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Hi all. I’ve just acquired a part built 3 wheeler running a 900 Suzuki motor. Needs the dreaded Iva test, but need lots of input. For starters, I believe I need a split circuit for the brakes. How does one proportion the braking circuits? One circuit for the fronts, and one circuit for the single wheel?

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Single driven wheel at the back. Sierra discs at the front, bike disc at the rear. I’ve taken off the m/c and servo which was driving a single circuit and am now  considering a dual 19mm m/c, with some sort of restricting valve on the rear circuit to prevent lockup.

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19mm cylinder is probably about right for the front brakes without a servo. Ford Fiesta used to use a trick inline limiter valve but even if you can get one, it'd be a bit trial and error. Might be better trying it with no valve and then if it needs one, use something like this:

https://www.merlinmotorsport.co.uk/p/wilwood-brake-adjuster-knob-type-m-ba-wil

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Hi guys....apologies for late response. After spending £25 on a fiesta MC/servo I now discover that the MC I had has actually two outlets!

one was being used by the pressure switch which fooled me. I can simply put the switch on a tee piece on one of the circuits.

you are not allowed to use adjustable pressure valves in line, IVA rules!. There is a trike version but the weight limit is 450kg. 

 

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17 hours ago, Davy said:

you are not allowed to use adjustable pressure valves in line, IVA rules!.

There is a trike version but the weight limit is 450kg. 

Sorry to doubt you, but I thought the rule was adjustable are acceptable as long as they cannot be adjusted from the driver's seat but they may well have tightened it up.

It's going to be a beast of a thing if it's over 450Kg

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Last thing I read/remember was that they can be installed & adjusted to suit before IVA ------ BUT the adjusting bar then needed to be welded solid so no further adjustments possible ---- then off to see the nice man at IVA.

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From https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/738819/individual-vehicle-approval-inspection-manual-passenger-vehicles.pdf

09B Service Brake Control / Mechanical Components

Note 4: Hydraulic valves that only operate automatically and react to vehicle loading or braking forces are permitted (Load Sensing and Gravity valves) Manually adjusted valves (other than to permit presetting the automatic function of a valve) are not permitted to be fitted even if they are rendered un-adjustable. Note

5: Bias bars and other mechanical adjusting devices fitted to twin master cylinders must be rendered inoperable by mechanical means e.g. lock wiring of components.

Note 6: Adjusting front/rear brake bias may invalidate approval and breach Construction and Use requirements.

So you can have them, they must be locked off not welded, but if you change them afterwards you could invalidate your IVA

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  • 1 month later...

As it's still technically a bike why not just continue to have split brake controls as per the original bike? I think your going to really struggle to find a proportioning valve that will really reduce the rear brakes so much that they lock up after the fronts as there is so little weight on them. Mind too that you will be requiring twice the hydraulic flow to the fronts than the rears which will only make things worse.

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