brake proportioning valve | The Z Club of Great Britain
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brake proportioning valve

Discussion in 'Rally & race' started by tel240z, Oct 4, 2015.

  1. tel240z

    Z Club Member

    So had a nice day at the SEKZ meet today until i needed to anchor up a bit quick on the way home (orange M3 yes the engines built) anyway cut a long story short after hitting the brakes avoiding a white car pulling out into the fast lane i spent about 20 seconds getting the car back in a straight line, now after collecting my thoughts i have come to the conclusion that the rear brakes locked up sending me into a sideways drift and even after letting off it was a bit of a hand full to get in a straight line again :eek: :eek: :eek: so its time to fit a bias regulator, remember the spa video of me and john (240z spins at spa) now when it comes to braking i don't skimp, i have had experience of the £20 ebay jobbies on my blue car and was not impressed i see tilton do one for £95 wilwood £60 and others at £195, now on the way home on my private road i done a few heavy brake tests at sub 50 mph and yes the backs do lock up a bit to quick even leading the fronts at times so have you guys got one installed and what sort is it or even had experience of one


  2. TomZupra

    TomZupra New Forum User

    Can't give advice (as you'd suspect) but I have a wilwood one in package if you want to give it a try
  3. Rob Gaskin

    Rob Gaskin Membership Secretary Staff Member Committee Member

    Terry, what type of rear brakes have you got i.e. drum or disc?

    Secondly have you still got the standard hydraulic components on your car?
    Last edited by a moderator: Oct 5, 2015
  4. SKiddell

    SKiddell Having a bad day

    Presumably you bypassed or deleted the original one!

    What’s is your configuration front and back?....servo, master cylinder, callipers etc.

    You should be aiming for around 70/30 split front rear

    I have exactly the same issue on mine as I deleted the fixed bias valve to diagnose a problem a while ago.
    I tried servo less and a Tilton balance bar for a while but it gave a brick hard pedal and I could not get the leverage required as the pivot point on the pedal is designed with a servo in mind.

    We have used a Wilwood one in the past (rally car) they are built well but seem to only be available with American fittings so you'll need some metric adapters.

    What sort of issues did you have with the cheap Ebay stuff?
  5. Rob Gaskin

    Rob Gaskin Membership Secretary Staff Member Committee Member

    Yeh that's why I asked Terry because as Steve says there is a proportioning valve in the system at the rear and if it's faulty it can cause rear lock-up.

    However I'm sure you will have changed the braking components significantly in which case it's function may not be appropriate any more.

    DJ fitted a proportioning valve on my Blue car (rear discs conversion) but I've never needed to adjust it. I know Matt has one too and he has rear drums still AFAIK.

    I've read that proportioning valves used to balance brakes on modified/competition cars are a compromise really and if you have made significant changes and want adjustablity then a twin system with balance bar is the best way to sort things. I have noted Steve's comments though. Member 'amocrace' did use a servo assisted twin master-cylinder balance bar system on his 240Z.
    Last edited by a moderator: Oct 5, 2015
  6. Rob Gaskin

    Rob Gaskin Membership Secretary Staff Member Committee Member

    From a 'Google' :

    A Proportioning valve is required on vehicles that have disc brakes on the front wheels and drum brakes on the rear wheels. Disc brake pads are normally in contact with the disc, while the drum brake shoes are normally not in contact with the drum. If the pressure was not proportioned the disc brakes would engage before the drum brakes when you depress the brake pedal.

    The Proportioning valve compensates for this, allowing the drum brakes to engage first before the disc brakes. The Proportioning valve does not allow any pressure to the disc brakes until a pre-determined pressure has been reached. The pre-determined pressure is low when compared to the maximum pressure in the braking system, this allows the drum brakes to engage before the disc brakes engage. Having the rear brakes engage first provides the control and stability needed to stop your vehicle safety.

    The proportioning valve reduces the pressure to the rear brakes. Whichever type of brakes your vehicle has, the rear brakes require less pressure than the front brakes.

    If equal braking force were applied to all four wheels during a stop, the rear wheels would lock-up before the front wheels. The proportioning valve only lets a portion of the amount of pressure to the rear wheels thus preventing rear wheel lock-up.

    The Factory Service Manual for the S30 explains the standard proportioning valve VERY well, have you got a copy?

    Also this is good:
    Last edited by a moderator: Oct 5, 2015
  7. tel240z

    Z Club Member

    Brake set up is Mazda servo and master cylinder wilwood 4 pots up front and my own MGF rear disk conversion, the brakes work very well with 2 inches of pedal travel and assistance
    equal to a modern production car, rear pad material is standard as i took on board that the MGF is rear engine and the braking is done from the back more than a front engined car and have performed well track and road although are obviously a bit to keen, Steve i found the cheap ebay jobies not very well made and just seemed like a restrictor and at time slow to release fluid back :eek: i have seen and worked on a lot of cars and trucks which have the load sensing valve attached to the axle which i know work rely well to the extent of adding weight to the rear axle while on a brake test sees the braking effort rise and reduce when removing weight using the same pedal pressure also the factory ones connected to the rear suspension look very well made and have a piston arrangement that slides in or out for bias adjustment, just writing this has given me an idea to maybe look into one of these and mount it on a perpose made bracket with an adjustable threaded wheel affair :cool:
  8. Rob Gaskin

    Rob Gaskin Membership Secretary Staff Member Committee Member

    So Terry have you still got the standard proportioning valve in your system? As you will realise that is just a pressure limiter and not load sensitive.

    I know you are a great engineer Terry and I'm not trying to teach 'granny to suck eggs' but I would just be interested to know.

    When I converted my track car to rear discs I was told to remove the 'guts' from the valve but I didn't - I NEVER EVER had my back brakes lock up. They did work and got quite hot at times (like the fronts) but never locked.
  9. Rob Gaskin

    Rob Gaskin Membership Secretary Staff Member Committee Member

    Attached Files:

    Last edited by a moderator: Oct 5, 2015
  10. tel240z

    Z Club Member

    Thanks for the input Rob and yes I missed that bit out about removing the datsun reducer valve so I have obviously getting too much pressure to the rears hasn't been a problem until recently what I need to do now is obtain a quality bias regulator I always intended to hence I run the brake pipe inside the car along the top of the tunnel
  11. strugrat

    Z Club Member

    I will be using this one.

    To my untrained eyes it looks as though it can replace the stock one altogether and provide adjustment for the bias if required.

    No idea how well it works and given the current status of restoration it will be sometime until I can give any feedback. Hope it helps.
  12. Rob Gaskin

    Rob Gaskin Membership Secretary Staff Member Committee Member

    Like this:

    Also bear in mind that the multi-connection unit on the inner wing of a 240Z is the unit that senses differing pressure front/rear and gives a brake warning light (i.e. letting you know if one circuit is 'down'). The proportioning valve is just on the rear line.

    I've learnt a bit due to this Thread and also that my car does not now have that warning switch.

    Attached Files:

    Last edited by a moderator: Oct 6, 2015
  13. Rob Gaskin

    Rob Gaskin Membership Secretary Staff Member Committee Member

  14. strugrat

    Z Club Member

    I dont think mine has it either. Valve looks good fitted. I couldnt find a picture of one on a Z.
  15. SKiddell

    SKiddell Having a bad day

    The OEM unit had a piston arrangement inside and IIRC on later cars was mounted on the bulkhead, whereas the manifold/pressure switch unit was mounted low down on the inner wing just above the driver’s side inner wing

    Most of the available aftermarket proportioning valves work by restricting flow and as a result affect pressure rise rate which in turn induces a lag on the rears allowing the front to react quicker with more available pressure.

    Any of the mentioned units will do that although that new Wilwood one is neat as it provides an integral manifold to split the fronts
  16. pmac

    pmac Active Forum User

    I think we might spec that on our proposed new build??
  17. Huw

    Z Club Member
    Staff Member

    My mate uses one on his track Mini. Got it inside the car down by the gear shift for 'ease of fiddling' or setting up - which ever term you prefer.
  18. SKiddell

    SKiddell Having a bad day

    Is that the five port mentioned or the generic 2 port, if its the 5 port isnt that a bit convoluted to bring all the front pipe work inside the car only to take it back out again, whereas the stock 2 port just breaks into the front/back brake line.
  19. Ian

    Z Club Member

    Running a wilwood valve on mine, mounted in the cabin for easy adjustment, works very well, could recommend.
  20. moggy240

    moggy240 INSURANCE VALUATIONS OFFICER Committee Member

    I will be using the 5 port version on my car ,just need to work out where I will fit it.

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