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  1. #1

    Default Booster and Master Cylinder when going from 4 cyl to 8 cyl?

    The car was a 2.3 originally, so it still has the OEM pancake booster and master cylinder. We changed the front brakes and spindles to 11" from a 1989. My plan is to use the double diaphragm 1986 GT booster (I think it's the same as 1987-93) but I'm not sure which master cylinder? I think the 87-93's have a 3rd port, so should I just get a new 86 replacement? Also, the lines to the proportioning valve will be different with the master cylinder moving further forward - are there off the shelf, new lines available?

    Thanks

  2. #2
    Moderator wraithracing's Avatar
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    The 86 booster and M/C will work just fine with your combo. I believe the actual M/C to Prop valve lines are the same and you should only have to gently tweak them to get them to fit the M/C in the slightly forward position. Shouldn't be any need to replace with new.
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
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    1982 GT Stalled RestoModification
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  3. #3

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    Thanks for the response Trey. That's what I'll do.

    Since I'm already at that point, is there any upgrade you'd recommend? Such as a cobra (or more modern) master cylinder with the plastic housing?

  4. #4

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    The smallest modern m/c with a plastic reservoir is a 15/16" model which has 28% more piston area than the 21mm m/c that you should use, with the combination of parts that are on your car.
    Jack Hidley
    Maximum Motorsports Tech Support

  5. #5

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    Unfortunately, my local auto parts store only has a cast iron reman unit. Since my current M/C is aluminum, he said he'd try to order me another and maybe I'll get lucky. I find it strange that it's cast iron, but that's what they have.

    Just in case, does anyone know of a place to get an aluminum M/C?

    If that doesn't work, what about a rebuild kit for what I currently have? I've never rebuilt one before but, since i was bored, I decided to see what made mine tick.
    I removed the snap ring, but the sealing ring friction kept the pistons in place so I gave a 'light' blast of air down the rear brake line hole and was able to remove the pistons. It could use a good cleaning, but all in all, it looks like a usable piece.

    Thanks

  6. #6
    FEP Senior Member Tigger's Avatar
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    May 2009
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    Portland Oregon
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    I just replaced my master in my Saleen a couple weeks ago. 12 years ago, when I bought the car, the master was bad. It was a sketchy drive home. I apparently went with a reman 12 years ago and that came aluminum. I bought a new one from the local Napa this time and it was cast iron. Was not too happy about it but I wanted the car drivable so I put the cast iron one in. I am torn if I will rebuild the aluminum one for later use or just toss it. The Napa one has a lifetime warranty.
    67 Mustang Coupe
    96 Tangerine GT
    86 Saleen #179

  7. #7

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    Update - So I removed the original 4 cyl booster, which was much more of a pain in the butt than I expected - it's amazing how little wiggle room there is. Then I replaced it with a 1986-1993 GT style booster, which went in much easier. My local parts store (not a 'chain' store) managed to find an aluminum master cylinder reman unit so I bench bled it and installed it on the car. Then I re-bent the short brake lines to the proportioning valve (as per Trey's suggestion), and re-bled the individual brakes.

    Seems much better now, but I'll have to put more miles on it to know for sure. Thanks for all the help guys!

    If the brakes still act strange, I'm going to have to replace the rear drums to discs somehow - I have a 9" axle that is slightly narrowed so it makes my brake choices very limited.
    Last edited by twinturbohow; 06-29-2021 at 11:00 AM. Reason: Added Trey's suggestion

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