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Uninstalling the OEM Anti-lock Braking System
Submitted by Steve "Bones" Ward
In 1992 Chrysler/Jeep did something we should all be thankful for. It re-did its antilock brake system on the Jeep Cherokee (among other vehicles). Unfortunately there were many owners (myself included) that were at the mercy of the very poorly designed ABS system that graced (plagued) XJ's built before the 1992 model year. Without a booster back up the old Bendix ABS system left the vehicle's occupants at the mercy of a single pressure pump and a two-part pressure accumulator system. To that Chrysler/Bendix added questionable pump to accumulator lines and other poorly designed components that have since been the object of many recalls (and at least one XJ fire).
Chrysler/Jeep (now Daimler/Chrysler) has tried to stave off a plethora of litigation by placing the system on a "lifetime" warranty. While this helps offset astronomical repair costs on this pitiful system (my est. for a system repair totaled over $1700 in 1999), it does nothing to warranty the lives of the XJ's occupants should the system fail at an "inopportune" time.
My answer to the POS Bendix system was to get rid of it after it failed me a second time. It isn't an easy feeling when you are beginning a project that hasn't been done before. I had people tell me everything from "it can't be done," to "it's as easy as a simple R&R" (remove and replace). As most projects go the truth was found somewhere in between the two. The hardest part was doing the first cut of the ABS pump lines thus voiding the system's lifetime warranty. If the swap didn't go well it would be expensive to re-place. Oh well, my turn to be the guinea pig.
Before I go into the swap a word of caution. The (working) ABS system uses very high pressure to accomplish its duties. Make sure you disconnect the battery and pump the brake pedal at least 50 times to remove the pressure on the fluid. This does not remove the captive pressure on the main accumulator (the small water tower looking thing inboard of the fluid reservoir). Treat the accumulator with respect, it can
hurt you! Also remember brake fluid is flammable, be careful and no smoking.
Find a donor for my swap. The local salvage yard had a 1991 XJ with a complete braking system. I took it all including the pedal assembly and hard lines. The master cylinder. and booster were taken as a unit and the lines were taken as templates for new lines if needed. On comparison the ABS and older booster/MC setups had the lines run out of opposite sides so I was glad I grabbed the donor's lines. I actually replaced the left front and rear line with the donor's for an easier install.
Out with the old. The old ABS stuff didn't go without a fight. It took a long time to remove the old pump lines from the firewall. DC did a good job of tucking them in under the wiring harness. I ended up cutting the larger line into several pieces with a compact tubing cutter. The right front brake line has to be modified and reused in the swap as it is also tucked up under the harness. One would either have to remove the engine or harness to swap it. The pump came out fairly easily. I wrapped its electrical connections with QUALITY electrical tape and zip tied them back out of the way. The same was done for the accumulator/modulator assembly. I also removed the pedal assembly and left front and the rear brake lines. The computer was then removed and it's connections wrapped. All sensors were removed as well. I cut the grommets off the front lines and used them to plug the holes in the fenders. The holes for the rear lines under the rear seat were plugged with large test tube stoppers. I was also doing a rear axle swap at the same time so I didn't have to block off the ABS holes in the drum brake backing plates, but it shouldn't take much engineering to come up with a viable solution for them. I removed all ABS fuses and relays from the power distribution box also.
Repair rust. My 1991 doesn't see much salt in mid Missouri but I did find a bit of rust lurking under the booster to firewall seal. It was brushed down to bare metal and repainted before installation of the "new" system.
In with the new. First off I replaced the left front and rear brake lines with those from the donor system. I then re-bent and double flared the right front line to approximate the donor's line position. At first glance the only difference between the ABS and standard brake system's pedal assembly was that the ABS system's has a return spring for the pedal. On closer inspection one finds that the pin that connects the pedal to the booster rod is in a different place. The standard pedal assembly must therefore be used. It bolts up using the same mounts as the ABS system's stuff did. Once the booster and MC were in it was time to connect all the lines. The proportioning valve from the donor system was installed in the same location as it was in the vehicle it came out of and the brake lines connected to it. I hooked up the single wire that had attached to the old ABS proportioning valve to the "new" proportioning valve (they looked the same, so what the heck)." It is important to note that the ABS and standard brake systems use different sized wheel cylinders for the rear brakes. Your local parts house should have dimensions of the two for comparison. Since I replaced my D35C axle with a D44 at the same time as the brake switch I do not know how this would have affected the swap. IMHO I would use which ever is the biggest ID cylinder as the XJ's brakes can use all the help they can get. I have gone to an ID size larger wheel cylinders on my D44 for better braking from the rear and noticed a fair improvement.
vacuum bleed the lines (or pump bleed if you have a helper). If the MC is new or has been drained you may have to bench bleed it prior to bleeding the lines.
Try'em out. I was worried that I would have all kinds of warning lights flashing when I started up my XJ after the swap. What I got was an improved brake system, no warning light problems, and no ABS worries or hassles. The proportioning valve sensor/warning light functions as on a standard system. The only downside I found was that my emergency brake light does not work. I figure it shouldn't be too hard to wire up a working warning light but haven't tried.
Do it all over again. When I went to 33's I found the 1991's standard brake system to be lacking in stopping power. I had read that the later braking systems (1996 and newer) had a dual diaphragm booster where the earlier ones had a single diaphragm booster. The new design was supposed to make a vast improvement in braking, so back to the salvage yard I went. I couldn't find any 1996 XJ's so I pulled the brake system out of a 1999. There were significant changes made in the pedal assembly mounting points along with the renewed body style in 1997, but I took the donors brake lines and pedal assembly again just to be safe. The pedal assembly turned out to be the biggest headache in this swap. There is about .75 inch difference in the booster push rod between the old 1991 system and the 1999 system. There was no way to use the 1999's pedal assembly so I modified the 1991's by cutting the welds that held the pedal bracket to the assembly mounting bracket. I then installed the mounting bracket in the XJ and adjusted the pedal assembly to a good pedal height in relation to the new push rod length and marked the new mounting position. I then pulled the mounting bracket and pedal bracket. Having no welder, I drilled and bolted the brackets back together in the new location. As with the first swap I used the left front and rear brake lines, but this time I also used part of the multi-pieced right front line to hook up to my remodeled original right front line. I did have to move the washer bottle forward about .5-.75" and fabricate a spacer for the lower bottle mount. After bleeding the system I found I could lock the front brakes if not careful but the rear seemed too soft. I replaced the 7/8" ID wheel cylinders on the D44 with 1" ID cylinders that had application on a 1972 Ford Pick-up. The difference in pedal feel took some getting used to but I have had good success with the swap. The brakes are vastly improved over the ABS (and the 1991 standard brake system).
I have had problems with shoe binding on the D44 with the Rabest Prostop shoes. I have actually destroyed two sets of them. I do not have an answer for the binding problem, but I seem to be an isolated case as I have yet to find anyone else with a similar problem. I know it's not associated with the larger wheel cylinders as the first time it happened was with the stock 7/8" ones.
Rear disk brakes. Rear Disks will be my next brake modification, but an engine failure and an in progress stroker build has delayed them for this year at least.
This is how I did the modification, and this article is intended to serve as a demonstration of the procedures that were required to complete the task. The article should not be construed as a recommended procedure, nor as a direct instruction sheet. If you do any modifications to your brakes, you do so at your own risk.
Steve "Bones" Ward
NAXJA, and the author of this tech article disclaim any and all liability associated with any "do it yourself" vehicle modifications and/or repairs.