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PostPosted: February 24, 2019, 5:57 pm 
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Location: Louisville KY
My clutch and brake mc's have 4" push rods. Each has a stroke of 1.25" (max from full out to full in).

I note that if I try to get 1.25" of rod travel to the brakes, this means roughly "a lot" of pedal travel. On a 10" pedal (MC attached at 1.5") the circular arc moves the pedal surface up and down quite noticeably, and it seems like I have to push the pedals forever.

Question -- of the 1.25" of total travel, how much am I actually gonna use? IF I set the pedals to not allow full outbound rod travel by, say, 1/4", am I gonna run into slipping clutches, dragging brakes? Or conversely, if I don't allow that last 1/4" of travel, am I gonna not have good brakes, not disengage the clutch, etc?

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PostPosted: February 24, 2019, 7:32 pm 
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Most master cylinders I've run need to be extended all the way so the reservoir hole will feed the cylinder. On the other side, are you using MC's that will tolerate going all the way to the internal stop? Many will damage the valve. Also you don't want to hit the stop cause once you are there pushing harder won't give you any more brake.


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PostPosted: February 24, 2019, 9:02 pm 
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hfmaxi wrote:
Most master cylinders I've run need to be extended all the way so the reservoir hole will feed the cylinder. On the other side, are you using MC's that will tolerate going all the way to the internal stop? Many will damage the valve. Also you don't want to hit the stop cause once you are there pushing harder won't give you any more brake.


Kinda figured that going to the all-in stop on either direction isn't good for all sorts of reasons. Any ideas on how must travel will normally be needed?

Thanks!

Tim

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PostPosted: February 25, 2019, 12:09 am 
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It depends on a ton of things. The big one would be of course what kind of calipers you are using, followed by pads, how much expansion you will have in your lines, the size of the master cylinders, etc. But remember, if you pick a MC that requires less pedal travel, it will require that much more force.


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PostPosted: February 25, 2019, 9:08 am 
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geek49203 wrote:
hfmaxi wrote:
Most master cylinders I've run need to be extended all the way so the reservoir hole will feed the cylinder. On the other side, are you using MC's that will tolerate going all the way to the internal stop? Many will damage the valve. Also you don't want to hit the stop cause once you are there pushing harder won't give you any more brake.


Kinda figured that going to the all-in stop on either direction isn't good for all sorts of reasons. Any ideas on how must travel will normally be needed?

Thanks!

Tim


The master must be allowed to extend completely. So when you are off the brake pedal the pushrod is not applying any pressure to the master cylinder but not loose either. It's not really the travel that you need it's the force that you can apply with your leg and then what the math works out to for the calipers and pedal ratio you are using.

From Wilwood:(#2 is the reason for the extension)

Brake pedals should be free to return when no pressure is being applied, allowing the master cylinder pushrod to return
to its undepressed position. In some cases, the master cylinder spring (internal) may not be strong enough to fully return
the pushrod; in this case an additional pedal return spring can be used. There are two important items for consideration:

1. The brake pedal should have an adjustable return stop on it when a strong pedal return spring is used. This
prevents the master cylinder from excessively banging the snap ring stop inside the master cylinder bore (visible
under the rubber boot). Adjust the stop so the pedal stops returning at the point when the master cylinder piston
retracts against the snap ring, Figure 1.

2. The master cylinder piston must fully retract. If the master cylinder piston is not allowed to fully retract when the brake
pedal is not applied, the primary inside seal will not return past the small pressure relief hole (visible within the master
cylinder reservoir on some master cylinders). This can cause excessive residual line pressure and contribute to brake
drag and an overheating condition, see Figure 1, Detail “A”.


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PostPosted: February 25, 2019, 11:02 am 
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Now is probably the best time to build in any limiters for the pedals, Tim. I hadn't seen the info from Wilwood, but realized I'd want a stop for the clutch pedal (blue in photo).
Attachment:
File comment: Clutch pedal & stops
DSC04282.JPG
DSC04282.JPG [ 141.88 KiB | Viewed 822 times ]


However, intuitively, based on my experiencing owning old cars with dicey brakes, I didn't want a stop on the brake MCs. Right or wrong, I reasoned I wanted every inch of stroke I could get in case I lose brake fluid. I've had that experience and know if you're "grounding out" with your brakes, it's likely low fluid. Like I say, right or wrong.

After playing with the pedal box I built in the chassis, I felt it was a bad idea, and psychologically unsettling, to have the brake and clutch pedal wobbling around in space when no pressure is applied. So, I built some simple stops that can be adjusted to keep them fully released, but not flopping around. I also left in some room for return springs if they're needed in future.
Attachment:
File comment: Stop plates for unextended pedals. Upper screw shows small springs and washers to prevent movement in use.
DSC04279.JPG
DSC04279.JPG [ 144.04 KiB | Viewed 822 times ]

Attachment:
File comment: Stop plates welded in place
DSC04284.JPG
DSC04284.JPG [ 137.48 KiB | Viewed 822 times ]


If your pedal box is removable, you can add some of those feature later perhaps. I just didn't want to have to disassemble it all once the car was built and modify it then.

Cheers

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

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PostPosted: February 25, 2019, 12:23 pm 
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I think 800psi is a good number for max decell braking pressure from the pedal assy. 75-100 lbs of pressure on the pedal is also a good range, so with your pedal of 6.66:1 (10/1.5) a bore of 5/8 would get you there with 75 lbs. 3/4 moves more fluid but the effort to reach 800 psi jumps to about 90 lbs of pedal effort.

It is a question of required displacement from the master to fill the swelling lines, calipers, mount deflection, slide friction, and piston movement to fill the pad to rotor gap to reach the pressure.

You will likely use all the travel available for the clutch. The pedals should have an adjustable stop just like the throttle so the throttle body does not run out of travel before the pedal, which will break the cable.

For the brake pedal, you can shim the master or adjust the rod to fine tune when the pedal bottoms out.
I'd set the brake and clutch pedal pad so a line through it and the pedal pivot is 30-40 degrees from vertical with the piston fully extended in the master to keep the compensation port (as described above) uncovered so fluid flows from the reservoir.Keep the pedal box removable for easier mods later if needed.

If you find after brake testing that you need more fluid transfer, either raise the master and mod the pedal for a numerically lower ratio for more effort and displacement or replace the master with a larger bore for more effort and displacement.

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PostPosted: February 25, 2019, 3:39 pm 
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Location: Louisville KY
So here is what I have today.

Attachment:
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fixed 20190225_140535.jpg [ 134.22 KiB | Viewed 801 times ]

Attachment:
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I might bump out the pivot point which would lessen the angle of the pedals. Of course, when I do that, I give up total travel, which is how I started this thread....

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Girlfriend thinks I'm nuts for building this....


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PostPosted: February 25, 2019, 6:29 pm 
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Angles look reasonable to me. Looks like 30-40 deg. You can replace the clevis with a female rod end and offset the clutch pedal in the pivot brkt for a single shear mount. Then you could use the adjustment without it hitting the pedal. You can also cut the corner off forward of the pads for more travel and notch as needed near the pivot. The clutch pedal is very lightly loaded compared to a brake pedal.

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PostPosted: February 26, 2019, 8:41 am 
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Tim
You already have the hole drill for a 2nd clevis and push rod on your clutch pedal. It relative easy to just make an adjustable rod that pushing against a stop for your clutch pedal.
The upper push rod [i.e. pedal stop] in the photo simply slide into the stop tube attached to the bulkhead. It is adjusted by turning the rod in or out of the clevis. davew


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PostPosted: February 26, 2019, 7:07 pm 
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I'll assume you are talking about a brake light switch and not a brake warning switch, which is part of an oem prop valve.

There is this if you want a hydraulic brake switch:
https://www.ebay.com/itm/210-11179-Adju ... 2561478649

This for a separate switch:
https://www.ebay.com/itm/Adjustable-Pro ... 1219098789

and here is a good switch you can fit easily:
https://www.ebay.com/itm/Brake-Light-Sw ... 2488132612

Push the pedal fully forward to the firewall. Tape a strip of card board to represent the switch finger to the pedal so the end of the finger is as long as possible and as low as possible. Weld a strip of 1/8 x 1 to the pedal. You could go with very thin metal but thicker will be easier for you to weld or you can use .050 sheet and make a flange to accept a couple screws through the pedal to hold it on. Make a brkt from another strip of 1/8 to hold the switch with the plunger pressed in above the end of the finger. You will need to offset all of the this to one side or the other to make sure the pedal does not contact the switch or brkt. There is a nut above and below the brkt holding the switch. When the plunger is pressed, the circuit is open. When the plunger extends, the circuit is closed.


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geekbrksw.JPG
geekbrksw.JPG [ 73.01 KiB | Viewed 716 times ]

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PostPosted: February 26, 2019, 7:14 pm 
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Miatav8,MstrASE,A&P,F wrote:
Push the pedal fully forward to the firewall. Tape a strip of card board to represent the switch finger to the pedal so the end of the finger is as long as possible and as low as possible. Weld a strip of 1/8 x 1 to the pedal. You could go with very thin metal but thicker will be easier for you to weld or you can use .050 sheet and make a flange to accept a couple screws through the pedal to hold it on. Make a brkt from another strip of 1/8 to hold the switch with the plunger pressed in above the end of the finger. You will need to offset all of the this to one side or the other to make sure the pedal does not contact the switch or brkt. There is a nut above and below the brkt holding the switch. When the plunger is pressed, the circuit is open. When the plunger extends, the circuit is closed.


Thanks MV8, you have just solved my brake switch placement problem that I have been trying to solve with the floor mounted brake pedal on my Topolino build. :cheers:

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PostPosted: February 26, 2019, 7:49 pm 
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My pleasure! This is the same switch used on my go4 tricycle.

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