That would work and is doable but not ideal. You'll have to do some very precision work to get the caliper centered and the 11.2 x 1.25 inch rotor size is not common size so you'll have to get a larger one turned down or have a custom one made. That's going to be pricey and difficult to service. My setup costed about $850 but you gotta know how to weld real nice.

Very correct in my experience. I found the Jag brakes feel great and can be modulated to a point then they lock up suddenly. They are difficult to control on that edge. I find the wilwoods with much easier to modulate and less likely to lock up. I converted one side at a time so I was able to compare stoping performance of each with Pirelli 235 series 17" front tires.

This make the Jag a bit difficult to update becasue you really have to do the rears first and then dial in the fonts for balance. There are a few options for the rears that retain an E brake.

- Stock size vented inboard upgrade (still 10.3 inches) wont help at all and pricey...Over the years I've grown to dislike the inboard setup.
- 1993 Solid outboard are 11.5 inches. I suspect XJS solid rotor outboard will be a marginal improvement but I dont know fore sure becasue I never tried it and the XJS had ABS at this point so there may be too much rear bias for a non abs car. Still could dial it in with perportioning valve adn this is probalbly the most balanced when using stock fronts but these are a two year part and will be very difficult to source.
- XJ40 or XJ8 large rear 12 inch vented rotors and calipers are plentyful and low cost. will offer alot of rear bias that will need to be controled with a perportioning valve to dial it in if you dont have larger fronts and ABS. Not ideal but doable. This is the rear setup I run but with larger fronts and ABS.


The Jag and most cars with out ABS have brakes that are heavily biased forward, the rears just follow so they are dont lock up in a wet turning condition and cause the car to spin out. So increasing the forward stoppng power will only get you so far. I have the XJ8 huge vented rear brakes. The rears are doing alot of work and my car stops amazingly well and wont spin because I have ABS. With the ABS disabled the rear will lock first. This suggests I could run a larger rotor up front but I'm going to try larger 275 series tires out back first and retest now that I moved the battery into the trunk and put the spare tire back in its place. One of the benefits to additional rear bias combined with Jag anti dive suspension geometry is now there is no dive on hard braking. I really like that because when driving hard I find front end dive very unsettling.

 

how did you switch to outboard rear brakes?

 

I saw one on ebay and snatched it up. For you it would be best to do the same thing and get a complete rear cage from a 1993 to 1996 XJS. The 93 to 96 has 3:54 power lock but it's low bias and has the outboard brakes. I dont know for sure but I think the 95/6 convertible had the huge 12 inch XJ8 vented rotors. Good luck finding one...but look and you can will find one. . I've never seen one again but you'd problably find them in a junk yard. In any case the the outboard 3:54 power lock is low bias so you have to upgrade the carrier to a 19 spline Eaton or Auburn to get a real limited slip effect.

If you cant find a complete unit you will have to use XJ8 or xj40 rear hubs. This is not recommeded becasue proper setup and geometry can be difficult to get back in to spec. You can get them with the hubs and axles and calipers as a set on ebay quite often. There is also a spacer that goes where to brakes disk used to be. I've never done an outboard conversion but I've read about it on the HAMB.

For you with the powerfull V12 your building I'd think this upgrade is essential because the outboard hub carriers are reinforced. The inboard hub carriers crack.

 

well I plan on getting to that after the motor cracks 450hp. which should happen with upgraded intakes.

can you get me the link to the outboard conversation?

 

Lots of good stuff here!

I bought custom made vented rotors for my rear inboard vented rotor conversion for just under $80 each from HRPWorld, which I thought was relatively inexpensive.

On my idea, the inside-half of the caliper stays in the same place, so it'll already be located with no need to center it. The extra 1/4" is added to the outside-half of the rotor by a spacer between the two halves.

Interesting! I wonder if they exhibit more control due to a taller rotor/longer torque arm. For instance, think of the more precise control you get on a bolt when using a long ratchet vs. a shorty ratchet.

Yea, the inboard setup certainly has its drawbacks. However, I did my inboard rear vented rotor conversion for under $400. Also, I'm pretty sure the setup will help fight fade with more mass, vents, etc. I might add a couple little air scoops back there too, maybe on the control arms.

Yea, this is precisely why I don't think increasing the stopping power on the front brakes is a good idea if you're going to keep the rear brakes stock. It sounds like your car has a more advanced setup with upgraded XJ8 rear brakes, etc. In that context it makes sense to go with larger brakes on the front!


It seems to me that there are two main ways to properly upgrade without installing ABS or a proportioning valve:

1) Keep the stock calipers and stock rotor diameter on both the front and rear. Increase the rotor thickness and increase the caliper capacity through the use of caliper spacers. While not ideal, it'll certainly fight brake fade and maintain the original brake bias.

2) Upgrade to taller discs and aftermarket calipers on the front of the car, and upgrade to taller discs and calipers on the rear of the car. (Like icsamerica says/did) This is probably the better solution, but a lot more work and considerably more expensive.

 

Calvin check out this thread... message #297 has a mention of it, thats all ive ever found on the subject.
Jag Jaguar IRS into a 46' International Harvester - Page 15 - THE H.A.M.B.

Also with a 450hp v12 stroker your gonna get some wheel hop when accelerating "briskly". I added two trailing arms on the bottom of the cage and elimintaed it. I'll post up some picts soon.

Fastkat, can you post the part number for those vented rear rotors at hrpworld. I saw a set installed and they had one major benefit...any leaking diff oil would hit the back of the disk and drip throught the vent, not the surface of the disc thus maintaining brake performance. That would be great info to have out there.

 

I think that's precisly what happening. I also think the slightly larger piston diameter helps that too.

I'm just think now....most of the XJS cars have a hulking V12 which puts more weight on the front axle so larger brakes on just the front without uprgading the rear might work out better after all. Our experinces are with chevys and I know that's a weight savings of atleast 300lbs on the nose.

 

http://www.englishparts.com/products...35/TJP190.html

 

[QUOTE=FastKat;771699



Interesting! I wonder if they exhibit more control due to a taller rotor/longer torque arm. For instance, think of the more precise control you get on a bolt when using a long ratchet vs. a shorty ratchet.[QUOTE]
I was discussing this with someone. the problem.is the further out.the surface us the faster it is moving. so I don't know if.that cancels out the extra torque put on.the rotor

 

[QUOTE=calvindoesntknow;772062][QUOTE=FastKat;771699
I was discussing this with someone. the problem.is the further out.the surface us the faster it is moving. so I don't know if.that cancels out the extra torque put on.the rotor[/QUOTE]


A faster spinng rotor with the same Coeffeciant of friciton (pad and caliper force) would generate more friction and more heat over a shorter period of time and that translates into better braking. Because thats what brakes do, they convert conetic energy into themal energy. The reason it works out is becuase, generally speaking, if you increase your rotor diameter 10% you increase the circumferance about 20% and the area increases about 30%. The surface area is what absorbs and disapates the heat so well. The down side is weight and thats why alu hats are popular on large rotors. Also as modern wheels have grown larger so have the rotors. It common now to fine 14 inch rotors that 1.1 inchs thick on performance cars

 

I am thinking of using z04 rear rotors which cost 225 a piece and will.be 14inch. I can get calipers from brembo or use wilwood. all depending on what I can get my hands on.

 

They're custom spec'd, so there isn't a part number per se. Here is a link to their page with info. The best thing to do is call them on the phone - they'll give you an email address where you send your custom specs.

Custom Race Car Brake Rotors

 

I really like the wilwood stuff. Their techline is awsome. Also the Superlights have a rigid cross bar over the top which keeps the caliper stiff. My experience suggests you can get a new wilwood for slightly more than a used brembo. When I was chasing down my feel issue I suspected the brake caliper was flexing under pressure because they are very light. I put a digital dial caliper on the brake caliper while applying the brakes and I observed no change.

 

the only reason I was thinking of using a set of used factory z06 brakes is because it would be very easy to get pads and parts in a pinch from any dealer

 

I was looking at these parts, and the Wilwood 120-11136 caliper has 1.75" piston diameter. The piston area is 2.40" sq.

According to Centric (via RockAuto), the front caliper piston diameter on the SIII XJ6 cars (and probably all of the later XJS cars) is 48 mm, which is about 1.89". The piston area is about 2.80" sq.

If all of this information is correct, it means that the aftermarket Wilwood caliper is exerting less force on the brake rotor than the OE Jaguar front calipers, and therefore shifting brake bias to the rear all other things held constant. Of course, this is only once piece of the equation. Other major factors are the height of the rotor, area of the brake pad, etc.

I would love to find a formula that helps determine the appropriate brake setup, taking into consideration rotor height and relative leverage on the rotor, force applied by area of the pistons, pad area, and coefficient of friction of pad material in the operating temperature range. I know they're all related, but I lack the knowledge to put a meaningful formula together!

 

Your research is correct. I have measured the piston in the Jag caliper with a caliper and it is 1.89" I got the caliper size numbers wrong when I typed it. At the time I simply chose the Wilwood caliper that was closest at the lowest price since this was an experiment. Wilwood also has a Caliper with 1.88/1.75 staggered piston size which would be closer to the Jag calipers and an upgrade I may consider.


Yes, less clamping force, but less is needed because the mechaical advantaged is increased as a result of the increase diameter of the rotor also expressed as the moment arm.

Have a look at this...I focused on the "clamp load" and "brake factor" sections.
Engineering Inspiration - Brake System Design Calculations

In real world testing I simply replaced one front Jag caliper and rotor with a Willwood caliper and larger rotor setup. After a normal pad brake in I observied the following...

-Inital light pressure bite was identical, car slows streight and normal.

-Medium application was identical and slowing down normal to a stop light was straight and normal with hands on or off the wheel.

- Medium high brake force makes the Jag pull noticeably toward the wilwood side when hands are off the wheel, suggesting the wilwood side has progressed in braking ability.

-High or rapid brake force made the Jag pull sharply towards the wilwoood side. The harder I pressed on the pedal the more it pulled. Suggesting as pressure increased the willwood setup was more effecient in converting pedal pressure into stoping power.

- When exerting very high pressure or enough pressure to get the both wheels to lock I was able to unlock and relock the wilwood side while the Jag side seemed to stay locked up. I was able to observe this on a wide and lengthy down hill sloped road near my home and experienced similiar results when testing in the wet.

It was at this point I thought the resuts were good and I installed the other side but the mid pressure feel was terrible because of flex in the adapter bracket I frabricated. Discouraged... I reinstalled stock Jag calipers and the feel came back but the stoping force was not enough to handle my wheel / tire / engine setup. I ruminated on the problem for a few days and desiced to cut the ears off the stock spindles and weld on new ears to solidify the wilwoods caliper mount. The feel returned. Total success.

 

interesting, but another possible confounding variable to consider is - was the Jag caliper clean or a bit dirty and gummed up compared to the newly-installed Wilwood?

 

The stock parts I was using for comparison was new Centric manufactured calipers, fresh skim cut rotors and Raybestos pads.

(All for sale and slightly used if anyone want them.)

 

Did the stock calipers and the Wilwood calipers use the same Raybestos pads for testing? What brand/compound pads do you run on the Wilwood calipers now?

 

I just finished powdercoating my brakes yellow (stock) with ebc yellowstuff and centric drilled and slotted rotors, which should last me till the winter when I change to bigger brakes