Decided to replace the front four pot calipers on my 1995 6.0. The seals were shot and so I bought a replacement pair off a company on eBay who refurbish them. after a bit of a struggle removing the near side caliper bolts ( good quality impact gun a godsend!). I wiggled it loose and then noticed a couple of packing shim washers from the two mounting bolts had dropped to the ground. Probably 20 thou and 10 thou each. This perplexed me as I had no idea the alignment/mounting of the caliper was to such a critical tolerance?
I can't quite see where the need for such fine tolerances exist as long as the brake disc doesn't bind on the caliper casting. Or am I missing something crucial here?

I'm thinking now I should have had the original calipers refurbished - only I can't tell which of the shims belong to the top or bottom mounting bolt.

Anyone got experience with this or a view on it?

 

The shims that dropped to the ground are probably item #21 in this illustration:

https://parts.jaguarlandroverclassic.../brand/jaguar/

The purpose of these shims is to take up the gap between the steering arm (#13) and the vertical link (#12). This has nothing to do with caliper alignment. Every old Jag I've worked on has these shims. Why Jaguar used this arrangement, I'll never know.

Caliper alignment requires shims between the caliper and the vertical link. Personally I've never seen such shimming on the Jags I've worked on but it's mentioned in the manuals and apparently others have seen them. This brings me to believe that Jaguar shimmed the calipers only 'as needed'.

The caliper must be parallel with the brake disc, obviously. Precise measurement here is awkward "in the field". Probably much less so when the entire front suspension sub-assembly was being assembled at the factory.

If the caliper and brake disc are parallel I don't see any problem with a slight lack of centering. In other words, if the caliper is biased slightly to the right or left, nothing bad will come of it. The caliper pistons have a lot of travel and will take up the distance the first time you apply the brakes. If, let's say, the outboard pistons need to travel .010" further than the inboard pistons, I don't see a problem, personally.

Why Jaguar simply didn't manufacture parts with more precise control over the finished dimensions ....so that shimming wouldn't be needed....is beyond me. Obviously, though, the process satisfied their requirements at the time

Cheers
DD

 

Thanks for the explanation Doug. That makes a lot of sense. The new reconditioned caliper is a a fairly snug fit next to the steering arm so I don't think it needs shimming but I will slacken off the bolts again again and check with a feeler gauge. I imagine anything over 10 thou should be taken up with shims.

 

take a look at post 19 onwards in this recent thread:
https://www.jaguarforums.com/forum/x...cement-231437/

It explains the reason for the shims between the steering arm and the caliper lower bolt, which are important.

Forget any need to shim the caliper, as Doug said, not necesary.

 

I have the shims on my 88. They belong with the longer bolt of the 2 from the calipers. When I replaced my calipers I had 2 shimmer side.

The help document (Kirby book) describes it as well as what is mentioned above already.

 

well of course, nothing is ever straightforward when working on a Jag.. After reassembly of the nearside new brake calliper along with replacement of brake calliper pipe line (CCC2616) and flexible line (MHF5670AA-F) all went back together nicely and I shimmed the lower (longer) calliper bolt (CBC4884 - which has a M12 x 1.25mm thread - more of that later!) using the method as suggested from the helpful advice given by the replies to my initial post. Trouble came when starting to work on removal of the offside front brake calliper. I should say at this point that I am fairly fortunate in now having a decent workshop with a 2 and 4 post vehicle lift and 40 years worth of collecting enough tools and enough garage equipment to set up in business! - this, after spending half those years grubbing around on cold floors, cars on axle stands, on my back with sweat running in my eyes, So, the XJS is on the two post post ramp, all wheels free in the air - the top (short calliper bolt CBC4885) comes loose with use of ingersoll 20v battery impact wrench - great tool! However, the lower calliper bolt just will not budge. lots of penetrating fluid and a 4 foot lever extension on the impact socket would not move it. Heated it up with MAPP blowtorch (carefully due to surrounding abs wiring etc) more penetrating fluid and left it overnight. Back next day to try with impact driver and still stuck. 4 foot lever on to it and some perceptible movement but this was the bolt head shearing off! - Bugger! ok - now what? decided best course of action was to remove the whole hub assembly from the car and try and deal with it on the workbench. This involved undoing track rod end from steering arm, upper ball joint by very carefully putting some load under the lower front spring pan using a trolley jack and short wooden 4" post - remember, the car is up in the air on the arms of a 2 post lift and too much pressure from the trolley jack will raise it off the lift support arm. So, that gave just enough spring compression to allow the upper ball joint bolts to be removed and swing out the whole hub to get access to the lower ball joint nut and the ABS sensor and brake lines which all came apart with gentle persuasion - being especially careful with the ABS sensor as it is a tight fit in the vertical link. Once the lower ball joint nut was off and a couple of clouts from a 2lb hammer, the whole assembly was off the car. Now what to do to get the steering arm off? if this had been an earlier vehicle, I would have probably just taken an angle grinder to it as steering arms can be had fairly cheaply secondhand. But this later, facelift model has a different part number steering arm and these are far less readily available (i have no idea what the actual difference is as they both look the same but there must be a variance somewhere I guess) with none to be found at time of this crisis. The steering arm felt like it was welded to the remainder of the lower bolt - now a stud without its hex head. So, after straitfoward removal of the upper M12 bolt along with the brake disc shields and more application of heat and penetrating fluid to the broken bolt and knocking to and fro with a lump hammer began to see some very small movement in it. Over several hours, and using two, 1" cold chisels as levers, the arm came off without any damage. This felt like a real victory! The remains stud though was still absolutely rock solid stuck in its threads in the vertical link so now I had to find a way to remove the old brake calliper. I decide to carefully cut around the lug with an angle grinder fitted with a new thin cutting blade as I already had a new replacement calliper writing to go on. That, and a bit of cold chisel work, released the old calliper. Now I unbolted the rear hub nut and removed the disc brake and tube from the vertical link leaving it with both upper a lower ball joints still attached to it. I now had about two inches of stud to get properly gripped in a bench vice and be able to twist out by simply unwinding the link from it. Here again, was a problem - the threaded part of the stud/bolt was absolutely and resolutely stuck fast. I was in danger of shearing off the remains of the stud by the amount of force I was having to use. So back again to heat and penetrating fluid over a whole day and over night, I managed to get tiny movement on it with much alarming creaking from the metal as it turned to and fro just millimetres at a time. Heating and cooling but each torturous tiny turn was met with huge resistance right up to the point where they finally, reluctantly, separated. I tried a new M12 x 1,25mm bolt in the now empty hole but it does not go more than half a turn. This leads me to think that the bolt has either been cross threaded when last fitted - or, that someone has used an imperial unf bolt instead of the correct metric one. Either way, i have ordered an M12 x 1.25mm pitch tap to see if I can successfully re-thread the link as it needs to take a good deal of torque when fitting a new bolt - eventually! - update to follow!

 

Hi Logiedurno

With the benefit of hindsight which is always a wonderful thing, you could have easily saved yourself all that pain and suffering by doing what Greg and Myself have done and invested in a Mains Powered Impact Wrench

For Jobs like doing Calipers, Cordless Tools can be a Waste of Time and the same thing goes for the Air Powered ones unless you've got a massive Air Compressor and even then that might not be enough

The First time I took out a Caliper Bolt, with help from a 'well meaning friend' no longer on my Christmas Card list, he sheared the Bolt right off the same as you did, then once he'd finished Showing off to the GF

He walked away and left me with a massive problem to sort out, as the Bolt or what was left of it was seized in the Steering Arm and since I couldn't drill it out, after a week of trying I had to cut through the Steering arm and then had to buy a new one

All for the sake of £35 for a Mains Powered Impact Wrench which makes this job easy!

Link Below: Also look at the previous page: 9 to see how a Spanner on the end of a 4ft Scaffolding Pole just wouldn't budge it

Using my Mains Powered Impact Wrench to remove a Caliper Bolt Including Video of my Impact Wrench in action

 

Yep my electric plug in impact gun is amazing. Better than my air gun with my 20 gallon compressor.

Same as drills plug in ones are way better than cordless for the heavy jobs