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#1235259 - 05/19/12 10:23 PM Re: Disc brakes: All the math that you never wanted to know [Re: Supercuda]
hooziewhatsit Offline
master

Registered: 10/05/07
Posts: 2629
Loc: State of Jefferson
Quote:

When you decrease the pedal ratio, you increase the stroke in the M/C. Power brakes systems use less pedal ratio, therefor more stroke at the MC for a given pedal travel.

Same bore M/C going from manual to power sends out more volume for a given pedal travel.

That's what is different.




But wouldn't that be true only if the brake pedal was also swapped to the corresponding 'correct' ratio?

ie, just throwing a booster behind a MC won't necessarily change the stroke, or will it? It should build more pressure, which I guess would necessitate a little longer stroke, assuming you haven't bottomed out the MC.

Another question: Do manual master cylinders have more travel built in to them than power MCs do? (assuming the same diameter bore)?
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#1235260 - 05/19/12 10:37 PM Re: Disc brakes: All the math that you never wanted to know [Re: Supercuda]
feets Offline
Senior Management

Registered: 01/20/03
Posts: 26830
Loc: Irving, TX
Quote:

When you decrease the pedal ratio, you increase the stroke in the M/C. Power brakes systems use less pedal ratio, therefor more stroke at the MC for a given pedal travel.






Please explain to me how the mechanical ratio of the pedal is modified when you install a booster with no other changes.
A brake booster is a straight through design. It simply uses vacuum to help push the pedal and reduce your leg effort.



Where are the levers and other gizmos to change the mechanical advantage?


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#1235261 - 05/19/12 10:40 PM Re: Disc brakes: All the math that you never wanted to know [Re: hooziewhatsit]
feets Offline
Senior Management

Registered: 01/20/03
Posts: 26830
Loc: Irving, TX
Quote:


Another question: Do manual master cylinders have more travel built in to them than power MCs do? (assuming the same diameter bore)?




To my knowledge, the only difference is the provision for a push rod retainer in the manual master cylinder.
I have installed power brake master cylinders on non-power setups.

If you try this you MUST make sure it is not possible for the brake push rod to fall out. That's why it's not recommended. It would suck to have the rod fall out and prevent you from hitting the brakes at a rather critical moment.

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#1235262 - 05/19/12 10:49 PM Re: Disc brakes: All the math that you never wanted to know [Re: Supercuda]
Frankenduster Online   content
Moparts proctologist

Registered: 02/15/10
Posts: 14872
Loc: Granite Bay CA
Quote:

When you decrease the pedal ratio, you increase the stroke in the M/C. Power brakes systems use less pedal ratio, therefor more stroke at the MC for a given pedal travel.
Same bore M/C going from manual to power sends out more volume for a given pedal travel.
That's what is different.




I thought that the travel of the piston in the master cylinders was about the same. I might be operating on a "fuzzy memory" here, but when I bench bled the master cylinder, I bottomed out the piston. When I put the master cylinder in the car, it appeared that the with the brake pushrod in the M/C, it bottomed out only a fraction deeper than the brake pedals travel. I'm certain that you don't want the pedal to stop 2 inches off of the floor because the M/C ran out of stroke.

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#1235263 - 05/19/12 10:57 PM Re: Disc brakes: All the math that you never wanted to know [Re: Frankenduster]
feets Offline
Senior Management

Registered: 01/20/03
Posts: 26830
Loc: Irving, TX
Some disc/drum masters don't have enough stroke for rear disc brakes. If the pedal it's a rock solid stopping point deep in the stroke you may want to check that out.
I know it's theoretically possible but I haven't experienced it myself.

The hot rod has a D150 manual disc/drum 1-1/8" unit pushing fluid to the AMG disc brakes.

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#1235264 - 05/19/12 11:37 PM Re: Disc brakes: All the math that you never wanted to know [Re: feets]
RichV Offline
top fuel

Registered: 01/20/03
Posts: 1671
Loc: Seattle WA
Quote:



EFFECTIVE RADIUS OF A ROTOR

To work with the actual braking ability you really need to find what is called the effective radius of your brake rotor. To do that you need to know the caliper piston diameter (only the biggest one for calipers with more than one piston) and the diameter of your rotor.
Effective radius is the total diameter of the brake rotor plus that same diameter AFTER you subtract the diameter of the piston. Then, divide by 4.
Use a "big" Mopar 11.75" rotor and the 2.75" caliper we used above.
11.75" minus the 2.75" piston is 9 inches.
So, 11.75" plus 9" is 20.75".
Divide by 4 and you get a 5.18" effective radius.





Effective radius of the rotor is unrelated to the piston diameter. It is the center of contact for for the brake pad to the rotor. Typical undergrad engineering calculation put it outboard of the center, but the taper wear of pads typically moves back inboard. So the center of contact is good compromise.

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#1235265 - 05/20/12 06:27 AM Re: Disc brakes: All the math that you never wanted to know [Re: RichV]
feets Offline
Senior Management

Registered: 01/20/03
Posts: 26830
Loc: Irving, TX
Quote:

Effective radius of the rotor is unrelated to the piston diameter. It is the center of contact for for the brake pad to the rotor. Typical undergrad engineering calculation put it outboard of the center, but the taper wear of pads typically moves back inboard. So the center of contact is good compromise.




What this calculation does is average the diameter of the rotor and the diameter of the rotor minus the piston diameter. Doing that finds you the center of the piston. That is going to be pretty close to the center of the pad.

Now, I'm NOT going to measure every stinkin pad in the world and spoon feed you the information.
If you want to use the calculation, go for it.
If you want to gather all the info from each individual setup and present it to the person requesting it in a 24 hour 7 day format then be my guest.

Again, put down the engineering texts and reread the part where I said these were good enough to get the average guy in the ball park without requiring a high level of math or engineering degree.

Now, are you frothing at the mouth or trying to accomplish something else?

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#1235266 - 05/20/12 08:17 AM Re: Disc brakes: All the math that you never wanted to know [Re: feets]
Supercuda Online   content
I Live Here

Registered: 09/04/07
Posts: 12671
Loc: West Texas
You can tell the A body guys.

The A body power setup uses an offset crank assembly to lessen the pedal ratio

You can see it in this link

http://www.ebay.com/itm/1967-MOPAR-MOPAR...R-/290681535604
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#1235267 - 05/20/12 08:38 AM Re: Disc brakes: All the math that you never wanted to know [Re: Supercuda]
feets Offline
Senior Management

Registered: 01/20/03
Posts: 26830
Loc: Irving, TX
Quote:

You can tell the A body guys.

The A body power setup uses an offset crank assembly to lessen the pedal ratio

You can see it in this link

http://www.ebay.com/itm/1967-MOPAR-MOPAR...R-/290681535604




Interesting.
It looks like it uses the crank mechanism to raise the booster for more clearance for valve covers. The 273 used a mechanical cam and I imagine things get a little tight under those hoods.

Have you done the math to calculate the actual mechanical advantage of this setup? It would require measuring the complete assembly including the pedal.

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#1235268 - 05/20/12 08:39 AM Re: Disc brakes: All the math that you never wanted to know [Re: feets]
Supercuda Online   content
I Live Here

Registered: 09/04/07
Posts: 12671
Loc: West Texas
Sorry, I do not own any power brake A bodies, I think my last one was in 1984. Since then they have all been manual brake setups. I am not a fan of power brakes in A bodies.
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#1235269 - 05/20/12 08:45 AM Re: Disc brakes: All the math that you never wanted to know [Re: Uhcoog1]
Uhcoog1 Offline
super stock

Registered: 05/12/05
Posts: 718
Loc: Houston Tx
Quote:


My duster has a 6.5:1 manual pedal ratio. When adding the power linkage, it drops to 3.5:1.





The 73+ had 15/16 master cylinders with power brakes.

I have an excel calculating booster help if anyone wants to see it.
_________________________
-'02 Dodge Viper Ex-World Challenge racecar
-'73 Duster, 6.1 based 392 hilborn hemi, tko600, full floater rear 9", Hellwig custom bars, viper brakes, built for road course

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#1235270 - 05/20/12 02:07 PM Re: Disc brakes: All the math that you never wanted to know [Re: Uhcoog1]
hooziewhatsit Offline
master

Registered: 10/05/07
Posts: 2629
Loc: State of Jefferson
Quote:

The 73+ had 15/16 master cylinders with power brakes.

I have an excel calculating booster help if anyone wants to see it.



Is it any different than the one at Pirate4x4 that just adds a multiplier to the pressure output?

Heck, send it to my username at hotmail.com.
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If you ever find yourself in a fair fight, your tactics suck.

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#1235271 - 05/22/12 09:50 PM Re: Disc brakes: All the math that you never wanted to know [Re: hooziewhatsit]
dusted72 Offline
member

Registered: 02/09/12
Posts: 29
Loc: Iraq
Feets you have just saved me weeks of headaches. I have been attempting to figure all this out with very little luck on where to start. I am planning a big brake swap on my Ram and have figured some stuff out but I really was wanting to get the specifics behind it all. I had been talking to Tom (70cuda383) on another board and he told me to come over here and check out your posts. Boy was he right. Thanks.

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#1235272 - 05/22/12 09:55 PM Re: Disc brakes: All the math that you never wanted to know [Re: dusted72]
feets Offline
Senior Management

Registered: 01/20/03
Posts: 26830
Loc: Irving, TX
Thanks, but remember this stuff will only get out in the ballpark. There are lots of other things that go into real brake system equations. Some of it has been discussed in this thread.

Feel free to use this as a basic guide. If you're saving your pennies to build something when you rotate home there's enough time to run lots of numbers.

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#1235273 - 05/24/12 11:15 AM Re: Disc brakes: All the math that you never wanted to know [Re: feets]
hooziewhatsit Offline
master

Registered: 10/05/07
Posts: 2629
Loc: State of Jefferson
Here's a file that compares manual to power brakes.

It looks like it takes the surface area of the booster and current vacuum to calculate the additional pressure provided.

Then it has two lines for each manual and power so you can compare different sized MCs. I think the table on the right is different foot pressures. For power it then adds the pressure provided by the booster (I think it's looking at the 9").

Although I think it needs to take into account pedal ratio somewhere in there

As always, use this at your own risk

edit: cleaned up file available a few posts down


Edited by hooziewhatsit (05/24/12 11:10 PM)
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#1235274 - 05/24/12 03:05 PM Re: Disc brakes: All the math that you never wanted to know [Re: hooziewhatsit]
Uhcoog1 Offline
super stock

Registered: 05/12/05
Posts: 718
Loc: Houston Tx
Quote:

Here's a file that compares manual to power brakes.

www.ma-uav.com/Manual_v_Vacuum_Brake_Pressures.xls

It looks like it takes the surface area of the booster and current vacuum to calculate the additional pressure provided.

Then it has two lines for each manual and power so you can compare different sized MCs. I think the table on the right is different foot pressures. For power it then adds the pressure provided by the booster (I think it's looking at the 9").

Although I think it needs to take into account pedal ratio somewhere in there

As always, use this at your own risk




This is my file, so I'll answer some questions on it. I'll clean it up and host a better version on my website later.

The pedal ratio is accounted for- but isn't in an obvious place for you to toggle. That is calculating off a fixed 9" single booster. The numbers at the top of the table are foot force in pounds.

I didn't realize hooziewhatsit was going to host this for download when I emailed it to him. I'll make it more user friendly tonight and make that version available for download.
_________________________
-'02 Dodge Viper Ex-World Challenge racecar
-'73 Duster, 6.1 based 392 hilborn hemi, tko600, full floater rear 9", Hellwig custom bars, viper brakes, built for road course

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#1235275 - 05/24/12 07:06 PM Re: Disc brakes: All the math that you never wanted to know [Re: feets]
dusted72 Offline
member

Registered: 02/09/12
Posts: 29
Loc: Iraq
Ok so after reading through this whole thread I am still a little confused as to what the actual equations are used for. I know how to get the answers but why? Am I using those to get the figures for the stock setup compared to proposed setup? I am just unsure. In particular the purpose of the area of a circle and effective radius of a rotor? I did the math for both stock and proposed. What does it mean if the stock are of a circle is 6.78inches and the propsed is 7.06inches? Same with the Effective radius? Stock is 5.07 and proposed is 6.23. I just don't know. Also are there any braking books out there that are a must read? I am in Kuwait right now and will be returning back to the states within the next 2 weeks so if there are any recommended readings out there please share.

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#1235276 - 05/24/12 07:31 PM Re: Disc brakes: All the math that you never wanted to know [Re: Uhcoog1]
Uhcoog1 Offline
super stock

Registered: 05/12/05
Posts: 718
Loc: Houston Tx
Quote:

Quote:

Here's a file that compares manual to power brakes.

www.ma-uav.com/Manual_v_Vacuum_Brake_Pressures.xls

It looks like it takes the surface area of the booster and current vacuum to calculate the additional pressure provided.

Then it has two lines for each manual and power so you can compare different sized MCs. I think the table on the right is different foot pressures. For power it then adds the pressure provided by the booster (I think it's looking at the 9").

Although I think it needs to take into account pedal ratio somewhere in there

As always, use this at your own risk




This is my file, so I'll answer some questions on it. I'll clean it up and host a better version on my website later.

The pedal ratio is accounted for- but isn't in an obvious place for you to toggle. That is calculating off a fixed 9" single booster. The numbers at the top of the table are foot force in pounds.

I didn't realize hooziewhatsit was going to host this for download when I emailed it to him. I'll make it more user friendly tonight and make that version available for download.




User friendly version posted here:
http://www.3gduster.com/brakes.html

Manual vs Vacuum

The equation isn't going to be correct down low, given it just adds the full vacuum force to the manual force you're pushing. It's a useful equation to get an idea for the upper end.
_________________________
-'02 Dodge Viper Ex-World Challenge racecar
-'73 Duster, 6.1 based 392 hilborn hemi, tko600, full floater rear 9", Hellwig custom bars, viper brakes, built for road course

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#1235277 - 05/24/12 07:55 PM Re: Disc brakes: All the math that you never wanted to know [Re: dusted72]
Uhcoog1 Offline
super stock

Registered: 05/12/05
Posts: 718
Loc: Houston Tx
Quote:

Ok so after reading through this whole thread I am still a little confused as to what the actual equations are used for. I know how to get the answers but why? Am I using those to get the figures for the stock setup compared to proposed setup? I am just unsure. In particular the purpose of the area of a circle and effective radius of a rotor? I did the math for both stock and proposed. What does it mean if the stock are of a circle is 6.78inches and the propsed is 7.06inches? Same with the Effective radius? Stock is 5.07 and proposed is 6.23. I just don't know. Also are there any braking books out there that are a must read? I am in Kuwait right now and will be returning back to the states within the next 2 weeks so if there are any recommended readings out there please share.




Go here, read it all, and use the excel:
http://www.pirate4x4.com/tech/billavista/Brakes/

The purpose of the math is to determine how much braking force you need and what balance you need. The usable brake torque is determined how much grip your tires have with the road surface (coefficient of friction between tires and surface). You can calculate the force needed by the caliper, and the master cylinder needed to produce that force. The diameter of the rotor determines the leverage.

The brake bias needed changes through the 'curve'. Assuming a 54/46 (f/r) weight bias when static in my duster, a .1 G braking even will require very close to a 55/45 ideal bias. It will change, ending up at a 75/25 ideal bias at a 1.3 G braking event. You need to calculate weight transfer at different G braking events.

Does that help?
_________________________
-'02 Dodge Viper Ex-World Challenge racecar
-'73 Duster, 6.1 based 392 hilborn hemi, tko600, full floater rear 9", Hellwig custom bars, viper brakes, built for road course

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#1235278 - 05/24/12 11:09 PM Re: Disc brakes: All the math that you never wanted to know [Re: Uhcoog1]
hooziewhatsit Offline
master

Registered: 10/05/07
Posts: 2629
Loc: State of Jefferson
Quote:

I didn't realize hooziewhatsit was going to host this for download when I emailed it to him. I'll make it more user friendly tonight and make that version available for download.




oops. Sorry

The cleaned up file is pretty interesting through... it says I should have roughly 900psi. I just got my brake pressure gauge, so at some point when I get some time I'll have to verify that.

Thanks for the file
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If you ever find yourself in a fair fight, your tactics suck.

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