MM proportioning valve delete, MM aftermarket pedal, SN95 GT front and rear running gear, 95 master cylinder.


where did i go wrong? thing wont even lock them up. pedal is hard as a rock.

 

Did you connect front and rear ports backwards?

 

ditch the 95 master cylinder(1-1/16") and get a 93 cobraR(1") or 95cobraR(15/16") master, or just try your original master cylinder(i think its a 7/8") with the bottom port plugged.

 

Uhh i dont know...

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I guess ill try the stocker

 

Drill out your brake pedal to move the master cylinder linkage mounting point further up on the pedal. I don't remember how far I moved mine, maybe an inch or so. I thought when you went manual brakes you wanted the bigger cylinder bore?

 

Definitely get a smaller piston M/C.

 

Smaller piston = Less #force output per #force input wouldnt he want a larger bore M/C?

 

Fixed.

It is amazing how much difference even a 1/8" smaller bore M/C will improve braking performance.

 

This is completely incorrect

Force= Area x PSI

Area PI x R^2

So lets use 1500psi input with a 7/8 M/C will exert 902psi which will again be changed at the piston

1500psi on a 15/16 M/C will be 1036psi

The only way to get more force with a smaller piston will be to increase the leverage at the peddle

 

Mathematics aside, I speak here from experience. I've been here. I had a large bore MC. I had a hard pedal. The engineer in me whipped out some quick calculations and I ended up with a smaller bore MC and it fixed my problems. Had a 1 1/8" bore SVO MC and went to a 7/8" bore and I went from super hard pedal that was difficult to modulate to a smooth easy feeling pedal that was easy to modulate.

 

I cannot comment on which size will work best in which application I was only pointing out the diffrence between small and large bore cylinders as it seemed some people had it backwards. Now as for the personal experiance, I removed the ABS from my car when I installed my hydaulic handbrake my brakes were very touchy and there was no feel I disconnected the booster vaccume line and they work and feel great. So that would be along the same lines as reducing the bore size I just removed leverage. That being said the peddle is much firmer now Im not sure how the smaller bore would give a softer peddle but if it does it does LOL.

 

Because it's about moving volume, not just pressure. To move 500mL of fluid with a large bore MC you barely have to move the pedal. You stated your piston area above, now factor in the stroke (Pi*r^2*h) to get a volume of fluid and you'll see that you have to stroke it further with the small bore to move the same amount of fluid. This is what's making the smaller bore MC easier on the manual brake conversion.

 

Some useful info here;

https://www.theturboforums.com/threads/362742-94-mustang-manual-conversion-brake-issue-please-help

Jess

 

Wow its awesome to see so many idiots tell people what to do when they have no idea. Most of those people have the same name "they" when one of my customers tried something on his car I ask why did you do that, they always tell me well they said it would work. now I see one of these they people. also I love how people respond without reading the post first, like he said it has a MM pedal which has a relocated pivot. Don't care how you cut it or tell yourself in your mind or think you are an engineer a smaller piston will always give a better pedal feel and easier to stop.

 

I can only assume you are referring to me.

1) I never gave anyone any advice on what to do or how to correct the issue.

2) show me one piece of info I posted that was incorrect.

I stated facts and then questioned why, it was than explained to me its volume issue. Which would lead to it ultimately coming down to a ratio issue which makes perfect sence. The same effect could be acheived by changing caliper piston size. seems the forum worked exactly as intended as I and I'm sure others learned something.

Ps: I have a huge student loan payment that allows me call myself an engineer, So run and tell that homeboy!

 

All arguing aside... For petal feel and brake response, which the OP is looking for, the ratio of MC bore to caliper Bore is what needs to be addressed. I am going to try to make this simple. The smaller the MC the less volume it will displace at a greater pressure. (softer petal and more brake response) The larger the bore the greater volume will be displaced at a lower pressure. (harder petal less brake response) The formula propose above does not address the MC to Caliper ratio, or the petal to rod ratio.

I had a hard time understanding the MC bore size effect on braking until I performed my own brake swap.

 

Forget about the volume calculations, that's just a distraction as the volume only affects the pedal free travel to take up the running clearance between pad and rotor. Once they are in contact it's all about pressure which is what generates the clamping force, and any additional pedal travel after that is down to things like the brake hoses expanding and caliper mount flex. Smaller M/C bore with the same input force (from your foot) will generate higher line pressure, which will cause the brake hoses to expand more, which is why the pedal feel will be 'softer' with a smaller M/C.

The amount of force you can put into the fluid is first and foremost determined by how hard your leg can push the pedal, which is the piece of the puzzle left out of the above calculations. So to generate more clamping force, it's a lot easier to go smaller on the M/C piston area or bigger on the caliper piston area or increase the pedal ratio than it is to get a new leg capable of pushing harder.

 

I don't like the way you worded that herder, the pedal does not feel softer just because the lines are expanding.

 

Where does the pedal feel come from, then? Fluids are incompressible. So are brake rotors and pads. Once the running clearance is gone, any additional fluid you push out of the M/C has to be going somewhere. So where does it go?

Have you ever had your hand around a rubber brake hose while a helper in the car stands on the pedal? If not, you should try it sometime.

 

That and a lot of flexing from the caliper mounting bits and pieces.