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Adjustable Pedal Box - Requirements


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Bias bar


The IVA manual makes it clear that adjustable bias pedal boxes are accepted now provided the adjustment mechanism is lockwired from operation (section 09B).


The required standard statements :-



It must not be possible to manually adjust braking rates between

axles see note 4 and 5


Vehicles fitted with adjustable twin master cylinders that have been

rendered inoperable by mechanical means to comply with RS 26

must have a label affixed on the master cylinder or the immediate

vicinity with legible text as detailed in note 6.

...and the clarifying notes...


Note 5:

Bias bars and other mechanical adjusting devices fitted to twin

master cylinders

must be rendered inoperable by mechanical means

e.g. lockwiring of components.

Note 6:

Adjusting front/rear brake bias may invalidate approval and

breach Construction and Use requirements.

So, what is the legible text that must be affixed via a label? This test is detailed in note 6 - what do I do, make a sticker up that just has the full statement of note 6 in it? Is it that simple?




Also, moving on to section 09D and RS statements 16 to 20...



It must be possible to check the fluid relative to the manufacturer’s

specified minimum level on all brake fluid reservoirs by the actual

fluid level being visible through a transparent section of the

reservoir, with the minimum level marked permanently on to this

section. As an alternative, a red warning lamp (see figure 1) must

be capable of illuminating when the reservoir fluid falls to the

minimum level.


An indelible label must be affixed in a visible position within 100

mm of the filling ports of the fluid reservoirs to ensure that it is

possible for the end user of the vehicle to identify the brake fluid

used in braking system. DOT fluid references and/or the Symbols

and text in table 1 are considered acceptable.


Where a warning lamp is provided as the only means of checking

the fluid level without opening the reservoir, it must be secure,

operational, visible during daylight and darkness from the driving

position, and fitted with a “test facility” that enables its operation to

be checked from the driving position without opening the reservoir.


The hydraulic system must be fitted with a red warning lamp,

sensitive to line pressure and capable of signalling the failure of any

part of the hydraulic system as soon as the brake is applied and

remaining lit as long as the failure exists (with the ignition switched

on). As an alternative, the warning lamp must be sensitive to the

reservoir fluid level, providing the reservoir is directly connected to

supply the pressure side of the master cylinder when the piston is

in the “brakes off” position, so that a failure of either part of a split

system would result in a continuous draining of the reservoir fluid

when the control is released (see note 2 and 3).


The hydraulic system failure warning lamp must be secure,

operational, visible during daylight and darkness from the driving

position, identifiable (i.e. labelled in a recognised form – see figure

1 for an example) and fitted with a “test facility” that enables its

operation to be checked from the driving position without opening

the reservoir.


Now 16 states about a transparent fluid reservoir, which is all fine and good, no issues there provided there are permanent low level marks on them. In these cases it clearly states "as an alternative" the use of a red warning lamp for low level. Since I have transparent, marked reservoirs, this means I don't need a warning lamp.


18 you start reading and it's quite clear if the warning lamp is the only method... which it isn't, because I can visually check, so you stop reading that paragraph as it doesn't apply.


Then you get onto 19 and that appears to override 16/18, because it states if you can't have a warning light that's monitoring brake line pressure drop then you need a fluid level warning light as an alternative.


So, given I've currently got 2 separate reservoirs for each master cylinder, I am thinking the easiest thing is to just switch to one of these and feed both from a single, partitioned reservoir with the fluid level warning in it.


I could fit these to each of the individual reservoirs but that just seems a faff.


Anyone disagree?!


Brake light switch


I see most people use these pressure switches in the line to switch the rear brake lights. Any reason for this over a pedal switch? Is it mandated or just 'easier' since it's at the back of the car already?

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bias systems are OK given what you have noted




Think you are building a zero


unless you are using a chassis with dual master cylinder mounts (a kit option), I would stay clear of other pedal systems in the zero.


zero brake switch is pressure type, there is no sensible place to put a push switch without making up brackets. you will need a T piece in the rear anyway so its easy to fit a four way, and zero looms are usualy made to facilitate rear switch.


res and res switch is best mastercylinder mount but others can work.

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Cool, thanks. First job when I get round to that area will be to just get some measurements of my pedal box with respect to the zero chassis and how easily it will mount. Picking up an unused kit means I haven't had the choice on the pedal box so if it comes to it, I'll be grinding off the GBS bracketry and welding up my own arrangement. Issues around strength and flexing fully understood ;) but I won't be chopping anything off until I know for sure it'll fit, don't worry :) !!

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If you have to have bias, which is just not neccesary on the Zero, and you are able to weld them in, then I would get the mount bits and pedal assembly, pre cut, from GBS.


Cockpit adjusters do not function because of cable run, so adjustment once done, is locked, lock wire or not, so not really of much use.


Do not try and fit floor mounted pedal boxes, every one I've seen requires removal to allow the vehicle to be driven properly.

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Ok, understood. What I'll do then is, when the pedals come back from dipping, rig them up temporarily and get a feel for if their positioning is good for me. One thing that I fixed in the Exmo was the pedal positions to my liking; which is to say amenable to a bit of heel-and-toe when necessary. If the standard GBS setup fits my size 8's comfortably then I'll stick with the standard setup.


What's the standard master cylinder used on the Zero anyway (heads off to search function.....) ?

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