HI all,

Im looking to replace the front discs and calipers on an XJS and wondered if anyone had any dimension of the standard calliper offset, lug mounting etc...etc...

Essentially I want to replace the current stock with willwood callipers and discs,. I think I can pretty much spec out a disc and bell (im looking to increase the disc size and thickness) from the standard Willwood catalogue put the calliper dimensions, location on the spindle, distance from the wheel centre to lug mounts I dont have.

Im looking at a 328mm / 12.88inch diameter disc by 28mm/1.10inch wide with a separate floating bell. But am unsure of the correct, or as near as correct calliper. Im aware that I'll need a bracket to be made up or adapt something from the Willwod range.

Any thoughts, advice, concerns etc.....always appreciated.

Thanks,

 

I'd suggest the standard front end brake setup on an XJS is really very good. No-one ever complained of the car being under-braked on the front end. Maybe some uprated pads, or even some grooved discs as the ultimate. But larger calipers and pads? I'd invest the money in other areas of the car, if I were you.

Cheers

Paul

 

What Paul said 100%.

All mine ran Semi Metallic pads, F & R, and I drove HARD, we were hundreds of miles from anywhere in those days, and a few hours at 100MPH was considered normal. None of the beasts ever had trouble coming down to zero in a hell of hurry, Roo's make huge dents in Jags, and Wombats wipe out front ends in a heartbeat.

Your car, your money, your call, but not an issue area for me EVER.

 

Agreed. A set of EBC Ultimax discs and red stuff pads is all you will need on a standard XJS V12 for fast road driving pushing out 300 BHP. On a 6 cylinder car getting towards overkill.

What you can do, if you have the money, is to take several kilograms off the unsprung weight at the front hub by fitting a set of these from Fosseway Performance. This will improve the ride a touch and lower pedal effort a bit. Plus rear upgrades as per the links:
https://www.fossewayperformance.co.u...rake-upgrades/

No doubt you can fix up something similar from the Willwood catalogue, but the actual braking performance will not require it; but reducing unsprung weight will give a real ride advantage. Whether you can get discs of the size you mention inside the facelift 16 inch rims might be worth looking at.

 

Thanks Paul,

I should have said the car gets tracked regularly and ive tried every colour of EBC brakes, which are good but after a while they do fade, plus drilled and slotted and dimpled discs from varying manufacturers.

the advice I have had is fit bigger discs and callipers. Ive checked out if the XJR brakes fit along with Aston Martin DB7 dynamic kits (which are like hens teeth and require a rebuild as they are dont make them anymore - AP).

The next best option for me is to go Willwood or another alternative. I opted for Willwood as they seem to have a good reputation and come recommended.

Thanks

 

justinb01,

Don't know if this is way over your budget, even with a cheeky offer?

Aston Martin DB7 i6 Driving Dynamics Front Brake Kit - Black Calipers - 28-27197 | eBay

Paul

 

Hi Paul,

I've tried! Not up for offers sadly! It does require a bracket to be made up which should be simple I would think.

I did see a complete subframe from a DB7 which required a complete refurb but spoke to AP and they wont service them or make parts for them any more so they are pretty obsolete hence looking at Willwood.

 

Just call Wilwood. They know the car, It’s a common upgrade for race cars. It’s all bolt on stuff. However You can spend some really serious money on them. The really light 6 piston calipers with floating disks. It Will put a really serious dent in your pocket book. Or actually spend less then rebuilding the stock calipers would cost, and still have good choice of pads.
If you run at a track like Elkhart Lake 4 mile track with 3 really high speed straights (155-160 mph ) followed by really tight corners. ( total of 14 corners ).
But a lot of tracks aren’t that hard on brakes. Realize that for SCCA Track night the stock system with clean fresh (Dot 4 or better) fluids are fine. Only a handful of tracks I’ve raced had the need for more than the stock system.
Yes, your car weighs 4662 pounds plus driver and fuel but big radius turns really don’t call for that much braking. And smaller tracks with a lot of tight corners, you’re going slow enough so that there isn’t a lot of heat generated.
Since my Vintage racing Jaguar XJS is light enough (2700 pounds) I can use Wilwoods ultra lite 4 pad caliper combined with an 1.25 thick 12” rotor. I just change pads according to the track. My rule of thumb is if I have 1/2 of the original thickness left after a race weekend the pad is too hard.
The stock rotor on the XJS is only .810 thick and something less than 12 inches. By going to the 1.25 thick vented 12” rotor that helps already. But don’t use a drilled or slotted rotor. While they do run a bit cooler under really hard ( glowing rotors) racing conditions they tend to crack. While I’ve never had one fail but magnafluxing them post race scares the bejesus out of me.
Realize that if you are going to run with SVRA In group 6 (Trans -Am etc). You are required to use stock calipers. So then you use Pottorfield PADS AND racing fluids. Some of which. Are really great but need replacing after each session. No you don’t need to drain the whole system. Just a few pumps on each caliper to get the cooked fluid out. ( crack the bleeder open and put your finger on top after each down stroke of the pedal. It’s crude and messy but fast. always refill after each caliper).
Are you running the inboard brakes, or later outboard brakes? If inboard I hope you at least replaced the solid disks for vented ones. And have a lot of air ducted in. I have 2 NACA ducks from each rear window as well as pick up air from the floor.
Then once hot air blows off the rotor I have ducts from the trunk going out where the license plate is. ( You have to have a way to get rid of the hot air once it’s generated. I use two 4” aluminum flexible dryer tubes over the fuel cell ).

 

Hi Mguar,

thanks for the info. I tried Willwood but they dont do a kit for the XJS / XJ6. I've been in touch recently and posted some dimensions that I had taken to see what they recommend.

 

Oops, You obviously talked to a new guy.
think the bolt pattern is 2&3/4 inch the same as your caliper. They fit right on. You don’t order a “kit”. You order the parts.
Same deal with the Rotors. But like I said the stock XJS is .810 thick and you’ll want the 1.25 thick 12 inch rotor. Calipers & rotors.
If you’re going to be racing at ELKHART LAKE. Or Watkins Glen, Maybe ROAD ATLANTA or Laguna Seca. I’d suggest you get the floating rotors. At home I’ve got a contact who can provide those.
I’ll send that tonight.

 

Thanks Mguar,

Ive been in touch with Wilwood and they say this is something they dont support even thought I sent drawing and dimensions. I'll just have to work it out myself and properly measure up the existing stock install and see how that translates over, with the obvious exception that I'll need to make up a bracket.

I just thought it would be a common swap and that someone had swapped in Wilwood kit before.

Thanks

 

Have you seen this?
https://www.fossewayperformance.co.u...xjs-brake-kit/

Do a Google search on "Jaguar XJS big brake kit", and you'll find at least one other option.

Jon

 

Hi Jon,

Thanks I'll take a look.

 

Worth pm ing ICSamerica, he has done great stuff as explained in this thread:
https://www.jaguarforums.com/forum/x...e-works-84536/

 

As I’ve said, I’ve done it twice. On my XKE V12 roadster and the first XJS I raced. Both vintage racers only.
I will be doing it on this one. ( the Group 44 tribute). I spoke to a Cam Bush or Bush Cam ( note got wet and are blurry )
He recommend the forged Dynalite (4 piston)
The caliper is a direct bolt on. No bracket required. While the 6 piston looks sexy depending on your weight you probably don’t need them. The 6 piston retains more heat than the 4 piston does Assuming you’re using the original type upright. You can even use your old bolts.

I didn’t do it, but COLEMAN ROTOR IS THE GUY WHO WILL CHANGE YOUR ROTORS INTO FULL FLOATING. Oops
I think his number is 906-863-1113. If you have a mostly original car without gutting the interior. And your track is hard on the brakes it’s probably worth it. But adds to the cost.
I assume you always go racing with fresh racing brake fluid. And bleed off the cooled fluids between sessions?
Realize too that the rear brakes are much worse than the front regarding fade.
I used to squeeze a 12” 1.25 vented rotor in the back. Yes some grinding of the lower rms is needed. And you’ll need to trim the disk by .200 in diameter.
Even with all that work the brakes will be locked up at full droop. Never a problem on the race track but I never drove it on the street either.

 

You might go on U-Tube look for Camp Chaos by ROBERT KNODT. He tried tracking his XJS at ELKHART LAKE and found the fade problem.
He’s got a few video’s of him on the track but the best videos are of him working on the rear end and race prepping it etc.
Really good stuff

 

Justin,

And if you decide to go racing at Laguna Seca, the £3000 cost to ship your car over from the UK will make the cost of the new brakes pale by comparison!

Cheers

Paul

 

Mguar
Please explain more clearly for the Willwood brake novice! Are you saying that

1. The forged Dynalite caliper will bolt straight up to the XJS upright without any modification?
2. What is the Willwood 6 piston caliper reference, and will it bolt straightn up to the factory upright?
3. Does it require a different disc, and if so, is there a WIllwood disc and bell that fits without modification?

Thanks

 

Short answer, yes. ( let me double check my measurements tonight).
But I’m not sure that’s the way you should go. Please help me understand your needs. Is this a mostly track car or an occasional track car?
What are the tracks like that you typically go to?
What sort of top speed do you get to? At the end of the longest straight what is that corner like? Tight 90+ degree's? Sweeping or banked? How many corners, how long is the whole track?
Are you wheel to wheel? Limited passing, or one st a time?
How much weight have you eliminated? Do you have the A/C and heat? Still using power brakes? How often do you change brake fluid?
Do you use DOT or racing fluids?
It’s not that I want to discourage you from using what you’d like. However re-engineering brakes is rather risky. Filled with potential traps.
While I’ve used WILWOOD and really like them for racing. I understand it’s not a bolt on and go sort of thing.

 

Regarding the disc. Yes and no. Stock disc is .810. Other than being a lighter caliper that sheds heat faster. It doesn’t move the needle much. The Thicker 1. 250 disc really helps get rid of heat and will tolerate a lot more before passing it on to the caliper. But you need the disc and aluminum bell.
If I remember correctly. (15--20 years ago) you need to shim the caliper out a little. Like Jaguar used to do to center the caliper exactly over the disc. Jaguar shims are very thin and expensive. So I used AN washers. (AN grade is aircraft and Aviation grade). Do not use hardware store grade washers. I don’t remember what bell I used. But it’s simple to figure out your needs. Stick the disc up in the caliper and measure to the back of the upright. It comes out some odd size which isn’t stocked. 2 & 15/64’s or something. Get the closest bell to whatever it is and shim the caliper out the extra you need.
Warning; aluminum clamped to steel needs to be periodically checked that the different expansion rates of the two metals hasn’t loosened anything.
Also warpage is greater with Aluminum/ Steel combination so you might look seriously at full floating the disc.