Bump for great tech!
Well... I finally bit the bullet and did this mod. Some of my (maybe useful) input is below.
The four bolts that hold the booster to the fire wall are 14mm. Take those off with a deepwell socket. The top right nut is a pain to take off, and I ended up threading my hand around the steering column to get to that nut.
This is very true... the nuts on the WJ booster are 13mm. I ended up using a 13mm 1/2" drive impact socket (my only deep 13mm socket), a U-joint adapter, and a 12" extension bar to do the upper right hand bolt, it made it simple, even fairly comfortable to do!
The locknut is a 16mm, as is the bolt. The nut is a 14mm. Take the bolt out, and put the nuts back on it so you don’t lose them. There is a metal sleeve with two clear plastic holders which needs to come off.
This is where mine differed. Yours is an 89 and RENIX, mine is a 91 and OBD-I - and mine had the later-model style attachment here, with a post welded to the side of the pedal and a clip ring that slides over the end to keep the booster pushrod on. No bolt involved.
Make sure to keep the fittings as you will reuse the ones going into the proportioning valve. Put something in the holes where the lines went so nothing falls in them. Don’t want any dirt or grime to fall in there.
I cut my lines with a pair of lineman's pliers about 1" up from each fitting on the proportioning valve - this had the bonus side effect of mostly sealing the lines off, at least enough to keep dirt out. It also makes it easy to get the fittings out, grab the prop valve with a pair of channel locks and use a deep well socket (7/16" and 1/2" as I recall, might have been 3/8" and 1/2") to remove the fitting. Avoids rounding them off trying to get a flare wrench into that tight space, and keeps you from breaking the warning light switch between the fittings.
There is a small plastic sleeve in the old booster rod that you need to make sure to remove. Shown here on the old booster. <snip>
Find a drill bit that is the same size as the hole on the old booster rod without the sleeve. In my case it was a 5/8’’ bit. Drill out the new booster rod.
The old rod uses a flat portion to sense when the brake lights should be turned on and off. This must be cut into the new rod. Cut off the old booster rod, and using vice grips clamp the cut off piece to the new booster. Use the drill bit to line up the holes. Make sure the cut off piece is in the right orientation, as you will have to grind down the new rod. You don’t want to mess this up. You can see the old piece clamped to the new here:<snip>
Now clean the firewall and anything else that you can reach if you want. I tried to get as much junk and mud out as possible, but this isn’t really needed. Also, you will need to hammer the pinch seam that is at the top, as well as the vertical one slightly to fit the larger booster. Picture of removed.<snip>
Picture of pinch seams “massaged” and cleaned up a bit.<snip>
Test fit the booster and see if any more pounding is needed. I have read that a ¼’’ spacer is needed to be added in between the firewall and booster to keep the brake pedal in the right position. I’m not sure why that ¼ would matter, but I ended up using washers to space the booster out, as it wouldn’t fit without them. So if you need a spacer, use one. Otherwise, I don’t think I would worry about it.
¼’’ of washers on the booster studs:
Slide the booster and MC into position. You will need new nuts for the WJ booster studs. Don’t know what size they are, but they are 1.25 thread pitch. Make sure no wires or lines are pinched, and then bolt the booster down.
Hook up the brake pedal and everything else. At this time, make sure that the brake lights are only on when you’re stepping on the pedal.
I measured the hole in my WJ booster pushrod and the hole in my 91 MJ booster pushrod and found them to be within 20 thousandths of an inch diameter. I deemed this not worth my time drilling as long as it fit properly... which it did. I didn't bother cutting the flat for the brake light switch either, it was 1/16" off and I just lightly bent the brake light switch bracket to account for this. On my 91 the vertical pinch seam was not tall enough to need bending so I left it alone, but I did have to work on the horizontal one - used channel lock pliers. Careful of the two vacuum lines that go along the bottom of it, and remember you'll have to flex them up over the new booster while installing.
The 1/4" stack of washers on each stud is required to bring the length of the pushrod from the mounting surface to roughly the same number - if you don't do this, the brake pedal will be MUCH higher. I test-fit some washers at home depot and found that four to five 1/4" flat washers work perfectly.
Bending lines:
This was the hardest part for me. I’d never bent or flared brake lines, but luckily I only messed up once.
Use an old coat hanger and bend it to how you want your lines run. Realize that the lines run into the opposite side of the MC than the old one. Also, keep in mind you will want your washer bottle to be bolted back in. <snip>
Using a couple of feet of 3/16’’ brake line, start bending. Now comes the complicated part. Make sure you keep the line fittings strait on where they go. Don’t want to bend up a line, and then realize the fittings are in the wrong place. Also, the flares are different on the proportioning valve and MC. The MC from the WJ uses a bubble flare while the proportioning valve uses a double flare.
The brake lines I got from NAPA were double flared, so I only had to use a bubble flare tool.
This was easy... I've had to replace all the other brake lines on both my Jeeps already, so I've had plenty of practice. I really wanted to keep those neat little flex portions in the WJ stock MC lines though, so I did something different here. I also don't have a bubble flaring tool. What I did was spin the hardline in the crimp for the flexible portion of the line (I didn't expect them to spin, but they did, without leaking) so that the first bend points down instead of up (where it was routed to the WJ ABS modulator) then cut them to the proper length, slide the MJ/XJ stock proportioning valve fittings onto the lines, and double flare them.
Install the MC side of the lines, but keep the lower end free. You need to “bench bleed” the MC before you can finish the lines.
Technically the booster and MC should be out of the car to bench bleed them, but I decided it would be easier to do it while in the Jeep.
This is how I bench bleed them. Notice the salad dressing bottle in the foreground and clear lines.
This is the part I forgot... which is why I ended up driving the XJ to work this morning :doh: so much air in the master cylinder I couldn't get the system to bleed at all. I am wondering if I may have to jack up the rear end of the vehicle to get the MC level enough to bleed properly, since it points up at a fairly significant angle.
Reinstall the washer bottle. Hopefully it will fit back in with how you have routed the brake lines. Make sure to install the right hoses on the right pumps and wires on fittings. I put the wires on wrong at first, so the front wouldn’t get water unless I pushed for the rear window wash, and when the front turned on, the wipers would move, and water would come out on the back window. Oops.
With the stock WJ lines as I did it, the washer bottle fit with about 1/4" to spare.
-If you have disk brakes all the way around other mods might have to be done.
The WJ has no proportioning valve and four wheel disc brakes, but from what I've read it uses the ABS modulator to perform the duties the proportioning valve formerly had. I'd agree that other mods are likely necessary.
EDIT - another thing. The stock single diaphragm booster pushrod has the pedal pivot hole well below the centerline of the four mounting bolts, while the WJ booster has it centered. This puts the WJ booster pushrod at a fairly significant angle when installed, especially with the pedal all the way down. Any thoughts on how this is going to affect things?
