Doug I’m aware of the change has they don’t line up!
That’s what I read in the red book the shims are for that reason has one shim came from the bigger bolt on the bottom of the steering arm it’s seems it has nothing to do with allotment for steering has it sits aft of arm!
I guess the shims for the caliper are needed Frank otherwise they would not be there lol. There are a lot of shims in the front end but once there in there correct location the system seems to work very well like a nice smooth ride!
I will keep you posted on update. Maybe it’s the rotor i will take it of and take to brake shop and see if it’s true!
When you add or remove shims on the steering arm’s lower bolt you effectively change the angle between the steering arm and the hub, therefore altering toe.
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No, Sawyer - with calliper offset the pistons would simply extend different distances to contact the rotor. Ie, the pressure on the disc would still be symmetric - centring the calliper with shims equalises piston distances…
The a possible cause of disc run-out is asymmetric disc pressure due to stuck piston(s) - combined with overheating. It’s less common on vented discs due to heavier construction…
As an aside; permissible disc run-out is 0,004". One effect of excessive run-out, apart from vibration under braking, is increased initial pedal travel. First move of the pedal brings the pistons in contact with the disc - run-out pushes the pistons further from the disc…
Frank
xj6 85 Sov Europe (UK/NZ)
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It’s been my experience that the stock rotors are pretty stout. I’ve owned my 88 XJ-S for over 20 years, and when I changed the brakes about 6 years ago, the stock rotors were severely heat checked and blue, but not warped.
I’ve yet to encounter any warping on a Jag rotor. Well that’s not true. The ’02 XJR-100 has warped rotors. The big ones. The drilled and slotted ones.The ones that aren’t listed by the usual suspects. Those Rotors. Rant over.
I’m also not too sure these rotors weren’t replaced by a substandard part. The PO took the car to Firestone to have a brake job done. I’m shaking my head…
Besides IMHO, the XJR is more of a Ford than a Jag. I prefer the Jags that were made by Jaguar. That’s just me…
Anyway
There’s two camps about shims.
Camp One – Shims aren’t necessary. The caliper and pads will center over the rotor. Fluid will take the path of least resistance.
Camp Two – Shims are necessary. Centering the caliper over the rotor will allow the pressure to be applied evenly to both sides of the rotor at the same time. The result being even pad and rotor wear.
I kinda fall in Camp Two. For a couple of reasons.
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If there’s a hard way of doing something then that’s the path I’ll take
. My first go around, as stated on either this thread or another one, My green XJ6 had shims everywhere. Between the steering arm and the calipers. Not being very confident in what I was doing, I figured I’d put it back the way it was. Thus shimming the steering arm and the front rotors. It was a frustrating proposition. Very fiddly. Succinctly stated - gravity is not your friend. It was really hard to get the shims to stay in place while threading the bolt through the hole anti-sneeze or grease didn’t work (for me). Next go around, I will give superglue a go at holding the shims in place. Top tip, a little heat will cause superglue to give up its grip. My luck, I’ll have the shims stuck to my fingers rather than where I"m attempting to install them. -
In my YouTube video, “Shims, Rotors, Calipers, Oh My” I show a rear rotor with uneven wear. I state the caliper was frozen, which is true, but I’m not 100% sure it is the cause of the uneven rotor wear. I’m voting the handbrake is the culprit. The pads with the most wear were on the side of the rotor with the most surface material. Go figure.
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Pressure will be evenly applied no matter, Mark - it is a function of line pressure to each piston, which is independent of calliper centring…
However, as the pads wear, the pistons must extend further - and at one stage, with asymmetric calliper position, the poistins on the ‘long’ side may reach end of useful travel…
A secondary use of shims is to ensure that the callipers are parallel to the rotors. And a third factor; the callipers are not intended to be ‘floating’ - the shims may be required to ensure that the callipers cannot move sideways…?
Frank
xj6 85 Sov Europe (UK/NZ)
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Totally not related. but as i was writing the post about brakes and shims and such, well I though I’ll see if I can find the brake rotors for XJR-100. I did OMG!!! are they expensive!
Part number JLM21749 $962 US or 744 pounds. FOR ONE ROTOR!
That’s 4 Grand just for Rotors!!! OMG!!!
I agree. If the caliper and rotor are parallel, a few thou offset to the left or right won’t make any difference in operation or pad wear.
I agree again, although as a practical matter I’d say that pads are commonly replaced before the last .002-.008" of piston travel becomes an issue
I always viewed this as the primary purpose of the shims, when fitted. A non-parallel caliper could obviously be a problem with respect pad-to-brake rotor contact. A small irregularity might be insignificant, though, as the pistons travel independently and will push the pad onto the face of the rotor flatly, if you get what I mean. The issue then becomes uneven contact between the piston and the backing plate of the brake pad. The real-world significance of this is questionable, IMO.
Taking the measurement to check for parallelism is not something that is not likely done very often in the field. I suspect the factory had a clever way of checking this during the assembly process. I’ve oft wondered why Jaguar simply didn’t demand more precisely manufactured parts.
At the end of the day, in my opinion, it’s all rather academic. After owning these oldie Jags and using them as daily drivers for 23 years I’ve never had any identifiable problem with uneven pad wear attributable to shimming nor have we heard from other owners reporting such an issue. It would likely be a very slight uneven-ness that goes unnoticed during routine pad replacement due to normal wear-out…and certainly never noticed as a braking deficiency while driving the car.
Far more common, and of greater concern, is uneven pad wear (and overtly poor braking performance) due to seized caliper pistons.
My hat’s off to anyone who goes though the effort of centralizing the caliper. I’d be less nonchalant if I had ever seen evidence that being so resulted in any palpable real world negative consequences 
Cheers
DD
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I quite agree, Doug - though the pistons hitting the pad backing plate at an angle will also ‘scew’ the pistons in the bores…
Frank
xj6 85 Sov Europe (UK/NZ)
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Update on rotor!! I removed bottom caliper bolt on both rotors and found the shims on top of bolt along with lock washer. I notice there is.a gap between rotor and steering arm! I installed shims which were.correct size and I also changed my brake pads to look quite semi metallic and sure what a differance! But my steering wheel is of to the left a bit not centred any more but car stays straight on road and on very hard braking at 70 stays very straight no pulling or shaking. Going to have alignment.done.again to see.What the print out will be. So Mr Dwyer is correct it has changed my steering the shims attended for a reason and probably not good for steering arm has I noticed its bending it has the boot threads are chafted from when I tried to put them in after rebuild the bolt now aligns properly!
So did you have a warped rotor? I’m curious because I believe I have a warped front rotor or rotors. My car sat for about 10 years before I bought it. The rotors and pads look like they were replaced shortly before the car was parked. I only checked the drivers side, spinning the tire it’s definitely not spinning smooth. I get a pulsating feel through the pedal when braking.
If they are carbon rotors, maybe. But I understand the XJR-100 uses your garden variety Brembos. Which means I’d be fabbing hats for Wilwood generic rotors before I’d ever consider wasting that much money.
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Hi Mark, what about RockAuto.com. Here’s a link:https://www.rockauto.com/en/catalog/jaguar,2002,xjr,4.0l+v8+supercharged,1440765,brake+&+wheel+hub,rotor,1896
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That does imply a warped rotor…
You can check the run-out with a gauge - permissible run-out is 0,004". Excessive run-out will also cause increased initial pedal travel…
Frank
xj6 85 Sov Europe (UK/NZ)
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Thanks Frank, that’s good to hear. I’ll have to look into that and buy a gauge.
Joe
Thanx for the link. Those aren’t the right rotors. I’ve got huge 13" drilled / slotted rotors part of the “R” package (“R” for Ram-it-in). This isn’t your normal '02 XJR it’s the anniversary edition XJR-100. They say the 100 is the 100th birthday for Sir William Lyons. I think it’s the cost multiplier for parts.
Absolutely everything is more expensive on THIS XJR than a normal XJR. It’s cazy!
O2 sensor was close to $400 bucks for ONE! I’m a cheap bastard. I refuse to pay more for something if I don’t have to. but conversly, I won’t scrimp when it comes to parts. I will make sure the parts are of the same quality or better than OE parts.
Unfortunately parts on this car have different part numbers along with special bend-over pricing.
Thanx for looking it up for me 
OH, and I’ve used the Centric Drilled and Slotted rotors on all of my XJ’s and theese Rotors are amazing!
Don’t get loaded calipers cause the pads are crap. clouds of brake dust. I went with the EBC pads instead. Organic pads will wear faster, but save your expensive rotors. Slotted or drilled and slotted rotors, brake fade isn’t as prevalent - or takes longer - so I opted for less brake dust and shorter brake life. The fronts are easy enough to swap out.
For what ever that’s worth
Mark
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You’re welcome Mark, I didn’t know yours was or is a special model. That’s funny what you suggested the R stands for. That make sense I have a 2003 Dodge Ram 1500, the R in Ram must stand for the same thing, lol. I’ve been spending a lot on that lately chasing a P0172 MIL. Those prices are crazy, hopefully you knew that before you bought the car or maybe it was a brutal awakening. Thanks for the heads up on the rotors and pads. I’m going to clean mine first and see if that helps. I think from sitting for 10 years that could be the problem and the rotors probably are not warped. Good luck on finding your rotors and hopefully at a better price.
Joe
Dodge RAM - funny that’s what I always thought. haha. Isn’t that error code a run rich? 02 sensor maybe? or EFI temp sensor gone breasts skywards or cooked wires from point a to b.
No I didn’t know that until I started pricing parts. I got the car for cheap the supercharger sounded like it had marbles in it. That was an easy fix - it just so happens that is the same M110 supercharger used on Ford and GM cars. so parts were cheap; and it would’ve been an afternoon job, if I didn’t get a wild hair and decide to polish the inside, replace the teflon wipes while I was at it. 16hrs to polish the inside. Was it worth it? probably not, but it looked cool when I was done.
If the car has been setting, chances are the calipers have arthritis from sitting and don’t want to move. It’s quite common, and is the main reason why Jags end up on craigslist for cheap.
keep us up on your progress!
Sincerely,
Mark
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