Brake master cylinder relocation
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Thread: Brake master cylinder relocation

  1. #1
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    Default Brake master cylinder relocation

    I've been thinking of moving the master cylinder forward of the cross member to make it easier to use non Renault parts. My plan is to put a bell crank on top of the cross member and have two push rods. As far as I'm aware this is street legal as there are plenty of production cars with complicated linkages and even some with the master cylinder just behind the head lights. According to the rules you are allowed to fabricate these parts, they just need to be inspected.

    There just isn't enough space near the pedals as most modern MCs have large flanges as they are meant to be mounted on boosters.

    I've done a quick proof of concept using plywood and cardboard. Down side is you can't have a spare tyre or a horizontal radiator. My radiator will be forward of the sway bar. The upside is I think I'll be able to fit a 7" inline booster. There will need to be some
    metal between the pedals and the bell crank mount for stiffness and I'm yet to work out what I'm attaching the MC to.

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    I'm open to comments, if this works it open up lots of brake options. The MC in the picture is a 7/8" tandem from a corolla.

    I think the pictures make the concept clear enough.





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  2. #2
    1000+ Posts robmac's Avatar
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    Didn't Frans do this task ?

    I recall he used a relay rod assy.

  3. #3
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    If it's been done before I'd like to see how it was done.

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    1000+ Posts robmac's Avatar
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    The 19mm VW MC doesn't have a large enough bore for my intended calipers, the BMW one mentioned in that thread would be big enough.

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    1000+ Posts Frans's Avatar
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    Quote Originally Posted by robmac View Post
    Didn't Frans do this task ?

    I recall he used a relay rod assy.
    Hi All, no I haven't done it this way. I have two separate MCs (one MC for front and another for back) with a balance bar in between applying different pressures as required for best stopping. MCs are at the back of the cross member.

    I'm sure Christian's idea will work but a warning from my experience. Although the mounting is in a different position the principle will be the same. Make sure that where you mount the linkage on the cross member it is anchored to the pedal pivot point. If you don't do that the cross member will flex and you will have a soft pedal. If you calculate the force you put on the pedal and multiply it by the link ratio you will realise the force on there and I think after a while something is going to give. My first effort proved that the cross member moved and my MCs where anchored in the cross member center line. Yours will be on top causing a torsional/rotational deflection.

    I hope my explanation makes sense. Its hard to explain without hands.

    Frans.
    JohnW likes this.
    Old enough to know better
    Young enough to do it anyway.

  7. #7
    1000+ Posts Frans's Avatar
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    Christian, I forgot to mention, if you lay the radiator horisontal/flat as mine in the race car then you will have space for the MC and a booster. Spare wheel not.
    Nothing states that a radiator has to be vertical.
    Regards, Frans
    Old enough to know better
    Young enough to do it anyway.

  8. #8
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    Frans, my intention was to have bracing between the cross member and the pedal pivot for the reason you have mentioned.

    The two MC setup with a balance bar isn't Street legal.

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    1000+ Posts alan moore's Avatar
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    I have recently been going through the brake system on the 4CV. The car has been sitting for a few years, and I had last overhauled the brakes maybe 20 years ago. I removed the 22mm master cylinder, and I believe now it was from a '70's BMW 3.0 Si, not an early 80's 5 series that I mentioned some years ago, although it could have been the same in both. I rekitted it as it had been stainless sleeved in the past, but had a lot of problem getting a good pedal on refitting.

    I had been very careful with the rebuilding of the R10 calipers fitted to all 4 wheels of my 4CV, in regard to alignment of the heavy internal spring slot to the bleed nipple, and even aligning the mechanism horizontally that does not allow the piston to move too freely and get pad knockoff, so that any air would bleed easily. I got some custom (legal) flexible braided brake lines made as well.

    After many attempts with a vacuum bleeder, and a pressure bleeder, and just pumping the brakes and having no success, I replaced the master cylinder with an identical one, but 13/16" or 20.6mm from a BMW 2002 wreck I have. It was also already stainless sleeved and looked to have been drilled more accurately as regards the fluid feed holes and compensating ports. I fitted new rubbers and gave it a quick hone and it all came together fine.

    The pedal now goes about half way down but is then solid. Renault on the R10 used 19, 20.6 and 22mm master cylinders, but I will see how it all works once it is on the road again. I also have fitted some new old stock Metal King pads to the front, and Textars to the rear. So a lot of changes.

    The BMW 2002 master cylinder basically bolts straight in. The hole centres are correct, the boss fits the hole in the bracket, only the Renault alloy bracket holes have to be taken out to 8mm, and the push rod is a combination of BMW at the master cylinder end threaded into the Renault part at the clevis, giving an adjustable length push rod. I fitted an external brake light pressure switch into an output pipe. The BMW is even set up with a remote reservoir standard. I used the BMW reservoir in the Renault position but really should have moved it to the drivers side of the boot to reduce the flex hose length.

    The only slight difference is that when mounted in the Renault, rather than the BMW, the M/C is canted about 20 degrees toward the drivers side of the car, and I started to think this was where my air holding was coming from, so I connected up the reservoir hoses, and filled it so that the fluid was coming through the outlets whilst holding the M/C in its upright position under the car, and then turned it to its mounting position and attached the pressure pipes before fully refitting it. It worked, but I really don't know what worked, holding the M/C the way I did with fluid dripping everywhere, or simply another M/C. Hopefully it will be another 20 years till I find out.
    '56 Renault 750 (16TS Power)
    '62 Renault Dauphine Gordini
    '89 Renault Alpine GTA V6 Turbo
    02 and 03 Renault Clios 1.4L
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    Extra options are always welcome. I've seen elsewhere that an MC is available from an A110 based on a Kangoo MC. I've tracked down the MC for next to nothing, $35, it's on its way from Germany. Surely the shipping would have cost that much. It has a small flange which means it may fit. Once it arrives I'll know more, don't have a great deal of time at the moment anyway.

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