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JMortensen

Question about dual master cylinders...

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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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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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On 12/28/2017 at 9:02 PM, NewZed said:
 

Genius! I didn't realize they moved to a paid accounts thing or I would've looked that up, I thought they just updated their settings and users had to click a checkbox or something.

 

On 12/29/2017 at 8:04 AM, JMortensen said:

I don't even remember having a photobucket account. Tried to log in, all I had were the wind tunnel test pics in there. I know I had more pics at one time, this is all I could find. 

dualmaster.jpg

thanks for getting these posted! These are super helpful in planning things out. and also I was mistaken, the posts were from Lunar's buildout, not yours. His posts were The ones not working. Either way, thanks again!

Now that you've had some time (I'm assuming you nstalled this setup and it's on now), how do you like the 3/4 and 7/8 MCs? would you prefer larger or have they been good? and how do you like the overall braking with the dual MCs?

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That's a tricky question, because pedal feel and overall performance have lots of different variables. Rotor size, caliper size, pad size, pedal leverage ratio, etc all affect how much pedal effort you need and how well it will perform. With the pedal ratio modded to close to 5:1 with 12.2" rotors, Superlight 1.75 4 pistons and Dynalite 1 3/8 4 pistons and Hawk Black pads and after messing with the balance bar a bit I think my brakes feel pretty good. In fact, if I stuck someone else in the car and didn't tell them, I doubt they would know that it was a manual setup. That said others running 6:1 ratios seem to like bigger masters, more like 1". 

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On 1/3/2018 at 6:52 AM, JMortensen said:

That's a tricky question, because pedal feel and overall performance have lots of different variables. Rotor size, caliper size, pad size, pedal leverage ratio, etc all affect how much pedal effort you need and how well it will perform. With the pedal ratio modded to close to 5:1 with 12.2" rotors, Superlight 1.75 4 pistons and Dynalite 1 3/8 4 pistons and Hawk Black pads and after messing with the balance bar a bit I think my brakes feel pretty good. In fact, if I stuck someone else in the car and didn't tell them, I doubt they would know that it was a manual setup. That said others running 6:1 ratios seem to like bigger masters, more like 1". 

Yeah I know those are all important factors, but I'm in the same boat as you were when this thread was started where I can spend the amount to fix my system or just do the upgrades I want to do in the future, so I'm potentially opting towards this if the MC rebuild kit from ZCAR doesn't fit my 71 (it's listed as a 72 and up, and they weren't positive on the fitment either, so who knows). I figure my setup will be pretty similar to yours, not exactly the same but it will give me a basis in my head of where to start. Either way, thank you for the info! You are the man!

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1 hour ago, TUME said:

http://www.jakelatham.com/radical/info/brake_calculators.shtml#MaxGBraking   Try this.

 

I`v got skyline 4-pots front and 2-pot calibers rear. With wilwood pedal assembly. Calculator gives .75 and .625 masters.

So I've looked into this but from what I can tell none of the values you can change actually affect the size of the Masters. It seems to be more of a tool that you would input your own master size (or a master size of what you want to test) to then find a pre-determined braking torque percent balance (at the end of step 3, after inputting the rest of the data). If I input my data in steps 1 -3 (some of the data being my best guess, I admit), then go d own to step 3 and begin testing various sizes of MC on front and back, you can achieve the desired ratio. Based off of my crazy exact calculations (that is sarcasm), my desired MCs would be 1 inch in front and .8125 in the rear for a very close to 50/50 balance (which is also just an assumption I'm making based off of limited knowledge). Am I correct in how this would work, and the guesses at the desired ratio? I will now just sit here and brace myself for some learnin!

 

image.thumb.png.380a547ab171f514f5bbf37b112c1044.png  

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It doesn´t tell you what size masters you need straight away. But you can test different sizes with this. There are not so many size of masters, just try different sizes and you see chances immediately.  it takes really a few minutes.

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7 minutes ago, TUME said:

It doesn´t tell you what size masters you need straight away. But you can test different sizes with this. There are not so many size of masters, just try different sizes and you see chances immediately.  it takes really a few minutes.

well yes, I am more so curious if you're shooting to get as close to a 50/50 braking ratio as possible or is there a more preferred ratio?

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Posted (edited)
Quote

Maximum braking performance occurs just before brake lockup, as a sliding tire has less grip than a rolling tire, thus tuning brake balance is all about controlling when the brakes lockup. As max performance obviously will occur when all 4 tires (& associated brakes) are doing the maximum work, an ideal brake bias is one that locks the front and rear brakes at the same time. In practice however, locking the rear tires typically result in a rapid spin, and locking all 4 wheels results in a slower spin, especially if the car is trail braking. For this reason, some “extra” front bias is normally used, because when the front brakes lockup the car remains stable (but you lose the ability to steer the car – it just goes straight) and this allows the driver time to recognize the brake lockup and reduce brake pressure to regain max braking performance and control. 

 

I would get near 50/50 with masters and use balance bar with fine adjustment. 

Edited by TUME

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