Fixing Jaguar IRS Brakes
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Just so you can get oriented to what I've got to deal with, here is the configuration as installed. You can see the thrust arms and pivot points on the secondary crossmember that was welded in to furnish the correct coincident pivot point for the lower control arms to rotate with the thrust arms without any binding. The OEM thrust arms actually are not geometrically absolutely correct, but was a compromise (I guess) to allow ease of fabrication and service. They had big rubber bushings arranged directly in front of the lower control arms and they would twist as the lower control arms moved up and down. Since I had to cut the intermediate crossmember to install the driveshaft, I decided that the solution to that "weakening" of the crossmember, I welded in the additional members from the primary IRS mount crossmember to the intermediate crossmember. You can also see the torque arms, that are solidly mounted to the center section and mounted to the frame with bushings on the sides of the frame. These transfer the forces imposed by the driveshaft torque to the frame. All of this has to come out to do a brake job.
This is a 1" by 3" board, trimmed to fit under the wheel well and cut to 15.5" (as I recall) to fit on the outside of the rear wheels to measure the camber of the Jag IRS. I downloaded an App called "Clinometer" that measures incredibly accurately any angle. The screws holding the phone fit very tight on the phone so it doesn't slip around while using / measuring .. pretty great !
Screen shot of the Clinometer screen when it's on. VERY accurate. Specification on camber is supposed to be -1/4 degree. Hard to measure.
Ok, Getting started. Luckily, I had the foresight to build a removable panel in the trunk that is gasketed, insulated, and carpeted with Zeus Fasteners in 8 locations so I can get to the rear end. After jacking the car up, dropping the tires, removing the shocks (unpainted patches on the crossmember), and lowering the center section with a floor jack and ratchet straps in case it wanted to fall.. I got it down to the floor.
New discs, disc spacers, piston seals, and pads. Spacers are used to adjust camber, which you should do first. They go between the drive flange on the center section, pushing the axle assembly outward, increasing camber toward the positive number (top of wheel tilted outward). Theory is that for every 0.020" spacer, it adds 1/4 degree to the positive for the camber of the wheels/tires. Specification is for the camber to equal -0.5 degrees. Seems ridiculous, but.. gotta do it anyway. The drivers side was pretty much on, so I did not add any more than the two that were already on that side. Since the passenger side was at about -1.2 degrees, I added two spacers to the existing three. (Axle was slightly short).
Passenger side disc on and camber adjusted with spacers. OK, so I cheated. To check the readings, I raised the wheel/tire mount to horizontal position, then measured the mounting flange and the surface of the disc, and subtracted the difference. Surprisingly, it came out to about -0.70 camber. That's close enough for me....
I decided against trying to recondition the old calipers so I bought some New Calipers from Rock Auto also. I disassembled to be sure the pistons were greased. They were, but I added a bit. Hope I didn't "F" up again. Look closely and you can see the small "flats" that are machined into the caliper that are to be used to measure the distance to the disc, then adjust the position of the caliper so that the calipers are centered on the disc +/- 0.010". The four holes nearest the camera are for mounting the emergency brake assembly..
Measurements and notes to figure out how much to shim the passenger side caliper to center it on the disc. The specification is 0.010" MAX from exact center. This worked, to cut two 0.020" "Big" shims that I bought to adjust the camber and then three each of 0.005" Caliper shims that I got from Moss Jaguars in California for a total of 0.035". Those shims are just about impossible to get onto the bolts, since a "normal hand/fingers" can't even touch the head of the bottom mounting bolt to get it started and not drop them off on the floor if the bolt moves back a bit. THAT is a pisser, because the calipers have to be first mounted to get the measurements, then taken off and then remounted with those dang shims. I use a dot of "gasket maker" on the shims to hold them in place while holding the approximately 15 pound caliper on my back/shoulders screaming at me, and getting the bolts started.... but it worked..
Final assembly of emergency brake assembly: Position the assembly on the disc, insert and tighten the two bolts with the extension on them. Be sure that the brass return springs are in the holes. Leave the pivot bolt loose to do this. Tighten the bolt slowly, jiggling the assembly and watch the position of the pads. Tighten the screw hand tight. Try to rotate the disc. It should not move. Start to loosen the bolt/screw until you can rotate the disc by hand. It's ok if you hear some scraping, as long as you can rotate the disc. Insert and set a skinny cotter key to secure the position of the bolt/screw. "Jack" the lever and test that it causes the disc to not be able to be rotated. DONE !
