with a fly cutter and drill the 4 mounting holes and ge tthe space that I need.

 

Would such materials be appropriate?  I can't figure why they woudl not but I wanted to ask and not assume.

 

I see no reason why not. Lexan would probably be better because it's stronger. There's no contact with fluids and no bearing load to worry about; it should work just fine. You could use the white foam gasket as in the below pic as a template.

 

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Would the 1/4" spacer have to be metal? I have TONS of Lexan and Lucite scraps and all are 1/4" thick. I could easily cut the proper hole in the middle with a fly cutter and drill the 4 mounting holes and ge tthe space that I need.

 

Would such materials be appropriate? I can't figure why they woudl not but I wanted to ask and not assume.

 

If you do this, draw a template please and post it on the tech page. Or here.

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Would the 1/4" spacer have to be metal? I have TONS of Lexan and Lucite scraps and all are 1/4" thick. I could easily cut the proper hole in the middle with a fly cutter and drill the 4 mounting holes and ge tthe space that I need.

 

Would such materials be appropriate? I can't figure why they woudl not but I wanted to ask and not assume.

 

If you do this, draw a template please and post it on the tech page. Or here.

Certainly.  Will be calling yards this week or next in search of the 95/96 assembly.

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I would shy away from using plastic for the spacer due to the potential for cracking at the pressure points around the four studs. Just my opinion. 1/4" steel plate would work as well as aluminum. Burn the center hole and drill the stud holes, hit it with a disc grinder and you're good to go. Or you could fab a spacer out of 1/4" x 1" flat bar.

 

I have a 96 MC with the spacer on standby for a future swap into the 91.

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I don't have a way to cut the center hole in aluminum or i'd go that route.

 

As for the material that I do have, it is used in bulletproof windows and in the windows in racecars. I plan to leave as much material as possible around the edges of the 4 screw holes.

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  • 3 weeks later...

Quick question regarding the 95-96 master/booster swap: I'm trying to trace down a slight vacuum leak and spongy brake pedal. Is there a gasket or o-ring between the master cylinder and booster where the RED arrow is pointing? I've forgotten  :dunno:  and the parts manual is confusing. Anyone remember?  

 

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