Brake caliper piston - Renault R8 Gordini
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Thread: Brake caliper piston - Renault R8 Gordini

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    Default Brake caliper piston - Renault R8 Gordini

    I am about to refurbish my rear brake calipers on my Renault R8 Gordini. I have disassembled them and it seems I need new pistons. Have anyone here bought new pistons from Mecaparts or other suppliers? The "self adjusting mechanism" doesn't show on the picture on the Mecaparts website. Do anyone know if I am required to move this over from the old piston?

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    1000+ Posts renault8&10's Avatar
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    I bought some and they donít have the thread etc for the adjuster
    KB


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    Ok, so the adjuster is not needed on these new pistons?

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    Hmm. Need more information.

    The pistons have a super-strong circlip-like spring inside the piston (which is a cylinder with a large ID). That spring is connected to a threaded rod that is sealed against the back of the calliper with an external nut and two annealed copper washers. The spring progressively slides out along the piston's internal diameter as the pads wear, I presume moving a small amount as the brake applications reduce the thickness of the pads. It's a good self-adjusting system in my modest experience since 1973.

    1. Are you SURE you need new pistons?
    2. Are the new pistons lacking the internal self-adjusting parts? If the new pistons are the same dimensions as the old ones, I suppose that the old self-adjusting mechanism would fit into the new pistons.

    Back to you both I think....

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    1000+ Posts renault8&10's Avatar
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    I would assume you need to swap them over from old to new pistons.
    How, I canít answer.
    KB


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    R8RX,
    You need the old adjuster slides, that come out of your current calipers. Check the size of the locking thread as some are M8 and some M9. The split in the slide ring needs to be inserted in line with the dot mark on the pad face of the piston. I align mine in the jaws of the vise and use the vice forces to insert the adjuster into the piston. You may need to do it piece by piece and remove from the vice and straighten a few times (hammer). Do this with the nut on the thread, as it aligns better. The pistons are good as they are now stainless steel.

    Again, as calipers could have been changed, check the thread size when assembling in caliper and always remember the copper ring on the thread before assembly into the piston. I always assemble with the caliper inverted. and then align the dot mark with the bleed nipple. And always fit the dust seal correctly, in particular in your country..

    Square seals will not fit in round seal grooves, but round seals can be forced into square seal grooves.

    Have fun,
    Ray
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    Too many posts! JohnW's Avatar
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    Geckoeng is on the money IMHO.
    JohnW

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    Quote Originally Posted by JohnW View Post
    Hmm. Need more information.

    The pistons have a super-strong circlip-like spring inside the piston (which is a cylinder with a large ID). That spring is connected to a threaded rod that is sealed against the back of the calliper with an external nut and two annealed copper washers. The spring progressively slides out along the piston's internal diameter as the pads wear, I presume moving a small amount as the brake applications reduce the thickness of the pads. It's a good self-adjusting system in my modest experience since 1973.

    1. Are you SURE you need new pistons?
    2. Are the new pistons lacking the internal self-adjusting parts? If the new pistons are the same dimensions as the old ones, I suppose that the old self-adjusting mechanism would fit into the new pistons.

    Back to you both I think....
    I am not 100% sure new pistons are needed. There are one spot of rust on each of the pistons but that spot is close to the front of the piston. So it may go clear of the internal seal.

    http://mecaparts.com/PhotosPieces/MP3308.jpg

    It does appear to me that the internal parts are not on the new pistons.

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    Quote Originally Posted by geckoeng View Post
    R8RX,
    You need the old adjuster slides, that come out of your current calipers. Check the size of the locking thread as some are M8 and some M9. The split in the slide ring needs to be inserted in line with the dot mark on the pad face of the piston. I align mine in the jaws of the vise and use the vice forces to insert the adjuster into the piston. You may need to do it piece by piece and remove from the vice and straighten a few times (hammer). Do this with the nut on the thread, as it aligns better. The pistons are good as they are now stainless steel.

    Again, as calipers could have been changed, check the thread size when assembling in caliper and always remember the copper ring on the thread before assembly into the piston. I always assemble with the caliper inverted. and then align the dot mark with the bleed nipple. And always fit the dust seal correctly, in particular in your country..

    Square seals will not fit in round seal grooves, but round seals can be forced into square seal grooves.

    Have fun,
    Ray
    Thank you! This sounds like a bit of fun How do you get the adjuster out of the old piston?

    I have bought correct seals so that should be ok.
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    1000+ Posts geckoeng's Avatar
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    R8RX,
    Hold the thread in aluminium jaws in the vise, and with 2 large screw drivers lift the piston from the slider.

    Think laterally ............. these are simple '60s cars, only a few special tools, and then sum ........

    Ray
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    Isnt the "adjuster mechanism" inside the piston more like a mandrel to stabilize the piston in its bore?

    I think I have seen complete pistons in one of the lesser known french webshops not to long ago.

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    1000+ Posts Frans's Avatar
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    Hi Reidar,

    No the adjuster mechanism is actually there to keep the pads close to the rotors. As the pads wear down the hydraulic pressure will force the piston out of the adjusting mechanism fraction by fraction and at the same time keep the pads from pulling away from the rotors or back into the caliper body. Call it auto adjust rather than adjusting mech.
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    Quote Originally Posted by geckoeng View Post
    R8RX,
    Hold the thread in aluminium jaws in the vise, and with 2 large screw drivers lift the piston from the slider.

    Think laterally ............. these are simple '60s cars, only a few special tools, and then sum ........

    Ray
    Thank you, i will give it a go. I feel it is better to replace the pistons rather than take a chance on the old ones.

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    Quote Originally Posted by R8RX View Post
    Thank you, i will give it a go. I feel it is better to replace the pistons rather than take a chance on the old ones.
    It really depends upon the surface finish. Superfine scratches seem OK but scoring or flaking chrome are not worth playing with IMHO. I did survive with pistons with serious flaking once, in Kenya, but the flaking was outside the seal (where it had been wet under the dust cover) and all was just fine.

    Having said that, I've thrown a few away in the past....
    JohnW

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    Quote Originally Posted by JohnW View Post
    It really depends upon the surface finish. Superfine scratches seem OK but scoring or flaking chrome are not worth playing with IMHO. I did survive with pistons with serious flaking once, in Kenya, but the flaking was outside the seal (where it had been wet under the dust cover) and all was just fine.

    Having said that, I've thrown a few away in the past....
    Yes, I know. It has started to flake on both rear pistons. But as you say, it is on the outside of the internal seal. If the new pistons are stainless steel the choice to replace them isn't difficult.

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    Quote Originally Posted by R8RX View Post
    Yes, I know. It has started to flake on both rear pistons. But as you say, it is on the outside of the internal seal. If the new pistons are stainless steel the choice to replace them isn't difficult.
    Yes, I would replace them too!
    JohnW

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    Quote Originally Posted by R8RX View Post
    I am about to refurbish my rear brake calipers on my Renault R8 Gordini. I have disassembled them and it seems I need new pistons. Have anyone here bought new pistons from Mecaparts or other suppliers? The "self adjusting mechanism" doesn't show on the picture on the Mecaparts website. Do anyone know if I am required to move this over from the old piston?

    Hi,
    Yes you certainly need to. I am doing the same with my car. Make sure that there is no rust on this part. I am electroplating the bolt and then wet & dry the ring to remove any imperfections. Use rubber grease when you reassemble. To remove the bolt ,use a vice on the nut & prise the old piston out of it.
    Good luck,
    Ross

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    I forgot to add a couple of comments!

    The leakage of brake fluid from callipers is, in my experience, not uncommon after refurbishing. It can be due to corrosion (that is roughness) in the groove behind the 'o' ring in the alloy calliper.. I polish the back of the groove (with great difficulty) with fine wet and dry rubbing paper. There's general confusion about round and square sealing rings and whether it matters which you use. Several opinions are out there and I'm not contributing! I've used square rings for ages. There might be two different round 'o' ring sizes.... I think that basically the piston should have a fair bit of resistance to the finger pressure when pushing it in, past that seal. If there is no noticeable resistance, something is wrong probably!!!

    Personally, and there are opinions about this too, I use Silicone brake fluid (Dot 5) because the corrosion behind the 'o' ring is caused, in my view and the opinion of others, by moisture in the hygroscopic conventional brake fluids. I've used this expensive fluid for nearly 3 decades now and have had NO problems, but that's just personal experience not a recommendation.

    Enough from me.....
    JohnW

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    Hi
    Just my.
    Use plenty of rubber grease when you reassemble them inside and out. Put it under the dust boot also to help prevent the ingress of moisture to the outer surface and Oring seals. Renault recommended this from day one when it was impossible to even buy the stuff anywhere else.

    It is also good for packing into the cylinders of drum brakes to help them resist corrosion. The new poor quality cast iron cylinders you buy now need all the help they can get. I have found them rusty inside when you buy them, so always strip them and grease them well with quality brand rubber grease and pack the boots too.

    Back in the day my mate went into Renaults Sydney workshop to ask about the special tool in the manual to remove and fit the Oring in the calipers. It said "only use a long soft flexable tool". The mechanic told him that was a finger
    Jaahn

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    Thank you very much for all your advice! This helps me a lot. What kind of grit are you using on the sandpaper? First dry and then wet paper? Or the other way around?

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    Ah, what grit indeed! Good question. Something fine that is already in the drawer has usually been what I've used. I think I've used nothing coarser than 120, always wet and dry paper used with water. I have a toothbrush handle with about 1 cm of the end bent at right angles and ground to fit in the groove and fold the wet and dry around it, and then rotate by hand. It's a bit fiddly but it works for me and my callipers rarely leak. It doesn't need a lot of work in that you don't want to take much meat off beyond cleaning out the fine corrosion products. With silicone fluid, you don't get that white powder from what I've seen so far.

    I wish I knew exactly why some calllipers specify square seals and some specify round seals! Someone out there might know, but I don't. Maybe they'll put me out of decades of misery, wondering why.....

    I have used square ones for many years as, in my logic, they have a wider seal surface at the back of the groove in the calliper.
    JohnW

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    Quote Originally Posted by JohnW View Post
    Ah, what grit indeed! Good question. Something fine that is already in the drawer has usually been what I've used. I think I've used nothing coarser than 120, always wet and dry paper used with water. I have a toothbrush handle with about 1 cm of the end bent at right angles and ground to fit in the groove and fold the wet and dry around it, and then rotate by hand. It's a bit fiddly but it works for me and my callipers rarely leak. It doesn't need a lot of work in that you don't want to take much meat off beyond cleaning out the fine corrosion products. With silicone fluid, you don't get that white powder from what I've seen so far.

    I wish I knew exactly why some calllipers specify square seals and some specify round seals! Someone out there might know, but I don't. Maybe they'll put me out of decades of misery, wondering why.....

    I have used square ones for many years as, in my logic, they have a wider seal surface at the back of the groove in the calliper.
    I tried square seals in my calipers recently and they leaked like a sieve, put round seals in and they worked a treat. No discernable difference in calipers that I could see.

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    I bought square seals, because my calipers had them. Don't know if there are any differences on calipers through the years.

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    One thing I do is use silicone grease on all seals susceptible to water ingress and precipitation and mating surfaces where I can't use a gasket. Use the really sticky stuff like that made by Dow Corning (food industry standard). It is basically impossible to dissolve in anything, won't dry, won't melt. You will see what I mean when you use it and can't wash it off your hands with anything. Water will go elsewhere. The best use is cooling system hose assemblies over metal ducts/spouts. That is the only thing I found prevents welding the rubber to the metal and starting corrosion. Hoses will come off easy no matter how many years later, they won't slip off and you don't need to tighten the clips with a drill rig wrench.
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    1000+ Posts Frans's Avatar
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    Quote Originally Posted by R8RX View Post
    I bought square seals, because my calipers had them. Don't know if there are any differences on calipers through the years.
    I'm not sure about the following idea in my head. I have always thought that the casting indent on the front of the caliper tells you what seal to use, square or round. Then on the other hand I can't say that I have stuck to this sign at all time.

    So, if this indent is square you use a square seal as in this picture???



    Then, when the indent is round you use a round seal as in here????



    Now don't take this as the whole truth because I have no black on white facts to prove what I'm saying but looking forward to comments on this.

    Regards, Frans.
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