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Thread: Conversion from Single to Dual Circuit Master Pump...

  1. #1

    Conversion from Single to Dual Circuit Master Pump...

    Hello All!

    I have a RHD '67S with the stock single master pump setup. I'm having some brake problems. After some time on the highway, the pump will sorta lose pressure and I'll have to pump it once to get things going. After that, things will be fine. Pressure is firm after that. Anyone any clue why?

    Anyway, I figure it's time to do up the brakes soon, so I'm keen to convert to a dual circuit master pump. How difficult is it? Anyone sells hard lines for RHD cars?

    Thanks in advance!

    Sprint.

  2. #2
    Goldmember ttweed's Avatar
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    Sprint-

    I'm not familiar with the RHD setup, but I did convert my LHD '67S to dual circuit MC. The hard lines can be easily custom bent and flared with hand tools, so I don't know if there are premade sets, especially for RHD cars. The main challenge is routing the new dual feed lines from the new updated reservoir. The MC is located in the smuggler's box on the '67, so I put the new reservoir in the later location (on the inside of the fender well) and had to drill holes to feed the tubing down to the top of the MC. DO NOT drill thru the gas tank while you are doing this!

    It's a nice update to do, but the MC may not be your problem. Are you losing hydraulic fluid? If there is no fluid leaking from it, and the pedal stays firm once you pump it, you just may have air in the lines or calipers. Do a thorough flush and bleed routine and see if it fixes the problem. A failed MC will usually let the pedal slowly go to the floor under constant pressure. or you will see fluid leaking around the pedal cluster or out of the fittings somewhere.

    TT
    Tom Tweed
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  3. #3
    Hello TT!

    Are the hard lines the same for all the pre-'89 911s? Anyone knows?

    The rears remain the same right?

    When you did the conversion, did you get the '68 & later master pump or one from a even later car? Hehe... I assume Porsche used bigger pumps on the heavier post '73 Carreras?

    Hmm... Why didn't you leave the reservior in the smuggler's box? Too big? Haha... I'm afraid of drilling holes!

    As for the pedal problem. I do have firm pressure and I've bled the system till I'm almost dying!

    Haha... Thank goodness the weekend is here! More time to tinker with the car!

    Sprint.

  4. #4

    Different theory

    Here's an off-the-wall theory...

    Was it raining when you were driving on the highway..?

    Rain + rotors + short amount of time = rust. Your pedal would be "ok" but the car wouldn't slow down initially...then start biting as the rust is cleaned off.

    Just a thought.

    Per

  5. #5
    Goldmember ttweed's Avatar
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    Originally posted by SprintStar
    When you did the conversion, did you get the '68 & later master pump or one from a even later car? Hehe... I assume Porsche used bigger pumps on the heavier post '73 Carreras?
    I'm not positive, but I think they went to boosted brakes in '74? The 19mm dual circuit MC was used at least thru '73, I think.

    Originally posted by SprintStar
    Hmm... Why didn't you leave the reservior in the smuggler's box? Too big? Haha... I'm afraid of drilling holes!
    Well, the updated reservoir is bigger and rectangular instead of small and round like the '67's. There really wasn't room for it in the smuggler's box with the Webasto heater still in there. It also comes with a metal strap/bracket for mounting it on the inside of the fender well, so that's where I put it.

    The hard lines may have changed when they went to power brakes, too, but I don't know much about the post-'73 models.

    TT
    Tom Tweed
    Early S Registry #257
    R Gruppe #232
    Rennlist Founding Member #990416-1164
    PCA National DE Instructor
    Read my surf novel!

  6. #6
    Haha.... I'm in Singapore. Too hot to need the heater!

    I'll try mount the reservioir in the smuggler's box. Hate to cut new holes....

    You didn't have to change out anything on the rears, right?

    Sprint.

  7. #7

    Re: Different theory

    Originally posted by GRMPer
    Here's an off-the-wall theory...

    Was it raining when you were driving on the highway..?

    Rain + rotors + short amount of time = rust. Your pedal would be "ok" but the car wouldn't slow down initially...then start biting as the rust is cleaned off.

    Just a thought.

    Per
    Hmm... Interesting thought, but I don't that's why I'm feeling. On Katie, the pedal sinks right to the floor, then firms up on the second try....

    Anyone had this happen before? Thanks!

    Sprint.

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