The brake imbalance discovered at Silverstone at the start
of the season could not be ignored. We had tried to fix it by using the
smaller-pistoned V8 calipers, but it didn’t work. Cutting a slot in the pad is
crude. It is time, despite our reluctance, to fit a proportioning valve into
The plan was not to go down the brand-name route, but
something a bit more mass market, and a bit more rugged. That didn’t work, because
somebody made what we might call a foolish mistake with a welder, and turned it
into a fascinating but useless sculpture. The rear pads were therefore carved
again, and we’ll test it.
Here’s where it gets tricky though. With different pads
front to rear, I may need to change brake bias as the race progresses and the
fronts heat up, as we found at Silverstone. That sounds like a recipe for a
mistake. A switch therefore for the rear pads, upgraded to the same spec as the
fronts would be smart, but I am damned if I’m swapping pads that have only been
in for one meeting. Testing required. Budget does dictate plans, more often
More and better ducting is added, particularly to the rear.
It is not hard to improve the rear ducting, as there was none. That there is
now some is better. I had a couple of ideas for rear ducting. I am a big fan of
using the car’s existing attributes. Instead of having to deal with the radius
arms as a problem, use them as part of the design. A fairly simple aluminium
scoop and deflector attached to that arm would in theory take air from just
behind the floorpan, where tumble and turbulence would otherwise cause drag,
and throw it at the rear disc.
But the mock-up is a large and ungainly device. It looks
like it would work, but there is no way to support the far side, the
disadvantage to attaching it to the radius arm is that it moves, so you cannot
attach it to the shell, and though a tie-wrap hinge solution often works, in
this instance it sounds like a wonderful way of throwing the ducts at someone’s
windscreen halfway through testing. A more conventional scoop and flexible
ducting solution is chosen instead. Same plan, but a more robust execution, and
£90 spent I didn’t want to. With more time, or thought, perhaps the other plan
would have been better. Maybe on the next car. But one.
The missing ingredient from a spare subframe is the diff. Building
one of Bear’s super-special diffs is not simple, but that’s his domain. All I
have to do is buy the bits. It’s actually cheap work, when you think about it,
because I get his time for free, the machining is done for pin-money, and the
parts, in racing terms, are not expensive. When the BMW boys are paying
£1500-2000 for a diff, £300 thrown at a Jag diff isn’t big money. And it works.
I can tell you that for free. How I survived some of the crap I’ve run in the
past I do not know, the one that unexpectedly turned itself into an open diff
under the trees at Oulton just as I tried to thread a 1600kg car through Druids
left a stain on my driver’s seat.
At the front end, more castor. We still have understeer,
which may actually be the result of the diff being pretty good. Crank on some
castor, see if that assists. We’ve already moved the seat a touch to get some
more muscle to the wheel, so we can add some steering weight. Testing would
later prove that this worked.
That’s done by stealing the top arms from Christine, Bear
solved this issue in 2010 and we built Helen to be able to accept castor
without beating the shell with a hammer. Bolt-on parts, for us, are an amazing,
infrequent, luxury. Racing an XJS is usually a tale of bespoke pieces, and a
file. And a hammer.
Finally a supplier came up with a new rear hub, I’d been
chasing that for weeks but it’s the usual tale, can’t get XJS, XJ40, X300,
X308. Can get XK8. It is the same concept, but it does not actually fit. Which
was an expensive pity. That would be later addressed by buying the driveshaft
to match, and that finally gave us the brand new, beefier, hub we’ve been
So, make it stop better, try to give it some more front end
bite. Shed a few kilos. Losing rear end weight is not always a great plan, but
it’s a balance shift of under half a percent, and I’m certainly not sensitive
enough to notice that.
She was nearly out of rubber, but the R888R is not yet
available in my size, and I’m not buying until it is, so we’d be on slicks by
the end of Brands, or praying for rain.
As Brands panned out, the above modifications were a mixed
bag. The castor change worked, less understeer, the car took pole position. The
brakes did not. A desperately-late lean on the pedal put us backwards in the
gravel with two ruined rear tyres, the imbalance front to rear was not
noticeably affected by the cheap and cheerful fix, we got that plain wrong.
With any fundamental problem, driving round that problem is fine and well in
testing, but if the heat of combat your brain has an adrenaline meltdown and
leads you to push beyond the safe limit, you’re in trouble you’re not coming
back from. The brakes therefore became a must-fix item.
The weight balance, as predicted, did us no harm at all. In
the rain, the car was, as ever, unbeatable, and that saved the day in race 2,
but she used to be better. Even I can feel that the reduced weight has stolen
some of her grip. There is, currently, no way around that. But if she’s winning
races from the back of the grid in the rain, good enough might have to do for
To address the brakes after Brands, finally we binned the
Jaguar master cylinder, and Bear finished adapting his home-made twin master
cylinder setup, a project he started in 2010 and then shelved. This took a lot
of time, because space is limited, nothing commercially available really seems
to fit without buying an aftermarket pedal box. We wanted to keep the pedal box
and servo as it is. With time and inspiration came a design that achieved all. Twin
cylinder, balance bar, remote adjuster in the cockpit, like a proper racing
car. And it works. You can indeed adjust the thing on the fly. There were some
teething issues, which were finally sorted for the second race at Snetterton,
but it worked, and you can stand on the pedal without fear. There is more
tuning to be done here, but the concept is now sound, and with some more
fiddling will come a proper late shove on the pedal that does not turn the car around.
In the heat of combat, the brain does not always work
properly. A big sticker and an arrow on the steering wheel reminds me which way
to turn that brake adjuster. To an outsider, the letter “R” and an anti-clockwise
arrow on the steering wheel may appear confusing.
A little further weight loss came in the form of an alloy
diff plate. We have, in the past, had diffs breaking free. The rear subframe is
not a great piece of work, we have to brace the subframe up, but even after you
do that the diff itself tears free, break bolts etc. We therefore use a ¼”
steel plate in place of the original tin, and high tensile bolts to get hold of
the diff 12 extra ways. Seems to be largely working thus far, but it’s heavy.
Swapping it for alloy loses some rigidity, but also 5kg. It’s worth the
experiment. Testing again would show that I can’t feel the difference. Whether
the total of 20kg knocked off the rear this season would be noticeable if done
in one instalment, or not, I also doubt.
Thus equipped, we raced Snetterton. Last race of the season,
and it’s a combination of power and handling. Helen set fastest lap in the
second race, with a half-respectable time that I know I could knock another
second off exactly as she is, just with practice and familiarity. The problem
with constant evolution is you’re always chasing a moving target, and I’m not
in the car often enough these days to do that. But we’re on the right track, at
least. This year has moved her on again. Technically, 2015’s fiddling has given
us 3 race wins from 6 starts, and 2 of them were from dead last. I don’t think
we’re done yet. There are a couple of game-changers that we could now invest
in, but, as ever, it’s money. When do you stop? Well, you can’t take it with
You can just whistle, and this jumps straight out now. After a winter of road cars, this was a joy to work on.
There may have been a slight spillage incident caused by a holed drip tray. Oops.
Rear subframe was removed, dismantled, and the diff internals inspected, just to be sure. The diff was fine, but I found other niggles. Which is why we do it.
In the traditional pre-race stance, no wheels and many parts removed. Yes, that is still a steel bootlid.
Kneeling in brambles to salvage V8 calipers is not the most glamorous aspect of motorsport. But it is cheap.
The vented rear discs are something I bought in 2010 and never needed. I can't claim this to be forward planning, I forgot I had them. Bear knew. Bears are handy.
And we're calling that ready. 2 whole days before we have to depart for Silverstone. A new record.