Front Rotor R & R Help
 

I was planning to put in new front rotors and pads this weekend, which I assumed was a simple straightforward job like every other car I'd done this job on. However, taking a look at the workshop manual my first reaction was 'holy crap, I probably should leave well enough alone and not even attempt that'.

I've never encountered lock wire before, and I'm not sure how to recreate it properly once it's all back together.

I read about adjusting "hub bearing endfloat" and it may as well as been written in French because I have no idea what that means or refers to and there is no diagram of it that I can see.

Shims? Are you kidding me?

Am I being a bit of a wimp, or is it really as difficult as it appears?

Well, I'd recommend you to get yourself a manual. Not kidding... Best would be official manuals from Jaguar.

Safety wire isn't really required as such. It was back in the day a thing they did just to be sure. Most will get away with simply torqueing the screws and done. Iirc endfloat was not that complicated.

Forget the lock wire if you wish....just use Loctite. Many others do so.

Shims:

Between the steering arm and the caliper will be a shim (or shims) that will fall out when you take the caliper off. Just be aware of them and make sure to reinstall them. They take up the gap between the caliper and the arm. These are often misconstrued as caliper alignment shims; they're not.

I personally have never come across a Jag that used the caliper alignment shims....but they're out there, apparently. Just be aware they you might have them. They'll be between the caliper and the caliper mounting

Adjust the wheel bearings as you've done on any other RWD car with the same (and virtually ubiquitous) hub/bearing design. Nothing exotic required. Everyone has their favorite method. I take mine down to zero free play and not an iota more. Others will chime in.

Cheers
DD

Thanks. I mentioned in my post that I have the workshop manual, which is the factory manual cd from the Heritage Trust. Amusingly, the first illustration in the front rotor section is of the rear brakes!

You are not being a wimp, and it is more complex than on modern cars!
If you decide to do it, post again and I'll suggest a step by step for you. But, think of devoting a weekend to it and having all the bits ready.


The worst aspect is removing the old rotors, as the five fixings are at the back of the hub, and (if you still have them) the fixing bolts can only be accessed from a hole in the shield.


Removing the calipers requires the two lockwired bolts to be undone, and they can be REALLY difficult. An impact gun is highly recommended by Orangeblossom, and they work! The shims on the lower of the two caliper bolts must be replaced where they came out from (between caliper and the steering arm, just note their position carefully and keep the two sides of the car separate.


The bearing endfloat does not have to be touched. What IS important is ensuring that the runout on the new discs when fitted is within 2 thou, and you need a dial gauge for this. Mainly it is a matter of VERY careful cleaning of the hub surface where the disc bolts up to it.
greg

Thanks very much, you and Daim have eased my mind on the lock wire front.

I still don't understand what "adjust the wheel bearings" exactly means. Probably because I can't recall ever removing a hub or messing with bearings (at least in this century). Sorry to be such dimwit.

Well, the adjustment just refers to how tight/firm the nut is on the stub axle which holds the hub assembly in place. Normally it is basically tight with no play at all and then undo half a turn or so (haven't got that in my head at the moment, ought to get my manual out :D) to counterbalance heat expansion (when the bearings move they will expand, if they can't expand, they seize).

OK, I'm going to cowboy up and tackle this, but I'll push it to next weekend when I'll have more time to allocate.

It looks like I'll need to have some things on hand like cotter pins, proper bearing grease and whatever type of dial caliber required (is it the jaws type or the plunge/travel type?)

Greg, I don't need full instructions, I think I've got a better idea now, but a fuller explanation on getting the endfloat or disc install correct would be helpful.

Hub bearings in Three bear terms. Not too tight, not too loose, just right. As in porridge temperature ratings.


But, as said hub removal not involved with caliper and pad service. But, in shipwright terms, not a bad time to do it...


Carl

The XJS is sort of like older Crown Victorias (if my memory is right) and there isn't a separate hub and disk to enable disk replacement. On some cars it is separate and you can just replace the disk and leave the hub/wheel bearing assembly alone. The XJS isn't like that, the hub has to be removed to unbolt the disk, and thus the wheel bearings also come out.

The bearings require a specific amount of clearance (endfloat) to work properly. I think it's around 0.003". So what you do upon reassembly is put the hub/disk back on the stub axle and then you have to tighten up the nut that holds everything (including the wheel bearings) onto the stub axle. How much you tighten that nut determines how tight or loose the wheel bearings are. It should be tightened until there is the specified amount of movement in and out (end float, or looseness); as I mentioned it's usually about 0.003" - the thickness of a single sheet of paper. That's where a dial indicator is used, of the plunger type, to measure that bit of clearance. Then the cotter pin and retaining collar is used to hold the nut in that position to keep the endfloat from changing.

Just to (possibly) help clarify things for Mac......


The rotors and hubs can be removed from the car as an assembly and then separated on the work bench. That's my preferred method.

Or......

You can leave the hubs on the car and remove the rotors via the hole in the tin shield, as you mention. Then, yes, the bearing adjustment is not disturbed....even if it isn't what it ought to be :)

IMO, however, replacing the brake rotors is an ideal opportunity to disassemble the hubs for cleaning, seals, and bearing repack, IMO.

Cheers
DD

Totally agree with Doug! A dial gauge with a plunger is best I believe. Fix the magnetic stand on a wishbone and set the plunger against the disc as far out towards the outer edge as you easily can.


The wheel bearings are taper roller bearings, and like Doug, I do up the nut very gently until there is no endfloat (you can hear it click a touch when there is) but NO tighter.
Greg

Hi Mac

I've done this Job a few times now and by far the worst is removing the Caliper Fixing Bolts, though maybe you do not have the Corrosion

problems that we have in the UK.

Even Spanners on the end of 4ft Scaffolding Poles would not undo them and as a last resort I bought a Mains Powered Electric Impact Wrench.

Which turned a very difficult job into a piece of Cake and was recently used to remove the Blades on my ride on mower, that were so rusty that

they could not be undone with anything else.

One of the most useful things that I have ever bought.

https://cimg3.ibsrv.net/gimg/www.jag...68efd604fb.jpg

Even Spanners on Scaffolding Poles would not undo the Caliper Fixing Bolts.

In order to undo them, I bought a Mains Powered Electric Impact Wrench, which made the job easy.


Heavy Duty Electric Impact Wrench 1/2" Drive and 4 Sockets 450NM TORQUE 1010W | eBay

The hubs MUST be removed to get a rotor changed... How else will you get the smaller disc bore over the larger hub size!?

Or am I missing something here!? Hub off, bearings need adjusting. Simple as that...

Oh, jeeez! I have things all bollixed up. My fault. Glad you caught this!

You are correct.

The HUB can be removed while leaving the brake rotor and caliper in place, via the holes in the tin shield.

However, you can't remove the ROTOR without removing the hub and caliper

Sorry.

Cheers
DD

I have this backwards.

You can leave the caliper and rotor on the car and remove the hub.

You can't leave the hub and caliper on the car and remove the rotor.

Cheers
DD

Whew??


Glad that task isn't on my pate at the moment!!! I'd not know where to start much less where to stop!!!


Bigger fish, a possible. My venerable Jeep conked out. Battery? Plus no run. Diagnostics to do. Fuel or ignition. Fuel pump, oh s...., the d... thing is in the tank. and top mounted. Drop the hitch, shield then the tank!!! And unhook it's many lines!!! No longer in my wheel house.... Maybe only a filter??? Still a down and under and weird couplings.


First order. get the battery to take a full charge. It fussed about that yesterday....


Carl

quick pic of new rotor, and calipers.

checked run out ,within .002 thou., sometimes you may have to check the hub runout.

EBC Gold, and wilwood calipers.

sometimes i spend money foolishly, but cant take it with me.

old pic of Grp44 race brake, 8 piston caliper, 1977.

Thank you guys!

Job done.

In retrospect, I'm not certain what I was hesitate about as the job isn't as complex or difficult as the factory workshop manual made it seem. Not to mention the workshop manual is incorrect -- not sure if this just ABS cars or not, but you have to remove 3 bolts to remove the calibers, not the 2 stated in the manual.

My worry about lock wire turned to be a bit of joke, because mine didn't even have the wire installed. So apparently when the rotors were last replaced by a Jaguar Specialist they were fine with Loctite. I was fortunate that my air impact wrench was able to break free the caliper bolts without too much fuss. I learned to repack bearings, which I'd never done before so that is new skill acquired.

I will admit that when you guys used the term "run-out" I didn't have a clue what you were on about, but a little googlefu and some youtube I had a quick "ah ha" moment. I can see how it might be easy to make a mess of this job, but I took my time and was meticulous with cleaning and re-grease so the run-out was below spec.

The most important part, my prior reported issues with the brakes just not feeling "right" are now gone! Thanks for the encouragement to tackle this, because I've wasted so much time trying to "fix" how the brakes felt since I installed the Bosch Quietcast pads. I don't know if it was the new pads or the old rotors or the combo of both, but it was driving me nuts because I just knew it was right.

The factory manual made it sound complicated? I have the metal bound workshop manuals and nearly everything is over-simplified. Nearly any work consists of "Remove part, assemble in reverse" with some added specifications and whatnot.

I've removed the front rotors once to turn them a bit and repack wheel bearings and it was pretty simple except getting all 3 bolt holes lined up. I didn't have a gauge to check end float so I did the old general "tighten while turning to 25 ft-lb and back off enough to replace cotter pin" and it has ran totally fine that way.