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40-48 Chevy brake question

Discussion in 'The Hokey Ass Message Board' started by fleetmaster, Mar 5, 2004.

  1. fleetmaster
    Joined: Jan 21, 2004
    Posts: 168


    hey there-i have a question for all owners of a 40-48 chevy. if your car has its master cylinder mounted under the floor i was wondering if you could help me. i am trying to decide where to mount the master cylinder on my 47 chevy coupe. i can't decide between the firewall or under the floor. i was hoping to run power brakes also. so, the question is, can anyone give me some dimensions of an under the floor master cylinder? Also, where exactly does it mount and how does it mount? How much ground clearance is left usually(does it hang below the frame)? And, is there usually still enough room to easily run exhaust? If anyone can help out that would be great. it would give me a better idea of which direction to go.
  2. Scott B
    Joined: Dec 31, 2002
    Posts: 548

    Scott B

    You might be cramped for space, in either spot. You are running a big block, right?
    Stockers mount in from the frame rail a few inches and are about even with the bottom of the rail. A booster will hang down a bit.
    Having not seen a big block in these, I can only guess how much room is on the fire wall. Small blocks leave lots of room there, so I think that would be the spot.
    I am planning on a firewall mount in my Aerosedan, just because it seems the most practical...
  3. fleetmaster
    Joined: Jan 21, 2004
    Posts: 168


    thanks for the info-ya-i am putting a big-block in it. the origianl plan was to go for the firewall mount just cause it was easier. however, my dad became concerned with the space issue and started talking about an under the floor mount, even though he never liked the one in his 34 ford. i am now also concerned about space on the firewall, but there is also that issue under the floor.
  4. just my opinion that the engine compartment looks better without it...

    it IS a close fit under the floor, and with the booster, it would hang down some, I saved a master cylinder and booster from another project for just this kind of application sometime in the future...

    I dont know how you feel about usin' foreign parts, but next time you are in a salvage yard, look at one of those old bullet side Datsun trucks...they have dual line master cylinder, and at least SOME of them had power brakes, the '73 "Lil' Hustler" that I tore down for parts did....the booster is small and would probably fit under the floor without much trouble, you could probably get one for cheap.

  5. Hellfish
    Joined: Jun 19, 2002
    Posts: 6,482


    the stock unit mounted on TOP of the frame. So, it's between the frame and floor. Everything is out of mine right now, so if you need to see where it goes, I could snap a picture this weekend. PM if you need it. The Filling Station offers a service where they convert your stock MC to a modern dual system. Everything mounts up exactly the same so you don't have to worry about that. I don't know about the booster part, but I think ECI or MPB has a under floor booster, and I think it mounts on the outside of the frame.
  6. What I do is gut the original master cylinder-and make a heavy rod that is sturdy/wont it thru the old cyl[ the back end unscrews,comes off]to a new mount for the newer dual master cyl -mounted to rear side of crossmember with a home built bracket.
    this saves your stock pedals and unclutters the firewall.
  7. cleatus
    Joined: Mar 1, 2002
    Posts: 2,277

    from Sacramento

    I used an RB's Obsolete kit to mount mine under the floor on my 40 Chevy.
    Its a 7" booster and does hang just a bit below the rails, but part of the bracket that bolts it up includes a pretty hefty plate that gives it some protection.

    I had to put a hatch in the floor to be able to lift off the top to fill it.
  8. fleetmaster
    Joined: Jan 21, 2004
    Posts: 168


    thnx guys for the info-wayfarer is bringing over some MPB stuff tommorow to look at-but all the info from you guys is gonna help a ton

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