Brake upgrades - what's your experience?


My master cylinder has started leaking and there’s work to do on the front suspension so it’s time to consider a front brake upgrade. The car is an early S1 with standard solid discs and 3 pot cast iron calipers. I’m a steady driver but need to press the pedal damn hard to bring the car to a stop compared to my 2008 Volvo - I guess that’s the way brakes were in the '70s.

Upgrades seems to be billet aluminium 4 pot calipers for the solid discs or similar calipers plus vented discs, with a variety of pad friction material. The total parts cost will be significant, but that’s OK if the improvement matches.

Anyone have any personal experience?


(Carl Hutchins, Jr. ) #2

I’ve no experience with the brakes of an S1.

But, I have the following thoughts.

  1. Your Volvo has ABS. A totally different pedal feel. My 94 Jeep as it as well. I note the difference in pedal feel when compared to my SIII. It isn’t a good vs bad, just dfifferent and trhe alter, a tad better.

  2. That is not to say that the S1 brakes are not adequate if all is in good condition.

  3. The hard pedal can be related to poor boost, a failed or failing cannister. Or, glazed pads front or rear or both.

  4. The infamous" rear calipers may have failed. A two wheel brake car!!! Been there, done that.

  5. A standard brake service job will often do wonders. Clean rotors, fresh pads, new or refurbed calipers, etc At times merely fresh pads…


(Paul Wigton) #3

Something’s not correct: in good nick, an SI’s brakes were pretty good.

You likely just need to go through and bring up to spec the stock system, before going through all the rigamarole of “upgrading.”

(Carl Hutchins, Jr. ) #4


My thoughts, but far more direct…

Rain, clean air, fires getting doused,

Billy came to the breezeway for his favorite kibble… Medicated, but he eats it anyway!!!


(David Jauch) #5

Does the pedal get harder when the engine is off and you pump it? If so, good. The S3 brakes are very good. It takes a while until the tyres lock up and when they do it really means I want them to. No problem if I push them hard, which I did once to check and never needed to later. They are almost comparable to my ‘00 BMW besides the ABS.
I find modern cars to have horrible brakes. A brand new Seat bites immediately and it takes me a while to brake really smoothly. Never drove a Volvo (I think once) but if you don’t like your brakes something should be wrong. A ‘71 S-Class has comparable brakes besides that smooth Mercedes-sink-in-as-you-slow-down-effect. The E-Type needs a bit more effort, but not much. Which is good as the clutch is even heavier.

I might tend to (never! It’s dangerous!) shut off the engine in heavy downhill stop’n’go (more like 900 feet in 15 minutes) and always hit the pedal until the assistance is gone. It does take ages to brake and a lot of effort; also the brakes feel very restricted, no ‘bite’ at all.

(Robert Wilkinson) #6

Frankie, two things are done relatively commonly. One is to fit the S3 master cylinder with integral reservoir. The only advantages are that it “cleans up” the engine compartment somewhat by eliminating the remote reservoir, and that it is much cheaper than the S1 version–that’s why I did it.

The other “upgrade” is to fit S3 brakes which have vented rotors and four-pot calipers. You also get bigger wheel bearings. I have the required bits but havn’t done the swap. I might, next time I need rotors if I live that long. Nobody has claimed that these brakes are better in terms of bite, but presumably they exhibit less fade. But I’ve not had a fade problem. They do weigh a lot more than S1 brakes–obviously not a plus.

(Frank Andersen) #7

Not on the Jaguar, Frankie - if ‘damned hard’ pedal pressure is required; something is fundamentally wrong…

This is not related to the old set-up - the upgraded calipers and vented rotors was not to reduce pedal effort, but to reduce possibilities of heat brake failure. The brake effect is related to pad friction coefficient and pad pressure. The latter a result from pedal pressure and brake booster assist - and neither is altered by your suggested upgrade…

That said; the upgrade is not necessarily a waste. But I think you should first examine your present system for faults, as suggested by others, before using money…

xj6 85 Sov Europe (UK/NZ)

(David Jauch) #8

Certainly another piston would add theoretical pressure but in any case I’d start by examining the vacuum to the brakes, if the booster leaks air, or something else is blocking it. I fully agree with Frank that whether an update would help or not the described effort is a wee bit too much.

(Frank Andersen) #9

The square area, which decides pad pressure, is roughly the same with 3 or 4-pots, David…?

xj6 85 Sov Europe (UK/NZ)


Pedal pressure is rather subjective - I think I have to press hard, but that is in comparison to my Volvos and '96 XJS. What I was hoping for was someone who had done an upgrade to a S1 and who could share their before and after experience.

Jaguar fitted 4 pot calipers and vented discs to the S3, and they wouldn’t have done that unless it was to bring better braking performance; so logically that upgrade to a S1 would do likewise. This is the upgrade I am considering

I suspect (but will check with Fosseway) that the pad to disc contact area is greater and thus less effort will be needed for the same deceleration. I have yet to find any published independent facts and figures to judge deceleration or pedal effort.

As to my car, the rear calipers and pads were replaced 3,000 miles ago (the discs were fine), the front discs and pads were replaced by a PO and show little wear and the front calipers were overhauled, the servo seems to be working and there is no judder or pull. So I suspect the present system is functioning as well as a 1971 set up should. Having said that I am stripping the front suspension and will have a close look this week before I finally take the decision.


(David Jauch) #11

Oh, you’re right. What was the reason for the switch though? Assuming area stayed the same. Did the pots increase in size or was the design flawed?
Before you start to mess around maybe Mark can tell if there’s a considerable distance, with his many XJs, or another lucky one…

(Robert Laughton) #12

Since you say the suspension needs work too, I’d find a S3 XJ complete suspension, with rack and pump, and swap it in. You’ll get the bigger brakes, stronger axles, and a rack with better/faster ratio.
If you can find an XJ12 suspension, use the thicker anti-roll bar but not the springs.

But, as said, the original brakes are good if working.


(Paul Breen pay palled it) #13

This is correct. My '72 has fully refurbished standard brakes. The pedal is a little heavier than our modern cars. Car pulls up evenly and confidently. Paul

(tony) #14

be aware the booster/servo gradually loses effectiveness. I had mine fully rebuilt.
its possible to take it out without removing MC or pedal box, there is a rubber bung & cotter pin

(Jochen Glöckner) #15


no experience with upgrades or with SI driving. Based on experience from the middle SII setup I can only add a few data points and remarks: As for the data points let’s start with braking power. Brakes can’t be any better than the tires on the tarmac. If you can produce a 4 wheel blocking at any speed the brakes need no upgrade. I did two wheel blockings braking down from 70 mph and felt like there were reserves. Never tried 100+ mph though.

Fading: Early SI tests found fading - maybe that’s why Jaguar put on vented discs on SIII. I haven’t done much alpine downhill driving so far and never provoked fading issues

Vibrations: Early SI tests found vibrations when braking down from high speeds (100+ mph) and attributed them to the soft connection of suspension to body. Maybe harder bushings can set this straight.

Braking effort: The SII power assistance is comfortable, but linear to a high extent. For city driving the tip of your big toe is sufficient. Yet, if you need more braking power you can step in harder and receive effective braking as described. Very modern cars, in particular compact cars, tend to over-assist braking on the first touch. You’re impressed, until you really need braking power and find out that there is hardly any more provided, no matter how hard you brake. - Of course, this is all related to the fact that most rear-ends are caused by little determined drivers stepping on the brakes too little and too late. Anyway, getting back to the SII brakes, they are clearly easier to handle than the unassisted brakes in the Spitfire and pretty close to the 2012 family hauler. And that’s all it takes for me.

Maybe you compare the parts nos for the boosters (my part no. is RTC1298 for RHD, relates to RTC1127 for LHD) - I wouldn’t invest into a SIII upgrade, unless maybe you run across a complete 1992 V12 ABS setup …

Good luck


75 XJ6L 4.2 auto (UK spec)

(Mark Lee (Pay Pal Patron)) #16

Here’s my two cents on the subject
Hard pedal
Cars today have, in my opinion over assisted brakes, and the anti-lock functionality works in conjunction with the anti-lock assembly to supply the appropriate “ease” of braking while keeping the wheels from locking up and skidding. That said, as long as the pedal is firm; I don’t think there’s a master cyl issue. To test the vacuum assist:

  1. while the car is running, when you put your foot on the brake, does the RPM go up? if not, that’s good that means the diaphragm / check valve is functioning probably and excess air isn’t being added to the fuel system.
  2. With your foot on the brake, start the car. the pedal should go down a bit this also indicates that the main booster is working as it should - no leaks.

increase braking performance.
Brakes on an XJ are a bit different than the norm meaning when the brakes are applied the back brakes are actuated before the front; with the appropriate modulation to keep them from locking up. Unlike (my experience) US cars where both the front and the rear are applied at the same time, again with the appropriate modulation to keep the rear tires from locking up. In order to keep this short, I’ll leave out my stories about front wheel drive cars, brakes with a 1/4 tank of fuel and how I’d find myself with facing the other direction.

Key components
friction material

  • Asbestos. This stuff rocks because of it’s ability to dissipate heat & its durability. Downside is the whole cancer thing.


  • Organics. This came into existence when people started dying because of the whole asbestos thing. Organic friction material are made of coconut shell fibers, Glass, Rubber (go figure), fibre carbon, Kevlar, and a binding agent aka glue. Each manufacturer add their own special herbs and spices to set their product apart from the competitor. Organic friction material offer low noise, dust, and the caveat is wear characteristics. The plus side is the friction material takes one for the team and extends the life of a rotor. Organic friction material performs works well in everyday driving, and / or low braking temperatures

  • Semi-metallic. This type of friction material is the middle child. Not Organic, and not metallic. The friction material is a combination of organic material with a bit of steel wool, iron, copper, friction modifiers and a hint of graphite thrown into the mix. Being the middle child, this type of friction material good at everything, and lots of brake dust. Semi-metallic material is a bit harder on rotors and calipers. The more metal in a friction material, the more the heat will be transferred to the bits the material comes in contact with. Semi-metallic pads have less brake fade than it’s organic sibling.

  • Full on metal. This time of friction material is comprised of metal particles bound together by pressure and heat. Like pot metal. The recipe between manufacturers are different. but the major contents is metal. Metallic also does everything well. Their noisy, with lots of dust, wear well, wear out the rotors as well, transfer heat to the caliper well, good range of operating temperature, but prefer the heat.

  • Ceramic the new kid on the block. Derived from racing, Ceramic offer low noise level, virtually no brake dust, high wear, aren’t hard on the rotors, don’t work that well when cold, but once they heat up, they offer a good bite, with virtually no brake fade. Due to the fact there is minimal brake dust with ceramic pads, these have become very popular amongst every day / city / high way driving compounds.

So what does all this mean?
Organics or ceramic - For every day, but do fade when temp starts to clime
Semi-Metallic are great for street performance, towing - essentially any application where braking temperatures are on the high side.
Track days - metallic or semi-metallic great for hard continual braking. Metallic pads are heavy on the brake dust too and shorten the life of the rotor, and other braking components.

Then there’s rotors.
The best move that I did was to put drilled and slotted rotors on my XJ’s world of difference. That’s where I’d start before swapping out the calipers. Drilled and slotted rotors offer a place for the gases that build up during braking and the heat from braking a place to escape as well as a the holes offer extra cooling characteristics.
Swapping out the calipers is a process. The uprights along with all of the bracketry and tie rod ends will need to be replaced too. Possibly the spindles. It was my experience the Series III spindles are thicker than the Series I and II brethren. If I remember correctly, the Series I and the Series III inner tie rods are different diameters as well. If so, these will need to be swapped out as well. Ball joints are the same between the Series I-III and the XJ40.

That’s all I got

(Frank Andersen) #17

Physics dictates that the pad/disc area is immaterial for braking effect, Frankie…

Only factor, apart from friction coefficient, is pad/disc pressure - which relates to piston area - and ratio of master cylinder area to piston area…:slight_smile:

The advantage of bigger pads is slower wear and, like vented discs, better heat dissipation. The main reason Jaguar changed to vented discs was heat induced brake fade. Not that it was common, but this is 2 tons moving a speed - and not all owners were meticulous in changing brake fluid regularly…:slight_smile:

As other have said; modern cars like your Volvo ‘grabs’ instantly when you touch the pedal - it doesn’t necessarily mean better brakes. The well behaved Jaguar comes on smoothly - with plenty of stopping power…

I’m not saying that the conversion ain’t worth it - but don’t expect too much change in pedal pressure…

xj6 85 Sov Europe (UK/NZ)


Was there an improvement after the servo rebuild Tony? I had the pedal box and servo out last year to deal with the effects of spilt brake fluid under the servo - didn’t realise you could take the servo out and leave the box in - was a right pain of a job. Thanks for the tip.


(Doug Dwyer) #19

Someone may have already mentioned this but very high pedal effort might simply come down to the brake pads

My first Jag, a Series III XJ6 bought 21 years ago this month, had very high pedal effort. Pressing the brake pedal was like trying to push down a brick wall with your foot.

Cutting to the chase: simply ditching the previously-installed metallic pads and installing organics completely solved the problem.

IMO, almost certainly money that could be better spent elsewhere.

I think upgrading to late Series II/ Series III brakes could be done fairly easily and inexpensively, satisfying the (real or perceived) need to upgrade without draining the bank.

Personally, I’ve never found Jaguar brakes to be lacking. In good condition, with the right pads, they’ll work quite well…and I enjoy driving hard-n-fast from time-to-time :slight_smile:

The vast majority of Jags I see on the road are being driven as though they were made of out glass. If you’re aggressive enough I’m sure the stock-configuration brakes can be overwhelmed but I have my doubts that many (any?) of us fall into that category.


(sawyer10702) #20

I got all my brake parts rotors. Calipers,pads from had a little problem with brake line hoses has they were metric for xj12 front end. But the brake system with ceramic pads is very good in the stopping department. I have 4 pot callipers with stock master for series one.