This project is to increase braking power on my '89 4.0L non-HO XJ with the old style single-diaphragm power brake booster. (At the end of this write-up are also some images showing the same upgrade on an '84-'86 XJ with the V6 engine).

After I went to 33" tires, I noticed that braking power was clearly not adequate anymore. It was OK with my 31" tires, but the braking system had to be in top shape in order to work satisfactorily.

The power brake booster is one step to increase braking performance, but doesn't necessarily kill the budget! More expensive upgrades include a rear disc conversion and upgraded front calipers, etc. This article is about the booster only, and only applies to the older XJs, manufactured before '95.

Before the introduction of the double-diaphragm brake boosters, the braking power in earlier XJs and (all) MJs was even worse than it is in the newer ones. Often, the older boosters are leaking and therefore causing all kinds of problems. However, there is a way to upgrade an older XJ or MJ to the newer style brake booster and master cylinder. It is not a direct swap, but with a few modifications, the swap can be as close as a direct swap as any other "upgrade".

First of all, this swap includes some "severe" work on your brake system, and this should not be attempted without the proper tools and expertise. However, with the right tools and a bit of brake work related experience, this swap is fairly simple.

At this point I want to express special thanks to Kevin Marcus (southern CA), who emailed me with great patience all the troubles he had when he attempted this swap. Also, I want to thank Richard Gauthier (southern CA), who was --to my knowledge-- the first who did this swap (I believe with the help of a shop), and I also want to thank Dan Ishum (southern IL), who provided me with some ideas and his 30+ years of experience as a mechanic, and Tim at Precision Rebuilders (St. Clair, MO) for doing this odd rod-swapping procedure. Last, but not least, I want to thank Bill Ansell for information regarding boosters and master cylinder part numbers and Brandon Shehan for providing the '96 booster pictures.

As I understand it, XJs came with the single-diaphragm booster from their inception in '84 through '94. For the '95 and '96 model years the bigger double-diaphragm boosters were used, and also --although with a different part number-- all the XJs from '97 and up. The boosters are the same for ABS and non-ABS models (again: with possibly different part numbers, though).

The mystery around those '95 and '96 boosters was be solved after all. Matt Homan gave it a shot and succeeded to swap his '96 booster into an earlier XJ without replacing the pedal rods. Some modifications are necessary, though. A full report from Matt is further below. At this point, I would like to express my thanks to Matt Homan for his submission about how he did this swap without the pedal rod swap.

Rob Shelley supplied me with some images and a short report on his '94/ABS double-diaphragm booster. I would like to express my thanks to Rob Shelley for the submission of his numerous images and comments on this booster. See for details below. Unfortunately, there is now word on the length of this '94 double diaphragm booster pedal rod. I personally suspect that there is a chance that it might be the same as the '95/'96 boosters (4-7/8" from spacer to center of eye).

The pedal rod of a '97 booster.
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The pedal rod of a '87 booster.
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Rod number:30739 ('97 XJ booster).
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Rod number:13711 ('87 XJ booster).
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This is the '97 booster after it was returned to me from Precision Rebuilders.
Tim at Precision Rebuilders did a very thorough job doing this swap, often checking back with me if this is really what I wanted done (i.e. and old rod in a new booster) and also provided me with numerous helpful hints and tips!
Also the '87 rod will stick out of the '97 booster a little bit more than on the '87. This is good, because the '97 booster uses a spacer between itself and the firewall (not shown on any of the images).

The master cylinder and brake boosters shown in the original position (A and B) and next to it (C), in the engine compartment of my '97 XJ w/ABS.
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Photo: Brandon Shehan

It appears that the '96 booster rod is another version that will not fit either into older XJs!

Or do they?

Matt Homan figured out how to make a '95/'96 booster fit without the need to swap the actuator rod! (Full report below the '96 images).

'95/'96 XJs had boosters with different part numbers and different rod numbers.

The rod number on this '96 booster is: 19902
The Chrysler/Jeep part number is: 52008647

Photo: Brandon Shehan

The rod number on this '96 booster is: 19902
The Chrysler/Jeep part number is: 52008647

Photo: Matt Homan
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Here is Matt Homan's report on how to use a '95/'96 dual-diaphragm booster without replacing the pedal rod:

I was at the local Jeep only junkyard looking for something else, when I started looking at the power boosters. I knew the later ones were better, so I compared the '96 to an older one. The rod lengths looked close so I measured and --bingo!-- they were exactly the same.
When I test mounted it for the first time, I realized that the mounting angle of the booster had changed since the pedal rod hole lined up perfectly with the hole in the brake pedal. I was expecting them to not line up as my plan was to mark where the rod intersected with the brake pedal and drill a new hole higher up on the pedal. When I took it back out and compared to the old one, my suspicions were confirmed. I took a pic today and it is attached [see image on the left].

Photo: Matt Homan
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I swapped in a '96 non-ABS booster (PN 52008647) into my '87 that was pretty much a bolt in. No pedal rod swap required.

 The distance on the old style booster from the back of the booster to the center of the hole in the rod is 4 7/8". The '96 booster (and the other years of the dual diaphragm boosters as well) use a 1/4" aluminum spacer between the back of the booster and the firewall. The distance on the ‘96 from the back of the alum. spacer to the center of the rod hole is the exact same as the earlier unit at 4 7/8". If you don't use the factory spacer, the rod will be too long. If your ‘95 has the same 4 7/8" (w/spacer) rod length, then it will work.

The '97 and up rods are way to long. The dual diaphragm boosters mount at a different angle than the earlier ones, negating the need for the offset rod hole. Compare the boosters side by side and you'll see the drastic difference in the mounting angle. When installed, the rod hole lined up perfectly with the hole in the brake pedal and the pedal was at exactly the same distance from the floor as it was with the old booster.

Photo: Matt Homan
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Two minor mods were required:

The diameter of the rod hole in the '96 booster is 1/2" versus 9/16" on the older ones. The bolt that goes through the pedal is 3/8", so a new 3/8" ID to 1/2" OD spacer is required to replace the original one. It cost about 59˘ at a hardware store. The brake light switch on my '87 wouldn't work so I simply used one from a '93 XJ (PN J5352620). My '87 (can't speak for other years) already had a mounting hole near the top of the pedal assembly that the '93 switch fit perfectly. The '93 switch is threaded and I just used a flat washer and nut to hold it in place. The wiring was adapted using simple male and female blade-type terminal connectors.

Big difference in stopping power and the swap can be done inexpensively if junk yard parts are used.

I used the '96 master cyl. and combo valve. I didn't try to fit the old master cyl., but I don't think it would work. The area where the booster push rod engages the master is different on '96 master. Also the new booster is angled up toward the hood and the '96 master is built to account for the angle. The old master might hit the hood. The '96 combo valve works fine (I have a stock D30 and D44 with drum brakes) and since it mounts on a little bracket that attaches to the master cylinder mount, it is much easier to get to than the stock one. I just used flare unions and bent up line extensions to the new valve. You can use the stock combo valve, but you still will have to bend up new lines from the master to the combo valve. The work is probably about the same and is the most difficult part of the whole conversion.

Somebody mentioned to me that the hole I used for the brake light switch was for a cruise control switch. That may be true, I don't have cruise. I don't think it would be hard to make up a bracket for the switch, though.

Someone also mentioned to me that the part number of the '96 booster was discontinued. Was the part number superceded by another part number? I run into this all the time with older parts. I find it hard to believe that DaimlerChrysler would not have a replacement to sell. If it is truly discontinued, then you can get a new booster at AutoZone for $95.

 My washer bottle bit the dust a long time ago and the space it occupied now is home to my RS9000 controller. The washer bottle may have to be relocated or moved a bit to clear the new booster.

The total cost for my conversion was about $130.
--$100 for the used booster, master, combo valve.
--$12 for the brake light switch and
--$18 for the misc. flare nuts, unions, and tubing.

   Matt Homan
[Submitted: January 12, 2002.]
©Copyright 2002 Matt Homan
All Rights reserved.

Thank you Matt!
Matt can be contacted at:  MHoman1@cs.com 

Photo: Rob Shelley

The following images here are taken by Rob Shelley from his '94XJ equipped with ABS (Inline-6 engine).
Even though it is tempting to assume that this might be the ideal candiate for a direct swap, it does not have the same rod as the earlier XJs and therefore may need either a rod swap or a similar adaptation as outlined above by Matt Homan . There are some extra connectors, etc. for the ABS equipment that may further complicate things.

Shown here is a '94 XJ with a double-diaphragm booster.
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Photo: Rob Shelley

Photo: Rob Shelley

Photo: Rob Shelley

Photo: Rob Shelley

Here is the pedal rod shown from inside the cab (underneath the dash). Here is Rob's comment:
"Although you can't see it from the picture, the pedal rod has the same type end as the '95+. There's a hump above the same size as the one below you can see. I just couldn't get the camera high enough under the dash to get a good picture of it. So, unfortunately the pedal rod is not the same as the older ones.
     --Rob."
[Submitted: December 1, 2001]
©Copyright 2001 Rob Shelley
All Rights reserved.

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Here are some of the tools shown that are required for this swap. "Common" tools, such as wrenches (SAE and metric), are not shown.

A: Double-flaring tool kit (with adapters on the right).
B: Miscellaneous flare nuts, etc.
C: Adapters for the new master cylinder (allows the use of standard brake lines and flare nuts).
D: Brake lines that are removed from the old master cylinder. Keep those, because those flare nuts are not readily available (1/4" thread on 3/16" pipe, and 5/16" thread on 3/16" pipe, whereas the latter is the problematic one, the other can be special ordered from Edelmann via your local parts store).
E: The new master cylinder (AutoZone or NAPA, etc.) and the new and old booster above it.
F: A flare nut wrench kit (SAE and metric).

Not shown: a brake line bending tool (not really required if you got some feeling in your finger tips left).
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Edelmann adapters (blue) with 3/16" flare nuts already in place (brass). Check your local parts store, but it must be a good one. AutoZone is not the place for that sort of "detail work".

Part numbers for the (blue) adapters:
Top:Edelmann 265000 "3/16x12-1.0"
Bottom: Edelmann 271300 "3/16x3/16"
(Approximately $3-$4each)

These adapters are for use with the new master cylinder. It is possible to obtain brake lines from the dealer and then remove the flare nuts. I have not yet researched this option too much because I personally prefer to keep standard parts whenever possible.
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Detail view of the new master cylinder with the adapters, flare nuts, and one brake line installed (for this image only.) The brake lines need to be bent first, of course.

Part numbers:
'97 master cylinder:
AutoZone: NM27058 $85.99

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Master cylinder removed.

At some point also remove the washer fluid bottle. It adds room to work and needs to be moved forward anyway by about 1".

Now into the interior!

The booster is mounted to the firewall with four bolts (red arrows).
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Back into the engine bay...

--pull the old booster out.

Another view with the mock (wire) lines in place. These are the samples for the real lines.

The rear line needs a tight bend away from the booster (towards engine) and then immediately around the electrical connector that sits between the two lines on the proportioning valve.

Newer XJs (such as my '97 XJ) have the proportioning valve mounted on a little bracket that is bolted to the booster. That might be an alternative method, but then custom extension must be made to relocate the proportioning valve (which is at least as much of a hassle than the tight custom lines).

It is a tight fit. Especially the rear line is a tough one. It almost collides with the new booster, but with some trick-bending, it will eventually clear. Also, the washer fluid bottle must be moved forward. Redrill the three holes and bolt it back down. In the end all worked fine and even looks very neat.

Fill the system with brake fluid and bleed the brakes.
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Another image showing the new master cylinder, the '96 booster, and the custom brake lines.

Please note that the engine bay shown in these images has seen its fair share of modifications and some parts in the images may not match other V6 engine bays. This is not important, however, since the focus here is on the new master cylinder and double-diaphragm brake booster, as well as the custom-routed hard lines.
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Summary: Not exactly a direct swap, but it is not very difficult to do with the right preparation. The pedal rod swap tip by Kevin Marcus proved to be a very crucial one!

The most time-consuming part was making the custom brake lines. The Edelmann adapters were of great help!

This upgrade works excellent and provides great results with a properly working brake system. Obviously, it does not fix problems that are elsewhere in the complex brake system. It is important that all brake components are in good shape and the system is well bled, otherwise this upgrade will achieve little!