R8 dual master cylinder conversion
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  1. #1
    Fellow Frogger! forzamacchi's Avatar
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    Default R8 dual master cylinder conversion

    Hello all... I am redoing the brakes on my R8 and I would like to convert to dual master cylinder. I have heard that the USA R10s came stock with a dual set up. I have also read older threads which speak about using a BMW dual master. Can anyone shed some light on this? Thanks Ben

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  2. #2
    1000+ Posts Frans's Avatar
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    Ben,

    There has been talk on this somewhere not long ago. I take it you would want a single master with dual outlets, or dual singles with a balance bar?

    As I haven't done the single with dual outlets the main thing to look out for is to have the same dia piston and if the mounting holes are the same it is a bonus. You will have to split the tubing as well so that the fronts and rears are separated. Remember to remove the regulator on the rear crossmember as well and replace with a T-piece. I have only heard good comments when it is taken out.

    Regards
    Frans.
    Old enough to know better
    Young enough to do it anyway.

  3. #3
    1000+ Posts alan moore's Avatar
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    The later A110 Alpines had a dual master cylinder and the same calipers as your R8. These master cylinders are still available at a price, but do fit directly, barring the brake lines themselves.

    I have fitted a dual BMW (22mm and I think from a late '80s 5 series) master cylinder to my R10 braked 4CV. It was not overly difficult, but did require me to make a new pushrod, and drill the mounting bolt holes out to 8mm, and fit a brake light pressure switch remotely in the line away from the master cylinder instead of the original R10 fitting in the end of the master cyl.

    I am also a great believer in removing the rear brake pressure regulator on all rear engined Renaults. All of these cars including the GTA still lock the front brakes first.
    '56 Renault 4CV (16TS Power)
    '62 Renault Dauphine Gordini
    '82 Renault Fuego GTX
    '89 Renault Alpine GTA V6 Turbo
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  4. #4
    Fellow Frogger! forzamacchi's Avatar
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    Wow...at a price is right... Just found the A110 @almost 400 EU... I am going to see how the stock set up operates first, then revisit. Is there any other way to update the safety of the single system? Thanks, Ben

  5. #5
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    Default R8 master dual cylinder

    I am planning on using the 19mm dual unit from a older Volkswagen bug it looks like almost a direct fit other than a bit of machining. will post pictures latter when I start the modification.

    The Volkswagen unit should be plentiful and relatively cheap they still stock them here in Canada.

    will keep you posted

    Manic GT

  6. #6
    Too many posts! JohnW's Avatar
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    Quote Originally Posted by forzamacchi View Post
    Wow...at a price is right... Just found the A110 @almost 400 EU... I am going to see how the stock set up operates first, then revisit. Is there any other way to update the safety of the single system? Thanks, Ben
    There are lots of opinions here, but I've never heard of a failure of the single pipe system. I honestly think that the right tyres (many posts and opinions to be found here in other posts) and good maintenance are the key items with higher importance than modifying the system. A number of us have removed that rear pressure limiting valve - three types were fitted and I'll bet almost none of them have ever been tested to see whether they are working according to specification. In my case, the rear pads now wear faster, which does suggest the system is working better than with the valve.

    Having said that, Alan's dual system makes perfect sense to me, as does your parallel logic. Has to be safer in the event of failure.

    Some of us run silicone fluid too, which helps as I think the risk of piston seizure is reduced, again making for more reliable braking.

    Cheers
    JohnW

    Renault 4CV 1950 (R1062)
    Renault R8 1965 (R1130)
    Renault Scenic Series II 2005 (wife's)
    Renault Scenic Series II 2006 (daughter's)
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  7. #7
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    R8 dual master cylinder conversion-r8-master-compared-vw-bug-master-3.jpgR8 dual master cylinder conversion-r8-master-compared-vw-bug-master.jpgR8 dual master cylinder conversion-r8-master-location-car.jpgR8 dual master cylinder conversion-r8-master-car-safety-valve.jpgR8 dual master cylinder conversion-vw-bug-master-setup-lathe-modify-r8.jpgR8 dual master cylinder conversion-vw-master-mounted-r8-master.jpgR8 dual master cylinder conversion-completed-r8-dual-master-using-vw-bug-unit.jpg
    Quote Originally Posted by manicgt View Post
    I am planning on using the 19mm dual unit from a older Volkswagen bug it looks like almost a direct fit other than a bit of machining. will post pictures latter when I start the modification.

    The Volkswagen unit should be plentiful and relatively cheap they still stock them here in Canada.

    will keep you posted

    Manic GT
    I have attached pictures I should note that the brake light switch has not been changed over I haven't looked into the thread size of the R8 brake light switch or a good replacement that will fit the extra ports on the VW master . I plan not to run the rear balance valve I will probably just run a second line to the rear right of the master .

    Hope this is useful total mod took about 1.5 hours because I had to figure it out .

    Manic gt.

  8. #8
    1000+ Posts alan moore's Avatar
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    Quote Originally Posted by forzamacchi View Post
    Wow...at a price is right... Just found the A110 @almost 400 EU... I am going to see how the stock set up operates first, then revisit. Is there any other way to update the safety of the single system? Thanks, Ben
    Mecaparts have the dual master cylinders in 19 and 22mm for 310 Euro complete with switch, but still pricey.
    '56 Renault 4CV (16TS Power)
    '62 Renault Dauphine Gordini
    '82 Renault Fuego GTX
    '89 Renault Alpine GTA V6 Turbo
    '02 and '03 Renault Clios 1.4L
    '13 Renault Megane RS265 Trophee+

  9. #9
    Fellow Frogger! forzamacchi's Avatar
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    Thanks guys.... I love the bug mod... Is your Manic GT on the road yet? Canadian sports car! OUI! John I am going to go stock first...just to give myself a starting point.....

    Sent from my Nexus 7 using Tapatalk

  10. #10
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    Not finished Manic Yet hope to have first one restored by year end.

    The weather is finally getting warm enough to enjoy doing the body work out doors and not needing the shop heat.

    Will post some pictures of project once completed . The total estimated time of project will be approximately 3 years .

    Manic gt

  11. #11
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    So for us less fortunate ones who dont have a lathe ,would it be possible to open up the hole in the bracket or is there not enough meat there ,lookes like the mounting bolts are the same spacing, pugs ps is that rusting pile of junk whats left of the vw

  12. #12
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    Default R8 master dual cylinder

    R8 dual master cylinder conversion-r8-master-compared-vw-bug-master-4.jpgR8 dual master cylinder conversion-r8-master-car-safety-valve.jpgR8 dual master cylinder conversion-r10-single-stage-master-car.jpg

    Quote Originally Posted by pugwash View Post
    So for us less fortunate ones who dont have a lathe ,would it be possible to open up the hole in the bracket or is there not enough meat there ,lookes like the mounting bolts are the same spacing, pugs ps is that rusting pile of junk whats left of the vw
    The VW master was turned down to the R8 size because I wanted to leave the stock bracket as it was in case for some reason I might want to go back to the original equipment . I decided to use my lathe because it would give me a factory look and it was easy to do but a steady hand and a bench grinder could probably do the same thing.
    The bracket from which I took the R8 master from was broken due to rust ! it almost makes me think it was under engineered (even though it has lasted for some 40 years or so) in answer to opening up the bracket hole to fit the VW master I think it would even make to weak . I had thought of building a metal bracket using the R8 as the template and having the VW hole and bolt pattern out of 1/4 inch by 2 inch angle iron and a section of tube but the idea was to keep it quick and simply .
    The VW mounting holes are 1/2 a hole wider a part so I used a rotary file to elongate the holes closer together than used washers to strengthen the bolt clamping for added support .
    I could of sent the R8 master out and had it rebuilt by sleeving it in stainless or boring it to the 22mm size but again I choose to use the VW master because it was cheap and stocked at the local parts supply store. The rusted out parts with the master you see is what's left of a Manic front suspension thanks to our Canadian winters .
    I also included a picture of a single master on a R10 as a reference and didn't,t see a safety valve on the single system so when upgrading to the dual master maybe the safety valve should be considered as well especially if you use a single reservoir.

    Hope this is helpful
    Manic GT

  13. #13
    Fellow Frogger!
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    There is also the option of using a R5 dual circuit master cylinder. New ones seem to be easy to obtain.

  14. #14
    Too many posts! JohnW's Avatar
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    This one has probably been solved and fixed by now. However, it does occur to me that the concept of fitting a servo brake system in the boot (trunk to you Forza) allows an easy way of fitting whatever master cylinder you want in free space on the servo unit. Of course you still have the primary MC under the front floor, but really it isn't too bad to access it with practice. Just a thought.

    Cheers
    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

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