my XJR is great, apart from the brakes.......................

Its not a sport car so I wont ever expect it to corner like an M3 but it could stop better!!

What callipers & Discs would go straight on with standard wheels? Has anyone done an upgrade before?

Would the ones off an XKR fit?

 

I suggest Akebono Euro Ceramic pads with drilled rotors. I was pleased with the increase in braking. But, only after break in and a good fluid change.

 

Ok. Cheers. Fluid was done last year. What rotars did you buy? I put brand new discs and pads all round last year but I'm still not happy with them. The car is so bloody fast, I plant the foot to teach some little punk in a type r some manners and before I know it I'm on the limiter in 3rd and at close to 135!! Brown pants moments have been had.

 

Only the XKR Silverstone brake caliper will fit, but the rotor for XK8/R won't fit because the depth of the hat is different. You will have to fabricate a rotor.

Straight bolt-on upgrade will be using a front caliper/rotor for XJ81.
A bit larger rotor and 2 pod bigger caliper.
I have never done this mod before, but I believe they will be a little more help.

 

Thanks, am very interested in "bolt on" options versus major fabrication that deviates from factory and would be high cost. Any other info on using the "XJ81" front calipers and rotors?

I too find the only significant performance deficit on the X300 to be the brakes. They have never failed to stop me in time, but as is often reported, the X300 brakes just feel "soft" and "spongey"

I have Akebono "Euro" ceramic pads with the stock rotors, and will be flushing and bleeding out the fluid this spring per the specific instructions that have been posted here. But I suspect that still won't firm up the X300 brakes enough for me.

So if there is a bolt on option to slightly improve the brake feel and bite, that would be great.

.

 

I wonder if the feel of the brakes is influencing you a bit too much? That's not a criticism, mind you. I've been there. It takes time to learn to trust the brakes due to the soft feel and lack of 'bite' sensation of moderate pedal applications.

I was always very impressed with the XJR brakes and even more so with the Akebono pads. When you really needed brakes I found the Akebono pads would grip very fiercely.....when you jump on 'em, not when you tickle 'em

Quote from Motor Trend road test.....again, FWIW.....

"The brakes are perhaps the XJR's most impressive component, halting the 2-ton-plus car from 60 mph in a mere 117 feet, equaling the 1995 Porsche Carrera's performance".

Twenty years ago, but, still.......

Just food for thought

Cheers
DD

 

If you just want to make it feel better, you can go for a set of stainless braided hoses from Goodridge.
That's rather cheaper than genuine hoses, it could be about time to change your old hoses anyway, so it will be a good choice. It will definitely make the feel firmer and solider.

 

As above, it may be the feel rather than absolute stopping power.

Can you lock the brakes? If so, you are at the limit. More locking
won't help.

If it is the feel, you could try the bronze brake pin bushings sold
for BMW's. Same caliper pin, hence same bushings. About $65
per axle.

Be aware that they require at least annual maintenance.

 

Thanks for all the feedback, but I think that either mine are not operating normally, or I indeed am over sensitive because I can't imagine the brakes on my XJR would ever be compared to a Porsche.

Not joking, my 95 Buick Riviera has worlds better brakes than my XJR at this point. It feels like getting in a sports car going from the XJR to the Riviera. The XJR is so worrisome that I won't let my son drive it unless he has to, and always remind him and my wife to give "plenty of space" to stop.

Although the brakes have never failed to stop me, I have had several skipped heartbeats where I thought I might not. I have almost rolled into things as I stabbed the brakes and not much happened until I pressed hard. It was a bit shocking. I've gotten used to them now, but I get a bit nervous in heavy stop/go traffic.

They feel like they have very little initial bite, but do slow the car adequately through mid pedal travel, but then right where one would seem to think the pedal travel would firm up and the brakes would really grab it feels like the pads are spongy and I have to really push to get them to grab. They almost somewhat remind one of feeling like they are non power assist brakes to a small degree.

I'm still of the opinion that the next step is to bleed the brakes per the procedure discussed on this forum and make sure there is no air. I have a power bleeder and as soon as the weather warms up we'll do that first thing.

As I mentioned, I replaced the pads and had the rotors turned as the first step which did make some difference, but not enough.

Question: Don't think it could be a problem with the booster do you? I don't seem to have any issue with the brake pedal "leaking down" when pressed for example. Any other tests?

The only other issue I know of with the brakes was that the ABS valve body failed at some point in the past and the previous owner replaced it with a used donor.



.

 

I would change the fluid and bleed the brakes, it should improve it significantly

 

Al,
what you describe is definitely not how these cars should be. As described above, the feel is perhaps different to what some drivers are used to, but the stopping power is there. A fluid change and bleed can't do any harm, and as Frozen Apple suggests, might well do the trick. Remember to follow the rather counterintuitive order for wheel bleeding set out in JTIS (shortest pipe runs first), and I find my power bleeder works better on lower pressure in the tyre used to pressurise it.
The booster could be the next suspect, but before diving in to it, check the vacuum hose. If it was leaking, you would be afflicted by poor idling and low speed running, but if it has collapsed internally, it would dramatically reduce booster efficiency (and be an easy fix)

 

Not sure if this means anything or not, but when the brake is pressed I can hear a very faint but constant vacuum "hiss" from the booster if one is very quiet (no radio or climate control fans blowing).

I've never heard a booster constantly hiss as I hold the pedal down on any other car, just an initial hiss sometimes.

.

 

Al,
Vacum hose sounds like a good place to start, followed by the booster itself.

 

Seriously, aside from defects such as a dying booster, if you can lock your brakes
bigger brakes won't help. This is basic physics.

 

Plums,
While I agree with your point about basic physics, there is a bit more to it than that, as both feel and fade need to be considered.
As referenced above, and widely elsewhere, the X300 brake pedal has a softer feel than "the norm", even when operating 100% perfectly. This is generally referred to in terms which make it sound like a bad thing, and some sort of design defect, but I think it in fact introduces a degree of sophistication which is missing from many modern cars. The ability to introduce the brakes progressively, and to modulate input is key to being able to make smooth controlled progress. My XJR is much easier to drive smoothly than my newish Range Rover, where one look at the brake pedal has the occupants of the vehicle nodding their heads! No doubt I could firm things up a little with braided hoses, but I rather like the XJR the way it is.
Fade is another important consideration, and while I think the basic setup is more than adequate for normal use, it doesn't take a big leap of imagination to see that it could become stressed in hard use, for example on Track, or if you live at the top of a mountain. These are heavy cars, and the issue is not so much being able to lock the brakes as being able to repeatedly haul off speed.
All this talk of brakes reminds me of a chance encounter with the late, great Tom Walkinshaw in the mid 1990s. I was the proud owner of my then 3 month old XJR, which I had contrived to park conspicuously in front of our business premises. True to form, it didn't take TW long to enquire who's it was, and I found myself in conversation with him. I am not sure what role TWR had, if any, with the X300 XJR, but they were involved with its predecessor, the XJ40 XJR. He was not surprisingly very positive about the car, but his one criticism was that the front discs should have been bigger. Larger discs had been tested apparently, but rejected by Jaguar on the grounds that they introduced "rumbling" to the detriment of refinement.

 

I agree.

After overcoming the initial (slight) weirdness I became fond of the soft-ish, progressive feel. However, waiting to replace that soft feel was a fierce grip when needed. I think that what Al seems to be lacking and what has him a bit concerned.




Good point.

For the most part my fastest XJR driving might be described as aggressive but not "wild man with his hair on fair" by any means. I can't remember any situations that required *repeated* stops from high speeds in close succession so I never had a brake fade problem....although I'm quite sure the X300 brakes can and will fade if worked hard enough.

The brake pads themselves can make quite a difference here. The Akebono seemed fade resistant enough to me.



Refinement has always been a big thing for Jaguar....right along with saving a couple dollars-per-car whenever possible

The later (V8) XJRs had the optional upgraded brakes. I suspect that only a minority of the buyers who selected that option actually *need* the bigger brakes. But, if you're selling a performance oriented car you offer brakes to match...for both practical and marketing purposes.

Cheers
DD

 

Actually, bigger brakes do good. Precisely saying, larger rotors/larger pads will do good.
Brake is a thing which transforms moving power into heat. So a larger rotor has more area to handle the heat, thus it can shorten the time which is needed until it is locked up. But it consequently shorten the stopping distance.

On real road, if brake is locked up the car will slip and drift along, and in that case a car needs more distant to stop. It will be uncontrollable too. So it will be important not to lock up but slow the car down as soon. From this point of view, larger brakes have an advantage.

Sorry my English is not so good and I doubt I could write all that I want to say though...

 

I think it is all about the cost. As I stated, XJ81 used larger rotors and 2 piston calipers for front due to it's heavy weight. But X305 used the same brake system as the other L6 models. The XJR brakes too.
So they must have thought the brake had "enough" capacity to handle all the models. But "enough" is just "enough", sometimes we want more... So it is natural that there are a lot of people who wants to upgrade the brakes.

 

Sorry if I missed it, but did you (someone) confirm that the XJ81 rotors and calipers are a direct bolt-on for the X300 with no modifications?

Also, has anyone actually experienced whether this is an actual improvement?


If indeed a "bolt on" affair that doesn't require any other changes in the braking systems, here are the parts I found that are from a 1994 XJ12 that seem to be what would be required:

JA-JLM11142 - 2 piston Brake Caliper | RH Front, XJ-40 V-12
- regular XJ6/XJR XJ40 & X300 share JLM11716

JA-JLM11143 - 2 piston Brake Caliper | LH Front, XJ-40 V-12
- regular XJ6/XJR XJ40 & X300 share JLM11717

JLM10928 Front Rotor 33.5cm x 32.5cm x 13.5cm Left & Right
- JLM10928 297-335mm diameter reported variously, couldn't verify
- regular XJ6/XJR XJ40 & X300 rotor share 305mm JLM20341

CCC4790 Front caliper hose Left & Right
- regular XJ6/XJR XJ40 & X300 rotor share MNA5680AA


Correct? Anything else?

.

 

Yes, it is straight bolt on, for the hub carrier/hub is exactly the same.
I thought that the rotor for XJ81 was larger than the normal ones, but I should've made sure. I will investigate it too and if there is any info I will let you know.

Or maybe at XJ40 forum someone knows about this??