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I just noticed that there are two small machined surfaces (front and rear) on the inside of the calipers, which, I suppose is where one should measure the perpendicularity of the pistons to the disc... I guess... and use spacers between the caliper and it's mounts to assure the 0.005 difference all around on the calipers... what a pain in the asssssssss...\
Finally got one disc on and ordered CARDONE calipers from Rock Auto.. My old buddy in California suggested taking them apart and clean, then use Wilwood Caliper Assembly Lubricant on all internal parts...
As for Ms. Palin, I don't know her or very much about her except that her achievements are admirable, but she seems to be just a bit of an odd duck...
Those machined flats are what I used to measure the gap between the caliper and rotor, if you get this measurement even (+-), the pistons will contact correctly. As far as adjusting the side gap, you are in for a treat.....it's much more tedious and irritating than you think. The caliper bolts to the differential without any shims, the adjustment is done by shifting the rotor in or out by adding or removing shims on the differential side of the rotor where it bolts to the output shaft. There were shims on both sides of the rotor when you took it apart..right? Good, don't throw them away or get them mixed up from one side to the other.
Here's an example: after measuring, you have .050 clearance on the diff side of the rotor and .070 on the U-joint side. You need to move the rotor .010 away from the diff which will give you .060 on both sides (perfect world). Reverse the shim placement if the rotor is too far the other way. But here's that treat I was telling you about, the shims on both sides of the rotor affect the camber of the wheel. It would be nice to know what the camber was when it was sitting at ride-height out in the driveway, but it doesn't really matter because you are going to have to measure and adjust anyway.
Just a quick outline of the process: bolt the rotors between the output shaft and U-joint including the shim packs that were originally in place. This gives you better odds of being in the ball-park with spacing. Bolt the rotors in place. Measure the rotor/caliper spacing and record it, don't try to remember it. Using the example above, you are trying to move the rotor, but you know the half-shaft will also move and change the camber. In order to keep the camber the same, but move the rotor, the amount of shims (thickness) that is added/removed from the differential side of the rotor has to be removed/added to the U-joint side. In the example, if there was a .010 shim on the U-joint side, move it to the diff side which will move the rotor .010 away from the diff, but move the U-joint .010 closer to the rotor, keeping the camber the same. I think I had to buy a couple of extra shims (different thickness) to keep both sides of the rotor happy. Once you get the rotor/caliper spacing correct, you won't have to mess with diff side again, but when you set the camber you will add/remove shims from the U-joint side of the rotor.
And each time you add/remove a shim, the 4 nuts that hold everything together have to come off, the caliper has to come off (only when centering the rotor, not for setting camber), do the math on shims to add/remove, and then put everything back together and measure again. I set mine up while it was out of the car and I also saved a little time on setting the rotor spacing by using standard nuts and good flat washers to secure the rotor instead of hooking up the U-joint/half shaft every time. When you are done with rotor spacing and camber settings, put new Nyloc nuts on the output shaft studs.
The biggest favor you can do yourself is to get the "rear suspension" and "brakes" section of the Jaguar shop manual. Just so happens there is a very knowledgeable guy on this forum named Jose who has a website with the complete shop manual and I believe you can down load for free. He will chime in here at some point.
One of the pitfalls you might have when you set the camber is establishing what the "ride height" is. The shop manual has the dimensions for the Jaguar, but yours might sit higher/lower. Ride height is the stance of the IRS with tires on the ground, a tank of gas, driver, maybe a passenger, whatever you might normally carry in trunk; just as you would have driving down the freeway. In this condition, the lower wishbones should be about level across the bottom of the cage tie-plate.
I had kinda figured out the process, but you put it together very well.. as it turns out on the passenger side, there were NO spacers of any kind ... I measured camber before taking it apart...a few days ago...So I have a "Target" to shoot for on the spacers..... Driver's side -0.7 degrees and had 4 spacers on the outside of the disc, nothing inside (pads looked "normal"), passenger side, +1.1 degrees and zero spacers anywhere... I just ordered 8 "Caliper spacers".. 0.005" like washers and got 4 or 6 0.020 round axle spacers with the discs.. just got the first disc on this afternoon, but tomorrow is going to be 74 degrees so I'll be hitting it hard to get the other disc on... calipers supposed to be here Sunday or Monday.. I'll see if I can find the shop manual..
I'll be checking the "front to back" alignment also, considering there are two machined surfaces to measure... It would seem that if the piston is not exactly perpendicular to the disc, it can get stuck, which is what it looks like mine did...
You're well on the right track Coupe, a comment on the front to back alignment. The caliper bolts up solid to the output shaft housing and the rotor bolts up solid to the output shaft. Those two should make a perfect 90* angle and you shouldn't have a difference front to rear (.001 or so for tolerances). If you have something much more than that, check your mating surfaces for crud or investigate for bent or mis-installed pieces. I found one output shaft on mine was bent and had a .005 run-out at the flange. It was actually bent in the shaft at the splines, I could feel it when trying to rotate the shaft by hand. Who knew?
If you get through this IRS overhaul with a grin, you might be a Jaguar mechanic in another life.
Not to disagree, but I also ordered some of these "Caliper adjustment shims"..... Seems they are made for the bolt / caliper adjustment position, which seems a whole lot easier than disassembly of the disc mounts to get it right.. plus the only size they have of the "big" shims is 0.020"...???????
Well,...that's the first I've seen those for the rear. Have you made a dry run yet to see what needs to be shimmed and how much? I would figure this out first and then determine the shim-packs you need to move the rotor in or out. You can then tell if you can use a .020 shim at all, remember, it's all in the math: you can add/subtract different thicknesses of shims to come up with the final pack thickness.
I, personally, would be reluctant to use the small .005 "caliper shims" to move the caliper much. If you need move the caliper away from the diff, you are dead in the water. If you want to move the caliper toward the diff by even .015-.020, you end up stacking those little shims and moving the caliper and output housing mating surfaces farther apart which puts more shear force on the mounting bolts and increases the chance of them loosening up. Definitely safety wire all the bolts that are drilled for such.
The caliper shims seem like the "cats meow", just be safe and think-through the whole operation. Here's a screen print of the shop manual with a quick run-through of what I was trying to tell you earlier.
Just as you mentioned in a prior post, shims can be shifted to the inside of the disc, moving it outward, then the small shims can be used to make up the distance to compensate..
As for bolt stresses, when fully torqued, they never see any shear forces, since the parts being bolted together "merge" into one part. The bolts only see the tension of its own "stretching". But they are loose, yeah, they take ALL the shear....
Awaiting delivery of the calipers and small shims Tuesday..
In truth, I probably should have left the shear thing out of my last post, for practical purposes a .005 shim won't make or break the caliper mounting. But technically, the shear force comes from the bolt holes in the solid parent mounting surfaces moving in opposite directions against the stationary bolt. If you put a shim(s) in between those two surfaces and move them apart, you are increasing the shear leverage against the bolt by the parent mounting surfaces. The shims don't become a solid extension of the original mounting surface in shear, only in compression. If you only use 1 or 2 of those caliper shims to fine-tune the clearances, I agree that nothing bad should happen. If you stack 4 or 5 of them between the caliper and output housing flanges, I don't think that would be wise. But in the real world, you probably wouldn't have a problem then either.
Thanks for expanding my brain Dave. I decided to look up the mathematics of bolt torque versus compression forces versus shear calculations. As I was fighting through that doing math on paper and calculator it suddenly occurred to me the following.
the caliper mounting assembly will never be stressed anymore then a locked up brake on that particular axle. The following is just some guesswork math but for a 3600 lb car I would estimate about 800 lb each on the rear wheels. With a coefficient of friction between the tire and the road in lock-up mode would probably be less than 0.80. For a 26 inch tire that would put a torque on the axle at around 700 foot pounds. So let's guess that the mounting bolts are 6 inches from the center line of the Axle. That would put a shear force on the two bolts of about 1400 pounds divided by 2 for the 2 bolts..Now let's assume that the bolts are just hand tightened and the metal surfaces Have not mated and merged into a solid piece due to the approximate 4000 lb of compression between the two pieces., the maximum Shear that the bolts would experiences is about 700 lb. The bolts are half inch diameter and grade 8. Looking at a bolt strength chart it says here that the shear strength is 22, 674 pounds. I am not very worried about bolt failure.
I'm doing this on my phone and I'm not sure how to copy the chart.
The two other specifications that just seems way crazy are the minus 1/2 degree camber which is hardly measurable and the 10,000th of an inch tolerance of the caliper position. Both of those just seem crazy to me.
after all of this research and looking at the condition of my calipers and pistons my mortal sin was that I did not use assembly Lube the first time which caused the rust which caused the sticking which cause the chewed-up pads.
Last edited by 49FordCoupe; 01-23-2021 at 10:46 PM.
You've laid the topic out perfectly Coupe, I just should not mentioned shear in my earlier post. It will obviously not be a problem. Great research on mechanical stresses.
As far as camber, the factory gives measurements and tolerances that they feel will make their cars operate the best. The car will most assuredly operate at other measurements and tolerances, sometimes better. Sometimes trying to "pick the white out of chicken sh-t" just isn't necessary, everyone decides where that point is.
Ok, boys and girls.. so far so good.. here's what's going on.. you might check back later to see if there are any more updates to getting my butt out of this situation...
01-21-2021, 03:57 PM
