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Question about dual master cylinders...


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I pulled my pedal box out again today and took a look. It appears as the pedal pivot to master cylinder pivot distance is roughly 3.25", and the pedal pivot to the middle of the pad at the bottom is roughly 13.625". So that means the stock pedal has a leverage ratio of 4.19. Not a whole lot of leverage.

 

I see cary talked about moving the pivot up ~.5", and that yeilds a leverage ratio of ~5:1. So I guess I'll follow his lead on this and drill the new pivot hole up about 1/2" inch. I was kind of hoping that the ratio would be closer to 6:1, but I don't think there will be enough pedal stroke if I move the pivot too high.

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OK, I cut the brake side of the pedal box off where it sits against the firewall. Trying to figure out what to do here. I have some .103" plate, and I have some .040 sheetmetal. My instinct is to build the thing with the sheet. I checked the thickness of the original sheet and it was .050, so a bit thicker. I don't have anything that thick, and the .103 is just so much overkill. I really think that the thinner stuff will be OK since this is the part that hits the firewall. Opinions?

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Also, Lunar, I got the Tilton balance bar and it looks like those washers you have are just not necessary. I don't think they'll hurt anything, but they don't really do anything other than perhaps keeping dirt out of the monoball area inside. I think you need to remove the jam nuts on the outer ends of the bar on both ends too. Otherwise they will prevent the balance bar from working.

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thanks, i'll take those jam nuts off then. I was really confused why they were included on the balance bar actually., because it's not like the "black box things" [ i dont know what else to call them] can spin off, because they're attached to the the master cylinders via the rod that threads into them.

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Are the connectors that attach the master to the balance bar (I guess its a clevis?) supposed to be right up against the tube that gets welded into the pedal? It seems like they should be close, but I'm pushing my pedal and the balance bar is pivoting not just left and right, but also up and down. I don't think this would cause any big problems, just doesn't seem like it's right.

 

I was really surprised at how much adjustment the balance bar has! Doesn't take much...

 

Also starting to look at the firewall and wonder what should be done there. My big idea right now is to cut out the area where the stock master bolts up, and make a little plate to fit in there that has the hole pattern for the duals, then weld it right into that little square. It's a bit confusing because there is the level of the masters respective to the pedal, and that height has to be transferred correctly onto the firewall, otherwise it won't all plug together.

 

I suppose the other possibility is to just hack up the firewall so that the masters just sit on the pedal assy and don't touch the firewall, but I'm not so sure I like that idea, especially since I used that .040 sheetmetal...

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I just looked at Cary's again, looks like he used a heavier plate and then cut the hole in the firewall so that he didn't have to make a corresponding plate for it. I think I may take what I have now, use it as a template and do the thing over in that .103" plate. I've done all the hard work, getting all the holes to line up and all of that...

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Are the connectors that attach the master to the balance bar (I guess its a clevis?) supposed to be right up against the tube that gets welded into the pedal?

 

The clevis' need to be straight out from the master cylinders so the pushrods get a nice, straight push. The clevis' can be close to the monoball mounting tube as long as they don't contact it during braking. The biasing action comes from moving the monoball pivot side-to-side within its mounting tube.

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I just looked at Cary's again, looks like he used a heavier plate and then cut the hole in the firewall so that he didn't have to make a corresponding plate for it. I think I may take what I have now, use it as a template and do the thing over in that .103" plate. I've done all the hard work, getting all the holes to line up and all of that...

 

The reason I did this was that the masters in their new location looked to be on top of some of the stiffeners in the firewall. It looked easier to cut out a section and build the pedal bix to have the strength. This was then bolted into the old location with some extra bolts at the bottom. I was also going to run a small piece of tube (bolt in) from the cage cross bar to the flange on the pedal box to make it stiffer. I never put the piece of tube in and the pedal was very solid with less movement on the masters than before (measured with a dial indicator).

 

On the balance bar my directions said to set the spacing the same as your masters, which in my case was 3.5 inches. There are also specific directions about how it should look loaded and unloaded.

 

Cary

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Yeah, I got the 2.5" spacing on the balance bar. Tilton apparently makes 4 different balance bars, all with different spacing. I like the way yours came out so I am doing it roughly the same way. Right now I have the plate for the masters done, and I have the original pedal box cut up. My plan is to bolt the masters in place on the firewall, then bolt the pedal box up, then tack everything together. That way it is all aligned correctly. Then I'll pull it back out and add some stiffeners.

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Well I welded it all together today... wrong. I somehow got the pedal box about 3/8" left of where it should have been on the plate (damn slotted holes). So I ground all the welds off and I'll probably weld it again in the right spot tomorrow. Oops...

 

Also figured out why my balance bar wasn't moving straight. It's because the right side of the bar where the cable hooks up is longer than the left side of the bar. As you'd push the pedal the right side would fall down. So I'm thinking that won't be an issue anymore after the cable gets installed.

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Finally got this done. I had to cut all the welds off from the first time, and this made my part look very ugly. Then I went and tacked it in place with the parts shifted 3/8". The wrong way. DAMN IT!!! So then I did it again, this time the right way. Got it reasonably close. Went to bolt it in the car, couldn't get the bolts started. Had to take it back out and open up the holes on the pedal box. 2nd time was able to get it on correctly. Hooked up the pedals and masters, everything looked peachy. Pulled it back out took the masters off again, and welded the box up. Now all I need are some bolts to weld in as studs and some paint and this sucker is done. This isn't that hard a project, but I sure managed to screw it up a bunch of times. FRUSTRATING!

 

I got 3/4" and 7/8" masters. Hopefully they work out the way I want them to. I had tried Tom Holt's spreadsheet a while back to figure out the sizes, and it turns out his spreadsheet has some errors. There were a couple parameters I could change without making any difference in the results of the spreadsheet. I think in particular rotor diameter, and I think pad size too. It's been a while.

 

Anyway, maybe I'll take some pics after I paint it.

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  • 3 weeks later...

Tilton offers balance bars in three different thread diameters: 3/8", 7/16" and 1/2". Which diameter are you using? My initial aSSumption is that 3/8" should be enough. I didn't find any tech about this on either the Tilton or Wilwood sites.

 

Any help would be appreciated.

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