I've started a thread over in X300 because some of their
owners have gotten a close look at the guts.

But the area being discussed, the pedal box and master cylinder
are the same on the X308. And it is really about my XJR anyways

https://www.jaguarforums.com/forum/x...ooster-145642/

 

I think in 2000 the x308 and x100 had a redesigned pedal and master cylinder 4 vs 3 bolt) with twice the pressure per pedal distance and a shorter pedal arm for less mechanical advantage.

See page 15
http://www.jagrepair.com/images/Elec...s%20Update.pdf

 

In that reference, it seems Jaguar reduced the mechanical leverage, but then
doubled the boost pressure. Unless they reduced the mechanical leverage
way out of the usual range, the effect combined with the increase in boost
would mean an even softer pedal.

It also notes a change from the previous generation cast aluminum pedal
box to their favourite high end material ... plastic.

Despite all of that, the basic design, and therefore the inherent weakness
did not change.

That weakness is the method chosen to anchor the pedal box which results
in excessive movement without commensurate action.

 

Plums you assume that the pedal box design gives a soft pedal because of flex? The only item left standard in my brake system is that item and I've no complaints. Maybe better pads and braided hoses will give you a better pedal, also when was the last time it got new brake fluid?

 

It's not exactly an assumption. It's speculation that Jaguar is not exempt
from behaviour that has been seen in other makes. Especially when the
particular mounting method has been chosen.

However, it is easy to figure out. Some have observed or filmed the
area while the brake pedal is depressed. But one clever person had
the best idea. He used a dial indicator.

That's what I'll be doing.

I'm not a fan of braided hoses since most OEM can manage to make
perfectly adequate hoses with embedded braiding.

ATE SL-6 within the last year with full gravity bleed. About 6 thousand
miles of light use. All hard and soft lines were replaced in 2010, front
to back. All OEM.

I don't think your particular car is a good comparison as it is fitted
with the Alcon's if I recall correctly. Stock master cylinder?

 

If the listed changes were coupled with a larger bore master cylinder(early and late have different part numbers) i could accept a increase in brake firmness feel. I drove a 2002 R1 last week and the pedal feel was slightly firmer (still could be in my head) then my 98 with brembos/ss lines. The pedal on my Xjr is very soft even with the upgrades.

I adjusted my throttle pedal about two weeks ago and was surprised to see how much the gas pedal actually flexed and twisted when pressed. In a rough guesstimate i was about 20 degrees from perpendicular before adjustment (throttle change was night and day after). Makes me wonder how much of this could be linked to your hypothesis of flexing pedal housing/mounting + upgraded plastic parts. As you mentioned the x300 has an aluminum housing And steel pedals. for some reason flexing firewall goes with check strap's ripping out of the doors; nice sheet metal...

 

About the throttle ...

I don't know about flex there. It doesn't need to take much load.
The slack is usually in the cable.

But, I did run across a automotive ergonomics textbook and it seems
all those LHD X308 drivers complaining about the gas pedal
might not be wrong.

One passage said that full extension of the pedal should not be
more than roughly two and a half inches(converted from metric).
We know the pedal takes more than that to get to the kickdown
position.

Another passage in the same paragraph said that full extension
of the pedal(flooring it) should not induce muscle tension and
should be possible with the heel on the floor. Again, not possible in
the X308 or X300.

No wonder we get shin splints.

Back to brakes ...

The early and late master cylinder are sort of a typo in that the
cataloguer seems to have made a distinction between the three and
four hole booster fixing and carried it throughout.

I have the distinct feeling that they are all 1.0 inch as carried over
from the X300.

The R1/Brembo like the Alcons is a special case because it is uprated hardware
targeted to better braking.

Here is a link showing someone using a dial indicator on a master cylinder:

Let's talk master cylinder braces - RX7Club.com

There are actually three major points of possible external flex:

a) the bottom of the pedestal style pedal box mount

b) the pedal box to booster mount

c) the master cylinder to booster mount

The last one is the one that sees the most force.

People have actually observed the formed sheetmetal of the
booster flexing under load.

Bracing the front of the master cylinder is actually very awkward
because it sits withing the false bulkhead box. But bracing there
addresses all three sources of deflection.

Bracing between the pedestal and firewall only addresses one
possibility.

As it happens, I have a complete setup from a X300 from pedal through
to master cylinder sitting in storage.

Firewall flex seems to be a big deal in RHD markets with vehicles that
were designed and made in primarily LHD countries. This is because
moving the pedal box to the the RHD position is often a secondary
modification. Some vehicles are even running rods across the engine
bay to connect the pedal on the right hand side to a master cylinder
still mounted on the left hand side!

Jaguar is the mirror image. RHD home market with pedal box moved
to the left for LHD export markets. Hmmmm...

Maybe that's why they use a drop in pedestal mount. Not the stiffest
possible configuration, but fits either side. The part number is the same
for all markets without considering LHD/RHD.

 

This is the difference between pressure modulation and movement modulation:

 

And a brake engineer said on another forum:

 

I'm a bit of a novice here. I bought a very nice 1998 XJ8-L two months ago (100K mileage). Runs great so far! Had the car fully inspected by a dealer. The components in the brake system are basically new, per dealer. BUT THE PEDAL IS SOFT. I have gotten used to it, but initially it was a worry. What I am getting from the thread above is that these cars are known for soft brakes, and I should live it with. . There is not a "simple adjustment" to firm them up, right??

Wesley

 

Correct, see the quote above:


.... the X300 is "notorious" for a soft pedal feel also. Interestingly the XJ40 with its hydraulic booster is not known for a soft pedal feel AFAIK.


That being said, the X300 was well regarded in braking performance, and the X300 XJR (which used the same system as the normal X300) was favorably compared with a Porsche 911 in stopping distance in at least one review I read.

But the soft "feel" has been discussed many times, including by 'yours truly' when I first bought my X300 XJR. I even posted a thread or two on the subject, worrying that there was something wrong. But at the time I was counseled by long time owners to let myself adjust to the feel, and I'd find that the braking was not just good, but superior.

I have to say that after a year, this is true. I've adapted to the feel/travel and now can apply and modulate the brakes as well as any other car I've driven. But when my family drives the Jag, they comment on the difference because they don't drive it regularly.

So the 'feel' issue isn't really an 'issue' for me any longer. Although I am following Plums' research with interest, as I'd be interested in any reasonable modification that would firm up the feel a bit. If effective, something like a simple brace would be low cost and easily implemented option for example.

Regarding the 'gas pedal' feel, that is another I initially found odd. The pedal felt like it was at an odd height and width, and its range of motion wasn't what I was accustomed to. I had even thought about some bolt-on pedal cover to increase its width, or rigging up a floor mounted pedal to actuate the OEM mechanism.

In the end I've gotten used to the 'gas pedal' as well, and it really doesn't bother me any more. The only problem I have sometimes is that he tip of my shoe catches on something under the dash above the pedal. I think it is the heater vent, but haven't checked. I only wear size 10/10.5 shoes, so I can imagine this may be a bigger issue for folks wearing gun boats


All that in mind, again, am very interested to see where Plums' research leads. It would be interesting to find a simple solution to firm up the system just a bit. Or worst case at least identify why it feels soft, even if it proves to be too difficult/expensive to fix.

.

 

The brake pedal on our '93 XJ40 is neither soft nor hard, but it has always required more pedal force than most cars with standard vacuum boost systems. The brakes do stop the car well, but the hydraulic system was problem prone, so several fellow XJ40 owners have converted to vacuum boost and most have been pleased with the results.

I'm curious to see what plums reports when he measures the deflection with a dial indicator.

 

You might be interested to know that in my estimation the gas pedal range of movement
in the X308 does not meet the guidelines set out in a automotive controls ergonomics
textbook. It says that the pedal working the gas pedal should not induce muscle tension to
floor, should be possible with heel on floor, and should not move more than two or so
inches. All three recommendations are violated.

Maybe Jaguar didn't have the budget for the book, or hired someone who had not
read it.


Heater vent. Almost got t-boned by a VW Golf on the first test drive because of it.

It can be fixed with a hacksaw blade, makeup mirror and flashlight.

- position makeup mirror so heater duct is visible

- shine flashlight at mirror to bounce light at duct
(remember angle of incidence and reflection from physics?)

- cut a couple of inches off the end of the duct

Size 10.5 shoes here

 

Waiting for help on the weekend.

I realised that there is no way the dial can be seen from the driver's seat
when it is setup to measure axial play.

 

Once you lock up all four wheels, there is no more a braking
system can do to stop you faster.

Unless there is something wrong, the brakes will
stop the car. No question.

There is no easy adjustment so long as you do not have
any air or moisture in your brake system.

The bone I am picking is the feel not the capability.

 

According to Wilwood (those who care about performance brakes will know who they are):