R8 brake booster
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  1. #1
    Member starkzmi16's Avatar
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    Default R8 brake booster

    Hi guys,

    Recently bought myself an r8 and it has a problem with the brakes gradually building up brake pressure and the pedal goes hard. It has a pbr vh44 remote brake booster and to release the pressure I am having to crack the bleed nipple at the booster. I have tried running it without the vacuum line and no difference. I have also adjusted the free play at the pedal with no difference. So my next thought was replacing the brake booster, but I am unsure if I need the vh44 or vh40, everything that I have read says the 44 is for drum brakes. So was chasing people's opinions.

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    Cheers Rory

  2. #2
    Fellow Frogger! alpinesau's Avatar
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    Rory,
    I have a VH44 on my R8 Gordini. It has been on there for over 30 years without an issue.

    Robert
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  3. #3
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    My gut feeling will be the many times mentioned internally collapsing flexi brake hose somewhere in the system. Back to basics.

  4. #4
    Fellow Frogger! bingham driver's Avatar
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    Try cracking the pipe from the master cyl to the booster, if that releases brakes its the master cyl.
    Otherwise its probably the booster cylinder(swollen rubbers).
    Once I thought I was wrong but, I was mistaken

  5. #5
    Too many posts! JohnW's Avatar
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    Quote Originally Posted by starkzmi16 View Post
    Hi guys,

    Recently bought myself an r8 and it has a problem with the brakes gradually building up brake pressure and the pedal goes hard. It has a pbr vh44 remote brake booster and to release the pressure I am having to crack the bleed nipple at the booster. I have tried running it without the vacuum line and no difference. I have also adjusted the free play at the pedal with no difference. So my next thought was replacing the brake booster, but I am unsure if I need the vh44 or vh40, everything that I have read says the 44 is for drum brakes. So was chasing people's opinions.

    Cheers Rory
    I won't add to the advice already given as that's what I'd do too. Is it the lovely dark green one with big headlamps and with a tacho in the right hand dash vent? Not many R8s have boosters added.
    JohnW

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  6. #6
    1000+ Posts Wildebeest's Avatar
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    Rory,
    Could there be a residual line pressure valve in the master cyl or the booster hydraulics? Something I've understood is that fully disc brake systems don't require these. Anyone?
    Faulty brake compensator, if fitted ?

  7. #7
    Member starkzmi16's Avatar
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    Thanks for the advice guys tomorrow I will pull down the original master cylinder and give it a clean up. As for the residual pressure valve I am not sure. I have recently bought this car but the brake booster was fitted se time ok and I am assuming the brakes were working correctly at some stage in this cars life. And no the car is blue not dark green.

  8. #8
    Too many posts! JohnW's Avatar
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    Quote Originally Posted by Wildebeest View Post
    Rory,
    Could there be a residual line pressure valve in the master cyl or the booster hydraulics? Something I've understood is that fully disc brake systems don't require these. Anyone?
    Faulty brake compensator, if fitted ?
    Interesting thought. There are two types of fitting inside those R8/R10/Dauphine/4CV master cylinders, one of which is for drum brakes (yes, non return) and one that allows movement of fluid both ways. Heaven knows what might be in the MC or the booster in that department.

    As a rule, you really don't need a booster on an R8. Go for the smallest diameter master cylinder (19 mm) and make sure the calliper pistons are not seized and they are pretty light.
    JohnW

    Renault 4CV 1950 (R1062)
    Renault R8 1965 (R1130)
    Renault Scenic Series II 2005 (wife's)
    Renault Scenic Series II 2006 (daughter's)
    Renault Scenic Series II 2007 (mine)

    CitroŽn CX Pallas 1980 (moved on to new custodian)

    National Co-ordinator, Renault 4CV Register of Australia

  9. #9
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    Quote Originally Posted by starkzmi16 View Post
    to release the pressure I am having to crack the bleed nipple at the booster.
    If cracking the bleed nipple releases the brakes, it sounds more brake servo (and backwards to the M/C) related rather than calipers, brake hoses and pressure limiter related. Try as Mr Bingham driver suggests, to isolate the problem to the servo or M/C.

    Then again, if the car is a new acquisition with an unknown history, it wouldn't do any harm to just replace all the wearable things in the brakes, seals, etc, and overhaul the servo.
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  10. #10
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    Renault 8 must NOT have a residual pressure 'foot Valve' in the Master Cylinder ( if it has then brakes will not fully release and will drag/ overheat. If brake pedal is progressively building up pressure, so that pedal becomes increasingly hard with no free travel it is USUALLY insufficient free play between brake pedal and master cylinder push rod...try slackening off the free play on push rod, at pedal end.

  11. #11
    1000+ Posts renault8&10's Avatar
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    Quote Originally Posted by Rod Slater View Post
    Renault 8 must NOT have a residual pressure 'foot Valve' in the Master Cylinder ( if it has then brakes will not fully release and will drag/ overheat. If brake pedal is progressively building up pressure, so that pedal becomes increasingly hard with no free travel it is USUALLY insufficient free play between brake pedal and master cylinder push rod...try slackening off the free play on push rod, at pedal end.
    That could be a real cheap fix if it is that!
    KB


  12. #12
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    If drum brakes need a "foot valve" and disc brakes don't then what about a drum/disc combination?

  13. #13
    Fellow Frogger! bingham driver's Avatar
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    The residual pressure valve(usually 7lb) is to stop wheel cyl cups from collapsing, causing leakage.
    This minor pressure is normally not enough to overcome caliper piston seal resistance.
    Excess pressure build up is usually caused by cup swell blocking the hole to/from the reservoir/supply pipe, stopping the fluid getting back
    thru the system when you release the pedal.
    Once I thought I was wrong but, I was mistaken

  14. #14
    Fellow Frogger! bingham driver's Avatar
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    Same symptom as no pedal clearance!
    Once I thought I was wrong but, I was mistaken

  15. #15
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    Quote Originally Posted by bingham driver View Post
    The residual pressure valve(usually 7lb) is to stop wheel cyl cups from collapsing, causing leakage.
    This minor pressure is normally not enough to overcome caliper piston seal resistance.
    Excess pressure build up is usually caused by cup swell blocking the hole to/from the reservoir/supply pipe, stopping the fluid getting back
    thru the system when you release the pedal
    .
    Hi,
    I have experienced this pressure build up twice when the fluid supply hole became blocked by corrosion/sh*t. On a trailer and a motorcycle. The brake drag heats the fluid at the wheels and it cannot return to the reservoir, just the same as the case of insuficient adjustment, cup swell etc. Wheel lockup both times. Front wheel on the bike and threw me off unexpectedly and in no time. However both times the vehicles were unused for quite a while before the incidents.
    jaahn
    Last edited by jaahn; 20th January 2013 at 03:20 PM. Reason: adjust prose !!

  16. #16
    Member Pepster's Avatar
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    I just saw this thread (a month late).

    Rory, you need to attend to this without delay! I had a similar problem with my R8G many years ago, where the brakes were getting more and more sensitive. So I decided to keep drive a bit more carefully and keep an eye on it. Bad move!

    One day while slowing down on a multi-lane road, the brakes locked up without warning. The car stopped almost instantly in the middle of the road, resulting in a collision between two other vehicles behind. So there I was in a panic, reaching under the car with a spanner to release the bleed nipple. Another bad move, because as soon as the fluid spurted out, the car started rolling. Could have easily lost my arm. Chased the car, jumped in and stopped it. Very embarrassing!

    Something in the booster was worn, but I'm not sure what. I won't be doing that again!

    Peter
    Last edited by Pepster; 21st February 2013 at 08:37 PM.
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  17. #17
    Member Pepster's Avatar
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    And while we are on the subject, does anyone know the correct VH booster for an R8G? I see many references to the VH44, but when speaking to Hydroboost recently, Terry mentioned the VH44J. So I'm a little confused.

    Peter
    1968 R8G 1300
    1965 R8G 1100
    1972 R12G
    1978 Virage
    1977 R12XL
    1971 R10
    1968 R10

  18. #18
    Member starkzmi16's Avatar
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    Have sorted the brakes out now, was the master cylinder. I bought a new one from mecaparts and re bled the system and now the brakes work very well.

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