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    • #56738

      🙄 can a 7″ brake booster be used in place of a 5″, how hard is it to install and will it give you less pedal effort than the 5″unit. I purchased a new old stock unit and would like to use it without switching the vacuum piston.

    • #60740

      Interesting question-one I had never thought of! I see no reason the larger booster could not be used in place of the smaller one-that is what Rootes did when they started using the 7 inch boosters on the later cars. I don’t even think they changed the brake master cylinder bore size when they did this either so I don’t know how much less pedal pressure you can expect. Mounting it should be no problem as long as it is mounted in the same location that the factory used when they went to the 7 inch booster.
      Are you using this on an Alpine or a Tiger? Not as much spare room to mount things on a Tiger! Good luck and let us know how the brakes work. Eric

    • #60741

      Here’s the story
      I rebuilt my booster for my 66 Tiger it works but the brakes stick very lightly and I only noticed this on a 20 mile test drive with mutable stops. When I rebuilt it I polished the bores with a wood dowel and 600 grit emery at the same time I saw a NOS brake booster on E-Bay and I dint want to loose it so I bought it. When it arrived I realized it was a 7″ unit!

      I figured I would make the best of it and use the 7″unit. before using the 7″booster I took it apart to inspect it even though it was sealed I found some of the assembly grease had dried out so it needed a thorough cleaning. After cleaning I inspected the bores they are pristine

    • #60742

      Here’s the story
      I rebuilt my booster for my 66 Tiger it works but the brakes stick very lightly and I only noticed this on a 20 mile test drive with mutable stops. When I rebuilt it I polished the bores with a wood dowel and 600 grit emery at the same time I saw a NOS brake booster on E-Bay and I dint want to loose it so I bought it. When it arrived I realized it was a 7″ unit!

      I figured I would make the best of it and use the 7″unit. before using the 7″booster I took it apart to inspect it even though it was sealed I found some of the assembly grease had dried out so it needed a thorough cleaning. After cleaning I inspected the bores they are pristine.

      Here is what else I found out the only thing different with the main body is the small end of the valve control piston, its smaller on the 7″ booster

      What I was going to do is take all of the seals off of my 5″ booster and use them in the 7″ booster body with my 5″vacuum cylinder. I didn’t want to by a new rebuild kit at $85 but with the control piston being a different size my new 5″ rubber pieces wont fit.

      Should I buy a new kit or give the body to a machine shop and have them bore out the high pressure bore to fit my 5″ valve control piston.

      I know its ling winded but any suggestions would be appreciated

      Jim

    • #60743
      mikephillips
      Member

      What you may have is the vacuum piston hanging up in it’s bore and taking a few seconds to release. The rubber seal that goes under the leather on it that comes in the current kits is too hard causing the piston to hang up. The proper lube for the leather seal isn’t apparently supplied. What I would try is to take the canister assembly off the 2 and swap them and see if the problem goes away. They will swap with no problems, although it might vary your brake pedal pressure requirements. If this fixes it you can either leave it that way or work on the original canister assembly to get it working better.

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