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  1. #1
    Fellow Frogger! R8 Dream's Avatar
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    Default R8 Gros Brakes

    I am at my wits end.
    I installed the Gros Brakes on my R8 using the R16 calipers up front with Fiat ones up back.
    I changed the master cylinder to the 22mm dia (Mecaparts MP2901).
    i filled the reservoir using high temp brake fluid (600 deg).
    all the lines are new.
    I did away with the rear valve, but fitted a proportioning bias valve.
    i started bleeding process but after the fluid dropped about 10mm in the reservoir, no further fluid went in.
    it seems it is going nowhere, and after pumping for over an hour, still nothing.
    i have bled systems before, ( never a renault- mainly holders, fords etc) but this has me totally stumped.
    is their anything obvious I am missing or should be doing?
    Angelo

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    1000+ Posts Kim Luck's Avatar
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    Did you put the input of the system into the correct port of the bias valve? Is the bias valve open or closed when the vehicle is level? These questions only you can answer!
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    Quote Originally Posted by Kim Luck View Post
    Did you put the input of the system into the correct port of the bias valve? Is the bias valve open or closed when the vehicle is level? These questions only you can answer!
    Hi Kim
    yes I am sure the correct port inlet was used. I have unscrewed it almost all the way up and car is level.
    i was thinking of trying to just bleed the front as nothing is happening at the back brakes.
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    1000+ Posts renault8&10's Avatar
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    Maybe try a vacuum bleeder at the rear?
    KB


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    1000+ Posts J-man's Avatar
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    Hi Angelo, you don't have a fluid extractor that you can suck it through from each caliper by any chance? Still won't work if something is not right with the circuit though.

    http://m.ebay.com/itm/281945406043
    cheers,

    John

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    Quote Originally Posted by renault8&10 View Post
    Maybe try a vacuum bleeder at the rear?
    just read a thread from 2013 from bazzamac that sounds like he had the same problem with his A110

    A110 Restoration


    i note he ended up having it towed to his mechanic after a suspect master cylinder.

    Ended up having to use a suction system to get the brakes bled.

    hope I can sort it out myself, but know there is always a last resort.

    angelo

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    Quote Originally Posted by R8 Dream View Post
    just read a thread from 2013 from bazzamac that sounds like he had the same problem with his A110

    A110 Restoration


    i note he ended up having it towed to his mechanic after a suspect master cylinder.

    Ended up having to use a suction system to get the brakes bled.

    hope I can sort it out myself, but know there is always a last resort.

    angelo
    Angelo sometimes the vacuum bleeder system is needed because the master cylinder is lower than the wheel cylinders some cars use a special type of valve that keeps the fluid from coming back into the master when you release the pedal some may have that valve built into their master unit . It is not a check valve so it does allow the fluid to return to the master but it is metered for sake of a better definition in the reverse flow direction .

    Manic GT

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    1000+ Posts Frans's Avatar
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    Make sure the master cylinder and pedal pushrod has play when the pedal is released. The piston of the master has to teturn to the circlip to allow the reservoir to fill it for the next pump action.
    Frans.
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    Quote Originally Posted by manicgt View Post
    Angelo sometimes the vacuum bleeder system is needed because the master cylinder is lower than the wheel cylinders some cars use a special type of valve that keeps the fluid from coming back into the master when you release the pedal some may have that valve built into their master unit . It is not a check valve so it does allow the fluid to return to the master but it is metered for sake of a better definition in the reverse flow direction .

    Manic GT
    thanks. There is an obvious theme here. It seems that I need a vacuum bleeder system to make any further progress here.

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    Quote Originally Posted by Frans View Post
    Make sure the master cylinder and pedal pushrod has play when the pedal is released. The piston of the master has to teturn to the circlip to allow the reservoir to fill it for the next pump action.
    Frans.
    I set up the pedal push rod at the same distance as for my standard 19mm master cylinder (standard R1132 R8) so hope the stroke distance is right. Is someone able to confirm that my set up pushrods length is about right?

    if my setup is right and with no leaks apparent around the master cylinder, I will see what I can find that will help with the vacuum bleed, or its off to the mechanics.

    angelo
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    Hi Angelo,
    Not sure if it is a single or dual master cylinder.
    If it is a tandem, there may be issues with the piston and spring setup not moving freely.
    This could mean that say if the fronts are bleeding OK, the fill port for the rears is not
    cleared by the seal, stopping fluid entering that chamber.
    This can be a common problem with new old stock masters that may be a little sticky with
    dried out assembly grease, or worse, surface rust.
    If this is the case, a strip down, inspection, reassembly may be required.
    Priming the master prior to installation may also be a good idea.

    Anyway, loosening brake lines and confirming fluid coming through as you work downstream
    will verify that fluid is getting through and pinpointing the problem.

    Do you have copper lines or new steel?

    Are your brake hoses good? Old ones can swell internally and block fluid flow.

    Hope this helps.

    Cheers, Steve.
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    It might also be worth trying to bleed the rears with the front up on ramps, let gravity assist you..

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    Quote Originally Posted by Steve K View Post
    Hi Angelo,
    Not sure if it is a single or dual master cylinder.
    If it is a tandem, there may be issues with the piston and spring setup not moving freely.
    This could mean that say if the fronts are bleeding OK, the fill port for the rears is not
    cleared by the seal, stopping fluid entering that chamber.
    This can be a common problem with new old stock masters that may be a little sticky with
    dried out assembly grease, or worse, surface rust.
    If this is the case, a strip down, inspection, reassembly may be required.
    Priming the master prior to installation may also be a good idea.

    Anyway, loosening brake lines and confirming fluid coming through as you work downstream
    will verify that fluid is getting through and pinpointing the problem.

    Do you have copper lines or new steel?

    Are your brake hoses good? Old ones can swell internally and block fluid flow.

    Hope this helps.

    Cheers, Steve.

    Hi Steve
    I am running a new single 22mm MC - purchased from Mecaparts (MP2901)
    has been sitting in car for around 2 years without fluid in them, but has always been inside in the dry.
    lines are all new - steel.
    hoses are all brand new too.
    there just seem to be no response when I pump.
    i would have thought under pressure, the fluid would have moved along the lines?
    if raising the front will really help, i might give it a go, but sounds like it needs some external vacuum to draw the fluid in the lines.
    Angelo

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    1000+ Posts alan moore's Avatar
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    Quote Originally Posted by R8 Dream View Post
    I set up the pedal push rod at the same distance as for my standard 19mm master cylinder (standard R1132 R8) so hope the stroke distance is right. Is someone able to confirm that my set up pushrods length is about right?


    angelo
    It is good you made it the pushrod same length, but given it is a different master cylinder, you will still need to check there is a small amount, maybe 1mm of freeplay from the pushrod to the piston, to be sure that the piston is able to fully come back. Perhaps as Steve K has said, the master may have been sitting for a long time and the piston isn't returning freely.
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    COL
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    What I have found with brake parts that have been sitting a few years is that the rubber grease dries out and gums things up.

    What I have done is to dismantle, wash out with methylated spirits and re-grease with some fresh rubber grease.
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    Regards Col

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    Hi Angelo,

    pehaps you you could try to the process in reverse if you don't have a pressure bleeder.
    buy the largest siringe, like for a horse.
    draw in the fluid and connect to the open bleeder and force the fluid back up to the master cylinder.
    the compensating port should be open allowing the fluid into the reservoir, make sure you don't overflow.

    regards
    martin
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    Quote Originally Posted by Ahh8 View Post
    Hi Angelo,

    pehaps you you could try to the process in reverse if you don't have a pressure bleeder.
    buy the largest siringe, like for a horse.
    draw in the fluid and connect to the open bleeder and force the fluid back up to the master cylinder.
    the compensating port should be open allowing the fluid into the reservoir, make sure you don't overflow.

    regards
    martin
    My mad motor bike friend always does this "backwards bleeding". My suspicions are Alan's/Col's/Frans', i.e. is there a bit of free play at the pedal, easily felt by hand and is the MC piston actually returning? If the latter, with the piston stuck at the wrong end, the pedal should just be springy with no hydraulic resistance.

    These things can be sooo frustrating. Maybe get it all sorted with just a tee piece at the rear and add that other valve later? That removes one variable!
    JohnW

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    Quote Originally Posted by JohnW View Post
    My mad motor bike friend always does this "backwards bleeding". My suspicions are Alan's/Col's/Frans', i.e. is there a bit of free play at the pedal, easily felt by hand and is the MC piston actually returning? If the latter, with the piston stuck at the wrong end, the pedal should just be springy with no hydraulic resistance.

    These things can be sooo frustrating. Maybe get it all sorted with just a tee piece at the rear and add that other valve later? That removes one variable!
    John et al

    The pedal feels entirely 'springy' and not at all with any hydraulic resistance, so the problem must be in the MC.

    I am afraid I have reached my knowledge/technical limit here and with the awful location of the master cylinder, with pedal assy etc, I just can't do it myself.

    I have only ever bled the brakes on 'normal' cars and never used any other system other than the two-man so to try the vacuum, syringe, reverse etc etc I just don't know.

    I am a bit confused, and dont have the confidence to attack this task myself, so a call to the mechanic tomorrow with a flat bed and he can sort it out. besides its the brakes, probably the most important thing to get right on a car, and I don't want o leave it to chance.

    Thanks everyone for your suggestions & comments, but I am truly disappointed that I have got this far, and had to give up now (quitting is not in my DNA, but every man gotta know his limit!).

    Angelo

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    Sounds like MC piston not returning properly doesn't it.

    1. As Alan and Frans said, pushrod length is critical. You should be able to feel a few mm max free play at the pedal, then the resistance increases as the piston presses fluid into the system.
    2. Piston stuck further up the MC (what it sounds like): gunged up through disuse or, as once happened to me, not returning properly as the rubber cap was slightly too large and didn't slide freely. There are 3 MC diameters.
    3. Maybe both.....

    Alan will know exactly what he wrote, but his idea to use Alan-headed bolts instead of 10mm spanner size bolts is, I reckon, a really good idea for holding the MC in place. It is a tad fiddly and this would make things a lot easier. I wish I'd done it years ago. Next time...

    I reckon you might end up pulling it out to sort whether the piston is stuck and why, and sort that out. Then put it in, and prior to all the joys of refitting the hydraulic pipes, check that you do have that wee bit of free play at the pedal before the pushrod actually presses the MC piston. When that is right, reconnect and all should be well. There's an awkward adjustment that can be made at the pedal end of the pushrod, giving a few mm plus or minus on that free play. If you thought the MC bolts were awkward.....

    My recent joys in this area when I really had to admit I wasn't happy with my brakes included double checking that all calliper pistons were correctly aligned (I've no idea what is needed for the "gros freins" but the "freins ordinaire" need a dot on the piston to be in the right place) and that the hoses were OK, regardless of appearance. I found one hose was lengthening slightly under pedal pressure, although it was externally OK. I could actually feel it lengthening (not ballooning) by grasping the hose with one hand and then getting someone to press the pedal gently. One new hose later, brakes are good. I prefer not to discuss how long they weren't quite up to scratch and a bit squishy, and it was clearly all in the hose structure!

    Have fun.
    Last edited by JohnW; 19th February 2017 at 07:40 PM. Reason: Missed a few words....
    JohnW

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    Hi Angelo, I had exactly the same problem with my Caravelle. Brand new master cylinder from mecaparts. The problem end up being a fault master cylinder. Where the feed pipe from the resevoir bolts into the cylinder there are 2 holes, one large one and one very tiny one. This very small one hadn't been drilled through. As soon as I cleared this hole every thing worked as expected. My master cylinder was purchased approximately 2 years ago. Hope this makes sense and solves your problem.
    Peter.
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    Quote Originally Posted by R1173 View Post
    Hi Angelo, I had exactly the same problem with my Caravelle. Brand new master cylinder from mecaparts. The problem end up being a fault master cylinder. Where the feed pipe from the resevoir bolts into the cylinder there are 2 holes, one large one and one very tiny one. This very small one hadn't been drilled through. As soon as I cleared this hole every thing worked as expected. My master cylinder was purchased approximately 2 years ago. Hope this makes sense and solves your problem.
    Peter.
    Hi Peter
    this narrows the problem considerably I think to the master cylinder.
    I did not take any note of this second hole when I installed it.
    I will pull it out next weekend and take a look and see what I have.
    thanks as what has happened to me does not seem normal.
    thanks
    Angelo

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    A similar problem I had with a new R10 master cylinder, The manufacturer had installed a shim washer behind the rubber cup, this resulted in the small hole being blocked, once removed it bled without problem.

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    Quote Originally Posted by R8 Dream View Post
    Hi Peter
    this narrows the problem considerably I think to the master cylinder.
    I did not take any note of this second hole when I installed it.
    I will pull it out next weekend and take a look and see what I have.
    thanks as what has happened to me does not seem normal.
    thanks
    Angelo
    Do you have an old one for comparison? This can help a lot. In one way or another it does smell like MC not YOU!

    I'd sleep on it, perhaps more than once.
    JohnW

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    Before removing the MC try bleeding at the MC itself ( yes I know it a bad spot to do this )
    If you remove the MC try bleeding it on the bench , just clamp it in a vice arrange a suitable gravity feed to supply fluid , then using a finger as a one way valve on the out let push the piston in and out with a phillips head screw driver.
    You can also check that the piston does return to the circlip.
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    1000+ Posts renault8&10's Avatar
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    Agree with above. I would pull the mc for further investigation before throwing in the towel. It's been 2 years, another week won't matter. The fact it has been in there 2 years without fluid could be significant as COL mentioned. I also wonder if you may have pressed the pedal/cylinder too far forward when there was no or little fluid in there and now the seal is stuck blocking the hole and not able to return.

    I only use 1/2- 3/4 stroke when bleeding brakes until you have almost got full pressure, as I have had a similar thing happen to me. Removing the mc and freeing up the cylinder should correct this if the case.
    KB


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