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Old 11-27-10, 03:02 PM   #1
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to move the brake booster and master cylinder under the dash?

Has anyone ever relocated the brake booster and master cylinder to under the dash on an 1987 rx7?----i have looked into a hydro boost system already and looks like that would work good for me .oh by the way im in the process of putting a 462 cubic inch big block chevy in my rx.oK back to the brake issue ---so i figure if i use a slave cylinder to push the booster this will work the same as the hydro boost (thats how that system works as well-the hydro boost ) the major issues of this will be bore diameter of the master that pushes the slave cylinder and the amount of stroke that the slave cylinder has --i can pull vaccume from the engine.the brackets to mount it and to bolt the slave to the booster i can machine-build.--------jason------oh by the way this solve would only cost me at the most $150.00 vs.$1600.00 for a hydro boost---thats if i buy a new master cylinder and slave cylinder as well --and it keeps all the brake lines metric unlike the hydro boost that uses a corvette master.and it would require no hydrolic lines to be made up .
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Old 11-27-10, 11:30 PM   #2
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not enough room under there for a booster and master cylinder with the way the dash is designed, maybe with a hollow carbon fiber copy but still, dash is heavily sloped and the dash is very close to it, how do you plan on keeping an eye on the fluids? brake system is extremely important, and designed pretty damn good on fc's. I will say i had to run my fc without a booster once dude to the vacuum line rupturing and it wasn't terrible, just harder to push.
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Old 11-30-10, 08:49 AM   #3
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well the valve cover on the big block is over 3 inches into the booster and the underside of the dash is gutted ---no heat or air-and i was thinkin that i would run the set up as close as i can run brake line wise to the master-- that will be inplace of the original booster and master-a single res. wilwood unit with a 3/4 bore-doin that will make the original master cylinder in line i hope with the glove box door.----i want to keep power brakes for the fact that the 462 cubic inch chevy weighs 685 pounds!and makes over 500 pounds of torque at 4200 rpm idles smooth and makes 464 h.p. at 5800 rpm--totally streetable pump gas engine -good heads oversize valves-mild cam-and its a m-22 muncie 4 speed........jason
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Old 11-30-10, 08:58 AM   #4
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and it has to be done to fit the engine in it -i have already moved the radiator support 5 inches forward ---its all part of it---huge full size big block truck radiator -and i will be moving the engine forward enough to clear the wishield wiper area--and that means the balancer -pan clearance to the sway bar is going to be another challenge---i used a hydro.throw out bearing on the clutch on my last car and will be using close to same set up on this one --just need to figure out the stroke on the brake master cylinder to match it up with either a slave cylinder or what ever i need with the correct stroke-i can make all the brakets and housings to mate all this up ---machinist and have too many machines at home as well.
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Old 12-01-10, 01:52 PM   #5
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Why not just go with a master that wouldn't need any boost? Something around 5/8" would work fine and run it through the stock bias adjuster. My dual master set up uses a 5/8 for the front and 7/10 for the rear with a small change in the pedal ratio to keep the force needed low(90lbs or so).

You should be able to find an older master from another car(truck?) and you could probably even raise it a little for more room. I lowered my pedal a little and kept it in the stock pedal assembly. The center line of the masters is pretty much in the stock location. With a custom plate covering the stock hole you could probably raise it an inch if needed.
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Old 12-02-10, 03:18 AM   #6
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been kickin around all of it --non power brakes with 4 wheel disks brakes is something i havent tried i believe that it takes more pressure to operate disk brakes than it does drum brakes? --true?---even if i cant fit it under the dash i could still move the whole set up to the rear of the car along with the battery (i can use all the weight tranfer to the rear i can get with the heavy big block )--yes just running a master and no booster would make things simple thats for sure.......jason
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Old 12-02-10, 08:11 AM   #7
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Yes, disks require more force than drums. Now, how much, I dunno.

jgrewe, would you count your setup "streetable"?
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Old 12-02-10, 10:48 AM   #8
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The big issue wouldn't be how much pressure you can build, it would be pedal travel. The 4 piston calipers need a lot of fluid to move those pistons. My 5/8 works out fine on my fronts for travel and I end up with line pressure in the 900psi range no problem, a 3/4 master would be low 800psi range with the same pedal effort. A 1/2" master would get you 1200psi but would probably give you a long pedal if you have any kind of run out on your discs or get any pad knock back. Once the pads are on the discs hard though you could stop the car with your big toe.
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Old 12-02-10, 08:21 PM   #9
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Oops, my math was screwed up, forgot about that whole pi thing. Those numbers seemed low when I first posted them...
3/4 will give you 1360 psi
7/10 will give you 1560 psi
5/8 will give you 1600+ psi
1/2 will give you 3000 psi

These are with 100 lbs of pedal effort (medium pedal) and a 6 to 1 pedal ratio. The stock pedal ratio is close to 5 to 1 and its tough to get a master to work well without boost.
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Old 12-03-10, 03:29 AM   #10
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mine will be street driven often --did you put a big block in a fc jgrewe?---the advantage to the system im thinkin of is that i can put it anywhere i want ---a master to push a slave cylinder thats bolted to the booster ---looks like just a master with no booster would work too ---im sure doing it the way im thinking can be done -im sure the drive rod for the booster comes out with out much effort and i can make my own drive rod connected to the slave cylinder ---i havent measured the distance the rod travels when the brakes are applied --that would have to match the travel of the slave cylinder.....everones input is greatly appreciated !!!-------jason
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Old 12-03-10, 09:56 AM   #11
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No big block in a Rex...yet.... But I like the idea. I just have years of building hotrods and race cars and I try to keep thing simple and light. If a single master on the firewall will clear the valve cover there is a lot less time, money and engineering to get that to work. If you want that clean firewall look, thats cool too.

The extra weight of the engine won't be that much of a factor with the size of the stock brakes, they will be fine. The big thing the driver needs to decide is how much foot pressure requirement you want to deal with.

A 5/8 master with a 6 to1 pedal set up is firm but not a leg killer. Find a dual circuit one of those, plumb it through the stock bias valve and your done for $100. I can get a picture of my stock pedal assembly that I modified to get the higher pedal ratio with the nice aluminum pedals.
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Old 12-04-10, 07:06 PM   #12
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that is exactly whats going in mine --462 cubic inch bbc----i dont think ive seen anyone use the stock booster and master mounted in a different place like that --and it would take only a single res. master on the firewall to push a slave cylinder (i already have a master for it)and that way it will still have the power brakes---these cars (rx7) handle good and are light and strong -make a good platform for h.p.---jason-----i as well like odd ball cars with a bunch of power.........as long as they are safe.
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Old 12-04-10, 07:51 PM   #13
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Thinking about it, I guess if you have a master and slave that are the same dia it wouldn't matter their size. You will have a 1:1 ratio from the pedal to the back of the remote booster and the brakes would have the same effort as stock.

The only concern then would be the strength/stiffness of the assembly that holds the slave and booster together and the amount of travel the master and slave need to push the booster.
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Old 12-06-10, 03:16 AM   #14
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now we are on the same page ---i can make all of the assembly that is needed to bolt it all together -just not sure of the stroke of a slave cylinder ? i guess it would be best to use the same diameter slave cylinder as the master?------- and the master on the firewall that will push the slave cylinder------i wonder why no one has done this yet?--as it is the same thing as a hydro boost all except the fact that you would use the same master and booster that came on the car and the booster is ran off of vaccum instead of yet another power steering style of pump ---and oh i forgot its like $1500.00 cheaper
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Old 12-06-10, 03:22 AM   #15
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i was thinking that i will remove the drive rod that has the clevis on it (on the back of the booster ) and make a new one . all this will have to be is a rod that has a spherical radius on each end to push fro m the slave to the booster. the housing that connects the slave and the booster i can make on lathe and machine it square on the bridgeport --there are 4 long studs on the back of the booster ---ill use those and come up with a mount that bolts to the bottom of that housing as well -just need to figure out another way to bolt up the front side of it to make to ridgid---the only other place to bolt off of in the front side of the booster is the 2 studs that hold the master on (i dont like that idea)-----ill get it...............jason
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Old 12-06-10, 03:29 AM   #16
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i have a pedal set with master cylinders and brake bias im trying to sell...
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Old 12-06-10, 04:47 PM   #17
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You might make that rod from the brake slave to the back of the booster adjustable. Check how much travel the stock pedal gives the push rod and go from there. If you can find a slave cylinder that gives you more than that measurement you should be good to go. Have you checked what the stock clutch slave travel is? You might have a set of clutch hydraulics to play with on the car already. Maybe a trip to an auto parts store to look through the books to find a slave cyl. that has a mount you can work with.

I would figure out the master and slave to use and then lay the booster and slave next to each other and let the design come to me. The diameters for that circuit wouldn't matter that much unless you want to get more or less travel of the slave for the pedal movement or to change the feel of the pedal. I'd also plan for -4 braided line to cut down on any restriction to fast fluid movement from the master to slave and back.
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Old 12-07-10, 09:53 PM   #18
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i do know that the diameter of the line and the bore diameter makes a big difference -the hydro.throwout bearing on my last car had a 5/8 master and a smaller line to start with and the clutch pedal didnt take much pressure at all to push ---but i do believe those braided lines are not dot approved --i blew the first line on that car after only 1000 miles!and i do still have the slave that was on this car ---i can check the travel ----i was thinkin that that would be the only down fall to this is the lag or delay with the extra parts .---it is an interesting idea
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Old 12-16-10, 10:06 AM   #19
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have u looked into the wilwood setups? they have options for inverted brake systems and also remote location setups also...

there are a few other manufacturers as well, but wilwood is the cheapest. i am running a 180 pedal setup on my truck with no booster...
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Old 03-30-11, 03:37 AM   #20
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i had a 90 degree mount on my 1929 model a coupe but there was plenty of room under the dash ---there is no room under the dash of the rx for that sort of set up --plenty of room on the passenger side now that all the air conditioning crap is gone.---have plenty of other stuff to build before i get to that point.thanks for the interest
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Old 03-30-11, 03:39 AM   #21
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i will check out the remote set ups .thanks
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Old 03-30-11, 03:39 AM
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booster, boostermaster, brake, car, chevy, cylinder, dash, fc3s, firewall, hose, location, master, metric, move, relocate, slave, wout

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